P0300 misfiring randomly

[99expo54]

99 expo with the 5.4. Obx long tubes with no cats, cold air intake, e fans, and edge programmer. Truck has ran great since the mods where done 5 months ago. Last 3 weeks i keep getting the p0300 code. Replaced all coils and plugs, pcv, and fuel filter. Didnt help anything. It will run fine one day with no codes, then other days it will throw the code every 3 minutes. Idles rough about 50% of the time. Motor has also been getting alot warmer than normal since this started....210-220 degrees. Head temp stays around 190-192 though. Any ideas? Im lost.

 

[Mediamonkey11]

Have you checked compression? Night be losing a cylinder, at least it'd rule it out.

 

[99expo54]

Have you checked compression? Night be losing a cylinder, at least it'd rule it out.

No i have not yet. I was hoping not to have too. Sounds like a pita on this motor. What do you think; bad ring or valve or something? When i changed the plugs, one was pretty oily.

 

[Mediamonkey11]

Then if a cylinder were bad, it'd likely be the rings... It wouldn't be harder than changing the plugs to check though.

 

[99expo54]

Then if a cylinder were bad, it'd likely be the rings... It wouldn't be harder than changing the plugs to check though.

What should compression be sitting af for psi?

 

[Mediamonkey11]

My guess would be around 175psi, however if you have a bad cylinder it'll read significantly lower than the rest. Ideally you want all the cylinders within 10% of eachother.

 

[99expo54]

Never mentioned ive been getting oxygen sensor codes since my headers where put on. Never made it run rough though. Could this cause these issues in the long run? Drivers side valve cover has a definite tick to it I also just noticed.

 

[FordandPolaris]

I would say the tick is of little concern and is probably not related. It is common on the old 5.4's to have a tick in the motor. Mine has been ticking for nearly 70,000 miles. Mine goes away after oil pressure builds up though, so if it stays around no matter the engine temp then that is different.

The O2 codes are most likely from the lack of cats. The computer looks for some kind of change between the forward sensor and the downstream sensor. If it detects nothing, it throws a code.

 

[RedDragon777]

does the edge programmer allow you to turn off your O2 sensors or just can tunes. I would recommend an SCT custom tuner and have someone like 5star make a custom tune for you.

 

[99expo54]

does the edge programmer allow you to turn off your O2 sensors or just can tunes. I would recommend an SCT custom tuner and have someone like 5star make a custom tune for you.

It does not allow me to turn off the sensors. Power hungry is writing my tunes as we speak.