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Re: Low turbo boost '86 5KCSQ
Rob O'Brien wrote:
> Alex, didn't you get "weird scary boost fun" with a bad vac line to the
ECU and 0.9 bar - Corvette-munching overboost?
Yes, but what happened in that case was that the pressure/vacuum
take-off (the small pipe that is pressed into the intake manifold facing
toward the passenger compartment with all of the lines coming off of it)
was popping out under boost, preventing the ECU from seeing the
manifold pressure and giving me overboost followed immediately by the
car _dying_ as soon as I let off the throttle (big vacuum leak). The key
was that the boost gauge would get "stuck" at 0.8 bar and not change,
regardless of throttle position, rpm, etc. Then when the engine managed
to develop some vacuum or just by luck the pipe would reseat, sealing
everything up and letting the car run normally (until it hit 1.2 bar again).
But the turbo was _definitely_ spinning!
(and I have to admit, hanging my head here, that my descriptions of the
extra power were a little, um, optimistic and, um, not devoid of
hyperbole...I think I was responding to the sound more than the
power...the wastegate was still working)
Still, you're right, this pipe and the associated lines should be checked to
make sure everything is tight and leakproof.
It's strange that your boost is increasing when you disconnect the WG
valve. Like you, my belief was that the valve functions under boost to
keep the WG _closed_ longer than it would with the spring alone...maybe
your hoses are mixed up or my brain is, but this has been posited many
times by many different sources -- it would be a big surprise to me.
All of this is leading me back to Phil's post some time ago about how so
much "tolerance" is built into the F.I. system to compensate for leaks,
goofy sensors, etc., and the importance of trying to get the car back to
spec. with everything tight.
Someone had a post in the archives about taking apart the wastegate to
clean it up & lubricate it for smoother operation..I'll see if I can find it..
Best Wishes,
Alex
'86 5KCSTQ