Engine misfiring

Hi Sargeandy,

This sounds more like a fuel issue. the P0300 code is a multiple cylinder misfire. This means that the one cylinder can misfire and then the next time it does not but a different cylinder misfires. Basically, this is a misfire that does not have any consistency to it.

There are a number of things that can cause this but the most common cause is the fuel system because we are looking for something that effects all cylinders not just one.

This could also be a coil but again, this is less likely than fuel.

https://www.2carpros.com/articles/engine-misfires-or-runs-rough

I would suggest starting with getting the fuel pressure while this is misfiring. If you have low pressure then it is either the pump or the regulator.

Let me know what the fuel pressure is and we can go from there.

https://www.2carpros.com/articles/how-a-fuel-pump-works

https://www.2carpros.com/articles/how-to-check-fuel-system-pressure-and-regulator

P0300 - Random/Multiple Cylinder Misfire Detected.
P0301 - Cylinder 1 Misfire Detected.
P0302 - Cylinder 2 Misfire Detected.
P0304 - Cylinder 4 Misfire Detected.
P0314 - Unspecified cylinder misfire.

We do not have service information for your brand, and you did not list an engine size so I cannot look up which type of ignition system your car uses. The typical suspects for multiple misfires include worn spark plugs and wires. Some cars have known problems with ignition coils too.

How many miles are on the engine? Have you checked compression? Have you checked the injector to make sure it is good?

If you remove the #2 spark plug, is there spark to it? If there is, there is either a problem with the injector, wiring to the injector, or low compression in that cylinder. It isn't hard to check.

First, remove the plug and check to see if there is a hot blue snapping spark to it.

Here are directions for checking spark, fuel injectors, compression...

https://www.2carpros.com/articles/engine-misfires-or-runs-rough

Do these checks and let me know what you find. You will need a few tools, including a compression gauge. Most parts stores will lend or rent them to you.

Hey Bev,

It sounds like the fuel filters need to be changed or the injector/fuel pump is going out which has been a problem with those cars. Also if you have a fuel dryer I would add that to the tank because moisture in the fuel can cause the problem;em you describers as well.

Let me know what you find

Best, Ken

Hi Bev,

when one of the cylinders is not firing is one of two tings, low compression or no fuel getting to the cylinder. If you can do a compression test over the weekend it might help narrow it down.

Let me know what happens

Yep, this will be an injector pump problem, pretty normal failure for diesel engines.

That is way too much information to digest. With absolutely no test results, clues, or observations to go on, about all you can do is replace the spark plugs and wires and hope for the best.

Next you will need to pursue the less-common causes. As a test, consider switching two injectors. Erase the fault code, then see if it sets again for the same cylinder or the one you moved the suspect injector to. This works too for spark plug wires, spark plugs, and individual ignition coils when those are used.

Next would be a compression test. If you find it is low on cylinder four, a "cylinder leakage test" will identify why it is low. I can describe that in more detail if it becomes necessary. The tester can be hard to find. A lot of shops do not even have one.

Timing is also critical, but that is not going to change for just one cylinder, so we can forget that.

Replace the ignition wires. Swap number 4 injector with number 1, 2 or 3 injector. See if the misfire codes changes to that pot?