Turbo - No Boost

[Guest]

Gents
My Turbo done a bold thing yesterday on me. The car was fairly warm as I had travelled a bit. As I took off at a roundabout I noticed a distinct lack of go. I looked at the factory boost guage to see it was only at about 1.2. Just to make sure I accelerated again and same thing. I thought the wastegate had stuck open. As the car was moving I switched it off and restarted. The fault cleared. I done a few trips yesterday and now I cant get the problem to come back. She is boosting no problem. Of late Ive covered about 1700 miles without as much as a glitch. Any one else have a similar issue....? [&:]

 

[homesea]

Yes, I do. Some times it will only run at 1.2bar I guessed it was some sort of safe map the car goes to if it thinks it has a falt. It will run at 1.2bar all the time with the TPS un-pluged. I wouls also like to know more if anyone has info?

 

[DavidL]

I know nothing about this but there is a piece in Clarks Garage about turbos only boosting to 1.2
There seem to be a couple of things that cause it. Might be worth a look, Its in the turbo (951) faqs I think.

 

[homesea]

Sounds like my cycling valve gone.

6.2 Turbo Does Not Boost Correctly

• It boosts to a level and will not go any higher
• It does not produce any turbo pressure at all
• It produces varying boost depending upon the gear you are in. (See 6.2.5 Other Mechanical Problems below - the kinked throttle cable problem.)

Diagnostic Suggestions: Clamp off the line from the cycling valve to the wastegate and drive the car. This will close the wastegate and direct all the exhaust to the exhaust turbine. Now drive the car but do NOT fully depress the throttle. Just go over 3,000 rpm to see if the turbo boost is working. (If it is and you depress the accelerator a lot then the turbo could spin too fast and over-boost the engine causing damage.) If the car then boosts OK it means that the cycling valve and line are where the problem lies. The wastegate is not being controlled properly. This could mean that the cycling valve is being given bad information due to a faulty DME, knock sensor or 'control units' or is faulty itself.
If the car doesn't boost properly then look for:

• A mechanical problem with the turbo
• A leak or other problem in the air intake system
• The wastegate sticking open
• A leak in the exhaust system
• Other mechanical problems
• Engine computer problems

These checks should point you in the right direction.
Other diagnostic checks:

• Does the car only boost up to 0.2bar or 1.2bar absolute?
  • If yes, then it's a likely problem with a connection on one of the various sensors (TPS, airflow meter, etc).

• Hook up an after-market boost gauge to get an idea of what the turbo is actually doing. (The turbo could actually be working but a slipping clutch could absorb all the turbo boost and make it seem as if there is no turbo effect.) The after-market boost gauge measures turbo boost pressure before the air enters the intercooler.

 

[Guest]

Thanks for your help Tom and David.... []

I'll check through some of that tonight and let yous know if I find anything which may cause it ....!