#3 misfire HELP!!!!

[Johnwimber1]

Hey guys so I have a #3 misfire on the 5.0 I’ve changed wire spark plugs coils even injector and still have the miss I can’t figure this thing out for the life of me and yes I checked compression and it’s normal what else possibly could be wrong? It’s weird because it going in and out of having a miss it isn’t constant but it’s pretty bad when it is I’ve tried everything please help thanks guys

 

[410Fortune]

I suspect a leaking EGR valve
Do you have the ability to do a smoke test?

You replaced just the one injector?
Have you checked fuel pressure?

Had a 2000 Ranger we converted to a 306, brand new Jasper reman engine. Used new just about everything on the build, all new gaskets when installing all the explorer parts onto the Jasper longblock. I have sealed up many many 5.0. Once we put the truck together everything was perfect for the first couple hundred miles. Then it developed a misfire. Like you we replaced the injectors, the coils, the plugs, wires, checked compression, leak down test, fuel pressure, etc etc etc. Finally did a smoke test and found a leaking EGR valve. The actually EGR valve on the back of the manifold had a pinhole leak. Misfire solved!

The PCM kept telling us misfire cyl 7

A new EGR valve and gasket solved it

In all my years of building and maintaining these 5.0 trucks that was the first time I have ever seen that.
Smoke test was how they found the leaking valve (truck was now 8 hours away from me)