workerbee

I have a '97 5.4L with the coil over plug design. I have a situation where cylinder #5 is misfiring at some times and but not at others and not enough that the "Check Engine" light turns on but more than enough to be a nuisance. And exchanging the coil and boot with a different cylinder does not move the problem. The fact that it only happens occasionally and only when the egine is hot makes me wonder if the Powertrain Control Module is bad. The OBDII reader diags report no issues with the fuel injectors but I'm not ruling them out. Has anyone had this problem? What was the cause? And is there anyway to test the PCM? I'd hate to have to buy one without knowing for certain....

NGM

Check for a vacuum leak.

torkum

It is possible that a sticking EGR can cause a misfire. What about the plug?

workerbee

The sparkplugs were replaced last year but I can't imagine a sparkplug causing a problem on an occasional basis. The EGR however, I'm wondering about. I have since discovered the truck runs much better when the atmosphere is dry and cool. If the humidity goes up and/or the heat, the misfiring is much more previlent. And again, the problem never shows up before the engine heats up.

Does that give some additional ideas?

czecher01

I've got a 98' f150 4.6 v8 and the same thing happened to me. Last year sometime before the winter I replaced the spark plugs and last month I had the same problem your describing here. The only thing diffenent is that my check engine light would blink when it misfired and stay on when it didn't. I checked the plugs and the boots finding out that there was some moisture in the boots themselves. I cleaned the plugs and the boots dry and it didn't happen again till it rained. But it didn't happen until about 2 days later. Looked at the plugs and the boots and they were in the same shape as the last time so I ended buying new plugs and wires and buying some speacial stuff to go around the boots to keep the moisture out. It has rained a numerous amount of times and the truck runs great!
hope this helps.
p.s. when i say that it rained, i mean that i was driving in the rain.