Misfire Issue when it rains

[StephenCasiday]

Hi everyone, I have this issue where when it rains fairly heavy my truck starts freaking out and starts misfiring very bad on Cylinder 6, i’ve checked the plug it’s solid, the wire is on as tight as it can be and the coil pack wires are binded or showing copper anywhere. Where should i start looking to try and figure this out? I haven’t seen anything about it online yet, but something is getting shorted and i have no clue where to start. Thanks. -Stephen
2005 Tahoe LT3 4x4 5.3 4L60e

 

[OR VietVet]

It sure sounds like you need plug wires. If they are original, replace them with Genuine GM wires. For giggles, use a spray bottle under the hood at night and spritz the wires with water and see if you see a light show where the spark jumps out. It should not.

 

[lyncht1967]

swap the 6 coil and wire with cyl 4. if problem moves you have a coil or wire issue. if so, switch wire back to 6..if it returns back to 6 its the wire. if it stays on 4 its the coil.

 

[Scottydoggs]

at night in the good and dark, use a old spray bottle on mist, with water in it, and spray the coils wires and down by the plugs. 90% of the time you'll see sparks jumping from them metal plug boots. why i toss them right in the trash if they are still on a car i buy.

if that dont yield anything. before dumping cash into it, swap the coil with the one next to it. see if the miss comes back or moves. if no change swap the plug wire and lastly pull the plug out and check it. if its not clearly fouled out, look for a black line in the ceramic part of the plug. they can crack and misfire then.
coil packs also crack, so inspect it when its removed for cracks. as well as for bare wire off the plug for it.

 

[StephenCasiday]

at night in the good and dark, use a old spray bottle on mist, with water in it, and spray the coils wires and down by the plugs. 90% of the time you'll see sparks jumping from them metal plug boots. why i toss them right in the trash if they are still on a car i buy.

if that dont yield anything. before dumping cash into it, swap the coil with the one next to it. see if the miss comes back or moves. if no change swap the plug wire and lastly pull the plug out and check it. if its not clearly fouled out, look for a black line in the ceramic part of the plug. they can crack and misfire then.
coil packs also crack, so inspect it when its removed for cracks. as well as for bare wire off the plug for it.

I did this, but nothing happened, i figured a faulty knock sensor was shorting and nope, i replaced them both and it’s still doing it, and only when it rains

 

[Scottydoggs]

you swap the coil plug and its wire with the cylinder next to it one by one too?

 

[StephenCasiday]

i am today i’ll get back to you when i do

you swap the coil plug and its wire with the cylinder next to it one by one too?

 

[Doubeleive]

if it only happens when it rains and not ANY other time cold/hot/dry
then I would be looking less at a plug/coil and more at perhaps a scuffed wire that shorts when wet, ecm/pcm harness, under fuse box, etc
look around and feel around the wires and see if one has been rubbing against something and has exposed bare wire. get under the vehicle and look up for the same with a flashlight.
are all of the splash guards in place?

 

[StephenCasiday]

if it only happens when it rains and not ANY other time cold/hot/dry
then I would be looking less at a plug/coil and more at perhaps a scuffed wire that shorts when wet, ecm/pcm harness, under fuse box, etc
look around and feel around the wires and see if one has been rubbing against something and has exposed bare wire. get under the vehicle and look up for the same with a flashlight.
are all of the splash guards in place?

Could you elaborate a little more on where specifically to look? and it’s only Cylinder 6 that misfires when it happens, and it bogs the truck down horribly, and the splash guards are the wheel well plastics? if so they’re all there, everything is on the truck besides the factory steps, but I don’t know where to look for the ecm or bcm, and the harness is still wrapped up pretty well from what i can see, a lot of the wires around the throttle body are exposed though, the plastic grommets are mostly gone up there

 

[Doubeleive]

Could you elaborate a little more on where specifically to look? and it’s only Cylinder 6 that misfires when it happens, and it bogs the truck down horribly, and the splash guards are the wheel well plastics? if so they’re all there, everything is on the truck besides the factory steps, but I don’t know where to look for the ecm or bcm, and the harness is still wrapped up pretty well from what i can see, a lot of the wires around the throttle body are exposed though, the plastic grommets are mostly gone up there

THE PCM (COMPUTER) is mounted in the left front of the engine compartment, has 2 big multi wire harness's connected to it. It is metal and clips into a big plastic holder