Still have a misfire
Teching In
Joined: Feb 2020
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I had a random misfire on my 04 gto changed the spark plugs and wires, checked coil packs, compression then I replaced the passenger side o2 sensor upstream and it went away for like a week now it's back and all of my spark plugs when I checked them were black and sooty, car runs and drives like crap any ideas? And it smells of gas all the time too and mpg is down
Thread Starter
Teching In
Joined: Feb 2020
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There are eight separate intake manifold gaskets on the LS1, so it's possible just one could go bad.
Since #2 cylinder is on a corner, the intake manifold bolts may need to be retorqued.
Edit: Just to clarify, I'm not referring to the throttle body gasket. The intake manifold gaskets seal
the intake manifold to the ports on the cylinder heads. There are ten bolts attaching the intake manifold
to the engine.
Since #2 cylinder is on a corner, the intake manifold bolts may need to be retorqued.
Edit: Just to clarify, I'm not referring to the throttle body gasket. The intake manifold gaskets seal
the intake manifold to the ports on the cylinder heads. There are ten bolts attaching the intake manifold
to the engine.
Thread Starter
Teching In
Joined: Feb 2020
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Teching In
Joined: Jul 2015
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I would take the intake manifold off and change the intake manifold gaskets first, it might have been off
previously and the gaskets not installed properly. If they are original, they are twenty years old.
What's the oil pressure when this misfire happens? Is there excessive rocker arm noise?
Low oil pressure from pick-up tube o-ring leakage and lifters with accumulated varnish could combine
to produce lifters that are not operating correctly. I don't know if this would cause a misfire, I'm just
speculating here.
previously and the gaskets not installed properly. If they are original, they are twenty years old.
What's the oil pressure when this misfire happens? Is there excessive rocker arm noise?
Low oil pressure from pick-up tube o-ring leakage and lifters with accumulated varnish could combine
to produce lifters that are not operating correctly. I don't know if this would cause a misfire, I'm just
speculating here.
Take the schrader valve out of the hose on your compression gauge and do a dynamic compression test(with the engine running)Disable the injector and coil for the cylinder you are testing.
Do it on a known good cylinder and the cylinder that you are having a problem with.
If it's a valve spring issue, it won't show up on a cranking compression test or leak down test.
The best way to do it is with a in cylinder pressure transducer with a scope, but a normal compression gauge will work in a pinch.
Do it on a known good cylinder and the cylinder that you are having a problem with.
If it's a valve spring issue, it won't show up on a cranking compression test or leak down test.
The best way to do it is with a in cylinder pressure transducer with a scope, but a normal compression gauge will work in a pinch.
TECH Fanatic
Joined: Nov 2011
Posts: 1,366
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From: Woodstock, GA
The motor is completely stock, thank you for all of your replies so far as they're greatly appreciated and greatly appreciate everyone that has replied, I think I might have to bust out the ohm meter and go to town lol, been racking my brain for a long time on this misfire that no matter what I do, it still misses on cylinder 2
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What are your compression numbers, specifically on number 2
From my experience on all sorts of low compression problems across all sorts of makes and models right around 130 ish is the lowest a cylinder will fire clean at idle.
You should have considerably more than that. If I remember right an LS1 will do right around 180
Edit: Stock LS1
What are your compression numbers, specifically on number 2
From my experience on all sorts of low compression problems across all sorts of makes and models right around 130 ish is the lowest a cylinder will fire clean at idle.
You should have considerably more than that. If I remember right an LS1 will do right around 180
Edit: Stock LS1
Staging Lane
Joined: Feb 2020
Posts: 80
Likes: 19
I had a very similar issue a while back. Mine was on an LT1 and not an LS1 but was very similar in nature. On cold start up the car ran fine. Once warm, I had constant misfires on #4 that made the car run awful. We hooked it up to do some data logging after I had exhausted all of the obvious. What we found was that in open loop the issue was not there. It only occurred after the car entered into closed loop. In my situation, the issue wound up being the ECU. We replaced the computer and flashed my tune on to the new one. After that the car never misfired again.
I had a very similar issue a while back. Mine was on an LT1 and not an LS1 but was very similar in nature. On cold start up the car ran fine. Once warm, I had constant misfires on #4 that made the car run awful. We hooked it up to do some data logging after I had exhausted all of the obvious. What we found was that in open loop the issue was not there. It only occurred after the car entered into closed loop. In my situation, the issue wound up being the ECU. We replaced the computer and flashed my tune on to the new one. After that the car never misfired again.
Thread Starter
Teching In
Joined: Feb 2020
Posts: 11
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Thank you all again for the replies, I'm going to give it another look this weekend as it's supposed to be pretty nice out (Chicago), I'll keep you all posted as I'm going to try everything everyone has suggested, much love to you all!!
Try checking the coil pack plug in. Unclip it and spray each connector with brake cleaner. After it dries, put some dielectric grease on the pins and reconnect. This has happen to me two or three times over the years on various cars.
