Engine Coolant Sensors

Copyright AA1Car

The engine coolant temperature (ECT) sensor is a relatively simple sensor that monitors the internal temperature of the engine. Coolant inside the engine block and cylinder head(s) absorbs heat from the cylinders when the engine is running. The coolant sensor detects the change in temperature and signals the Powertrain Control Module (PCM) so it can tell if the engine is cold, warming up, at normal operating temperature or overheating.

The coolant sensor is extremely important because the sensor's input to the PCM affects the operating strategy of the entire engine management system. That's why the coolant sensor is often called the "master" sensor.

Many of the fuel, ignition, emissions and drivetrain functions handled by the PCM are affected by the engine's operating temperature. A different operating strategy is used when the engine is cold than when it is warm. This is done to improve cold driveability, idle quality and emissions. Consequently, if the coolant sensor fails or is giving the PCM a false reading, it can upset a lot of things.

HOW THE COOLANT SENSOR AFFECTS ENGINE OPERATION

Input from the coolant sensor may be used by the PCM for any or all of the following control functions:

* Start up fuel enrichment on fuel injected engines. When the PCM receives a cold signal from the coolant sensor, it increases injector pulse width (on time) to create a richer fuel mixture. This improves idle quality and prevents hesitation while the cold engine is warming up. As the engine approaches normal operating temperature, the PCM leans out the fuel mixture to reduce emissions and fuel consumption. A faulty coolant sensor that always reads cold may cause the fuel control system to run rich, pollute and waste fuel. A coolant sensor that always reads hot may cause cold driveability problems such as stalling, hesitation and rough idle.

* Spark advance and retard. Spark advance is often limited for emission purposes until the engine reaches normal operating temperature. This also affects engine performance and fuel economy.

* Exhaust gas recirculation (EGR) during warm-up. The PCM will not allow the EGR valve to open until the engine has warmed up to improve driveability. If EGR is allowed while the engine is still cold, it may cause a rough idle, stalling and/or hesitation.

* Evaporative emissions control canister purge. Fuel vapors stored in the charcoal canister are not purged until the engine is warm to prevent driveability problems.

* Open/closed loop feedback control of the air/fuel mixture. The PCM may ignore the oxygen sensor rich/lean feedback signal until the coolant reaches a certain temperature. While the engine is cold, the PCM will remain in "open loop" and keep the fuel mixture rich to improve idle quality and cold driveability. If the PCM fails to go into "closed loop" once the engine is warm, the fuel mixture will be too rich causing the engine to pollute and waste gas. This condition may also lead to spark plug fouling.

* Idle speed during warm-up. The PCM will usually increase idle speed when a cold engine is first started to prevent stalling and improve idle quality.

* Transmission torque converter clutch lockup during warm-up. The PCM may not lockup up the torque converter until the engine has warmed up to improve cold driveability.

* Operation of the electric cooling fan. The PCM will cycle the cooling fan on and off to regulate engine cooling using input from the coolant sensor. This job is extremely important to prevent engine overheating. Note: On some vehicles, a second coolant sensor or switch may be used for the cooling fan circuit only.

TYPES OF COOLANT SENSORS

Most coolant sensors are "thermistors" that change resistance as the temperature of the coolant changes. Most are the "NTC" (Negative Temperature Coefficient) type where resistance drops as the temperature goes up. With this type of sensor, resistance is high when the engine is cold. As the engine warms up, the internal resistance of the sensor drops until it reaches a minimum value when the engine is at normal operating temperature.

A typical GM coolant sensor, for example, may have around 10,000 ohms resistance at 32 degrees F and drop to under 200 ohms when the engine is hot (200 degrees). A Ford coolant sensor, by comparison, may read 95,000 ohms at 32 degrees and drop to 2,300 ohms at 200 degrees.

Resistance specifications will vary depending on the application, so any sensor that does not read within its specified range should be replaced.

Coolant sensors have two wires (input and return). A 5-volt reference voltage signal is sent from the PCM to the sensor. The amount of resistance in the sensor reduces the voltage signal that then returns to the PCM. The PCM then calculates coolant temperature based on the voltage value of the return signal. This number can be displayed on a scan tool, and may also be used by the instrument panel cluster or driver information center to display the temperature reading of the coolant.

On some applications, a "dual range" coolant temperature sensor may be used. When the coolant reaches a certain temperature, the PCM changes the reference voltage to the sensor so it can read the coolant temperature with higher accuracy (higher resolution).

On some older vehicles, a different type of coolant sensor may be used. Some of these are essentially an on/off switch that opens or closes at a predetermined temperature. The sensor may be wired directly to a relay to turn the electric cooling fan on and off, or it may send a signal to a warning light on the instrument panel. These older coolant sensors are typically single wire sensors. On other older applications, a single wire variable resistor temperature sensor that grounds through the threads may be used to send a temperature signal to a gauge on the instrument panel. These are typically called temperature "senders" rather than sensors.

