Chasing Misfire

[badandyturbo]

Hello friends. I have been hunting down a misfire in cylinder 2 for a bit now and I need some help.

Code is P0302. Misfire cylinder 2
I have swapped coilpacks.
I have swapped plug wires.
I have replaced the spark plug.
I have replaced the injector.
I have pulled the valve cover and checked rockers.
I have used 87 octane and E85.

Truck misfire is only noticeable at temp on idle. Cold start and driving it's fine.

Any other ideas?

 

[avalonandl]

Head gasket or intake gasket is my "guess"

 

[donjetman]

Somebody here recently finally cured their misfire problem by replacing either the coil pack wire harness. See post# 36 in the following thread: https://www.tahoeyukonforum.com/threads/persistent-misfire-cylinder-3.115593/page-4

 

[OR VietVet]

What is the compression on that cylinder compared to the others?

 

[Doubeleive]

Like Ron said compression test and I would check the injector harness voltage, check all 4 connectors on that side and see if they all read the same, it's not uncommon to have a bad harness.

 

[OR VietVet]

Yea, if you have a compression problem, that simple basic test could have saved you all this time chasing the problem and any parts you threw at it.

 

[badandyturbo]

Thanks for the advice. I will do the compression test first.

 

[OR VietVet]

If you do that compression test be ready to do a dry and wet test. If the compression is low, compared to other cylinders, then remove that tester and spit a little oil in that cylinder to see if the compression comes up. If it does, then rings are suspect, if not, then valves or head gasket is likely.

 

[badandyturbo]

Ok so the compression is good. I have also used a noid light to check the injector. Its firing correctly. I am running out of options......

 

[Doubeleive]

maybe hook up a scanner and get a live data feed going and try wiggling the injector wire harness and see if it correlates with that. If the hardware is good then it must be electrical.

 

[swathdiver]

Ok so the compression is good. I have also used a noid light to check the injector. Its firing correctly. I am running out of options......

@01ssreda4 @randeez @iamdub @gooffeyguy @gpracer1 @ScottyBoy @Scottydoggs @mountie

 

[Scottydoggs]

do crank sensor learns do magic on the ls engines like they do for the 3800 world? seen doing one fix a lot of crappy running engines over the last 10 years. all had misfires.

could be the crank or cam sensor, or the harness to one or both.

try scanning the truck running after its been misfiring, if you shut it off a pending code will clear. might have a hidden code you just have not seen yet.

 

[kbuskill]

Ok so the compression is good. I have also used a noid light to check the injector. Its firing correctly. I am running out of options......

I'm with Don on this one. Check the coil packs wiring harness that he posted about earlier.

 

[swathdiver]

do crank sensor learns do magic on the ls engines like they do for the 3800 world? seen doing one fix a lot of crappy running engines over the last 10 years. all had misfires.

could be the crank or cam sensor, or the harness to one or both.

Interesting Scott, what do you think Andy?

 

[badandyturbo]

I'm with Don on this one. Check the coil packs wiring harness that he posted about earlier.

I have not checked the new harness but it has been replaced.

 

[Scottydoggs]

I have not checked the new harness but it has been replaced.

if the harness is new, and it didnt fix the issue, id say its good.

might need a crank learn, some times the 3800 would set a code for it, but they always seemed to run ok. then the times they dont set a code and misfire and crap the crank learn fixes em right up.

need a tuner (hpt or efi live), or a tech 2 or the likes to do the crank learn. crazy but it takes all of 1 minute to do tops. you just set up the tuner to do a learn then e brake on, stand on the foot brake, in park and floor it to the rev limiter and let off. and its done lol

 

[swathdiver]

if the harness is new, and it didnt fix the issue, id say its good.

might need a crank learn, some times the 3800 would set a code for it, but they always seemed to run ok. then the times they dont set a code and misfire and crap the crank learn fixes em right up.

need a tuner (hpt or efi live), or a tech 2 or the likes to do the crank learn. crazy but it takes all of 1 minute to do tops. you just set up the tuner to do a learn then e brake on, stand on the foot brake, in park and floor it to the rev limiter and let off. and its done lol

We can do that Andy if you want.

 

[badandyturbo]

We can do that Andy if you want.

i'm down to try anything.

 

[swathdiver]

i'm down to try anything.

Ok, maybe this Saturday or next week. Another buddy passed away. You know you're getting old when most of your friends are in boot hill!

 

[OR VietVet]

James, don't I know it. Next year is my 50th high school reunion and I am dreading seeing who has passed. My American Legion is slimming down as well.