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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 05-08-2007, 07:43 PM   #1
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Default Vacuum issue

I have a question on a vacuum leak issue. I have replaced the UIM and LIM, a new PCV valve and MAP sensor and there is a slight hissing sound coming from the engine now. I have read other posts and I do have all the o-rings replaced and all is snug. Now I was looking at the illustration in my service manual and it appears that there is a spring in the PCV housing. I did not notice a spring from the old original UIM and did not recieve one with my new one from APN, is this spring necessary? I let the car idle and removed the oil fill cap and it almost stalled but recoups and continues to run. I read B. Buttermore'* post on a vacuum issue : (We had an L27 with a nasty vacuum leak to the crankcase caused by failed LIM gaskets - I don't doubt that the L36 could do the same.) I just changed the LIM gaskets and sealed them pretty good w/ silocone whats the probability there is a leak and if so how can I locate it ?
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Old 05-08-2007, 11:48 PM   #2
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Spray throttle body cleaner around the LIM, UIM and throttle body gaskets, as well as any vacuum fittings. Check the EGR tube from the EGR valve to the LIM also.
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Old 05-10-2007, 05:18 PM   #3
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I recently did my UIM/LIM work, and noticed my vacuum lines were getting dry-rot.

I made a trip to the parts store and took care of it. Runs smooth now.
Advance Auto has a package of 7/32" tubing that can do the whole car and then some.

Give it a try.
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Old 05-10-2007, 05:22 PM   #4
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Take the pcv valve back out and make sure there in only one o-ring on the bottom. Shine a really bright light in the hole. You have a vacuum leak to the crankcase, and that is almost certainly the cause.
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