FINDING THE COOLANT SENSOR

The coolant sensor is typically located near the thermostat housing in the intake manifold. On a few vehicles, the coolant sensor may be located in the cylinder head, or there may be two coolant sensors (one for each cylinder bank in a V6 or V8 engine) or one for the PCM and a second for the cooling fan.

The sensor is positioned so the tip will be in direct contact with the coolant. This is essential to produce a reliable signal. If the coolant level is low, it may prevent the coolant sensor from reading accurately.

COOLANT SENSOR SYMPTOMS

Because of the coolant sensor's central role in triggering so many engine functions, a faulty sensor (or sensor circuit) will often cause cold driveability and emission problems. A bad coolant sensor can also cause a noticeable increase in fuel consumption, and it may cause a vehicle to fail an emissions test if it prevents the engine management system from going into closed loop.

Keep in mind that many coolant sensor problems are more often due to wiring faults and loose or corroded connectors than failure of the sensor itself.

The coolant sensor's impact on the engine management system, cold driveability, emissions and fuel economy can also be influenced by the thermostat. If the thermostat is stuck open, the engine will be slow to warm up and the coolant sensor will read low. Or, if someone installed the wrong thermostat for the application or removed the thermostat altogether, it will prevent the engine from reaching normal operating temperature and cause the coolant sensor to read low.

COOLANT SENSOR DIAGNOSTIC FAULT CODES

On 1996 and newer vehicles with OBD II onboard diagnostic systems, a faulty coolant sensor may prevent some of the system monitors from running. This will prevent the vehicle from passing an OBD II emissions test because the test can't be done unless all the required system monitors have run and passed.

The OBD II system should catch the fault, turn on the Check Engine Light or Malfunction Indicator Lamp (MIL), and set one of the following diagnostic trouble codes:

P0115....Engine Coolant Temperature Circuit
P0116....Engine Coolant Temperature Circuit Range/Performance
P0117....Engine Coolant Temperature Circuit Low Input
P0118....Engine Coolant Temperature Circuit High Input
P0119....Engine Coolant Temperature Circuit Intermittent 

On older pre-OBD II vehicles, the Check Engine light may come on if the coolant sensor is shorted, open or is reading out of range. GM coolant sensor codes include codes 14 & 15, Ford codes are 21, 51 & 81, and Chrysler codes are 17 & 22.

COOLANT SENSOR DIAGNOSIS

A visual inspection of the coolant sensor will sometimes reveal a problem such as severe corrosion around the terminal, a crack in the sensor, or coolant leaks around the sensor. But in most cases, the only way to know if the coolant sensor is good or bad is to measure its resistance and voltage readings.

On vehicle systems that provide direct access to sensor data with a scan tool, the coolant sensor's output can usually be displayed in degrees Centigrade (C) or Fahrenheit (F). The coolant sensor should read low (or ambient temperature) when the engine is cold, and high (around 200 degrees) when the engine is hot. No change in the reading or a reading that obviously does not match engine temperature would indicate a faulty sensor or a wiring problem.

The internal resistance of a coolant sensor can also be checked with an ohmmeter or DVOM (digital volt ohm meter) and compared to specifications. If the sensor is open, shorted or reads out of range, it must be replaced.

If the resistance of a coolant sensor is within specifications and changes as engine temperature changes, but the engine is not going into closed loop, the fault is in the wiring or PCM. Further diagnosis will be needed to isolate the problem before any parts are replaced.

One trick here is to use a sensor simulator tool to feed a simulated temperature reading through the sensor's wiring harness to the PCM. If the wiring continuity is good but the PCM fails to go into closed loop when you send it a "hot coolant" signal, the problem is in the PCM.

COOLANT SENSOR VOLTAGE CHECKS

You can also use a voltmeter or digital storage oscilloscope (DSO) to check the sensor's output. Specs vary, but generally a cold coolant sensor will read somewhere around 3 volts. As the engine warms up and reaches operating temperature, the voltage drop should gradually decrease down to about 1.2 to 0.5 volts. If you're using a scope to display the voltage signal, you should get a trace that gradually slopes from 3 volts down to 1.2 to 0.5 volts in three to five minutes (or however long it normally takes the engine to reach normal operating temperature).

If the voltage drop across the coolant sensor reads at or near 5 volts, it means the sensor is open or it has lost its ground connection. If the voltage is close to zero, the sensor is shorted or it has lost its reference voltage.

