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2002 Trans Am Misfire on 2 cylinders Puzzled

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12 Sep 2019 15:51 #33575 by Adam Davis
Replied by Adam Davis on topic 2002 Trans Am Misfire on 2 cylinders Puzzled
its only getting misfire information from knock sensors, you've got to verify for sure which cylinder is missing, can you do a old fashioned temp reading on exhaust manifolds from cold t verify which cylinder is missing.
also your fuel trim looked real good so you need to get your o2 sensor data up, need to see if running rich or lean if its switching perfectly you've got fuel issues.

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14 Sep 2019 14:59 #33597 by dhessco
Replied by dhessco on topic 2002 Trans Am Misfire on 2 cylinders Puzzled
Here are the O2 switching. Would you verify they are working good?

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15 Sep 2019 10:40 - 15 Sep 2019 10:44 #33607 by Noah
I didn't see this mentioned previously so I figured I would bring it up. The misfire counts on cylinder one are likely just an effect of the cylinder 3 misfire.
Notice how when you disabled other cylinders that another cylinder would start counting up, all though considerably less than the actual misfiring cylinder.
It also appears that the computer is accurate in flagging the missing cylinder based on the results of your testing.
I think it would be safe to focus your efforts on cylinder 3. Your compression test seems to back this up as well.

As for your last post, I don't notice any problem with your oxygen sensors. Looks like maybe b2s2 took a little longer to heat up and become active, but certainly nothing that would contribute to a single cylinder misfire.

Cylinder 3 being low on compression points to a mechanical issue.
The misfire that goes away off idle points more specifically to a valve sealing issue (in my experience).
I trust that you know your tools better than I do, and after reading the instructions for that harbor freight leak down tester I believe you are using it as described, but I don't trust the results of that test/tool.

Personally, I would repeat that test on cylinder 3 at true TDC with the valve train assembled and dial up the pressure or see if you can borrow a different brand tester from your local parts store.

I completely understand why you performed the leak down test like you did, but by removing the rocker arms you're entirely removing the camshaft, pushrods and lifters from the equation.

I just had a Malibu yesterday with a valve sealing issue and I couldn't pin point the source of the leak until I cranked the dial up to 100psi. Then you could hear air coming out the exhaust.

I hope you get it figured out, keep us posted!

"The circuits in cars are not nanby-pamby Chinese consumer electronics "
Last edit: 15 Sep 2019 10:44 by Noah.

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15 Sep 2019 10:42 #33608 by Cheryl
Exactly Noah. Misfires that get better off idle are mechanical issues in my experience as well
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15 Sep 2019 16:50 #33613 by dhessco
Replied by dhessco on topic 2002 Trans Am Misfire on 2 cylinders Puzzled
Thanks for the detailed explanation!!

I went ahead and replaced all the injectors, the car was sitting for 10 years so couldn’t hurt...

Miss is still there. Gonna borrow another leakdown tester. Arg...

So based on my findings it sounds like it could be a lifter not pumping.

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18 Sep 2019 13:33 #33668 by rpd1125
Replied by rpd1125 on topic 2002 Trans Am Misfire on 2 cylinders Puzzled
Hey guys Ruben here in Phoenix Arizona. If you wouldn't mind quick entertaining taking the leakdown tester on both cylinder 1 and 3 individually and cranking up the pressure to a good 80 to 100PSI and watch for bubbles and any air coming thru cooling system reservoir. It sounds to me like you have coolant leak into these two cylinders especially with them be right next to each other. If you bring that cylinder to TDC and crank up some pressure with the leak down tester you will more then likely see air coming thru the cooling system which means your diagnostics are done my friend.

This rather silly test has nailed down a few of those misfires that just take up so much time. Please keep me posted but I think this may give you some insight

hope it helps
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18 Sep 2019 13:35 #33669 by rpd1125
Replied by rpd1125 on topic 2002 Trans Am Misfire on 2 cylinders Puzzled
I have found this to be the problem on not only GM but also a few acuras and one Nissan too. Its one of the most sneaky misfires to misdiagnose. Nut super easy to nail it with 100 percent certainty

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