Runing rough at idle in P/N and on decel (11/14) - Page 5 - 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 11-04-2007, 02:20 PM   #41
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My engine was warm but it wasn't fully warmed up..

My heads weren't decked and I have a ZZP GT1 cam with no retard/advance.
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Old 11-04-2007, 03:01 PM   #42
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Mike I would expect at least 150 Psi ....

we see 8.5 : 1 engines as good as 160-170

and you have the 9.4 : 1

I would expect 150-170 and the lowest reading cylinder should be at least 70% of the highest and no lower than 100 psi

Never know with a hit that hard mike.. Anything is possible

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Old 11-04-2007, 03:08 PM   #43
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I read recently that as a "rule of thumb," each +8 degrees of intake duration should equal about 5 psi lost compression. Thus a GT1 cam versus stock (with no decking, etc.) should lose somewhere around 20-25 psi compression versus stock, so I'd expect perhaps as low as 135-140 psi or so on your setup, fully warmed up.
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Old 11-05-2007, 04:25 PM   #44
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Ok, I think I may give the rear head gasket a shot.
It would only be $30 something for the gasket and just add fluids. I have the other set of TTY head bolts from when I did the front head and my revised LIM gaskets are in great shape.

I may wait a few weeks since I just did a mobile 1 oil change..

I'll do the head gasket and then do the compression test with the engine hot and heat soaked.
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Old 11-06-2007, 06:16 PM   #45
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Sounds like you guys are on the right track. Hope you have some positive results, Mike.
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Old 11-07-2007, 01:54 AM   #46
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Had a problem much like this which almost drove me nuts until I ran a resistance check of each fuel injector. Found two that were down to 6 ohms resistance instead of the 11.8 to 12.6 ohms stated in the sevice manual. They seemed to work okay when cold and the resistance measured about 8 ohms but when engine warmed up the resistance dropped to around 6 ohms and thats when the misfire problems started. Put in new injectors and it worked fine after that. Did the same as you first putting in all those other parts without any luck.

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Old 11-07-2007, 08:36 AM   #47
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Catching up here..

Mike..I can check my compression tonight and while it might not be a good indicator..we should have TJ check as well.
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Old 11-07-2007, 02:00 PM   #48
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Thanks Ben.

I'll definitely check that out flatlander. Thanks.

And sounds awesome Bill.
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Old 11-08-2007, 08:28 AM   #49
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Mike...I suck..will try and remember tonight.
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Old 11-08-2007, 10:36 AM   #50
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Quote:
Originally Posted by BillBoost37
Mike...I suck..will try and remember tonight.
Haha. Don't sweat it.
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