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Old 11-19-2012, 08:28 PM   #1
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Question Cylinders 1 and 3 misfiring

1995 L27 3.8 Silhouette.

So far I've replaced:

Coils
Plugs
Plug wires
TPS
ICM
Crank sensor
Cam sensor
brand new wiring harness to the ICM, CKS, CPS
ECM
Checked the harmonic balancer for bent or broken vanes
It'* not the injectors either, it is NOT mechanical as it shows up with a timing light on those two cylinders. All other cylinders are steady as can be.
Compression is 165-170

It'* ONLY 1 and 3. And random, it misses on every 3-5 revolutions.

Any ideas? I've already sunk about $500 trying to fix this.
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Old 11-20-2012, 07:55 AM   #2
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the only thing i can think of is the connector from the pcm to icm, did you go over that real good? you didnt use thread seal or anything on the plugs?
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Old 11-20-2012, 09:19 AM   #3
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Since the misfire shows up on the timing light the assumption is the misfire is due to a lack of spark. The ignition coil gets only one signal to fire spark from both towers from the ignition control module (this is because both towers belong to the same circuit inside the ignition coil). So, if only one tower is firing off spark... there'* something wrong inside the ignition coil itself. Since you are getting spark off one tower from each of two coils, but not the other tower, it would indicate the coils are bad. I know you changed coils, but just for *&G'* change the 5/6 coil pack over with one of the other positions and see if the misfire follows the coil pack.

Ignoring signs it seems to be a spark issue, another issue that could cause misfire on 1 and 3 is a bad intake manifold manifold gasket. Any loss of coolant lately?

Like Justin said, check the connector at the ICM.
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Old 11-20-2012, 02:02 PM   #4
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Just a hunch but I had this problem before and a smoke test revealed that the orings on the injectors were bad.
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Old 11-20-2012, 03:35 PM   #5
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Quote:
Originally Posted by mello View Post
Just a hunch but I had this problem before and a smoke test revealed that the orings on the injectors were bad.

I was thinking about injectors too, but his comment about being able to see the misfire with a timing light leads me to think this is a spark issue, not a fuel issue. Doesn't hurt to check it out though. You might be right.
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