Turbo leakage on 86 900T

Are you saying you're still leaking boost? What does your boost gauge read when going up a moderate incline in 2nd/3rd gear with the throttle wide open?

Check the Hooter valve. The vacuum line to it should not leak. My best guess is that the checkvalve on the vacuum reservoir for the HVAC system (RHS front fender) is broken. I just went through this recently. The best fix is to repair the seal the best you can so that it holds vacuum then put a real checkvalve (like the one in the crankcase vent line) in the line to it. This is not easy. I was able to disassemble the checkvalve and reassemble it with the existing seal and it does hold vacuum now. Another possibility would be to remove the complete checkvalve and fashion a nipple then have only the external checkvalve. Let us know how it goes. The checkvalve is poorly designed and will break seal after 10+ years.

KeithG

Grunff wrote:

I did check the hooter valve but not really carefully when it was apart.

I went out this morning and turned the distribution box control after the car had been sitting for more than 12 hours. It hissed and opened and closed the appropriate vent doors, which indicates to me that the HVAC reservoir and check valve is functioning properly. I did have a problem with that once and discovered a hose pinched shut by a wire tie.

Charles.

I tried the boost this morning with premium gas (tank nearly empty). I got about 25-28% into the yellow.

Then I filled up with mid grade. Now the boost only seems to go about 20% up.

The boost used to go about 2/3 - 3/4 (67-75%) into the yellow.

The whooshing noise starts as soon as the guage touches the yellow.

I am starting to wonder if there is not a second problem, like the knock sensor or a false knocking affecting the boost and the wooshing sound is not related to the low boost?

The car immediately idles upon starting it, there is no "hunting" to indicate a vacuum leak. This makes me think the air is being released somewhere between the turbo and the throttle plate. Or maybe in the turbo itself? But the waste gate doesn't make that sort of noise, does it?

Charles.

Ok, you have quite a *big* problem there.

Possible, but I think you need to eliminate all leaks before you start thinking about that.

Maybe, but they only hunt when you have a really big leak. A small leak will flatten your boost without causing hunting.

There's really not much in the turbo to leak. The waste gate is a big piece of steel. There's nothing there that could leak.

You need to figure out where you have a leak. It will be a fairly big leak. Start the engine, and spend a bit of time eaxmining all hoses, big and small. If you have a butane/propane torch, use it to direct a stream of butane/propane at any possible leak spots (torch NOT lit). Listen to the idle. If it goes up, you've found the leak.

Okey dokey. Probably a good investment at this time to get a 'mity vac' it will allow you to pull a vacuum and put a little pressure on things to look for a leak. #1 replace all the vacuum lines if they are not new. Silicone is the preferred material, though OE rubber is fine #2 replace the vacuum fitting bushings on the intake. There are 3 and these are notorious. They are cheap and live about 10 years or so. If they are hard or swollen, they can pop out a bit to allow a pressure leak and then be sucked back in under vacuum at idle. #3 pressure and vacuum check the lines from the intake out. Just because the vacuum reservoir can hold a vacuum does not necessarily mean that the check valve is OK. It can seal reasonably well under vacuum and then leak under pressure.

KeithG

charles stoyer wrote:

I am beginning to think the leak is in the hooter valve, but I will pursue it. that propane test seems interesting. Also I think maybe the low boost and leak are independent.

I looked in Bentley and there are a number of things that could cause low boost, the solenoid valve, knock sensor, pressure sensor (this one is under the kick panel).

Also it said that it could think the cruise control was on which would limit the boost.

So the search continues. I will let the group know what I find.

Fortunately, I do have my wife's perfectly boosting 85 900T to swap parts with until I identify the culprit.

Have you tested it? All you have to do is suck on the small hose. Easy test.

Very useful for finding difficult to find leaks.

Ok, but you can't fix your boost without fixing your leak (whereas you /can/ fix your leak without fixing your boost).

The list is much longer than that :-(

Good luck.

Handy.

Under the dash, below the speaker are the boost sensor and the overboost=20 protection switch.

On mine the overboost protection switch had a leaky diaphram. I simply=20 removed it from the circuit (fully intending to replace it but never=20 did) and joined the ends of the hoses together. The hissing stopped, and=20 the normal boost resumed. On a US car it is below the drivers side, on a=20 british car, it is below the passenger speaker. I could hear it when I=20 hit boost, and being a driver on the "wrong" side, I could hear it=20 coming almost from the passenger speaker. While you are in there, you=20 will be able to see and adjust the clutch and brake cruise switches=20 attaced to the pedals (not the brake light switch). I think it is about=20 =A330 GBP to replace, plus time to get the knee bolster down and hunt=20 under the wiring loom.

--=20 The poster formerly known as Skodapilot.

Thanks for all suggestions. So far, I have sucked on the hooter valve vacuum hose and it does hold vaccum. So it seems the SHHHH does not come from there.

I also did the Bentley test on the Turbo solenoid valve on the radiator cross member, and it passed. No flow until battery voltage, then solenoid clicks and there is flow.

No time yet to check out other components.

I am beginning to suspect the APC thinks the cruise control is on.

Charles.