924Board.org

[Chaos]

Ahhhh. The breather adapter. Gotcha.

Anyway, just did the TB rebuild a couple of weeks ago. Might be a good time to make sure all is torqued properly.
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'81 US 931 "Rochelle"

[Chaos]

what... type of material are these gaskets supposed to be made out of? the ones for the recirc valve end caps?
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'81 US 931 "Rochelle"

[ideola]

[Chaos]

Ok awesome. The one side seems intact. Haven't gotten the last bolt out to check the other side, though. Puzzling over that at the moment. Meanwhile, I think I see a clamp missing on that 2" rubber hose from the intake manifold to the recirc control tube. I'll have to take the alternator out to really inspect it up close and personal.
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'81 US 931 "Rochelle"

[Chaos]

So, that little 2" piece of hose is DEFINITELY hosed up. (Pun totally intended)

It actually was clamped on both ends, but not remarkably well, and it was also pretty chewed up both inside and out. I'm going to hit a few parts stores to see if I can find a reasonable substitute locally. Fingers crossed that this is the cause of my boost leak.
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'81 US 931 "Rochelle"

[Chaos]

Welp... Replaced that piece of hose, re-tightened up a couple of other elbows... Just finished getting everything put back together, went for a spin...
Nothing. No improvement. Still pulls nicely, but boost is still lacking pretty severely. Guess I'm just going to have to wait to get her into the shop for that smoke test. Bummer.
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'81 US 931 "Rochelle"

[Paul]

Maybe the waste gate is stuck partially open?

If your idle speed has not changed, probably not a vacuum leak.
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White 87 924S "Ghost"
Silver 98 986 3.6l 320 HP "Frank N Stein"
White 01 986 "Christine"
Polar Silver 02 996TT. "Turbo"
Owned and repaired 924s since 1977
Porsche: It's not driving, it's therapy.

[Paul]

Also might be a stuck recirc valve, make sure it is still "clicking" when the throttle is blipped.
_________________
White 87 924S "Ghost"
Silver 98 986 3.6l 320 HP "Frank N Stein"
White 01 986 "Christine"
Polar Silver 02 996TT. "Turbo"
Owned and repaired 924s since 1977
Porsche: It's not driving, it's therapy.

[Chaos]

had the recirc taken apart earlier. everything seemed fine in there, but i'll check for that tomorrow. never really noticed the noise. I'll have someone stand outside and listen for it. Definitely thanks for that tip.

Wastegate being stuck partially open seems like a pretty big possibility, now that you mention it. that would explain how the turbo sounds fine, spools fine, but pressure builds slower than normal and peaks lower than normal. guess that's going to have to be at the top of my list of new suspects.

Definitely still going to check for vac leaks b/c i'm only pulling around 10Hg at idle and I've gotten more than that before. I know that's low. Will probably have the guys at the shop scope out the WG at the same time they do the smoke test.
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'81 US 931 "Rochelle"

[Paul]

Any update?
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White 87 924S "Ghost"
Silver 98 986 3.6l 320 HP "Frank N Stein"
White 01 986 "Christine"
Polar Silver 02 996TT. "Turbo"
Owned and repaired 924s since 1977
Porsche: It's not driving, it's therapy.

[Chaos]

Hey sorry man. Didn't have this thread set up to notify me.

So to answer your question... yes and no. Little bit of turmoil at the shop had the tech stop the vacuum system test before he got to pin down the source of the leak. There is definitely a leak though, and he gestured to me in the area of the turbo. Then, it occurred to me that when I checked the end caps' gaskets for the recirc valve, I was never able to get the bolts to tighten. So, those threads in the housing are stripped out to some degree.

Meanwhile, while they were working on the car trying to diagnose the seeming fuel cutoff issue (which they were leaning towards the fuel pump relay), something spontaneously clogged the injection system between the fuel dizzy and the cylinders, so they're trying to locate that issue currently.

Obviously, in the meantime without fuel, she won't run. And if she won't run, we can't do another smoke test... yada yada yada. Need to get the turbo and wastegate rebuilt anyway before I install the TMCC and boost controller I bought from Dan so... they've got a good local guy who can set me straight with that housing and a rebuild... Might swap the cold side to the 951 version anyway... I dunno. We'll see where this all leads us.
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'81 US 931 "Rochelle"

[Chaos]

I guess it's time to bring back this old thread, because the old girl is finally running again, and I'm sure I could use some assistance from the ol' toofah-hive-mind!

So - quick update - poor thing has basically just been sitting, non-functional, for the past 3 years, primarily in the custody of a shop who had apparently given up on any cars that weren't 911s, but didn't have the stones to tell me I was outta luck. Eventually, I got her home, and shortly thereafter had another local shop help me get her back on her feet and officially in running condition, once again.

Fast-forward to now: After all this time, the situation at hand really hasn't changed at all. Not producing proper boost (still topping out at 4-5psi) or proper vacuum at idle (~-10 to -13 Hg)... but as previously stated, the vacuum readings don't appear to be any different from what they were before the sudden boost decrease.

