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2002 Trans Am Misfire on 2 cylinders Puzzled

  • dhessco
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08 Sep 2019 19:08 #33482 by dhessco
I have been studing scanner danner videos and I believe I have covered the basics here, but now im stuck. I even tried to hire a local mobile mech. paid him $45 to tell me he didnt know.

2002 Trans am LS1 5.7
I rescued the car so I have an unknown history of how it ran before it sat for almost 10 years.

I am fighting a Misfire on cyl 1 and 3.

So Far I have verified it is not The coil, Wire, or Plugs
Also it is not the Fuel injector, I changed it out and still missing.
Compression is 180 on cyl 1 and 155 on cyl 3, 180 on all the rest
The miss goes away when revving the engine.
Changed the Intake gaskets AND even got another ls1 intake to put on and same issue
Vacuum is a steady 25
New Spark Plugs
New Battery
New PCV
Cleaned the MAF with maf cleaner
Cleaned the throttle body (it was really clean already)
Car only has 22k miles on it, was sitting outside for over 10 years
Wire brushed all the grounds

Here is a Video of what I have done. I have a tech 2 scanner, but admittedly it is beyond my skill level to understand all the functions
I only have access to a tech 2, but my neightbor has the most bad to the bone autel scanner, but he doesnt know how to use his either.




Steak dinner to the person who figures this out!! I am lost.

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08 Sep 2019 19:19 #33483 by Cheryl
It’s been my experience with misfires that get better off idle are mechanical issues. You performed a compression test but if it were me I’d perform a cylinder leak down test. Also wondering if there’s carbon on the intake valve soaking up the fuel?? What do fuel trims look like?
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08 Sep 2019 19:21 #33484 by Cheryl
Also since you have the tech 2 scanner I’d perform a crank variation relearn

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08 Sep 2019 21:21 #33488 by dhessco
Replied by dhessco on topic 2002 Trans Am Misfire on 2 cylinders Puzzled
Cheryl, Thanks! I will get you a video of fuel trim data tomorrow, Also I did the Crank Relearn. but will do it again as well.

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09 Sep 2019 05:09 #33499 by Cheryl
How about the leak down test ?
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09 Sep 2019 09:45 #33506 by Andy.MacFadyen
Replied by Andy.MacFadyen on topic 2002 Trans Am Misfire on 2 cylinders Puzzled
2 cylinder misfire on adjacent cylinders I always check for a firing order mix up.

" Welcome to the 21st"


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09 Sep 2019 13:04 #33509 by Tyler
I'd also like to know the leak down for #3 compared to a known good cylinder. While you're there, it may be worthwhile to check running compression compared to a known good.

Besides the misfire, how well does it run? A V8 with one cylinder down should still move itself down the road.

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09 Sep 2019 18:48 #33519 by dhessco
Replied by dhessco on topic 2002 Trans Am Misfire on 2 cylinders Puzzled
For this is an LS1 i think it is impossible to mix up plus wires or coils, are you asking if the tech 2 is wrong? and it is actually cyl 2 misfiring?

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09 Sep 2019 18:49 - 09 Sep 2019 20:04 #33520 by dhessco
Replied by dhessco on topic 2002 Trans Am Misfire on 2 cylinders Puzzled
arg. did the leak down test incorrectly. i have to wait until tomorrow.
Last edit: 09 Sep 2019 20:04 by dhessco.

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  • Noah
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09 Sep 2019 19:00 #33521 by Noah
I think you need to dial up the pressure on your leak down tester when you hook it up.
It looks like you've got little air going in, therefore little leakage.
I turn mine up to 40lbs. That's where top dead center becomes important because if the connecting rod isn't straight up and down, the air pressure can push the Piston through the rest of a stroke.
Also I wouldn't remove the rockers or any part of the valve train. You could be masking a problem that could be making the valves hang open.

"Learn, apply, repeat."

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09 Sep 2019 20:33 #33523 by dhessco
Replied by dhessco on topic 2002 Trans Am Misfire on 2 cylinders Puzzled
Here is the Compression and Leak Down test. The compressor is set at 100 psi. These are Harbor Freight gauges and the left gauge is not the pressure going into the cyl.

I took the rockers off because i really wanted to test the sealing of the valves without laboring to find actual TDC

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10 Sep 2019 18:41 #33530 by dhessco
Replied by dhessco on topic 2002 Trans Am Misfire on 2 cylinders Puzzled
Cheryl,

Here is the Crank Relearn and the Fuel trim data.. Thoughts?

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10 Sep 2019 19:09 #33531 by Cheryl
Fuel trims look real good. So was the leak down test done with the air pressure going in the cylinder bumped up like Noah suggested? Second I’d be half tempted to check the misfire counter on your scanner. Example unplug #5 #4 etc injector and see if it’s accurate. Usually gm is accurate in the misfire counters.

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10 Sep 2019 19:12 #33532 by Cheryl
Also mind posting video of vacuum gauge reading?

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10 Sep 2019 21:25 #33537 by gav09
I would like to see you do a running compression test. 150 psi is about 20% less than your known good. Technically its in spec but I would say not good.

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11 Sep 2019 17:40 #33546 by dhessco
Replied by dhessco on topic 2002 Trans Am Misfire on 2 cylinders Puzzled
Hey Cheryl here you go it is the readings

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12 Sep 2019 14:27 #33573 by dhessco
Replied by dhessco on topic 2002 Trans Am Misfire on 2 cylinders Puzzled
Any thoughts??!

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