1987 930 No boost...how do I troubleshoot?

[gabrielzorz]

Thanks ahead of time.

I own a 1987 stock 930, I recently removed the engine and sent it in to be rebuilt. Now that its done and I've installed it, I have no boost! Anyone seen this problem or know how the procedure in order to troubleshoot it? I called the mechanic and they said they would have to look at it--they are 90 miles away, I would like to fix it myself.

Thank you!

[Zef]

No real boost or indicated boost...Seem than no air is getting there...

[john walker's workshop]

slide the intake boot off the turbo just enough so you can see if you can spin the turbo. maybe something fell into it. that's the sleeve on the left side of the turbo, down low. two clamps and work it off a bit. check that the o-rings are still whole at the turbo neck, and into and out of the intercooler. the wastegate probably isn't stuck open, but see if there's exhaust coming out of the wastegate pipe at idle. shouldn't be. top hose on w/gate is the vent, side hose to intake. in stock form anyway.

[gabrielzorz]

john walker's workshop:
I DID YOUR TEST AND THE TURBO SPINS REALLY GOOD.
MY GESS IS THAT THE CHOKE OR BUTTERFLY VALVE IN THE HEAT EXANGER IS NOT OPENING TO LET THE AIR CIRCULATE. ELCTRICAL?
ANY IDEAS?

[Fishey]

930 has CIS so if its a boost leak (vac leak) it will run like crap. I am guessing that when you say it has no boost you mean the gauge? or are you talking about actually no acceleration from the turbo? I would honestly think the gauge could have been left off upon reinstall. The later of the 2 is far less likely without having a major vac leak that would be very noticable in terms of a rough idle or a absolutely bad running car. The other options are less likely but I guess possible.

1. Wastegate is loose and exhaust is bypassing the turbo (would be very loud)
2. Turbo has no impeller blades (but you said it did)
3. The heat exchanger has nothing to do with boost and butterfly valves would not effect it in any way.

[john walker's workshop]

so you feel no "set you back in the seat" action on acceleration?

[gabrielzorz]

fishey,

When I mean no boost I am talking about no physical boost as the engine is not developing power.

Thanks for your help!

[gabrielzorz]

Originally posted by john walker's workshop
so you feel no "set you back in the seat" action on acceleration?

exactly...no power, no actual boost

[911boost]

Are you building RPM's, or does the car cut out in the lower RPM range?

Do you have access to a hand held pressure gauge. If so, T off the line going from the intercooler to the wastegate, and run the hose up into the cabin hooking up the gauge. If this gauge shows boost, it will rule out the turbo. You should also see the pressure drop as the WG opens up.

You're best bet is to start with one item and rule it out, them move to another. John's advice was good, and it sounds like the turbo spins freely.

Liek Fishey said, the HE shouldn't affect anything.

Bill

[john walker's workshop]

did you check the o-rings yet?

[911pcars]

Begin with a compression test to make sure the basic integrity is okay (cams timed correctly, valve clearance okay, etc.), then begin checking the turbo system for adequate exhaust volume.

The turbocharger is purely mechanical. If exhaust gases go into the turbine section and the compressor wheel spins fast enough, it should produce pressure.

However, two things could be happening; not enough exhaust flow (wastegate is open) and/or pressure leak/loss between compressor and engine intake. As J. Walker suggests, see if exh. gases are exiting the wastegate pipe. Since you have confirmed the compressor wheel rotates (it's not stuck), verify the path to the intake is not leaking. Did you install a blow off valve after the turbo outlet?

Hope this helps,
Sherwood

[gabrielzorz]

REINSTALLING THE ENGINE I ALSO INTALLED A NEW STAINLESS STEEL MUFFLER. THE OLD ONE HAD A PIPE CUMING FROM THE SMOG SYSTEM TO THE CATALITIC, THIS OUTLET FROM THE SMOG SYSTEM IS FLOWING OUT TO OPEN AIR. IF IT WAS EXAUST I IMAGINE IT WOULD TAKE POWER FROM THE EXAUST TO THE TURBO BUT DONT THINK THIS IS EXAUST BUT I AM NOT SURE. WHAT DO YOU GUYS THINK?

[911boost]

Can you take a picture? That could be bad.

[john walker's workshop]

if it's after the turbo it would not make any difference.