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2003 CTS consitenty random misfire on bank 1 resolution
Posted to Technical Discussion Forum on 12/12/2016 13 Replies

Because it was so long ago that this was initiated and not sure on the notification process on who replied whether they will be automatically emailed of an update as I never posted this in Tech help and I want to give anyone who follows this a chance of what the cause was. A brief rundown on what was the issue and what I was theorizing on for anyone who may be interested , but missed the post:

The engine presented from another shop that had replaced a cat on bank 1 in attempt to repair the misfire. I was told that it ran better and most misfiring was gone, except for a slight misfire on bank 1 at idle and it was random, but would code. Cyl 1 was the main one then 3 and very rarely you would see 5 count 1 if you let it idle long enough. Raise the idle just a touch and the misfires would cease. Both long terms would at zero and bank 1 ST would hold around - 3-4 and bank 2 ST would be +2. Shop had swapped injectors bank to bank and misfires did not move. Coils and plugs had been replaced.

I have disciplined myself to check mechanicals first short of a visual inspection for the obvious on misfires. Cranking relative compression indicated nothing suspicious, however cranking vacuum and exhaust had something to say as the vac pulls were almost even, yet every other one had a push that was almost twice as high. Move forward with doing an in cylinder compression on bank 1 cyl 1 and bank 2 cylinder 6 suspecting something was going on with bank 2, and cyl 6 that may be effecting cyl 1 given the cranking vac pattern, i.e., a little EGR effect. Found exhaust on bank 2 cyl 6 was opening about 32* BBDC and bank 1 cyl 1 was at about 48* BBDC. With no cam specs to go off of I informed the shop it was my opinion that bank 2's exhaust cam was opening late. They informed me that they had purchased the tool set to set it up and it was correct. I returned the vehicle (it didn't drive bad, but felt like it did not have all the power it should have) and asked them to call me over when they had the front cover off. I witnessed it was dead nuts on, - ouch. I did count the teeth of the cam gear and came up with a value of 15.6 degrees of crank rotation per tooth which still supported my theory of valve timing. We removed the bolt on the exhaust cam and looked to see the pin deformed or missing, yet it was perfectly centered and square in its alignment slot.

I retrieved it once it was reassembled and started digging deeper. I did forward my screen shots to one of my instructors who has taught me just about everything I know on in cylinder testing among other things and he responded that he did not think I had a valve timing issue causing misfire. Re-verified all my testing and would come up with some slightly different numbers on valve opening/closing events but still supporting a bank to bank difference. I then posted it here, in this forum for some more eyes on my problem. I also put out to the shops I service, that I was looking for one of these products to base line off of, which I received the day after Thanksgiving. No codes, fuel trim was actually almost identical to mine and both EVO's were in the mid forties, so again I'm looking at bank 2 as the culprit. While I appreciated everyones input, I have to call out Shannon Lindsey for doing most of the heavy lifting the entire time I was wrestling with this. He discovered that there were multiple cam positions depending on what product the engine ended up in along with the engine displacement variations. I then returned the vehicle to the shop and they removed the cam covers and discovered that bank 1 had both exhaust cams installed and bank 2 had both intakes.

I never had a chance to hear it ,but the shop assured me that it idled like glass and no more coding for misfires and given I have known good from the loaner, I didn't feel the need to get it back. The vehicle owner was pleased as this had been to four other shops prior to the one I was helping. Again thanks to all who gave their advice and especially Shannon who made himself so available.

You can probably seek all the shots and uploads if interested through the title ,but be fore warned as I'm deeming the above as brief summary compared to all the correspondence and details, screen shots. Feel free to contact me if you are interested in something specific.

Paul Sanders
Parkway Auto Rebuilders
Harvey, Illinois, USA

13 Replies Received (View Replies)


car Vehicle Data

2003 Cadillac CTS 3.2L

Engine3.2 L
Trans5-speed Automatic (Electronic)