Misfire Help

D M

CEL free! (again)
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Developed a misfire a few weeks ago, noticed it would only do it when starting the motor after already at operating temp. P0204- is an injector issue but Is this heat soak related? I cannot get it to replicate when the engine is cold, and sometimes it goes away quickly while driving or lasts a long time and I have to let it cool back down.

I replaced the spark plugs with Autolite XP985s, my old ones were roached, but it just cane back today when going to the grocery store... parked in the hot parking lot under the sun, shopped for 15 minutes, cane back and boom threw the code. @Jerry Bransford or anyone else, do you think the heatsoak shielding would fix this? Or am I to start testing pcm, coil pack, etc. I replaced the injectors at 100k (@134k now) so id be suprised if its them.
 
Check your injector harness. Also inspect the harness where it runs behind the valve cover. These are problem prone areas. You may possibly have high resistance in the #4 injector circuit.
The heat soak issue usually occurs on the #3 injector.

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Check your injector harness. Also inspect the harness where it runs behind the valve cover. These are problem prone areas. You may possibly have high resistance in the #4 injector circuit.
The heat soak issue usually occurs on the #3 injector.

View attachment 429666
When you say check the harness, do you mean with a resistance meter or for just loose/frayed connections?
 
Inspecting under the hood, this is the only thing I found out of place
IMG_2103.jpeg
 
Just ran my code reader on it. Its P0204 and P0304. Its saying injector circuit fault on #4 and misfire on #4. This is so confusing that it only happens on a hot start though
 
Just ran my code reader on it. Its P0204 and P0304. Its saying injector circuit fault on #4 and misfire on #4. This is so confusing that it only happens on a hot start though

Even though you replaced them, you still might have a bad injector. Try swapping the #4 injector with one from a different cylinder. If the problem follows, replace that injector. BTW, what brand injectors did you use?
 
Even though you replaced them, you still might have a bad injector. Try swapping the #4 injector with one from a different cylinder. If the problem follows, replace that injector. BTW, what brand injectors did you use?

Will do, just swapped 3 and 4. Cant remember the brand. Theyre the blue 4 port ones for our TJs
 
I would swap 2 injectors and see if the fault moves, then you will have a starting point for troubleshooting.
 
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Am still waiting waiting for it to pop back up, swapped 3 and 4 and nothing yet
 
Maybe you got lucky and jiggled something just right and fixed it. :love:

I can only HOPE. Ive noticed it only does this when warm, so I really think its heat soak related. Ended up installing the DEI kit today to see if this helps. Time will tell
IMG_2109.jpeg
 
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I can only HOPE. Ive noticed it only does this when warm, so I really think its heat soak related. Ended up installing the DEI kit today to see if this helps. Time will tell

I was thinking more along the lines that maybe when you installed the injector that you didn't get something exactly straight so that it sealed when cold but the heat caused an air leak or something, and when you moved it it went in right. But I'm just guessing. I do hope that it's fixed.
 
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It came back!!!! But im happy about this. I swapped the 4th injector to #3, im sitting in traffic, start taking off, realize its running rough and see a CEL. Pulled over and checked... P0203!!! I'll be replacing this injector soon.
 
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It came back!!!! But im happy about this. I swapped the 4th injector to #3, im sitting in traffic, start taking off, realize its running rough and see a CEL. Pulled over and checked... P0203!!! I'll be replacing this injector soon.

Good job on your diagnostic skills.
 
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