Code P0304 at first and now P0300

Hi,

The images didn't upload for some reason. As far as the issue, when you indicate smelling fuel, does it smell like raw fuel, or does it seem like a rich fuel mixture from the exhaust?

I ask because there are several things that can cause a rich fuel mixture and a random misfire. For example, if the vehicle is running extremely rich, it can be caused by excessive fuel pressure, a faulty MAF sensor, a faulty engine coolant temperature sensor, and the list goes on.

Let me know if there are any other codes. Also, let me know if your scan tool has live data. If it does, check the ECT (temperature sensor) to see if it is accurate, also, let me know what the short-term fuel trims are.

I will watch for your reply.

Take care,

Joe

Hi,

I read through the pics all but the last one. I can't read that one. The fuel trims look fine. The one thing that has my focus is the intake air temp sensor, (IAT). The engine was at 194F and the IAT says 73F. What was the outside temperature when this test was done?

Let me know. If you are driving at highway speed, normally I see the temperatures approximately 10 degrees above ambient temp. If that is the case, the day you checked this it would have been approximately 63 degrees.

Let me know your thoughts.

Take care,

Joe

Okay, the temperature looks correct. If the misfire has returned to cylinder 4 again, that has to be where the issue is coming from. The flashing check engine light happens as the misfire is occurring.

So, since the plugs are new and coil packs and that made no change, I suspect we either have excessive fuel pressure due to a faulty fuel pressure regulator, or we have a fuel injector leaking in cylinder 4.

What I need you to do is check the fuel pressure and fuel pressure drop-off. Fuel pressure drop-off is when the key is turned off and the pump stops. It's the amount of time it takes for the pressure to fall. If it happens very quickly, then there could be an injector leaking.

Here is a link that explains in general how it is done:

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

Please keep in mind, engine compression in cylinder 4 may be low enough to cause this as well. If the mileage listed above is original on this engine, it is a good possibility.

If you look below, it provides the directions specific to this vehicle for testing pressure and drop-off. Note: It provides two ways of doing it. One is with a scan tool that can communicate with the modules, and the other is without. I included both just in case.

Let me know what you find.

Take care,

Joe

See pics below. If this tests within spec, we will need to check engine compression.