When working on 1985 and up Chrysler products, watch out for a sudden voltage increase as the engine warms up. This is normal and is produced by a 1000 ohm resistor that switches into the coolant sensor circuit when the sensor's voltage drops to about 1.25 volts. This causes the voltage to jump back up to about 3.7 volts, where it again continues to drop until it reaches a fully warmed up value of about 2.0 volts.

Sometimes a coolant sensor will suddenly go open or short when it reaches a certain temperature. If your voltmeter has a "minimum/maximum" function, you can catch sudden voltage fluctuations while the sensor is warming up. If you are viewing the voltage pattern on a scope, a short will appear as a sudden drop or dip in the trace to zero volts. An open would make the trace jump up to the VRef voltage line (5 volts).

If the coolant sensor reads normally when cold (high resistance and 3 or more volts), but never seems to reach normal temperature it could be telling the truth! An open thermostat or the wrong thermostat may be preventing the coolant from reaching its normal operating temperature.

COOLANT SENSOR REPLACEMENT

Most coolant sensors are not replaced unless they have failed. A coolant sensor that is shorted, open or reading out of range obviously can't provide a reliable temperature signal and must be replaced for the engine management system to function properly. But many experts also recommend installing a new coolant sensor if you are replacing or rebuilding an engine. Why? Because coolant sensors can deteriorate with age and may not read as accurately as they did when they were new. Installing a new sensor can eliminate a lot of potential problems down the road.

It is also a good idea to replace the coolant sensor and thermostat if the engine has experienced a case of severe overheating. Abnormally high engine temperatures can damage these components and may cause them to misbehave or fail prematurely.

Replacing a coolant sensor requires draining some of the coolant from the cooling system. You do not have to drain the entire radiator. Just open the drain valve and let out enough coolant so the coolant level in the engine is below the sensor.

This would be a good time to check the condition of the coolant, and to replace it if the coolant is more than three years old (conventional coolant) or five years old (long life coolant). A coolant change and a flush would also be a good idea if the coolant shows any signs of contamination.

The threads on the coolant sensor may be pre-coated with sealer to prevent coolant leaks. Tighten the sensor carefully to prevent damage.

Once the new sensor has been installed, you can refill the cooling system. Make sure all the air is out of the cooling system. Air trapped under the thermostat may cause the engine to overheat or the coolant sensor to not read correctly.

Engine Coolant Temperature SENSOR

P0115 - Engine Coolant Temperature Circuit Malfunction

OBD-II Trouble Code Technical Description

 Circuit Malfunction

What does that mean?

The ECT (Engine coolant temperature) sensor is basically a thermistor that changes resistance with temperature. Usually a two wire sensor, a 5Volt reference from PCM (Powertrain Control Module) and ground signal to PCM. This is different from a temperature SENDER (which usually operates the dash temperature gauge and operates in a similar way as the SENSOR, only it's a different circuit than what a P0115 is referring to). As the temperature of the coolant changes, the resistance changes on the ground signal to the PCM. When the engine is cold, the resistance is high. When the engine is warm, the resistance is low. If the PCM detects a voltage condition that seems abnormally low or high, P0115 will set.

Symptoms

Symptoms of a P0115 DTC code may include:

• MIL (Malfunction Indicator Lamp) illumination will always occur
• Vehicle may be hard to start
• May blow a lot of black smoke and run extremely rich
• Engine may want to die or backfire in tailpipe
• Engine may run lean and increased Nox emissions may be apparent (Requires gas analyzer)
• Cooling fans may run all the time when they shouldn't be, or not at all when they should be

Causes

Usually the cause can be traced to a bad ECT sensor, however that doesn't preclude the following:

• Wiring or connector damaged at sensor
• Open or short in reference or signal circuit
• Open or short in signal circuit
• Bad PCM

Possible Solutions

First, visually check the sensor for damage to wiring or connector and repair as necessary. Then, if you have access to a scanner, determine what the temperature of the engine is. (If you don't have access to a scan tool, using the dash temperature gauge may not be an effective way to determine coolant temperature. This is because the P0115 code is referring to the ECT SENSOR, and the dash gauge is operated by, usually a one-wire SENDER. Basically a different sensor that the code doesn't refer to.)

2. If the engine temperature is abnormally high, around 280 deg. F, that's abnormal. Unplug the sensor on the engine and see if the signal drops to, say, negative 50 deg. F. If it does, then it's a good bet the sensor is bad, internally shorted, causing a low resistance signal to be sent to the PCM. However if you want to be sure it's the sensor and not the wiring, there's a couple tests you can do. With the ECT sensor unplugged, check that you have 5 volts on the reference circuit with KOEO (Key on engine off). Also you can check the resistance of the sensor to ground using an Ohm meter. The resistance of a normal sensor to ground will vary a little depending on the vehicle, but basically, if the temp of the engine is around 200 deg. F., the resistance will be about 200 Ohms. If the temperature is about 0 def. F., the resistance will be over 10,000 Ohms. With this test you should be able to tell if the resistance of the sensor matches the temperature of the engine. If it's not accurate according to your engine's temperature, then you probably have a bad sensor.

