Code P0304

Hi,

Is it only cylinder four that has the misfire code? Interestingly, the A/C places a load on the engine and allows the idle air control valve to allow more air to enter the combustion chamber. I'm wondering if the fuel injector is starting to fail in cylinder four.

If it is only cylinder four, I don't feel it would be things like a vacuum leak or low/high fuel pressure because that would affect all cylinders and you would likely have a P0300. So, it makes me think about what I mentioned or even if the cylinder compression is low on that cylinder.

Tell me, have you removed the spark plug and ignition wire for inspection to cylinder four? If so, was there anything out of the ordinary found?

If not, take a look through these two links and let me know if you are comfortable performing them or if you have already done this. Also, if you don't have them, most parts stores will lend you a compression gauge and fuel pressure gauge free of charge.

https://www.2carpros.com/articles/how-to-test-engine-compression

https://www.2carpros.com/articles/how-to-test-a-fuel-injector

Let me know. Also, let me know if you have checked fuel pressure and fuel pressure drop-off.

Take care,

Joe

Hi,

They aren't adjustable on this vehicle. Also, you would hear a ticking sound if they were loose.

The sound you hear may indicate a possible issue with a plugging catalytic converter, but I don't feel that would cause only one cylinder to misfire.

Since it is specific to one cylinder, I feel that is where we should focus. If it was random or multi-misfire with different cylinders, then I would be looking at other possible issues.

Regardless, let me know what you find with the tests. Also, let me know if there is anything I can do to help.

Take care,

Joe

Hi,

First, connect the pressure gauge. Turn the key on so pressure rises. When you turn the key off, it should only drop about 10 PSI within five minutes.

Let me know if that helps.

Take care,

Joe

Hi,

The valve core in the fuel pressure port is similar to the valve core in a tire. There are tools made specifically for them. I attached a pic below, so you have an idea of what it looks like.

The compression is a concern. The idea that it is 90 dry sounds too low. Also, you went up 36 psi wet, so I suspect the compression rings are worn in that cylinder.

Interestingly, Ford doesn't provide a minimum compression required. Instead, they tell us between the lowest and highest cylinders, they need to be within 75% of each other. Basically, with that cylinder at 90 psi dry, there can't be a cylinder with more than 112 psi. Even 112 is somewhat low. If I recall (from memory) I used to see them around 150psi +.

You could check all of them to see what is found. However, my theory is low compression in the number 4 cylinder is causing the misfire.

Let me know.

See pic below.

Hi,

The valve core should be tight. My concern is with the compression. Are you comfortable checking all of them?

Joe

I'm sorry. I thought that is what was loose. I was wondering how you were able to tighten it with an open-ended wrench. LOL

Are you sure the adapter is the correct one? That doesn't make sense unless the threads are damaged on one or the other.

Joe

The only thing I can say is it has to be the wrong adapter. Have you tried seeing if a local parts store to see if they have one?

Joe

Hi,

I can't believe how many faulty parts and tools such as this I am seeing anymore. As far as driving it, let's do our best to get it running the best we can.

I have a feeling the ultimate cause of the issues is compression. Let me know if you checked the other cylinders.

Take care,

Joe

Okay. If you have the chance, you may consider testing all cylinders so we can compare. I have a feeling the fuel pressure isn't the issue.

Let me know.

Joe