Scantool shows different readings than DMM - Page 2 - GM Forum - Buick, Cadillac, Chev, Olds, GMC & Pontiac chat


1992-1999 Series I L27 (1992-1994 SE,SLE, SSE) & Series II L36 (1995-1999 SE, SSE, SLE) and common problems for the Series I and II L67 (all supercharged models 92-99) Including Olds 88's, Olds LSS's and Buick Lesabres Please use General Chat for non-mechanical issues, and Performance and Brainstorming for improvements.

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Old 06-26-2006, 09:17 AM   #11
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Coils have been tested numerous times and I have switched them out and the ICM several times. I cant manage to get the adapter to the compression tester down the plug hole I may need to take off the exhaust manifolds... grrr. any suggestions on the compression test would be helpful too!! thanks guys... you fella'* are the best.
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Old 06-26-2006, 09:30 AM   #12
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Yikes..tougher problem going on here.

Ok.. First off...Let'* buy a new plug. Dropping a plug can cause any number of cracks and small things that may show up intermittantly. Secondly.. is the miss always on the same cylinder or two cylinders?

When swapping coils and ICM did you clean the mounting plate of any corrosion, check grounds in the engine bay? The problems you are describing could be power related and not necessarily an injector or plug.

One of the biggest culprits we find after normal maintenance is up to par is power fluctionation caused by corrosion etc. Check battery cables at both ends of all cables. While the cables are off the battery..pull the rubber boots off and look under for corrosion.
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Old 06-26-2006, 12:01 PM   #13
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Quote:
Originally Posted by BillBoost37
Yikes..tougher problem going on here.

Ok.. First off...Let'* buy a new plug. Dropping a plug can cause any number of cracks and small things that may show up intermittantly. Secondly.. is the miss always on the same cylinder or two cylinders?

When swapping coils and ICM did you clean the mounting plate of any corrosion, check grounds in the engine bay? The problems you are describing could be power related and not necessarily an injector or plug.

One of the biggest culprits we find after normal maintenance is up to par is power fluctionation caused by corrosion etc. Check battery cables at both ends of all cables. While the cables are off the battery..pull the rubber boots off and look under for corrosion.
Bill.... new plugs, ALL are firing now... i jhave a rough idle (sounds like a single cyl miss) and when i free rev it up and down the RPM eventually it will backfire through the intake with a *pop* and then run funny make a whining sound (Supercharger) and struggle with minimal power.

Battery-new, terminals good.
ICM, replaced plate and checked the ground connection underneath... weird.

I can't figure why my Scantool shows 12.8 Volts and at the battery 13.8.... I am wondering if the ignition is cutting out.... or the BCS. Don't know too much about it, but my guage seems fine until the *pop* and then everything is bobbing around.
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Old 06-26-2006, 03:04 PM   #14
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Let'* leave the boost out of this for now... Unless your boost gauge is giving you nothing or full all the time.. it shouldn't be an issue.

Check the battery cables at both ends, ensure you pull the booties.. let us know what you find. Actually pull things apart..I was surprised at how much corrosion was beneath my connections that looks fine from the outside.
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Old 06-27-2006, 10:49 AM   #15
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will do... I am in Memphis for the week, I will be home this weekend... will check it out. (again, hehe.) The voltage thing is weird, and the miss is even more weird. I can pretty much produce it at will... I do have a scantool... the other thing that I don't know about is the ESC counter, it jumps numerically higher when the engine misses. I think that is the Electronic Spark Control... but, why is that jumping? Thanks guys!!
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Old 06-27-2006, 11:00 AM   #16
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there is a miss counter of sorts..maybe that'* what it is on your scantool

How can you produce the problem at will?
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Old 07-25-2006, 04:42 PM   #17
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well, my miss is that my #2 cylinder has 50 PSI. great. Looks like that extra rear head gasket will get used. grrr. thanks guys, I will update in the future.
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Old 07-25-2006, 05:05 PM   #18
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Quote:
Originally Posted by jaye22
well, my miss is that my #2 cylinder has 50 PSI. great. Looks like that extra rear head gasket will get used. grrr. thanks guys, I will update in the future.
Take a read at my thread:

http://www.bonnevilleclub.com/forum/...289&highlight=

I had the exact same symptoms as you, but never got into checking the voltage at the injectors. To make a long story short, I ended up giving the car away. The guy I gave it to said it got progressively worse and he finally took it to a well-known shop. They changed the harmonic balancer and it said that it runs so smooth you can't even tell it'* running....with 190,000 miles.

Something to think about....
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