Now that we're all caught-up...
Question One: Can someone tell me the ID of that connector at the top of the turbo control line (intake manifold side)? I know I checked it out a couple of years ago, but I'm really wondering what the hell I replaced it with. I really want to replace it again with something appropriate.

Question Two: Exactly how boned are we on wastegate diaphragms? IIRC, everything I've read says they're NLA. Has anyone come up with a replacement/substitution? I'm still holding the WG high on the list of suspects.

Meanwhile, I've flushed and changed the oil, flushed the fuel tank and lines from the pump to the filter (which was also replaced), replaced the ground strap on the battery, got her running on a belly full of Techron and good fuel... Trying to do what I can to get the little odds and ends taken care of, while I let the Techron work its magic and then start trying to sleuth out my boost/vac leak situation.

Until yesterday, she was running rather rough both at idle and warmed up. Low RPM was pretty stumbly, in-boost range was decent, but not great. Yesterday, I hooked up the multimeter and saw the duty cycle lurking in the 80-90% range post-warm-up. Naturally, I went and made some idle screw and mixture adjustments, got her to sit right around that magical 45-50% area, and now she's purrin' like a kitten(with a weak turbo) across all ranges... but only once she's warmed up. Idles/runs like an overweight dog during the warm-up cycle. Oh yeah, fun stuff, indeed.
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'81 US 931 "Rochelle"

[ideola]

Failed wastegate diaphragm would result in overboosting, not underboosting, so I don't think that's your culprit. However, if you want to go down that path, the only place I know to get wastegate diaphragms is Patrick Motorsports. Be warned, however, that the thick heavy asbestos gasket between the lower and mid housing pieces is NLA, and I have not found a solution for that yet. I am planning to attempt to make my own out of some materials on McMaster-Carr, and will post back with results soon.

Your vac and boost readings both indicate a leak in the intake tract. Bear in mind, it is quite likely that there are multiple points of leakage. The most effective way to find these is to do a smoke test. I have not built my own smoke tester yet, but there are several articles on the web that show different methods of building a DIY smoke tester. The method I am favoring are the cheap party fog machines, and that's what I'll be trying first if I ever get around to it.

The biggest suspects are all of the rubber elbows and vac lines in and around the intake. Many of these are NLA or hard to get as they have to be shipped from Germany. I have identified every section of hose for the 931, and I've developed kits to replace everything using high quality silicone. I don't have it on my website yet, but will be posting it soon. In the meantime, you can PM me for details.

The other likely culprits are: the boot that connects the airbox to the AFM; the boot that connects the AFM to the turbo inlet; and the throttle body itself. For the TB, we already have a rebuild kit for S2. For S1, there's nothing available. For the big boots, I've seen that rubber dry and crumble to the touch, so have a good look at those.
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erstwhile owner of just about every 924 variant ever made

[Chaos]

Dan, I knew you'd have damn fine insight for me!

Just yesterday, I've ordered myself a bunch of 13mm and 16mm silicone hose to replace all of the long, (mostly old, braided) soft lines that run all around the engine bay. And I'm just now ordering a right-angle coupler-reducer to go from the AFM to my intake tube (the air box is looong gone).

The one thing I definitely didn't think about, because it's completely out of sight most of the time, is that bellows from AFM to turbo!
You, sir are a genius. I'm sure that piece is probably a hot mess, since I'm certain my engine mounts are pretty badly worn, and it has GOT to be seeing way more flex than it should at its age.

Any tips on what to replace that with? Another silicone coupler (I'm guessing 3" diameter), or try for an OEM replacement despite the fact that they're probably NLA?

Thankfully, I've rebuilt the TB and also replaced all the elbows with your kit from The Garage just a little over a year ago, and the car's seen very little action since then. So, for the moment, those should be ok. Next time (probably soon), I'll go silicone for those elbows, as well. That said, I think I actually do have one of those cheap fog machines, so I'll absolutely get on trying a DIY smoke tester approach.

Oh, and as for the WG situation, I agree that the diaphragm isn't likely the issue at the moment. Just kind of a side-question, as my next highest-priority objective on the list is to get the WG and turbo both rebuilt. I mean, it's not an issue right now, but at 35-ish years old, I don't need it to be in a hurry to become one, either.

PS - following tips I read in some older threads just yesterday, I went out and scoped out my ignition system after work last night (before starting to dive into CIS parts) and found my plug wires are all a shambles, so I've got another set of those on the way, as well.

Steady progress!
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'81 US 931 "Rochelle"

[Paul]

Make sure the recirc piston is installed in the correct end of the valve. Sounds much like the issue I had in the nineties.
_________________
White 87 924S "Ghost"
Silver 98 986 3.6l 320 HP "Frank N Stein"
White 01 986 "Christine"
Polar Silver 02 996TT. "Turbo"
Owned and repaired 924s since 1977
Porsche: It's not driving, it's therapy.