94 911 Turbo Bogging down under boost, black smoke

[ricksgem]

I just replaced a rebuilt turbocharger and she ran fine for a week, then started bogging down and choking under boost, with a cloud of black smoke. Fine if not under boost, but then what fun is that? It is getting worse each day.

I assume the black smoke is uncombusted fuel and that, even though I can hear the turbo spinning, the pressure is not building. My boost gauge is reading 0.0, could this be some kind of air leak or some other kind of problem?

Any help or ideas would be great!

Rick

[pkracer21j]

99% sure you have a boost leak between your turbo and your intake manifold. my oring at the throttle body/intercooler blew out on me years ago and I had your exact symptoms.

[ricksgem]

I have had problems with this o-ring since I have had the car, I use a gob of silicone on it to make a tight seal, it may well be the problem. Last time this had a leak in it the car wouldn't idle at all so I ruled it out in my brain, but I will rip it all apart tomorrow and see.

[930LDR]

Ditto on vacum leak. I lost a nut securing my intercooler one day at the track and had the exact symptoms. Sometimes these things like to spit out O-rings around the down pipe if there isn't a tight enough fit and you are generating enough boost.

[ricksgem]

This is probably the problem, the o-ring is a bit loose, should I get a new o-ring or is there a technique to secure it in there...

[beepbeep]

It's probably leak somewhere between turbo and engine. Fuel injection meter air that is sucked inb by the turbo, but as portion of it is leaked out but fuel is still added engine goes rich.

Be careful, you can damage your turbo by doing this. Big leak will send turbo into overrev and cavitation.

[930LDR]

When I installed my HFS I couldn't get the down pipe o-ring to stay in place using the stock down pipe. I ended up cutting the lower lip off of the downpipe and joining the turbo to the downpipe with a piece of silicone hose and some clamps. Haven't had an issue since.