Sylvie Willis
Misfiring fuel injectors can be caused by a variety of issues, including engine mechanical problems, faulty ignition systems, control circuit issues, imbalanced air and fuel delivery, and sensor and module problems. If you are experiencing a misfire, it is important to address the issue immediately to prevent further damage. While replacing a fuel injector is an option, it is an expensive one and should be considered a last resort. Before attempting to replace the injector, it is recommended to bleed fuel pressure, remove the intake manifold, and remove the rails. This article will provide a step-by-step guide on how to replace a misfiring fuel injector, including common issues to look out for and potential solutions.
| Characteristics | Values |
|---|---|
| When to replace a fuel injector | As a last resort, as it is the most expensive option. First, try decarboning the valves, bleeding fuel pressure, removing the intake manifold, and removing rails. |
| How to replace a fuel injector | 1. Start with a cold car, disconnect the battery, and remove the connectors on top of the fuel rail. |
| 2. Remove any clips or nuts holding the fuel rail in place and physically pull out the individual fuel injectors. | |
| 3. Press the injector into the rail until it stops. Attach the metal clip, if equipped. | |
| 4. Reattach the fuel rail. Line up all the injectors over their respective holes, then press each injector until they slide into place. | |
| 5. Bolt down the fuel rail. Reattach the fuel line. | |
| 6. Plug in fuel injector electrical connections. Reconnect the battery. | |
| 7. Turn the key to the on position and wait 10 seconds before turning to engine start. After the engine drops to the normal idle RPM, turn the engine off. | |
| What to do if there is still a misfire | Check the wiring to the injector. |
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What You'll Learn
How to check for a misfiring fuel injector
If you suspect that your car's fuel injectors are misfiring, there are several warning signs to look out for. Firstly, check if your car is having trouble starting or staying running. Excessive engine vibration is a common sign of misfiring fuel injectors, which can occur due to a lack of fuel in the cylinder. You may also notice that your car is struggling to accelerate or losing power. This is because the fuel injectors are responsible for supplying fuel to the engine, and if they're not working correctly, the engine won't be able to run at full power.
Another way to check for a misfiring fuel injector is to pay attention to any unusual sounds or smells coming from the engine. A misfiring fuel injector can cause popping sounds, exhaust manifold backfires, and strange smells. Additionally, you may notice that your fuel consumption has increased, and your emissions have risen.
The Engine Control Unit (ECU) plays a crucial role in monitoring and controlling the fuel injected into the engine. If the fuel injector fails to deliver the correct amount of fuel at the correct time, the ECU will detect fluctuations and trigger the "Check Engine" light to illuminate. If this light is flashing, use an OBD2 code reader to determine the trouble code.
Finally, rough idle or engine stalling at low RPM could also indicate a problem with the fuel injectors. This is often due to debris build-up at the injector nozzles, which affects the quantity of spray and atomization of gasoline. However, it's important to note that these issues could also be attributed to other components, such as grimy air filters or spark plugs. Therefore, it's always best to consult a mechanic if you suspect any issues with your fuel injectors.
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How to bleed fuel pressure
To bleed fuel pressure, you should first remove the intake manifold and then the rails. You should also decarbon the valves, as this is more likely to relieve your single-cylinder LNF misfires. You can pull the intake to check, or use a $20 borescope to sneak into the brake booster fitting hole (remove fitting).
If you only replace one injector instead of the entire rail assembly, you will need to replace the other seals, using special tools ($100) to resize new seals.
If you have changed the injector and PCM and still have a misfire, there may be a problem with the wiring to the injector. You can check this by testing for 12 volts at the injector without turning over the engine. Simply turn the key to the on position and disconnect the injector connector. Connect the positive lead of your voltmeter to the injector terminal that is connected to the PCM. Connect the negative lead of your voltmeter to the engine block. You should see 12 volts at the injector terminal.