3. Now, if the temperature of the engine according to the scanner is around 280 deg. F. and unplugging the sensor doesn't cause the reading to drop to negative 50 deg. F, but it stays at the same high temperature reading, then you'll need to repair the short on the signal circuit(ground) to the PCM. It's shorted directly to ground somewhere.

4. If your temperature reading of the engine according to the scanner is showing negative 50 deg. F or so, (and you don't live in the arctic!) unplug the sensor and check for a 5V reference present at the sensor.

5. If there isn't, then check at the PCM connector for proper 5V reference. If it's present at the PCM connector, then repair the open or short on 5V reference from PCM. If there is no 5V reference present at the PCM connector, then you're done with your diagnosis and you may have a PCM fault. 6. If the 5V reference circuit is intact, then check the ground signal to the PCM using the previous ground resistance test. If the resistance isn't normal for the temperature of the engine, then ohm the resistance of the ground signal to the PCM by removing the ground signal wire from the PCM connector. The wire should have no resistance, unplugged from the PCM to the sensor. If it does, repair open in the signal to the PCM. If it doesn't have any resistance on the ground signal wire and the resistance test of the sensor is normal, then suspect a faulty PCM.

Other coolant engine light codes: P0115, P0116, P0117, P0118, P0119, P0125, P0128

How a Fuel Pump Works

A fuel pump is used to supply fuel to the fuel injection system or carburetor, depending on the year of the vehicle. Older vehicles use a mechanical pump to deliver low pressure fuel to the carburetor, while fuel injectedvehicles require an electric pump capable of the high pressures required to make the system work efficiently. A fuel injection system is more efficient than its predecessor the carburetor and can better operate in extreme conditions, while becoming more dependable at start up.

Typical Electric Fuel Pump
Simply put, the purpose of a fuel pump is to draw fuel from the fuel tank then to deliver it to a fuel injector or carburetor. All vehicle engines operate by way of a mechanical pump or via a fuel injected pump. Chances are if your engine requires a mechanical pump it is quite old and has fuel pumping at a low pressure from a fuel tank to the carburetor. Most likely your engine uses a fuel injected pump as do most modern engines and transfers fuel at high pressure into the fuel injector system from an electrical pump mounted either inside or outside the fuel tank.

Typical Fuel Injection System
Mechanical Pumps
Before electronic fuel injection, most carbureted vehicle engines used mechanical fuel pumps to move fuel from the fuel tank into the fuel sections of the carburetor. However, more recently, as vehicle engines shifted from carburetors to fuel injection, mechanical fuel pumps are increasingly being replaced with electric fuel pumps. This is because electronic fuel injection systems generally run more effectively at higher fuel pressures than mechanical pumps.
Fuel Injected Pumps

Fuel injection pumps, which are usually electric, are located within the fuel tank or near the gas tank in order to maintain a steady amount of fuel and to utilize the fuel in the tank to cool the pump. Fuel injection pumps are part of an electronic system, which means that they are controlled by a computer system that oversees key factors including the air to fuel ratio, the contents of the exhaust gases and the actual position of the throttle.
When Fuel Pumps Fail
There are a couple of reasons why your fuel pump will fail, be it electric or mechanical. Electric fuel pumps can experience wear and tear on the armature, brushes or bearings. In addition, roller gears and pump vanes can also wear down. This will cause a gradual loss of pressure and poor engine performance. Some causes of fuel pump failure can include rust or dirt because they can get past the inlet filter sock, which is designed to filter these sediments. When this occurs the fuel pump will break down because of contaminants that have infiltrated the pump and cause it to jam. This will result in having the motor overheat and burn out. Sometimes a fuel pump will not work properly if it is not given the proper amount of fuel needed to run adequately. Your vehicle’s fuel pump relies on fuel running through it to cool and lubricate it. Starving your fuel pump for fuel can cause your vehicle's fuel pump to fail prematurely. Mechanical fuel pumps usually rupture the diaphragm that is used as the pump, and will leak a small amount of fuel externally (from the weep hole) or just not have pressure.

How to Test a Fuel Pump Video

How to Replace a Fuel Pump Outline
To replace your fuel pump first start with a nearly empty tank then make sure that the transmission is in park, the parking brake is activated and the front wheels are secured. Next elevate the vehicle with at least two jack stands for safety and disconnect the filler neck from the fuel tank itself. This can be done by removing the hose clamp that holds the hose to the fuel tank. Then remove either the rear or front two bolts that fasten the fuel tank to the vehicle and gently lower one side of the tank. At this point you should be able to reach the fuel line and wiring connectors, which should be disconnected prior to removing the two other bolts. Now you can remove the fuel pump from the tank and insert a replacement pump. When replacing your fuel pump opt for the same type of pump.

