use2windsurf

I have read numerous posts and I wanted post my situation. everything was working great until a few days ago when I noticed my boost was low, the car wasn't pulling like it was. Boost gauge was showing 1.4 bar max and my aftermarket boost case backed it up. I took the car out to see if I could better quantify what I was seeing and after a few hard runs, the boost improved a little to 1.6 bar. it pulls better now but isnt where it was. I have read everything from the wastegate, to the BOV, Cycle valve, etc. With my circumstance of of about 1.6 bar which is not extremely low which improved with 'exercise' , would one suspect the wastegate just opening too early which I could address with shims? Or should i look to the cycle valve?

Swagger93

Unplug the cycling valve power connector. Drive car. Does the car behave the same as before or a bit slower (but more consistent)? If so, begin troubleshooting the valve. The cycling valve just "fools" the wastegate into into "believing" there is less boost than there actually is because the wastegate will always (ideally) open at the same pressure level. Erratic or low boost levels are indicative of a possible failure.

You can pull the wastegate hose from the cycling valve as a diag tool as well. This will allow your car to boost to explosion time, so get on it slowly. If the boost climbs and seems like it won't stop, at least you know your turbo, fuel and ignition system are working, and it is a KLR, cycling valve, vacuum signal line or wastegate problem. Again, this will destroy your engine if you are not very careful.

Wastegate failure is usually slow and is typically indicated by a loss of ability to maintain boost, not generate it initially. If the wastegate is causing the problem you describe, shims will not fix it.

use2windsurf

Thanks for the suggestions. So here is what I did:
- Before tests, 7-8 PSI boost
- disconnected connector to CV, It did accelerate smoother, 6-7 PSI boost
- reconnecect connector to CV, disconnected line from CV to WG, 10-11 PSI before I backed off.

so looking like it is the CV? I do notice that once the boost peaks, at least in the normal setup, once it peaks I lose a little boost, ie, doesnt hold it.

I have the LR chips and 3 bar fuel regulator. should i just install a manual boost controller and bypass the CV?

THANKS

Swagger93

You should be making more boost than that. I would suspect the cycling valve. Make sure none of the signal lines are leaking. I wouldn't rule out the wastegate entirely--they are a total crap design on the 951.

A manual boost controller is cheap, so it's a cheap diagnosis tool and possible replacement part all in one. I'd say pick one up as your next move.

I did make some shims out of some stainless steel sheet metal, a Dremel tool and a hand drill. I was 19 and super poor college student at the time. It helped, but the difference wasn't that impressive. Now I'd buy a Tial or Tial knock off and just get rid of the factory one.

This might be a good time to test for leaks while you're chasing down boost issues. There's a nifty tester you can build. You just need a PVC pipe end cap, some rubber couplers, hose clamps, bicycle pump, and a bicycle valve with a brass fitting you can thread into the PVC cap. You can pop it on the end of a charge pipe and pump up your system. I guarantee you'll hear hissing from at least a few places. All my cars leaked like crazy before I did this. It doesn't really affect peak boost, but you will notice a big difference in throttle response on the freeway and stuff. A car with no boost leaks feels way more "positive"

This is also a faster way to bleed your brakes and clutch.


One thing I noticed when I switched to a simple twisty ball valve manual boost controller (when the cycling valve in my last 86 failed) was that boost comes on in a much different way. With a turbo the size on the 951, you can make almost full boost with the throttle plate only partially open--I've noticed this in many of my turbo cars. With the stock cycling valve, at least with the factory or Weltmeister chips I have used, the power level will be more linear and correlated to throttle position, i.e. when your foot is only half down, you will get only so much boost and power; when your foot is on the floor it will be full boost full power.

The linearity is nice, but those cycling valves are all aging and bound to fail. You could always buy an electronic unit that allows you to program boost, obviously.

Good luck.