Benzor

I have an 1986 951 with ~85k miles. Was recently off the road for 2 months while I did the clutch. Now it is limited to 5PSI, and I'm really scratching my head on what could be wrong. Car is completely stock.

Before the clutch, car would boost to ~9PSI, but clutch would slip when really on power, esp. on shifts 2-3 and 3-4. I had a long history of testing prior to 9PSI (car would only run 3PSI), turned out to be a clogged muffler.

Here are the tests I've run since the clutch:
- Pressurize intercooler and intake at intercooler inlet: No leaks, very slow (2-3 min degradation from 15psi to 10 psi). Caught lots of small leaks previously.
- Checked accuracy of aftermarket boost gauge when intake pressurized - same to +/- 2 pis
- No exhaust from downpipe down : limited to 5psi of boost
- Check for exhaust leaks in crossover pipe: some wind, hard to differentiate from flywheel
- Startup vaccuum is 12, warm is 16.5.

Prior to the clutch, I had also done / checked:
- Wastegate open & close with external pressure : worked fine
- Replaced CV valve with known good valve, including bench test.
- Replaced the BOV with new OEM
- Block off plate on waste gate - was not the solution (was clogged muffler)
- Clamped wastegate line - was not the solution (was clogged muffler)
- Replaced all vacuum lines with new, venturi delete
- Capped the test port on the crossover pipe with a new lug nut
- Rebuilt throttle body to fix air leaks
- New fuel filter
- Put new muffler and catalytic converter in

As I see it:
- There could be a leak in the turbo outlet pipe. (Has been recently replaced)
- Turbo could have suffered a low-oil or low-coolant event, is no longer working. To my knowledge, turbo is a rebuilt unit put in 10 years / 15k miles ago.
- The computer could be opening the WG early, due to a faulty signal
- Any others?

I'm really at my wits end here !

Bruce

gconnoyer

Any way to bypass whatever control the computer has on the gate? (For instance, the CTSV's have a solenoid attached to the WG with PCM control that limits boost. We just run bypass it if we're looking for anything over 9-10spi. ALSO, the factory wastegate is very weak, and if its hooked up normally, how you would think to hook it up, it will only hold about 4psi for some reason.

Could also be the turbo. I dont know if you can reach the turbo, but check impeller shaft play. Check on the hotside as well if thats not a giant pain to get to.

Benzor

I had checked the impeller play before the clutch, fine. Hot side requires taking half of the engine off.

I can bypass the control on the WG - clamping the vacuum line to it. Will try that and retry the blockoff plate, to see if that's it.

BoulderGeek

I had a similar problem with my Volvo V70, last year. Turns out that when I replaced the Turbo Control Valve (wastegate actuation solenoid), I had the vacuum lines crossed. I was only getting 5PSI, even though my ECU tune said I could have 15. Swapping those lines returned control.

Just a suggestion to look at the path of vacuum lines to the intake vacuum source and wastegate.

konakat

You will probably get more assistance in the Turbo-specific forum. Most of the turbo guys hang out there.

Van

Status of your BOV?

944hal

I just had a similar problem, but more sporadic. Sometimes I had boost, and then it would bleed down to about 5 PSI. I changed out the cyclic valve (under the intake) and it ran good for two laps, then quit boosting. Not sure if the cyclic was the problem. However, just discovered, while replacing the wiring harness, that the positive wire on the knock sensor was broken. It could have been making intermittent contact. I suspect that could be the culprit. Don't know yet. I have to put it all back together and can't really test it until the end of August (track car only). Point being, it could be old wiring contributing to your problem.

Benzor

BOV is in good order - new one recently.

Wiring on the cycling valve is an interesting hypothesis. Will test by clamping the line first, then seeing if I can test continuity in the wire - thanks.

JacRyann

Clamp the line between the cycling-valve and wastegate. This removes all KLR/CV control. Gently do a couple runs with increasing throttle. Should be able to hit +20psi boost. If not:

- wastegate spring weakened
- collapsed inner pipe in downpipe/mid-pipe sections

Benzor

Woohoo! It was the cycling valve. I clamped the line, and power came back, then re-arrnaged the wires to cycling valve and gave it a sharp tap, and it works. So now I have to figure out if it is a permanent solution.

Boost is now at 9PSI, so I've got some more sleuthing to figure out how to get to 11psi, but feel that is a more manageable problem.

Thanks for all your help!