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Posted by: Porschef Sep 15 2015, 07:01 PM

Drove the car to work today and it's running very well. When I got home I wanted to check a couple things. Don't know why I did it, but the last thing was to spray some carb cleaner around to check for vacuum leaks. When I sprayed some under the plenum, she almost stalled out. Sumbitch! I thought I'd found all the vacuum leaks.

Question is, what's under the plenum that might allow it to suck air? Could there be a crack?

Great, gives me another excuse to wrench on the car. Also should allow me to lean it out a bit more at the AFM. It's L-jet, btw.

Any ideas?

Posted by: 76-914 Sep 15 2015, 08:36 PM

Absotootly! It's just a metal box and they do rot out. Pull it and check. Easy, peasy.

Posted by: r_towle Sep 15 2015, 08:41 PM

Aliens

Posted by: rick 918-S Sep 15 2015, 08:48 PM

I can reassure you there are no Aliens under there. Don't worry.

Posted by: r_towle Sep 15 2015, 08:49 PM

Don't believe him, he was assimilated long ago

Posted by: boxsterfan Sep 15 2015, 09:19 PM

This is *exactly* what an alien would say.

Posted by: McMark Sep 15 2015, 09:22 PM

Yup, seen plenty of rusted out plenums.

Posted by: Porschef Sep 16 2015, 04:14 AM

Thanks gents, that'll give me plenum to do this Saturday; I'll watch for both aliens and rust...

Posted by: Porschef Sep 17 2015, 05:50 PM

Looks fine. I don't know what was making it almost want to stall with carb cleaner but I'll go through everything again

At least I can clean up the compartment a bit.

Posted by: 914_teener Sep 17 2015, 06:27 PM

How did you check it?

Posted by: Mike Bellis Sep 17 2015, 07:14 PM

Run some green locktite across the welded seam. The green stuff is penetration grade and will seal any minor leaks in the weld.

Posted by: 76-914 Sep 17 2015, 07:19 PM

water or air test it.

Posted by: Porschef Sep 18 2015, 04:17 AM

Thanks guys. Mike, I thought about using RTV or some such but the green Loctite sounds like a great tip.

Posted by: falcor75 Sep 18 2015, 04:23 AM

Check the gasket between the plenum and throttle body?

Posted by: Porschef Sep 18 2015, 05:53 AM

Yes I had and it was bad, replaced it a year or so ago. It was when I sprayed the carb cleaner under the plenum that it would almost stall.

Posted by: RobW Sep 18 2015, 06:37 AM

Make sure you have your accelerator pedal stop intact and adjusted to stop the cable from over torquing the plenum.

I went through 2 plenums the hard way on my /4 AX car before figuring this out.

Posted by: Porschef Sep 18 2015, 10:40 AM

Rob, had your's split at the seam underneath?

Posted by: Porschef Sep 18 2015, 10:42 AM

Double post

Posted by: SirAndy Sep 18 2015, 12:12 PM

Check the trough-tubes on the plenum. Almost all cracks i have seen where around those tubes and they can be somewhat hard to spot.

A pressure or water test will show ...


EDIT: Oh, wait, this isn't a 2.0L? Nevermind then ...

Posted by: RobW Sep 18 2015, 01:52 PM

Like Andy said. The plenum gets torqued by the throttle cable extended farther than the mount can go. The whole plenum contorts and lets in air. More structurally than the seams.

Posted by: Porschef Sep 18 2015, 02:00 PM

Andy, it's a 2056 with Ljet. Should that matter?
Trough tubes, are you referring to the runner connections?

Rob, I'm pretty sure the cable isn't yanking on the plenum, but I'll check after reassembly.

Thanks gentlemen

Posted by: SirAndy Sep 18 2015, 02:27 PM

That's why i said "Oh, wait, this isn't a 2.0L? Nevermind then" ...

The 2.0L D-Jet plenum has hollow tubes that go through the plenum.
The 1.8L L-Jet plenum (which is what you have) does not.

And no, that has nothing to do with the intake runners.

Posted by: Porschef Sep 18 2015, 02:31 PM

Ahh, ok.

Danke

Posted by: RobW Sep 18 2015, 02:34 PM

Sorry. I've only owned 2.0s and burned 2 plenums in succession Axing.

Posted by: r_towle Sep 18 2015, 05:47 PM

See, it's aliens.

Posted by: Porschef Sep 18 2015, 06:49 PM

Uh, Rich, I'm starting to think you're right...

Posted by: r_towle Sep 18 2015, 07:37 PM

It won't leak when you put it back together, therefore......aliens.

Posted by: Porschef Sep 19 2015, 12:10 PM

Ok, so, I put everything back together, started her up and tried the carb cleaner routine. Sprayed it under the plenum, and after a few seconds, the idle dropped and it wanted to stall.

Damn! No difference. No aliens either. So wtf?

Then, it dawned on me, after getting a whiff of the cleaner...

What was happening is the cleaner was getting heated, and then sucked into the snorkel. I verified it by adding a length of tube so it could suck fresh air from outside the engine compartment...

So I'm real good at removing and replacing the plenum now. Gonna add it to my skill set list

Car was running so well. Lesson learned, don't fix what ain't broke