I have a fully stock 89 930 with less than 30k miles. All parts are factory original including the intercooler, turbo and wastegate.

Problem: The car runs great initially. Once it gets up to temp following an initial start up in the morning the boost comes on normally, at the right RPM level and is very predictable. Actually the boost is quite easy to predict and you can get it to pull very strong with slight throttle movements. It is a great feeling! But after 30 minutes of running, or if the car sits in the sun and you restart the boost begins to drop out and eventually will not come on at all. With zero boost getting up large hills is very difficult.

Possible solutions from what I have read include the turbo, a vacuum leak, or the wastegate. I am new to turbos and still need some help.

I have traced all vacuum hoses connected to the main turbo parts (sensors, cooler, etc.) and they all look fine. But is a visible inspection enough? Do I need to track all possible vacuum leaks or just those in and around the turbo system? How do you do this? The motor is a bit noisy (in a very good way) and I am not sure I could hear a leak without a listening device.

I think the problem is probably the wastegate. The factory manuals provide the means to test this, but I don't have access to an air compressor. Should I just replace the diaphragm and spring since the car is 20+ years old and will probably need this anyway? Thinking is that this part is failing and works well when cool but as it heats up it fails to work properly.

Final option is to probably do the above but also have the turbo rebuilt. But I don't think a turbo can work at one point and then not at all later. Yes it too is 20 years old and will eventually need attention but I have not heard of one the stops working when hot. It either spins or not. Original parts are a must as this is an unmodified car.

Thoughts?

 

Good description of the problem RobT.

I'm no expert yet, but if you had a vacuum leak it wouldn't run well at all, so you can prolly rule that out. Not sure the wastegate would wait to fail when it gets hot either? Maybe somebody with experience with wastegate falures could chim in?

IMHO it kinda sounds like it's heat soak, which would point to the intercooler & fan...

 

It sounds like it could be a fouled spark plug or a bad plug wire. Both can change personalities when hot. I would do all of the easy things first. Also, I had a similar problem and it turned out to be the plug in the panel on the left rear side of the engine compartment. It was slightly out of its socket so I pulled it out and cleaned the prongs and that cured my problem. As far as rebuilding the engine I would not do that unless you have just won the lottery and can't get out of your front door due to the mound of cash in front of it. That can be a costly endeavour and you will run into the old "For just a little more we can upgrade this item".

 

That's pretty weird. Zero boost when hot....you're talking not only not registering boost on the gauge, but no actual boost felt in the performance of the car? Does the car run like crap when that happens (i.e., stutter/miss, etc) or is it still running smoothly and you can tach it out, but just with no added power?

Even with extreme heat soak as mentioned, I would think that you would still build some boost. After all, you would still be compressing some air - though less of it when hot vs. cold.

I'm leaning toward WG issues. Maybe (and this may be a stretch) your WG spring has lost it's temper and really shows up when hot. A weak spring will let the valve open sooner - maybe way too soon - and you'll never build boost. Just a theory...I've never heard of this happening.

 

Thanks for the advice and thoughts. I will check on the plugs, and my guess is a full tune up is in order and this might help. Generally speaking the wires all look good, but they are also OLD. I am now wondering if this is an ambient temp issue where performance is simply robbed as the intercooler is not up to the task since it is stock. The car runs fine when it is in the no boost condition, just very sluggish as in lack of power. It does not stutter or miss. Today it is a bit cooler outside and it is hard to reproduce the problem. Engine temp normal, boost is normal but not as wonderful as when ambient temp is cooler. I am guessing wastegate spring may be the issue or it simply does not like to run when the temp is over 88 degrees.

 

Back when I still ran with the stock IC and turbo, I never had problems reaching full boost even on the hottest days (95+ degrees). At those temps and heat soak realities, the the greater risk is one of detonation.

 

A broken WG spring or a frozen turbo wheel would give you the same outcome. With a broken WG spring you should feel exhaust coming out of the WG pipe all of the time and a potato in the little pipe trick would give you some idea if it is the spring. If it is a frozen wheel you can pull the rubber hose on the intake side back a little and see if you can spin the wheel with your finger. I misunderstood you before because I thought you could get some boost but not much.

 

Still having the problem? I had an old air boot that would collapse under heavy intake when warm. The old rubber would get soft, collapse, stick together and cut off the air intake.

 

Yor are right about the rubber boot....it can get so soft because of age and or oil collecting in it that it gets sucked together under hard or harder acceleration....in my case with a Kokelin IC........it would actually stop the car and I would have to reach down...turn the key all the way to off..with the clutch in...and then restart the car......on the roll...if its mushy...time to change it.

 

RobT, have you found anything, yet?

I developed a similar problem in my car today. It seemed to run fine yesterday when I ran some canyons, but when I autocrossed it today I had trouble developing boost. Granted autox courses aren't kind to stock power delivery for a 930, but the car felt especially sluggish on the course. I thought I had a wooden block under the throttle pedal. Afterwards when going home I noticed it took forever for the turbo to spool up and the boost gauge maxed out at around 0.6 bar instead of the full 0.8 that it normally pulls. Seat-of-the-pants dyno corroborated those figures.

 

Since the problem seems to be temperature related I'd recommend checking warm control pressure. Was there any black smoke evident when under boost?

 

Sorry for not getting back guys. I don't get to drive the car that often making it difficult to diagnose. I am still having the problem and it seems to be heat soak to the best of what I can tell. Most of the seals look to be in good shape as is vacuum. When cooler she builds boost with abandon. If you stay mostly on a freeway with lots of air it does ok, but not as great as when cold. No smoke whatsoever, but drags a bit when the AC is running. Once the weather cools off I will try to repeat the problem. Plus I need to install a real boost gauge which is now in the garage ready to go in. This should help with diagnosis as seat of the pants is not always accurate when you don't drive it enough.

 

Rob, what was the cause of your problem?

My suspicion...a partially obstructed exhaust, catalytic, and/or muffler.