You should also check the following:
- Make sure the injector connector is properly seated
- Check the injector wire for continuity from the PCM to the injector connector
- Check the injector wire for resistance. If the resistance is too high, the wire is faulty and needs to be replaced
- Check the injector ground wire for continuity from the injector connector to the engine block
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How to remove the intake manifold
To replace a misfiring fuel injector, you must first bleed the fuel pressure, remove the intake manifold, remove the rails, decarbon the valves, and replace the seals.
- Remove the air filter and air filter container.
- Open the hose clamp with a flathead screwdriver.
- Remove the carburetor's fuel line and any vacuum lines attached to the carburetor.
- Remove the links attached to the throttle by unscrewing the screws with a screwdriver.
- Loosen the nuts holding together the carburetor and intake manifold.
- Remove the upper radiator hose from the intake manifold by loosening the screws with a flathead screwdriver.
- Loosen the bolts fastening the intake manifold to the engine.
- Clean the surface of the engine.
- If the manifold is glued down, use a urethane or nylon mallet to gently tap it from the front towards the firewall until it pops and slides out. Alternatively, use a putty knife or flathead screwdriver to pry it up and off.
- Run a razor blade along the front and rear of the intake to slice through any sealant. Then, run the razor blade along the sides of the intake to break the seal.
- Prep the new intake manifold for installation by checking for any leaks from the gaskets and applying gasket sealant on both sides of each gasket.
- Fit the new intake manifold into place next to the engine block.
- Replace the bolts, screwing them in and securing the intake manifold to the engine.
- Reinstall the upper radiator hose, distributor, carburetor, links to the throttle, carburetor fuel line, vacuum lines, and air filter.
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How to check the injector connector
To check the injector connector, you can test for 12 volts at the injector without turning over the engine. Turn the key to the on position and disconnect the injector connector. Connect the positive lead of your voltmeter to the injector terminal that is connected to the PCM. Connect the negative lead of your voltmeter to the engine block. You should see 12 volts at the injector terminal.
If you have changed the injector and PCM and still have a misfire, with only 0.50 volts coming from one of the 2 injector wires, then there is a problem with the wiring to that injector. Make sure that the injector connector is properly seated. Check the injector wire for continuity from the PCM to the injector connector. Check the injector wire for resistance. If the resistance is too high, then the wire is faulty and needs to be replaced. Check the injector ground wire for continuity from the injector connector to the engine block. If the wiring is good, then the PCM may be faulty.
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How to check the injector wire for resistance
If you have replaced the injector and PCM and are still experiencing a misfire, the problem is likely with the wiring to the injector. To check the injector wire for resistance, you can follow these steps:
- Make sure that the injector connector is properly seated.
- Check the injector wire for continuity from the PCM to the injector connector.
- Check the injector wire for resistance. If the resistance is too high, the wire is faulty and needs to be replaced.
- Check the injector ground wire for continuity from the injector connector to the engine block.
If you have checked all of the above and the wiring is good, then the PCM may be faulty.
To test for 12 volts at the injector without turning over the engine, simply turn the key to the 'on' position and disconnect the injector connector. Connect the positive lead of your voltmeter to the injector terminal that is connected to the PCM. Connect the negative lead of your voltmeter to the engine block. You should see 12 volts at the injector terminal.
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Frequently asked questions
Misfiring can occur due to engine mechanical problems, faulty ignition systems, control circuit issues, imbalanced air and fuel delivery, sensor and module issues, or a dirty or clogged fuel injector.
Before replacing your fuel injector, it is recommended that you first try decarboning the valves, bleeding fuel pressure, and removing the intake manifold and rails.
It is recommended that you get a professional to replace your fuel injector.
If you have replaced your fuel injector and are still experiencing a misfire, there may be a problem with the wiring to the injector. You can test for 12 volts at the injector without turning over the engine. If the wiring is good, then the PCM may be faulty.
PCM stands for Powertrain Control Module.
