Runing rough at idle in P/N and on decel (11/14) - Page 4 - 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 10-31-2007, 01:02 PM   #31
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Quote:
Originally Posted by BillBoost37
TPS is good right?

Vacuum is good...

You've checked compression and know that all valves are sealing 100% right?
The TPS is good and so is vac. I haven't done a compression test yet though..

Quote:
Originally Posted by jr's3800
Would the connector in the fire wall possibly have a couple of different pin locations?

The car you have had an L67, ans you installed the L36 with wiring harness..
I compared the L67 harness that was still in the car with the L36 and they did match up at the firewall plug. (That was one of the first things I checked when I got the car )

Quote:
Originally Posted by agrazela
Maybe I missed it, but how are your fuel trims? Any indication of a lean condition?
It'* back there somewhere and the fuel trims are good.



So.... Compression test time?
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Old 10-31-2007, 03:14 PM   #32
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Do me a favor and check the EGR one more time...specifically, where the tube bolts into the LIM.

My wife'* car was having very similar symptoms to yours, until I figured out that some d*mned idiot (me ) stripped the threads in the LIM where the EGR flange bolt screws in. Thus, the flange was not sealing well and giving me occasional fluctuating idle, lean trims, etc...but, like you, problems would show up only when warmed up and idling and decelerating...no problems when running / accelerating.
It was one of those maddening, intermittent things that passed all visual inspection, and would never happen when I was actively looking for the problem

(BTW, I fixed it by finding some good threads in the LIM with a longer bolt (spare LIM bolt Boosty sent me some time ago) and some washers as spacers between the bolt head and the EGR flange)

P.*., if you need a good compression test kit, you can borrow mine (but you'd have to pay some serious cross-country shipping )
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Old 10-31-2007, 04:40 PM   #33
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Well..
I had the plate that unbolts the EGR to the LIM off and I inspected the tube as best as I could. I couldn't find any cracks or carbon deposits..
I also sprayed the crap out of that area specifically with maf cleaner (alcohol) and it didn't change the idle.

I can check it agian this weekend though.

Did your wife'* car have a good idle while in drive?
As soon as I put it in gear, it idles good.

Thanks for the compression tester offer. I'll let you know.
I'm not positive but I think one of my buddies has one.
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Old 10-31-2007, 05:31 PM   #34
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Quote:
Originally Posted by 95naSTA
Did your wife'* car have a good idle while in drive?
As soon as I put it in gear, it idles good.
Nah, it had a fluctuating idle when in Drive, also.
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Old 11-03-2007, 04:34 PM   #35
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I did a compression test today..

Remember I do have a cam so compression will be lower..

Front bank:
1 = 115 - 125
3 = 120 - 130
5 = 120 - 130

Rear bank:
2 = 90 - 110
4 = 120 - 130
6 = 95 - 115

I put a few drops of atf in the low cylinders and it went up to 120 - 130.

When I had everything apart to repair the front head, I only replaced the front head gasket since I didn't have to take off the rear head.

So... even though the oil test is pointing to rings, should I replace the rear head gasket? Maybe the crash loosened it up?
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Old 11-03-2007, 04:48 PM   #36
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I don't know if I would even worry about the rear at this point... Those are all on the low side..

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Old 11-03-2007, 08:15 PM   #37
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I don't know if this may or may not help but I will tell you about an experience I had. I toasted a bearing on my 85 mustang'* stock motor. So I found someone down the road that had a 90 that was wrapped around a tree. We pulled the motor and swapped some parts on the long block then installed it. As I drove it for some testing the car kept overheating and we couldn't figure it out. Then we blew air into the cylinder and found it blowing into the radiator. We pulled the heads and found the impact moved both heads, poped the gaskets, and bent the bolts . Yeah so I am not saying this is the case but it might help to look at things from a different approach.
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Old 11-03-2007, 08:31 PM   #38
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Mike How hard did you hit that Tree?

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Old 11-04-2007, 02:03 PM   #39
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Blownville, I might have hit that hard.

Quote:
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Mike How hard did you hit that Tree?
This hard:
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It was a wooden utility pole.. my car actually knocked it down.




What should stock compression be?

Any guesses as to what it should be with a mild cam?
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Old 11-04-2007, 02:10 PM   #40
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Did my compression about a month ago (fully warmed up...still got the blisters on my forearms to prove it ).

Stock cam, stock heads (aside from SR rockers), and got 160 +/- 5 psi all around.

With a cam, I would expect compression to go down.

But are your heads decked? If so, how much? What kind of head gaskets? What cam is that you've got again (S1X?). Is your cam advanced (or retarded) from spec?
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