Calling all engine gurus-Help w/rough idle, misfire, knock - 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 11-13-2005, 09:50 PM   #1
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Default Calling all engine gurus-Help w/rough idle, misfire, knock

97 SSE 125K miles
Rough uneven idle
RPMs drift down and back up
"Surges" and shakes at idle
Under moderate load, KR up to 9 to 11', misfires across all cylinders
No MIL, No Freeze Frame data
Air Fuel Data look ok, O2s look OK

Replaced
MAP
TPS
IAC
Fuel Pump and Sender
All 3 Ign Coils
Spark Plugs w/Wires

Cleaned TB, ran GM Top Engine cleaner thru

I'm afraid I'm hurting this engine-- help!

Daron
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Old 11-13-2005, 11:06 PM   #2
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Does it burn any oil? If you tap on the block with a hammer while it'* idling, does the KS count go up by exactly one?
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Old 11-14-2005, 09:18 AM   #3
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Sounds like the knock sensor is working because of the high KR reading. Or it'* reading faulty. Check for exhaust leaks in the manifolds, excessive heat and compression.

Something seems to be causing it to run so badly that the knock sensor is picking it up. How long has it been doing this? Maybe a bad tank of gas?
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Old 11-14-2005, 09:53 AM   #4
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I will try tapping on the block w/ a hammer later on today, and let you know what I find.

It'* been doing this for quite a while.

I've even switched to 93 Octane w little difference. The sensor noise channel is very active, ranging greatly as the engine RPMs change. If idling for a while in the drive thru it will start to get hot, and the surging and shaking sensation gets worse.

-How do I really check for exhaust leaks?
-How do I check the compression?

Also, listening clostly to the engine running, this is like a tapping sound at idle from the engine on the passenger side, or almost like bubbles. Under moderate load, I get a "tinny" rattling sound from farther down on the passenger side. Do not know if these are related.

Autotap still is not finding any DTCs stored, or FF data which I don't understand. But there is still plenty of KR and misfiring.

Daron
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Old 11-14-2005, 09:55 AM   #5
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Oh yeah...

it does seem to burn a little oil, and it does leak it too. It doesn't leave spots on the pavement, but the block is always oilly and sludgy on the outside.

Thanks for the help you guys,

Daron
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Old 11-14-2005, 10:01 AM   #6
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If you did plugs etc.. please check the wiring.

That noise on your passenger side is going to most likely be the cause. Need to somehow figure out what it is.
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Old 11-14-2005, 10:03 AM   #7
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I did the wires, I even cleaned up all the grounds in that area.

It doesn't always misfire and apply KR when I hear that noise though, and vice versa.
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Old 11-14-2005, 10:28 AM   #8
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A lot of things could cause this. Keep digging.
Clogged injectors - add fuel injection cleaner.
Clogged cat?
Rich 02? - remove and check color of tip.
vacume leak,
Check for spark at each plug with pencil type gage.
Fuel regulator diaphram - pull vac hose and check for gas smell.
Crank or cam sensor....
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Old 11-14-2005, 10:27 PM   #9
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Check your injectors. Sounds like it picked up some bad gas. Same thing happened with my dad'* truck.
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Old 11-22-2005, 02:27 PM   #10
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Just thought I'd update and see if anybody else had any thoughts--

I swapped the injectors around, the misfire counts on my AutoTap didn't seem to be affected.

Spark Plugs are white-ish tan.

Compression test was OK.

Why am I not getting an codes either???
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