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Vacuum leak on '90 Olds Cutlass
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paul40475
New User
Aug 4, 2011, 12:45 PM
Post #1 of 5
(3022 views)
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Vacuum leak on '90 Olds Cutlass
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I have a 1990 Olds Cutlass Supreme, with a 3.1L engine; 130K miles. Recently I developed a vacuum problem that causes the engine to accelerate in steps and under a load, such as climbing a grade, the AC vent switches to the high volume vent (defrost/floor vents). I cannot find any vacuum hoses or connectors leaking and when I check each vacuum line with a pump, they all hold a vacuum. Because it seems to only occur during an engine load, I am thinking it must be an ECM controlled device. In 2005 I replaced the ECM with a dealer replacement. Replacement was for a non-idle problem.
Thanks for any advice in correcting this annoying problem.
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Hammer Time
Ultimate Carjunky
/ Moderator
Aug 4, 2011, 12:46 PM
Post #2 of 5
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Re: Vacuum leak on '90 Olds Cutlass
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The mode selection is done through a series of air doors that are operated by vacuum. When there is either a partial or total loss of vacuum, the system will default to either defrost or on some vehicles, heat. Acceleration can also have an effect on the doors for the same reason.
Look under the hood for a small black plastic hose coming through the firewall. Follow it to the vacuum source looking for any breaks, cracks or leaks. Also follow any other lines that branch off because they may go to a vacuum reservoir (storage tank) and a leak there will cause the same problem. Using a vacuum gauge to determine if you have full vacuum at any given point is the best way to find it. You can cut into the line anywhere and splice it back together with a piece of vacuum hose. Find the broken line, you found your problem.
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We offer help in answering questions, clarifying things or giving advice but we are not a substitute for an on-site inspection by a professional.
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paul40475
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Aug 4, 2011, 2:58 PM
Post #3 of 5
(3004 views)
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Re: Vacuum leak on '90 Olds Cutlass
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Thanks, Hammer Time, I found the leak under the plenum. I am ordering the entire vacuum harness and that should take care of the problem. The MAP sensor cannot function, but the ECM did not set a code, which bothers me a lot. All I got from the ECM was the precode of 12.
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Hammer Time
Ultimate Carjunky
/ Moderator
Aug 4, 2011, 3:28 PM
Post #4 of 5
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Re: Vacuum leak on '90 Olds Cutlass
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That's not supposed to set a MAP code. It will only do that if there is an electrical issue with the MAP but it may set a rich O/2 code, depending how bad it was. I'm not so confident you found your A/C issue though. that's usually the result of a problem specific to that line.
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
We offer help in answering questions, clarifying things or giving advice but we are not a substitute for an on-site inspection by a professional.
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paul40475
New User
Aug 8, 2011, 8:27 AM
Post #5 of 5
(2970 views)
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Re: Vacuum leak on '90 Olds Cutlass
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The line that goes to the MAP sensor may split under the plenum, (I haven't pulled off the plenum yet), but it comes from the same junction at the plenum intake port. The one going to the cabin HVAC doors comes off right beside of it. The MAP sensor line will not pass smoke in either direction, yet it won't hold vacuum from a hand pump at the vacuum input junction. It may have a check valve in it too. I will let you know what I find, (as soon as my plenum gasket comes in), for the benefit of others on the forum. Thanks again Hammer Time.
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