My son-in-law has a 2008 F-150 with the 5.4. His truck has developed an intermittent miss fire in cylinder #2. (No other codes shown other than cylinder 2 misfire) His CEL will flash several times while it is miss firing. Sometimes the light stays on, sometimes it doesn’t. When it does stay on, it usually goes out on its own in a day or so. He recently had the plugs changed (116K) and the problem surfaced shortly thereafter. I initially thought it was a bad coil so we replaced it. When that didn’t cure it, we took it back to the shop where he got the plugs changed. They thought it was a faulty spark plug but that didn’t pan out either. They cleaned the fuel rails and swapped out the #2 fuel injector but the issue is still there. They took it for a test drive with their code reader attached. No issues were found other than the cylinder #2 misfire. I should mention that they treated the truck with Sea Foam the day before the plugs were changed. They put it in a vacuum line and in the gas tank. We were told that this would soften and clean carbon deposits which would make the spark plugs come out easier. They were right because none of them broke off. Anyone have any suggestions?

 

Have them check base compression on #2.

 

Thanks, will try that.

 

you might inspect the electrical plug on the injector and coil... make sure the wire didn't get bent / cracked , or the two pins inside the plug got damaged during reinstall........ also check the boot on the coil if it was not replaced with the new coil.

 

Looks like maybe a head gasket issue. A compression check showed # 2 at only 50 pounds and number one at 100. Upon checking #2 again, it was showing 100 with cylinder # 1 at 50. Cylinder 3 was normal. The mechanic said that he has seen it once before where a blown head gasket allowed the compression to leak back and forth between the two cylinders. The truck also needs an exhaust manifold so now would be the time to swap that out with no labor cost.

 

So much crap builds up around intake valves that some have had sticking valves . Just heads up when you have head off anyway . All that oil from crank case ventilation craps up in intake . No pcv valve, its kind of built into the valve cover on drivers side .
Check out carbon build up around spark tips . A lot of us are cleaning that area out with carb cleaner during plug changes as it can damage new plugs going in and change heat range .
Nice to know what you find .

 

Thanks for the tip. I'm not sure what they plan to do at this point. (I am gently trying to persuade them to repair and keep the truck) I will keep you all updated as to what we find out.

 

The issue was found to be bent exhaust valves in # 1 and #2. They were not properly closing. The pistons and both heads were not damaged. Further inspections showed that the cause was 20 out of 24 valve springs were so weak that they could easily be compressed between your thumb and finger. Four new valves and 24 new valve springs and a gasket set. We will also be replacing both exhaust manifolds as they were cracked. The engine is not back together yet, I'll let everyone know how it turns out.