Installing a different type of replacement pump can create difficulties. Your fuel pump is a vital component of the fuel system, so its electrical draw, flow and pressure characteristics must be in specification with the remainder of your vehicle’s system. Having a different fuel pump substituted for another can result in a mismatch, creating durability, noise and, most importantly, engine performance problems. Always check the system fuel pressure after a fuel pump replacement. It is also a good idea to replace the fuel filter and the fuel pump relay when replacing the pump, due to the extra amperage an old pump can draw through the relay.
Fuel Pump Best Practices
When selecting the correct fuel pump for your vehicle’s engine, be sure to have the engine size, year, make and model of your vehicle. Having this information handy will allow you to obtain the correct fuel pump specifically calibrated to your engine's performance specifications. In addition, make sure the fuel tank is clean. Although this should be self evident you must inspect the fuel tank carefully to make sure there is no dirt or rust inside and clean it as needed. Be sure to check the fuel lines for cleanliness as well at this point. The reason for these examinations is to prevent the most prevalent cause a fuel system failure, dirt. Take an extra few extra minutes and replace the fuel filter when replacing the pump.
Basic Maintenance
The main preventive maintenance you can do with a fuel injection system is to keep your throttle body clean and your fuel filter changed.

the mass airflow sensor or map sensor, throttle body, throttle position sensor, idle control valve, fuel pump, fuel pressure regulator, fuel lines, and oxygen sensors.

Black Smoke Engine Exhaust System

00:00

01:47

Check for Diagnostic Trouble Codes

Black Smoke from Engine
Black smoke is caused by too much fuel being processed inside your car's engine and then released from the tailpipe of your car. Malfunctions in fuel delivery or internal system leaks will cause black smoke to come from the tailpipe. Before fuel injection became available in automobiles in the mid 1980's, the carburetor was the main fuel and air mixer in most vehicles. A carburetor was a simple device that supplied the engine with proper fuel to air mixtures. Carburetors performed two operations 1. meter air flow 2. deliver the correct amount of fuel to air mixture. This mix could be kept even during the wide range of extra factors associated with an engine such as high temperature, cold starting, hot starting, idling and acceleration.
The primary difference between a carburetor and a fuel injection system is that the fuel injection system atomizes fuel by pushing it through a small nozzle under pressure, while a carburetor utilizes vacuum created by air flow into the intake manifold. Airflow in an injection engine is controlled by the throttle body; fuel is distributed directly in each cylinder. This creates better fuel control, lower emissions and faster acceleration. The process of measuring the amount of fuel a fuel injector is dispersing is determined by the PCM (powertrain control module). The fuel injection system has several parts: the mass airflow sensor or map sensor, throttle body, throttle position sensor, idle control valve, fuel pump, fuel pressure regulator, fuel lines, and oxygen sensors.
Cause of Black Smoke
Black smoke is caused when the mix of fuel and air becomes un-balanced. Normal mixture is 14.5 parts air to1 part fuel. When the fuel to air mixtures change because of a malfunction the mixture can go as high as 14.5 to 2 or 3, two to three times the proper amount. The black smoke is the excess fuel generated from the rich mixture and can be cause by one of the following:

• Plugged Air Filter
• Shorted or stuck fuel injector
• Failed fuel pressure regulator
• Vacuum leak
• Shorted Computer Sensor

Troubleshooting Black Smoke for Exhaust
Testing for a Blown Fuel Pressure Regulator Diaphragm - A fuel pressure pressure by using a diaphragm/spring combination in conjunction with intake manifold vacuum. When the fuel pressure regulator diaphragm ruptures it allows raw fuel into the vacuum feed line and then into the intake system of the engine. This condition creates a rich black smoke from the tail pipe on start up and while running. To check for this condition remove the vacuum line from the regulator, if fuel is present in the line the regulator has failed. Some GM (CPI Injection) are designed with an internal regulator that you must remove the upper intake manifold to inspect. Most fuel pressure regulators are on the fuel rail on top of the engine in plain sight. If you cannot locate your fuel pressure regulator consult a repair manual.

Removing the Vacuum Feed Line
Testing Fuel Pressure Regulator - The fuel pressure regulator adjusts fuel system pressure depending on the load of the engine. Vacuum is applied to the fuel pressure regulator to control system pressure. When the fuel pressure regulator is not functioning properly it causes the fuel pressure to be above normal operating pressure. This condition causes excess fuel to be injected into the engine causing a rich mixture that produces black smoke. To test for this condition (engine off) remove the protective cap and attach the fuel pressure gauge.

