Cylinder #4 Dead miss...Please Help!!

[350jeepcj5]

Well, i have a problem. about 2 months ago i replaced all 8 spark plugs and all 8 cops on my expy, went on a 600mile round trip through the mountains pulling a trailer and everything went beautifully. Fast forward to now, my wife told me the other day that she was on her way home and the expy started to shake/miss, but went away. I didnt think much of it because it was late, so i left it go. Next day she calls me on her way home same thing, except this time i got a code, cylinder 4 missfire, clear the code everything was ok again. this morning go out and start it up, its is missing bad. So i pull the coil off and pull the plug out everything looks okay. I went to the store and exchanged that coil for a new one also bought a new plug because they are cheap. Reinstalled, same thing. With it running i can pull the coil wire off of cylinder 4 and notice hardly any change, pull it off of any other an i can hear a noticeable difference. So where should i start now? Get a noid light and check to make sure the injector is firing? Check to make sure coil is firing? Th way it was intermittent makes me think it is not an internal issue, am i right to think this?

 

[toms89]

Well, i have a problem. about 2 months ago i replaced all 8 spark plugs and all 8 cops on my expy, went on a 600mile round trip through the mountains pulling a trailer and everything went beautifully. Fast forward to now, my wife told me the other day that she was on her way home and the expy started to shake/miss, but went away. I didnt think much of it because it was late, so i left it go. Next day she calls me on her way home same thing, except this time i got a code, cylinder 4 missfire, clear the code everything was ok again. this morning go out and start it up, its is missing bad. So i pull the coil off and pull the plug out everything looks okay. I went to the store and exchanged that coil for a new one also bought a new plug because they are cheap. Reinstalled, same thing. With it running i can pull the coil wire off of cylinder 4 and notice hardly any change, pull it off of any other an i can hear a noticeable difference. So where should i start now? Get a noid light and check to make sure the injector is firing? Check to make sure coil is firing? Th way it was intermittent makes me think it is not an internal issue, am i right to think this?

Odds are mechanical issues would not come and go they just get progressively worse. Electrical issues can be intermittent due to the nature of vibrations, moisture, corrosion, etc... So electrical would be my bet.. Sounds like your on the right track.

A compression test could eliminate mechanical issues though..

 

[Captain Morgan]

Hey Tom89, since he unseated the 12v plugs to the cops, he might not have a really good connection there?

I wonder if checking the prongs on the plug and maybe burnishing that up wouldn't hurt?


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[350jeepcj5]

Hey Tom89, since he unseated the 12v plugs to the cops, he might not have a really good connection there?

I wonder if checking the prongs on the plug and maybe burnishing that up wouldn't hurt?


.

I will check this tonight, i am also going to check to see if i have power and ground on each plug, the injector and the coil. which wire would be which, as far as hot and ground go?

 

[350jeepcj5]

well i drove the expy to work this morning, strted up fine and went about 300 yards and started missing, then it straightend out and started missing, did that all the way to work, was better if i ran it with od off though. Checked codes at work and got a multiple misfire code. went into work and at lunchtime took the scanner out and let it run a while, the multiple missfire code was gone and it had the cylinder 4 missfire back. i tried to moniter missfires on the scanner but it wouldnt show them to me? its an otc genisys if that matters.

 

[350jeepcj5]

little bit more info, truck starts and runs as it should after sitting, then begins to miss. you can hear a loud ticking while it is running smotth, then it goes quiet and starts to miss. Do you think this could be a bad injector on cylinder 4?

 

[celticfdguy]

I am dealing with the SAME exact issue...

I am replacing the spark plug tonight... Going to figure out how I can test out the engine coil as well. Ill keep you posted.

 

[toms89]

I will check this tonight, i am also going to check to see if i have power and ground on each plug, the injector and the coil. which wire would be which, as far as hot and ground go?

With the ignition on you will have positive battery power at each coil. It should be Red/LG wire and common to all the coils. The ground leg varies in color depending on the coil. The ecu opens the ground wire to "fire" the coil and you always have battery + power.

 

[toms89]

little bit more info, truck starts and runs as it should after sitting, then begins to miss. you can hear a loud ticking while it is running smotth, then it goes quiet and starts to miss. Do you think this could be a bad injector on cylinder 4?

If the ticking sounds like an exhaust leak check to make sure the plug is not backing out. You may be about to launch a spark plug!!!

 

[Captain Morgan]

Yeah good catch

What's the likelihood that the COP isn't sitting on the plug all the way, or the spring in the COP is not all the way down against the plug?.

An air gap in the plug line would let the cylinder for randomly and make a pronounced TICK sound.

Thee are HV checkers you can buy that will light up, but they are made to work with a COP screwed down. (it is bolted down right?)

Try raising the hood in complete utter darkness and looking for sparks, and turn a funnel around to your ear to use as an amplifier and see if you can locate the exact source of that ticking.


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