I have a 2004 f150 w/ a 5.4 triton. The truck developed a missfire about a week ago. At idle the truck runs horrible and the engine shakes arond very bad. when driving the truck it also runs very rough, worst when the truck shifts into over drive and lugs. I changed the coil packs plugs and injectors. the check engine light comes on and shows a P0357 code. primary/secondary circuit malfunction. But the cylinder 7 plug when pulled is black with all kinds of wet carbon build up. (Like Sludge). None of the other plugs look like this.. Whats the problem?

 

I'd swap the injector to a known good one and see if the miss move. If it does replace it. if it dont move the coil see if it moves (you should probably move the coil first)..

 

I changed every coil pack, plug and injector. I cleared the DTC's and the code reappeared. Sometimes the code did jump to other cylinders but now has stayed on the "G CIRCUIT" or #7 cylinder. The plug is what worries me. Its Black and wet. Just like the plug isint firing at all. But i had a spare plug and made sure the fire was traveling through the coil and the plug.

 

compression test next.

 

Just ordered the adapter to fit the 5.4. If the compression comes back low what would be the base problem? If the compression comes back normal (dont think it will) whats the case? So whats the normal compression rate for the 5.4. about 105,000 miles. Buy the way both CATS were also removed to see if this was the problem. temps were also very weird. o2 sensors were reinstalled. Exaust man said that one CAT was cloged the other was on its way.

 

It's not the exact compression numbers you get that's important - it's the consistency between cylinders.

 

Did the compression test and found some bad news. Cylinder 7 compression is "ZERO". Just bought valve springs and new rocker arm.Pulling the valve cover off shortly to see whats happened internaly. Ill keep you updated.

 

I have the same issue, the dealer pulled the valve cover and could not find anything wrong and wanted to pull the head to see if it's a stuck valve or a cracked head. let me know what you come up with. I have a 2004 5.4 with 63,000 miles

 

Going through this now, with an 08 with 68K on it. Computer says #3 cylinder isn't firing. Replaced the coil pack, it's got spark. Don't have the tool to do the compression test and have to wait until Monday.

Worst part is that it's my wheelchair hauler so I'm stuck home until we figure this out.

*sigh* My chevy friends are getting mileage out of this, I'll tell ya.