Attach Fuel Pressure Gauge
Support the fuel pressure gauge for observation, and then turn the key to the on position. The fuel pressure gauge should jump up to your system pressure. If you do not know your system fuel pressure consult a repair manual. Actual fuel pressure will vary slightly but should be fairly close to specification.

Fuel Pressure Gauge
Then, start the engine, the fuel system pressure should stay the same. While watching the gauge, snap the throttle, the fuel system pressure should jump up about 5 psi. If the system fuel pressure does not respond the fuel pressure regulator has failed. If the fuel pressure gauge falls the fuel filter is plugged or the fuel pump is failing. When testing is complete, remove the fuel pressure gauge feed line and replace the protective dust cap

Testing a Fuel Pressure Regulator

Check for Fuel Injector Malfunction - When a fuel injector malfunctions it can allow excess fuel into the engine. The fuel injector is manufactured with a control valve that allows fuel to flow at prescribed amounts. If this valve sticks open it will flood the cylinder with fuel. This excess fuel causes black smoke from the exhaust system. To test for this condition the injector fuel rail must be removed and injectors tested. It is difficult to fully test an injector, but an basic operation test would include pressurized air and a 12 volt power source.
While an engine is running you should be able to hear the injectors clicking as the electronic valve opens and closes. To aid in this inspection use a stethoscope and touch it against each injector. If no audible sound is heard test fuel injector pulse and supply voltage output (this test is used for most cars). This test will tell you if the computer system has operating voltage and injector trigger signal. Remove an electrical connector from a fuel injector (all injectors need to be tested) probe both sides of the connector with a grounded test light or multimeter (voltmeter) (black lead) switched to DC voltage (there are only two terminals). Have a helper turn the key to the "on" position without cranking the engine and observe the test light.
The test light should illuminate one side of the connector only and the multimeter should be at about 12 volts. Next, switch the test light or multimeter (voltmeter) lead (black) or to the positive side of the battery to test the system ground injector trigger, probe the side of the connector that did not light up, have a helper crank the engine over and observe the test light, it should blink on and off or the multimeter (voltmeter) should bounce from 0 to 12 volts. (Note: if no injector pulse is present try disconnecting the remainder of injectors and re-test, if a fuel injector is shorted it can shut down the injector driver causing no injector pulse. If injector pulse returns plug the injectors electrical connectors in one at a time until the pulse fails and then replace that injector).
If this test revealed that there was no pulse but system has power, the PCM is not generating a fuel injector trigger. If there is no trigger to the fuel injector it will not allow fuel to enter into the engine. Some of the most common reasons that can cause this condition include a shorted fuel injector, injector wiring damage or shorted PCM. While the injector trigger wire is off, test the fuel injector windings by setting the multimeter (voltmeter) to ohms and attach the leads to either side of the injector. Your reading should be between 11 and 18 ohms. Test all of your injectors; if one injector reading is considerably different from the others replace that injector. Check the fuel pressure regulator, remove the vacuum line feeding the fuel pressure regulator, check for the presence of fuel, if fuel is present the diaphragm inside the regulator has ruptured and is feeding raw fuel into the engine causing it to run rough.

Fuel Injector
Check Air Intake Boot - An air intake boot is designed to transfer air from the mass air flow meter to the throttle bore. The PCM monitors this air flow and corrects fuel input. When an air intake boot fails it causes the PCM to respond by inputting more fuel than is necessary. This condition causes black smoke from the exhaust system. To check for this problem remove air intake boot to inspect for cracks or tears and replace if needed.

Torn Air Intake Boot
Check Engine Light - Service Engine Soon
If the check engine light is illuminated the PCM has detected a malfunction that could be causing the problem,scan the PCM to retrieve trouble codes and repair as needed.

Preventive Maintenance
To check your car's mixture you will need to use a gas analyzer to test your exhaust gases. This will measure the carbon monoxide, hydrocarbon, nitrogen oxide and oxygen content of your exhaust. During a normal smog inspection the fuel/air mixture is tested and a report generated. When a tune up is performed the spark plug end insulator can tell you whether you have a lean or rich mixture. Brownish grey is the desired color and confirms proper mixture. Black and sooty means the mixture is too rich while white to light grey confirms a lean mixture. Fuel injection systems rely on pressurized fuel to operate. Maintaining this pressure is mandatory for the system to function properly. Replace your fuel filter with every tune up to keep your injection system operating properly.
Maintenance
Maintenance for a vehicle is something that is often overlooked. From blank stares when asked when the last oil change occurred, to the even stranger looks that occur when asking when the last tire rotation was completed. It is very important to maintain oil changes and tune-ups that are performed on schedule. Proper maintenance to your car is a good way to keep all internal engine parts from becoming damaged prematurely. Without oil lubrication an engine will quickly become severely damaged. Anytime you are able to lengthen the life of the engine and help avoid breakdowns it is beneficial to the motoring experience.
Sometimes it is advisable to seek a professional ASE or other certified mechanic to trouble shoot the problem for the blue smoke condition. Never avoid engine problems as they can cause a simple and inexpensive repair to escalate to a costly repair that could have been avoided. Choosing the right mechanic or repair shop for your needs is often the biggest issue, however many times it can take just a referral from a friend or relative in order to find an appropriate repair shop. Poorly maintained engines are much more prone to problems such as smoking. The excessive friction leads to catastrophic engine failure. Preventative maintenance is cheap insurance to ensure that your vehicle runs as smooth as possible for many miles to come.
If further technical assistance is needed, our certified car repair technicians are ready to answer your car questions.
Related Car Repair Information

