TURBO BOOST

I have a 88 911 turbo, it seems to me that it take’s higher rpm’s for the turbo to kick in, the car has 65,000 miles on it and runs great with no smoke, sometimes when I’m accelerating slow the turbo wont kick in to around 6000rpms, when I get on it hard it comes in around 4000rpms and I think its loosing it’s kick, is the turbo going? Can I just rebuild the turbo? And does the motor have to come out to replace the turbo?

Sounds like the turbo is crapping out or gone. At slow accel. the turbo is not spun hard and if the bearings are "gone" then the gradual exhaust pressure rise is not enough to overcome the bearing problem.

However when you give it the right foot hard, then the turbo gets a harder nudge and starts to spin earlier. but it will still feels weak as far as power goes. You will not get smoke because that is a condition of the engine(the turbo only pumps air).

Yes, turbos can be rebuilt and they can be removed with out removing the engine. If you take it apart yourself (and you can) just feel the play in the shaft(there should be none).

s

[This message has been edited by H20911 (edited 09-01-2000).]

Hello Bob. Watch your boost gage to see if you are building to 0.8 bar(stock spring) before the wastgate totaly opens up and ends the rush.(saving your expensive parts too). If it is opening early things will seem a bit flat. You can accelerate these things slowly and not build boost. This save lots of gas but is not a lot of fun. (see blowing out the carbon thread) A turbo rebuild won't hurt, but I think you will find the gate is your culprit. My P wrench told me that I should let everything come up to temp, then at least once each drive spool it up to open the gate and keep it from accumulating moisture that can cause problems. Carbon and wastegate maint can be fun!!!
Hope this helps get you started
david 89 turbo cab


[This message has been edited by 5axis (edited 09-01-2000).]

It sounds to me like the wastegate is stuck open, perhaps 1 mm off the seat ... plenty of room to vent off all boost at lower rpm's but not enough to bleed off everything above 5500 rpm or so. If you can find the vent from the wastegate, an assistant should be able to carefully monitor the output gas flow from that vent while you do an experiment. From idle, there would be some gas flow there at the vent, if the valve is stuck as I suspect. But, just to confirm, try blipping the throttle from idle for a couple of seconds. A normally operating wastegate would allow boost buildup during those two-three seconds of building revs, but there would be a dramatic outflow from the vent if my stuck-valve theory is correct.

I would recommend trying to find the vent when the engine is cold ... after you find it, start the engine and allow a ten-minute warm-up before trying the experiment. You should have a conclusive answer in less than 15 minutes after you find the vent and a willing assistant to perform the experiment!

------------------
Warren Hall
1973 911S Targa

I would say that David and Warren have a better handle on this the I. Mine are just general statements regarding the spooling of turbos. Let us know what you find.

Good luck!

s

We have a 1987 930 and one of the first things I did was to put a long neck intercooler on it which eliminates the pop-off valve. That is the thing under the intercooler and there is a sliding valve in ti with a spring that boost has to overcome and shut before the boost can build up and unfortunately it is not an item that is ever checked on a service. But it will get goop in it from the terrible gas we have now and will stick or move slowly due to the buildup of the goop. You might hear a bang when it shuts if the boost has come up and finally over comes the spring inside. To clean it you have to pull the intercooler and associated plumbing and you can take off both ends and clean it well. I used to use a little synthetic hi-temp grease to lube it on reassembly. You would also want to use new o-rings on all the turbo piping so there are no boost leaks. Good luck.

THANKS GUY'S I'M GOING TO TRY FINDING THE WASTEGATE VENT THIS WEEKEND TO SEE IF IT'S STUCK OPEN, AND TRY TO CLEAN OUT WASTEGATE BY FLOORING IT UP TO 6000RPMS. LIKE OWNER'S MANUAL SAY'S (AFTER IT'S WARMED UP OF COURSE) HOPE THIS WORK'S I'LL LET YOU KNOW. BOB