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number 3 mifire help

Spartanzz

Spartanzz

New member
Ok so iv got a cylinder 3 misfire code up and you can feel the misfire but the catch is its only at idle... one you give it gas and it goes above 1k rpm there is no sign of a misfire no sputtering nothing. The plugs are new the icm is new the coil that leads to 3 and 6 is new I have also switched around plug wires and injectors could it still be a wire cuz I was told they are different lengths and that could mess with it?
 


Try to get a new wire that is the correct length...I used to have issues on that on my old buick.
 
Sounds like you eliminated fuel and spark. How about vacuum leaks? They don't have to be big to effect idle.

What kind of car?
How many Miles?
What year?
supercharged or NA?
Has the lower intake gasket been changed?
if NA, has the upper composite intake been changed yet?
 
Ok, sorry about not giving all the details. Car is a 1998 pontiac grand prix GTP with the L67 we have checked all the vaccume lines and there are no leaks found one a while back but fixed it for sure. The car has just under 147k miles on it. From what it looks like the previous owner put no LIM gaskets on so those should be ok. I may try and get a set of wires soon to see if it helps just trying to get a general view on what could be causing the misfire only at idle...
 
If you try everything and that doesn't solve it.. swap the ICM. I know..it fires both towers etc etc. I've seen two cases where the icm didn't fire on one of the two cylinders. Odd eh?
 
Well not too long ago my icm stopped firing on 3 and 6 so replaced that and before that happened o still had the idle misfire then got a brand new icm and idle misfire still there...I still drive the car every day so its not bad enough to destroy disability at this point its just getting annoying lol
 


Spartanzz said:
From what it looks like the previous owner put no LIM gaskets on so those should be ok..
Click to expand...

Stock LIM gaskets are a none failure point with that many miles. As I understand it is normally a coolant leak but still something to check
 
yeah ill give it a look over looking at starting to mod so may get my hands on a ported SC and LIM just gatta find a good deal on um.
 
You can do them yourself very easily with a die grinder...thats what I did when I first took a stab at it...its fairly simple as well.

For the LIM gaskets...if they are black...then they are the junky plastic ones that need replacing...if they are gray...then they've been done. If they are plastic it is possible you are getting a very small vac leak on cylinder #3 or a dribble of coolant which isn't helping either.
 
ok yeah the LIM gasket is black and orange...so may look at getting some new ones just for the hell of it. Also only catch with me doing the porting on the LIM and SC is 1. iv never done it before 2. i dont have an air compressor :( idk maby i can find someone who will help me do it while i have the LIM and SC off for the gasket replace.

Also is it worth spending the money to get the intake gasket set from zzp? or should i just go to autozone and get the set there?
 
You don't want plastic ones. The ones from ZZP should be aluminum.

Fel Pro #MS98014T should be aluminum, please verify. Amazon and Rock Auto have them for $50. Advance and AutoZone look like $75
 


ok cool iv got a few tickets to pay before i can buy them but i will for sure order them once i can. I was also told the misfire could be a burnt valve but wouldnt that be a constant misfire?
 
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