Vacuum leak - GM Forum - Buick, Cadillac, Chev, Olds, GMC & Pontiac chat


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Old 08-23-2007, 03:38 PM   #1
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Default Vacuum leak

I posted about hearing a turbo/whistle sounds after modding my intake, and then I started getting check engine lights, p0440. I found the source of the leak in the first minute looking for it, once I was assured it was a vacuum leak. Here'* a pic... it'* coming from where the steel piece goes into the block. That'* not a charcoal filter, is it? I have no clue what it is or how to fix it... was hoping you guys could hand off a clue.



By the way, drilling out the airbox did not cause it, I think the guys that put the transmission in were a little bit clumsy with the tranny install.
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Old 08-23-2007, 04:18 PM   #2
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That'* the trans modulator. If the modulator itself is leaking, head to a Napa and tell them you want an adjustable vacuum modulator for the transmission for a 96 Bonneville. You may be able to ask for one for a 97, but when Ben went to buy one for his 97, they tried telling him his car didn't need it. There is a thread on this forum regarding what it should look like so you know you have the right one.

Now if the modulator itself is okay, and you don't want to deal with an adjustable one, I suggest you make sure that the little bolt and bracket are tightened and holding it into the transmission case securly. That little device controls the line pressure in your transmission. A leak means less vacuum, less vacuum means more line pressure(and unmetered air entering the engine). Too much line pressure risks breaking hard parts in the transmission(shifting with a bang), overworking the pump, and god knows what else.
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Old 08-23-2007, 04:22 PM   #3
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Ok. I took it off and transmission fluid dripped everywhere, that'* before I saw your reply lol and I took a guess at what it was. So could this lead to any transmission symptoms?
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Old 08-23-2007, 05:00 PM   #4
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Well I put it all back together, and noticed the two rubber hoses between the actual vacuum line and the modulator were completely dry rotted. For now I put zip ties on them real tight, and that fixed the leak, but next time I'm out towards the auto parts store I'll have to get a new coupler.
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Old 08-23-2007, 05:14 PM   #5
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You don't need to buy special coupler pieces to replace those. Just take one in or get an ID measurement and buy some rubber vacuum hose. It'* typically less tha $2 a foot.

While you are at it, I suggest you take a good look (and feel) at the rest of your vacuum lines, including where they connect to your throttle body and evap. cannister (under your intake airbox. It makes sense to replace all of them at the same time, since they are all the same rubber, just two different ID sizes. For less than $3 you can replace them all except for the elbows and the tee.

You'll be glad you did.
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Old 08-23-2007, 05:16 PM   #6
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Actually, that was the plan, and I did take a look at the rest and they look just fine. Me thinks that when they put that transmission in through my warranty, they took that coupler off of the old vehicle because it'* shot all to hell. Only one that looked iffy was the one going into the evap can. I still may replace them all while I'm at it though.
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Old 08-23-2007, 05:19 PM   #7
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Yeah, it'* cheap enough to do and then you have the peace of mind knowing that all of them are new and won't crack tomorrow, or next week, or next month...you get the picture.
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