Dedra Turbo gone wild

[Josh]

My 1992 Dedra SE Turbo sometimes gives HUGE accelleration.

I fitted a 1bar boost guage to see what was happening.

Sometimes, I get a very short burst of EXTREME accelleratio and the boost guage goes way past its 1bar limit.

This seems to happen more often if the car is cold.

It only seems to happen once per journey.

Any ideas why?

[Rok]

I own a similar car like you and I noticed that sometimes the car pulls better when it is cold (I assume that this is because of cold air and good intercooler cooling when the air is cold - cold air has more oxygen in the same volume as hot air so here comes ''more power'').
But I must say that I don't know what is mine turbo pressure because I don't have a meter instaled - I was told 0,6 Bar and 0,9 Bar in overboost situations, so I'm a bit confused when you say that you have pressure past 1 Bar, because you have a pressure regulator instaled in your car which cuts your ignition when pressure achieves cca 1,3 Bar (don't take for granted this value, but this is the max value that this pressure regulator can measure).
You should try to look for any leaks around turbo hoses, wastegate valve and overboost solenoid valve.

[Ian Wightman]

I experience exactly the same condition in my '92 Dedra turbo SE but I have been advised that this is a fault and will result in engine failure . I do find my Dedra to be slow, comparatively speaking ,when not in "super- boost" mode so I wondered if the problem actually is affecting the normal boost detrimentally and also occasionally giving too much . I have noticed that some smoke can be seen (in the rearview mirror) when the super -boost operates . I feel that the fault is more likely to be electrical because of the once-per-journey effect, but don't have any idea what might be the cause.

[Brian Hilton]

Are you sure that what you are getting is not the overboost situation which cuts in for a few seconds when you really put the boot in, this is standard feature, check handbook for it's operation.

[Josh]

I was not aware that there was a Series 1 Thema style Overboost facility.

All the handbooks were stolen from the car as I was paying the dealership from it

The "problem" was far too inconsistent and only happened once per journey. Does not make it sound like a factory fitted facility.

I have almost eliminated the problem by removing any possible leaks from the vaccuum and turbo piping (intercooler leaking and pipe to Bosch recirc valve loose).

[ALAN COOPER]

dedra turbos have boost drive not overboost it is a bit more sophisticated but still allows for extra boost over a short period for improved acceleration