Black Smoke Engine Exhaust System

00:00

01:47

Check for Diagnostic Trouble Codes

Black Smoke from Engine
Black smoke is caused by too much fuel being processed inside your car's engine and then released from the tailpipe of your car. Malfunctions in fuel delivery or internal system leaks will cause black smoke to come from the tailpipe. Before fuel injection became available in automobiles in the mid 1980's, the carburetor was the main fuel and air mixer in most vehicles. A carburetor was a simple device that supplied the engine with proper fuel to air mixtures. Carburetors performed two operations 1. meter air flow 2. deliver the correct amount of fuel to air mixture. This mix could be kept even during the wide range of extra factors associated with an engine such as high temperature, cold starting, hot starting, idling and acceleration.
The primary difference between a carburetor and a fuel injection system is that the fuel injection system atomizes fuel by pushing it through a small nozzle under pressure, while a carburetor utilizes vacuum created by air flow into the intake manifold. Airflow in an injection engine is controlled by the throttle body; fuel is distributed directly in each cylinder. This creates better fuel control, lower emissions and faster acceleration. The process of measuring the amount of fuel a fuel injector is dispersing is determined by the PCM (powertrain control module). The fuel injection system has several parts: the mass airflow sensor or map sensor, throttle body, throttle position sensor, idle control valve, fuel pump, fuel pressure regulator, fuel lines, and oxygen sensors.
Cause of Black Smoke
Black smoke is caused when the mix of fuel and air becomes un-balanced. Normal mixture is 14.5 parts air to1 part fuel. When the fuel to air mixtures change because of a malfunction the mixture can go as high as 14.5 to 2 or 3, two to three times the proper amount. The black smoke is the excess fuel generated from the rich mixture and can be cause by one of the following:

• Plugged Air Filter
• Shorted or stuck fuel injector
• Failed fuel pressure regulator
• Vacuum leak
• Shorted Computer Sensor

Troubleshooting Black Smoke for Exhaust
Testing for a Blown Fuel Pressure Regulator Diaphragm - A fuel pressure pressure by using a diaphragm/spring combination in conjunction with intake manifold vacuum. When the fuel pressure regulator diaphragm ruptures it allows raw fuel into the vacuum feed line and then into the intake system of the engine. This condition creates a rich black smoke from the tail pipe on start up and while running. To check for this condition remove the vacuum line from the regulator, if fuel is present in the line the regulator has failed. Some GM (CPI Injection) are designed with an internal regulator that you must remove the upper intake manifold to inspect. Most fuel pressure regulators are on the fuel rail on top of the engine in plain sight. If you cannot locate your fuel pressure regulator consult a repair manual.

Removing the Vacuum Feed Line
Testing Fuel Pressure Regulator - The fuel pressure regulator adjusts fuel system pressure depending on the load of the engine. Vacuum is applied to the fuel pressure regulator to control system pressure. When the fuel pressure regulator is not functioning properly it causes the fuel pressure to be above normal operating pressure. This condition causes excess fuel to be injected into the engine causing a rich mixture that produces black smoke. To test for this condition (engine off) remove the protective cap and attach the fuel pressure gauge.

Attach Fuel Pressure Gauge
Support the fuel pressure gauge for observation, and then turn the key to the on position. The fuel pressure gauge should jump up to your system pressure. If you do not know your system fuel pressure consult a repair manual. Actual fuel pressure will vary slightly but should be fairly close to specification.

