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2002 gmc envoy_slt
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Discussion Starter · #1 ·
56886

I had my valve cover gasket replaced and the truck sat for two weeks before I finally started it and now has cylinder 1 misfire and runs rough.. I replaced coil and plug and still same code cyl 1 misfire. I pulled coil and plug and started the truck with the plug and coil connected outside of the valve cover and the spark plug actually has a constant spark but i could only see it in the dark..problem is I don't have any idea how bright it's supposed to spark!?? I need help, I was just trying to fix the oil leak! Ran great before
Can I rule out the coil connector because I actually have some spark?
 

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Discussion Starter · #2 ·
Also I put 3 new coil packs on cylinders 6, 5, and 4.. should I spread them out more with the firing order? Like put new ones on 1, 4, 6 ?
 

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Since this began with work that involved disturbing much of the engine wiring harness,,, I would closely inspect the fuel injection wiring. Maybe the old and likely brittle wiring broke. There is a 8 terminal wiring connector (only uses 7 wires) back near the throttle body under the resonator. That is the ground wire and 6 fuel injector wires. It may be necessary to test that with a meter to see if there is a good connection. I would evaluate all even though the misfire is reported as cylinder #1.

Or it could be something else entirely!!
 

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Discussion Starter · #4 ·
I need to look into that, so far I could only see that type of a harness wire set leading away from the coil packs
56888
 

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I need to look into that, so far I could only see that type of a harness wire set leading away from the coil packs View attachment 56888
That is exactly the one. Those are your fuel injector wires and a ground.

EDIT: wrote that too fast. Not injectors and a ground, it is a 12vdc power supply and 6 injector wires that the PCM grounds to energize.
 

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Discussion Starter · #7 ·
On YouTube I saw a vid that said to check resistance on the pins to that harness by putting and leaving one lead on the common and touching the other lead on each pin separately .. but I actually got consistent numbers across all the contacts
56894
 

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Discussion Starter · #10 ·
I'm waiting on my mechanic to help do that..
Seems like fuel isn't making it to the plug?
What would give it no compression on a cylinder after a valve cover gasket job??

Thanks for the replies
56895
 

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NEVER NEVER NEVER shove a test light probe into an electrical connex. It spreads the tabs and from that point, the connection will be questionable.

This is what probes are for ::::: LINK HERE

56899


Your: "can't tell if the spark's good enuff" .......... or words to that effect.

BLUE is the correct color for a spark. If it's BLUE - it's good.

RED - ORANGE - YELLOW sparks are NOT good.
 

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Discussion Starter · #12 · (Edited)
Solved..
Fuel injector one replaced and now no misfires!... The injector just decided to stop working during the valve cover gasket job, makes no sense at all.. just very coincidental with the timing it seems as the Fuel injectors aren't even disturbed during a V.C job and everything worked fine before I finally started to fix the oil leak!
 

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Did you take any other pictures? Please PM me if you did. I'll try to answer tomorrow (Sunday 04/12-21)
 

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Since this began with work that involved disturbing much of the engine wiring harness,,, I would closely inspect the fuel injection wiring. Maybe the old and likely brittle wiring broke. There is a 8 terminal wiring connector (only uses 7 wires) back near the throttle body under the resonator. That is the ground wire and 6 fuel injector wires. It may be necessary to test that with a meter to see if there is a good connection. I would evaluate all even though the misfire is reported as cylinder #1.

Or it could be something else entirely!!
I recently purchased a 03 trailblazer and had a misfire and changed all the plugs and coils but it still had misfire, come to find out one of the new coils was missing the spring that connects the Coil to the plug! But it's all good now.
 

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To minimize the risk of damaging a boot or the spring in it, always use some dielectric grease.
 
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