I have a 98 4.0 that was having misfiring problems.I replaced the ECU and it ran good for ten miles then started acting up again.I am a heavy equipment mechanic so i know a bit about what I'm doing.I replaced the spark plugs,ohm tested the plug wires,new dis. cap,new rotor,checked the injectors and their connections,used a noid light on the injector plug ends,cleaned up the throttle body...all the usual stuff..even replaced the fuel pump module a few weeks ago.Ran good till the other day then..poof..started misfiring.No check engine light has come on either.It doesnt misfire all the time..it idles a little rough but will run fine for a few minutes then will start sputtering for a few..sometimes longer periods..sometimes shorter..HELP..I am stumped.Any advise would be appreciated.I also checked the MAP sensor voltage and it is what I have read on here and is working properly.I have searched on this forum and still havent seen the "golden" fix.

 

I stuck it on my Snap On scan tool and it threw out codes PO700 transmission fault...but it is shifting fine..PO108 MAP sensor voltage to high...But i tested it like someone on here said and it was in the parameters and when i drove it it went from 1 volt at idle to maximum of 3.8 volts at speed..and PO205 injector 5 control circuit fires improperly.I switched the injectors around and still has this code.I also checked the wires to injector..all same ok...now i'm really stumped..HELP PLEASE

 

Never mind...I fixed it..run good and normal again.

 

what did you do to fix it? what was the problem?

 

Yes, please share the fix so we can all learn!

 

I stuck the noid light on the number 5 injector wire one more time and this time it was very bright and was constantly on.I began checking it with my multimeter and it had 12v going to it.I started checking the wire back to the ECU and took off the tape and wire loom.I eventually found the wiring harness at the back of the engine was very close to the exhaust manifold and wiggled the wires and it started running normal and the noid light was working properly.i pulled the wires apart and rewrapped them.I didnt find any bare or melted wires but I guess they got hot enough that they fused together that number 5 wire must have shorted with another wire.It seems like it always the easiest thing to fix but the hardest to diagnose.