Fuel Pressure Gauge
Then, start the engine, the fuel system pressure should stay the same. While watching the gauge, snap the throttle, the fuel system pressure should jump up about 5 psi. If the system fuel pressure does not respond the fuel pressure regulator has failed. If the fuel pressure gauge falls the fuel filter is plugged or the fuel pump is failing. When testing is complete, remove the fuel pressure gauge feed line and replace the protective dust cap

Testing a Fuel Pressure Regulator

Check for Fuel Injector Malfunction - When a fuel injector malfunctions it can allow excess fuel into the engine. The fuel injector is manufactured with a control valve that allows fuel to flow at prescribed amounts. If this valve sticks open it will flood the cylinder with fuel. This excess fuel causes black smoke from the exhaust system. To test for this condition the injector fuel rail must be removed and injectors tested. It is difficult to fully test an injector, but an basic operation test would include pressurized air and a 12 volt power source.
While an engine is running you should be able to hear the injectors clicking as the electronic valve opens and closes. To aid in this inspection use a stethoscope and touch it against each injector. If no audible sound is heard test fuel injector pulse and supply voltage output (this test is used for most cars). This test will tell you if the computer system has operating voltage and injector trigger signal. Remove an electrical connector from a fuel injector (all injectors need to be tested) probe both sides of the connector with a grounded test light or multimeter (voltmeter) (black lead) switched to DC voltage (there are only two terminals). Have a helper turn the key to the "on" position without cranking the engine and observe the test light.
The test light should illuminate one side of the connector only and the multimeter should be at about 12 volts. Next, switch the test light or multimeter (voltmeter) lead (black) or to the positive side of the battery to test the system ground injector trigger, probe the side of the connector that did not light up, have a helper crank the engine over and observe the test light, it should blink on and off or the multimeter (voltmeter) should bounce from 0 to 12 volts. (Note: if no injector pulse is present try disconnecting the remainder of injectors and re-test, if a fuel injector is shorted it can shut down the injector driver causing no injector pulse. If injector pulse returns plug the injectors electrical connectors in one at a time until the pulse fails and then replace that injector).
If this test revealed that there was no pulse but system has power, the PCM is not generating a fuel injector trigger. If there is no trigger to the fuel injector it will not allow fuel to enter into the engine. Some of the most common reasons that can cause this condition include a shorted fuel injector, injector wiring damage or shorted PCM. While the injector trigger wire is off, test the fuel injector windings by setting the multimeter (voltmeter) to ohms and attach the leads to either side of the injector. Your reading should be between 11 and 18 ohms. Test all of your injectors; if one injector reading is considerably different from the others replace that injector. Check the fuel pressure regulator, remove the vacuum line feeding the fuel pressure regulator, check for the presence of fuel, if fuel is present the diaphragm inside the regulator has ruptured and is feeding raw fuel into the engine causing it to run rough.

Fuel Injector
Check Air Intake Boot - An air intake boot is designed to transfer air from the mass air flow meter to the throttle bore. The PCM monitors this air flow and corrects fuel input. When an air intake boot fails it causes the PCM to respond by inputting more fuel than is necessary. This condition causes black smoke from the exhaust system. To check for this problem remove air intake boot to inspect for cracks or tears and replace if needed.

Torn Air Intake Boot
Check Engine Light - Service Engine Soon
If the check engine light is illuminated the PCM has detected a malfunction that could be causing the problem,scan the PCM to retrieve trouble codes and repair as needed.

Preventive Maintenance
To check your car's mixture you will need to use a gas analyzer to test your exhaust gases. This will measure the carbon monoxide, hydrocarbon, nitrogen oxide and oxygen content of your exhaust. During a normal smog inspection the fuel/air mixture is tested and a report generated. When a tune up is performed the spark plug end insulator can tell you whether you have a lean or rich mixture. Brownish grey is the desired color and confirms proper mixture. Black and sooty means the mixture is too rich while white to light grey confirms a lean mixture. Fuel injection systems rely on pressurized fuel to operate. Maintaining this pressure is mandatory for the system to function properly. Replace your fuel filter with every tune up to keep your injection system operating properly.
Maintenance
Maintenance for a vehicle is something that is often overlooked. From blank stares when asked when the last oil change occurred, to the even stranger looks that occur when asking when the last tire rotation was completed. It is very important to maintain oil changes and tune-ups that are performed on schedule. Proper maintenance to your car is a good way to keep all internal engine parts from becoming damaged prematurely. Without oil lubrication an engine will quickly become severely damaged. Anytime you are able to lengthen the life of the engine and help avoid breakdowns it is beneficial to the motoring experience.
Sometimes it is advisable to seek a professional ASE or other certified mechanic to trouble shoot the problem for the blue smoke condition. Never avoid engine problems as they can cause a simple and inexpensive repair to escalate to a costly repair that could have been avoided. Choosing the right mechanic or repair shop for your needs is often the biggest issue, however many times it can take just a referral from a friend or relative in order to find an appropriate repair shop. Poorly maintained engines are much more prone to problems such as smoking. The excessive friction leads to catastrophic engine failure. Preventative maintenance is cheap insurance to ensure that your vehicle runs as smooth as possible for many miles to come.
If further technical assistance is needed, our certified car repair technicians are ready to answer your car questions.
Related Car Repair Information