1996 3800 series II, elusive Vaccuum leak
 

Found my vaccuum leak VIA a smoke machine. This one was a tough one to locate.
Anyone ever run accross this before?

It's only been off and on twice, each time for the lower intake gasket replacement.

Common problem, and a real pain to find.

I constantly suggest pulling that tube and looking for that to tons of folks. Vaccum or P0171 ...this is a very common cause and you can't typically find it with carb clean testing.

I just replaced the tube with a brand new one. GM part# 24508516. I still have the problem but not as bad.
Smoke test did not reveal any other leaks. I did notice that the new pipe ends were not compressed as the original, which makes sense as it is brand new. looks kind of like a compression flange. When tightening the flanges I noticed that the flanges on both ends of the tube do not sit flush right at the tube side of the flanges, but the flanges are flush at the bolt ends and the bolts are tight. the flanges just don't seat squarely. I'm thinking that after a few heat cycles they should seat better. No? I took it for a short test drive and it stalled only once on decel. The problem seems to be getting better but I have my doubts and hoping. I did disconnect the battery overnight hoping to reset everything. I do not see any information, even on dealer world, about installing this pipe. I may have to go in for another smoke test if the problem persists.

Any thoughts on the pipe flange issue? If it's an issue at all.

The annoying part about this whole thing is the fact that there was no driveability issues prior to the upper & lower intake reseal. It was just preventative maintainence. Go figure.

I'm assuming this to be a 3800 Series II NA motor, but your sig suggests that might not be the case. What car/motor are we talking about?

Yes,
1996 Buick Regal 3800 series II w 242k miles. Been a great motor.

:/ my egr bolt is rusted so tight. suggestions?

Please post your issue in a new thread that you start.


GRTP, have you checked the O-ring on the back of the upper intake? With engine movement this hose to the brake booster might flex...might only happen in gear and under load.

Yes I wiggled all the lines. The lines are even new including the fitting itself at the back of the plenum. I just put the smoker on it again and can't find a leak anymore. Every vaccuum line I disconnected during the smoke test shows smoke in those lines. The only thing that has me concerned is I had smoke coming out the oil filler cap when I removed it. Otherwise no smoke at the cap. I had the smoker on it for almost 10 minutes. The pcv valve is also new and the orings for it also new. Thought sure finding that cracked egr tube and replacing it would have cured it. I replaced th Idle air control valve & map sensor before I found the cracked pipe so that is new as well. It gets embarrassing throwing new parts at it with no results. If I disconnect the IAC while it's idling erratically it smooths right out but idles at almost 1200RPM. It's not throwing codes since replacing the EGR tube and the fuel trim numbers are much better, but still up there at 16%. They were up over 20 % at one point on the stft.. I'm thinking chasing a wiring issue now at the IAC.

Not sure. Need to sleep on it.

Any ideas? I'm determined to find it as it is a challenge.

Thanks.

I've got one more trick... the elbow at the brake booster is a check valve. If it goes bad...you have a vacuum leak.

I'm stretching pretty far here, we gotta get this one soon.

And I wouldn't expect the smoke to get past the pcv checkball either. It's in there to keep the crankcase from pulling air.