Z34 dropping 2 cylinders intermittently.......WTF need some help!

[EricTkiwi]

ok folks, here is my issue. I have a 92 Chev Z34 with about 145k on it. I love my car. about 6 months ago, it sarted to drop 2 cylinders periodically. It didnt happen often then but as time went on, it became more and more frequent. Now, it typically starts up and runs fine but will drop the 2 cylinders shortly after heading down the road. So last week I pulled the ICM and coils and had them checked. All the coil packs ohmed fine and the ICM tested good as well. So I put it back together with the same issue once I started it again. So I determined which coil was dropping and replaced it. No difference. I am gonna change plug wires and plugs today but am pretty sure thats not the issue. I have noticed the battery cables have been pulled hard (bare wires showing at both ends) from some previous owner so I am gonna replace them as well. I gues what I need to know is the following:

Can an ICM drop only one cylinder intermittently?

What other possibilities can cause an intermittent with the DIS system?

Any suggestions or comments would be greatly appreciated since i am at the point of throwing components at it now.

I have a TECH1 scanner from GM but OBD1 doesnt give very much info.

Thanks and hope to get a lot of feedback!

Eric.

[Garrett Powered]

replace the cables and clean ground points for good measure. you will not regret that on an almost 20 year old car.

 

 

so what did you do, pull two of the wires off the plugs with the car idling and no change? you are sure it is spark not fuel?

 

 

you could also try a cks (crank sensor).

[mfewtrail]

If it's actually two cylinders that are missing, it probably is a coil pack or the icm even though they "tested" good. The ICM can fail in such a way that it will not provide power to all of the coil packs.

 

If you know which two cylinders are missing, take the coil pack from those cylinders and swap it to another position on the ICM. If the coil pack is bad, the miss will now be on another two cylinders...if there's no change and the same two cylinders are missing, the ICM is to blame.

[alec_b]

I second the vote on ICM. My bonneville did that when it got hot. It'd run great for about 10 minutes, then drop 2 cylinders and stay that way till it cooled way down. I swapped coils as you did with no change. ICM's can be had for ~$45 dollars.

[EricTkiwi]

As I stated in the first post, I replaced the coil that wasnt firing with a new GM one. No help. Yesterady, I picked upa set of wires, plugs, pos and neg battery cable, and a new ICM from my local dealer ( who i used to work for so cost + 10%). I put the Neg cable on and cleaned my grounds. Got it back together, relearned the idle ( with my GM Tech1 scanner....don't ask) and the car ran better than ever. I drove here and there all evening at it was fine. Then I got in the car late last night (cold engine) started it up and right off the bat missing two cylinders. Today I am gonna replace Pos cable ( since I gotta deal with starter anyway) and ICM. I am holding off on cables and plugs till i get this sorted out and can clean the intake and seafoam the engine. I am leaning towards the ICM also but it just seems strange it would intermittently drop one coil pack. Any more tips or advice would be appreciated.

[digitaloutsider]

I had the same problem on my Regal a long time ago. It was the ICM.

[Garrett Powered]

there is another equally important engine ground strap that you could replace while you are at it. it should be by the battery tray and runs to the block.

 

it will really wake things up.