Can a Bad Egr Valve Cause a Misfire? Answered!

A car developing an engine misfire can send you into panic mode, no matter the cause! The exhaust gas recirculation valve, or EGR valve for short, is a problematic component of an engine that can cause problems such as a misfire.

The thing with that is the EGR valve is rarely the direct cause of the misfire. It is usually another issue causing it, such as a carbon blockage, preventing the EGR valve from operating correctly. Which if you’re interested is all explained in more detail below.

Role of the Egr Valve

The Exhaust Gas Recirculation (EGR) valve is an emissions control system; I guess you could similarly to a catalytic converter. Its role is to reduce nitrogen oxide (NOx) emissions, improve engine performance and fuel efficiency. It redirects some exhaust gases into the engine to be re-combusted. By introducing colder exhaust gases into the combustion process, the EGR valve lowers the combustion temperatures inside the engine cylinders. A cooler running engine reduces the formation of harmful NOx gasses.

Can a Bad Egr Valve Cause a Misfire?

A bad EGR valve can cause a misfire if it is faulty. However, there are specific issues related to the EGR valve that are more likely to cause the problem. These include:

  • Flow disruption – If the EGR valve becomes stuck in the open or closed position, the flow of exhaust gases into the intake manifold becomes restricted. Any alterations to the air-fuel mixture in the engine cylinder being combusted can potentially lead to misfires.
  • Blockage – Carbon deposits can accumulate in the EGR valve and its passageways over time. A build-up can restrict or block the flow of exhaust gases, impacting engine performance and potentially causing misfires.
  • Leak – A leak in any part of the EGR system can affect the air-fuel ratio and cause misfires. A leak means exhaust gasses are escaping, which can be caused by a faulty gasket, leaking clamp, or a vacuum leak (most EGR valves are vacuum-controlled, but modern versions are electronic).
  • EGR valve malfunction – If there’s a faulty EGR valve internals, sensor, or control solenoid, it could stop the operation of the EGR valve. This can result in an engine operating without an EGR valve working when it thinks it is working. As a result, it may begin to misfire.

One thing to note is when an EGR is faulty, you can usually expect the engine warning light to illuminate on the dashboard, so a misfire may not be the only symptom the EGR valve is bad.

Signs the Egr Valve Has Failed

Aside from the fact the engine may be misfiring and the engine management light will be illuminated, there are a few other signs that indicate the EGR valve has failed or is failing, which include:

  • Rough idle – A faulty EGR valve can contribute to the engine running rough or shaking at idle. Usually, the vibrations will not be so noticeable when driving the car.
  • Reduced engine performance – The vehicle may feel sluggish, struggle to accelerate, or have a delay when pressing the accelerator. This is usually a sign the EGR valve is stuck open, and the engine is struggling to cope with the number of exhaust gasses drawn back into the engine.
  • Increased fuel consumption – Another problem with an EGR valve stuck open or closed. It can increase fuel consumption as the engine struggles to cope with excess or lack of air (oxygen). It injects more fuel to counteract the issue.
  • Excess exhaust smoke – If the EGR valve is stuck in the closed position, gasses are not returned to the engine. Instead, they are emitted from the exhaust. You may notice more smoke than usual, but this will never be excessive because of an EGR valve.
  • Engine stalling or difficulty starting – A bad EGR valve can sometimes cause the engine to struggle to start or continue to stall once running. This is a sure sign the EGR valve is stuck open when it should be closed on start-up until the engine is warm where it should open.
  • Failed exhaust emissions – As EGR valve contributes to the removal of nitrogen oxide (NOx) gasses. If the EGR valve is not functioning correctly, NOx emissions will increase, resulting in a failed emissions test. With no other warning indications, this is the most common way of finding out your EGR valve is no good.
  • Strong smell of exhaust gassesA strong smell of exhaust gasses could indicate a blockage in the EGR valve or a leak is present.
  • Knocking noise in the engine – If the EGR valve is stuck in the closed position, cold exhaust gasses are not passed back to the engine to cool combustion temperatures. This causes the temperature and pressure inside the cylinder to rise, which causes fuel to detonate without a spark from the plugs. You can hear a loud knocking noise from the engine when a spark knock occurs.
can a bad EGR valve cause a misfire

What to Do if You Have a Bad Egr Valve

If you suspect a bad EGR valve, you should first plug the car into a diagnostic machine, especially if the engine management light is illuminated. This will confirm if the EGR valve is causing the problem.

If it is faulty, or if you’re sure it is without an OBDII code reader, you can try cleaning the internals of the EGR valve before just replacing it.

A common cause of an EGR valve failure is a build-up of carbon causing a blockage. You can sometimes clean the blockage by removing the EGR valve, soaking it, and cleaning it with some carburetor cleaner and a stiff wire brush.

Next, refit and clear the fault codes where possible; sometimes, they can clear themselves if the car’s ECU detects everything is working as it should. However, if the valve internals have failed, you must replace the EGR valve. Just remember to clear the fault code before you drive the car again.

It’s good practice to use fuel treatments that aid in cleaning and preventing EGR valve failures occasionally. As well, as some spirited driving occasionally will help prevent a build-up of carbon that develops when idling and lots of stop-start type driving.

How Far Can You Drive With a Bad Egr Valve?

It’s not advisable to drive with any element of the car not working correctly, including the EGR valve. In some cases, you could drive around for long periods without knowing the EGR valve is problematic. So, how far you can drive depends on the failure and the problems it’s causing.

For example, if the valve is stuck open, excessive exhaust gas recirculation can lead to carbon build-up, fouling of spark plugs, or other issues that can affect your ability to drive. If the EGR valve is stuck closed, you can get a spark knock which will cause the head gasket, rods, pistons, piston rings, and cylinder walls to fail. So I would advise you wouldn’t want to drive far.

Final Words

Although EGR valves can cause a misfire, it’s fairly uncommon; you’re more likely to experience another issue, such as a rough-running engine caused by blockage of carbon and soot in the EGR valve. The good news is nine times out of ten, you can clear a blockage by removing and thoroughly cleaning the EGR valve.

Now that you know how temperamental and problematic an EGR valve can be, instead of finishing reading here, next read How to prevent EGR valve failure. You’ll be able to save yourself all the troubles of worrying about an EGR valve causing a misfire.

My name is Tom although my friends call me Tommy. Messing around with cars and bikes has always been a hobby of mine even from a young age. So I made it my day job 17 years ago. I am a fully qualified mechanic as you would expect. I've worked in all different areas of the motor trade, valeting, panel beating, engine repairs, I'm sure you get the idea. I enjoy sharing my wealth of knowledge and experience with others, which is the reason I spend a lot of time here writing for this website.

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