LS-1 Powered

I am having cylinder misfire at the #3 cylinder. Weird part about it is, it only happens when I turn the AC on full blast. When I don't have the AC on I dont have the misfire. I turn the AC on to low speed, I dont have a misfire. I turn the AC onto its highest setting, I have a very hard, pronounced misfire! Its a very noticeable misfire and shakes the truck! I got a log of it so you all could see it. I checked all my spark plugs wires thinking one came loose but nope, it still does it. Any suggestions? I believe this issue is going to be mechanical right? Probably a spark plug? How do I know which cylinder is #3 from looking at the engine?

madmann26

iTrader: (7)

cyl 3 is 2nd one on drivers side.

driver side is 1,3,5,7
pass side is 2,4,6,8

LS-1 Powered

thank you! Guess I'm guna pull the spark plug and go from there.

B52Bombardier1

Could be the fuel injector. Check the shop manual for whatever impedance your fuel injector should be and then measure that injector's impedance. I'm thinking this is an electrical problem, obviously. High electrical consumption makes a weak fuel injector fail.

My crazy two cents theories . . .

Rick

LS-1 Powered

Spark plug was fine no obvious reason for the misfire. That rules out the spark plug and the spark plug wire. I just put brand new lt4 injectors in the truck. You really think injector could be bad?
is there a way to look at the hp tuners log and see if it is an injector? Also to test impedance does the manifold have to come off?

FFDP

iTrader: (2)

Can you raise the idle 100rpm to see if it stops?

LS-1 Powered

yes I can ill do that now. Is there a idle adjustment when the ac is on? Or just bump the idle in general? Whats the theory behind doing this? Just trying to learn.

B52Bombardier1

For me, the fuel rail needs to come off to replace an injector but not to simply check the suspect injector impedance.

Rick

68Formula

Swap the spark plugs between 3 and 2, and see If the misfire follows to cylinder 2. If not, swap the injectors between 3 and 2, see if it follows. If neither does, then something else is going on.

LS-1 Powered

great way to test it thanks! I'll give it a try when I have the time to pull the intake manifold.