NM

Hi All

Having got rid of overboost on my UK MY98 5 months ago I was supprised to get it back again. The first time was due to excessive oil in the engine contaminating the pipes, restrictor and sensor after a service. After cleaning all the necesary parts and draining the excessive oil I had months of overboost free motoring.

Back in early December I topped my oil level up after my wifes friend car broke down due to no oil in the engine. I noticed no problems. Last night I suffered the hitting the wall feelings some 4 weeks after topping up the oil . The only changes I have made since topping the oil up is a boost gauge and filling up with Optimax on the last 4 visits to the petrol station rather than UL.
Milage covered approx 1000 miles from oil top up.

Question is

Is it oil contamination from excessive oil (lies between full and empty), Optimax or something to do with the addition of the boost Gauge???????

Any comments guys.

Cheers

Neal

john banks

If you were running very near to overboost then a combination of high octane and cold weather could have done it again. You need to look at the restrictors and see if they are oily. I can't advise exactly on a MY98 as to where they are, but you could feel along the pipes from the turbo nipple and any that go to/from the solenoid inside the right side of the engine bay by the suspension tower.

Steve Terzo

I have the same problem on mine MY98, I think it's oil contamination, as it has the same problem when the ambient temperatures are high.
But, I only seem to get it when exiting R/H corners??
I've run the car on Optimax since August and never let the fuel run low.

Steve.

NM

Cheers for the advice guys, I will check out the oil contamination at the weekend. I have just filled up with UL so will see if its optimax related. I will give it a few days for the ECU to register the lower grade fuel then take it for a good blat in the countryside.

Steve strange that it only happens on RH corners

I will keep you informed

Cheers

Neal



[Edited by NM - 1/23/2002 7:14:34 AM]

NM

I seem to have lost the Overboost since I changed back to UL from Optimax!

I took the car for a good blat ensuring hard accelerating between 3k5 and 5k on the rev counter in every gear. Not a problem!
The weather was virtually the same damp and cold. I havent touched the pipes to the boost sensor so it must be the fuel.

Therefore am I right in saying that Optimax was giving the car more power but my car is running very close to max boost and the Optimax took it OTT? How can I change the car set up to enable me to use Optimax as well or do I have to wait till the summer to use it due to the warm air ?????

Cheers

Neal

john banks

By adjusting restrictors (I don't know exactly how on MY98) you could get your boost about the same and then enjoy the benefits of higher octane.

NM

John

What am I looking for a larger diameter hole or smaller on the restrictor? Might I loose power by changing the restrictor ?
What sort of gain would I see (boost etc) and could it damage my engine?

Not sure how it works really, any info would be most appreciated.

Cheers

Neal

john banks

I honestly don't know on MY98 - there have been posts about it before if you look back even a month or two.

The idea is to get the same boost with your Optimax so you benefit from extra ignition advance over normal unleaded = more power/torque or same power/torque at lower boost whatever you are looking for.

When my PPP was installed it was suggested to me by the dealer to run on unleaded to stop it overboosting. I insisted they fix it by getting the restrictors right. The same problem occurred when I fitted a downpipe.

I think people that do not suffer these sorts of problems with higher octane or with downpipe are either lucky or were running suboptimal boost to start with - either that or their boost is miles away from their cutout anyway.

It IS worth getting it right and running on the best octane you can.

DJB

The restrictor dampens the effect of the inlet manifold feedback to the waste-gate actuator. If you take away the restrictor altogether this leads to a very flat response, in effect the waste-gate opens too early preventing a rapid build of boost. I have a MY98 and went through a stage of fiddling with the restrictor size. From memory, I think that the standard size is around 1.2-1.3 mm. If you make it smaller, you will improve engine response (turbo spools up more quickly) but you risk over-boost cut-out. Making the restrictor larger has the opposite effect and will make overboost less likely. Small changes to the restrictor can have dramatic effects - changes in increments of 0.05 mm are required for fine tuning.

D.

john banks

Same as MY99/00 then. You can use a restrictor valve - see one of the posts in the Dawes FAQ in drivetrain on how to do this. I never got my drilled restrictors just right.

NM

Cheers guys

I think I will stick to UL at the moment then try Optimax again when it gets warmer. Dont fancy fiddling with the restrictor down to 0.05mm.

Cheers

Neal

john banks

The point I was making was that a valve will give you the equivalent control to 0.02mm, so is worth trying. Find the thread on restrictor valve replacing original restrictor in Drivetrain. I also linked to it in the Dawes FAQ. It is worth persisting.

AndyMc

Hi guys

My my98 has a history of overboost and over the last three years I have slowly narrowed the cause down. Originally I used to clean all the pipes,the solenoid and the brass restrictor,now I just clean the restrictor.In the past I have also tried different sized restrictors but have found the standard fit 1.2mm restrictor is the best on my car.
The overboost normally returns shortly after an oil change even if I only fill to about half way, cleaning just the restrictor makes it go away again.
I also changed to optimax when it first came out and have also recently fitted a Scoobysport down pipe and neither has affected peak or held boost.
So to sum up my boost control is fine so long as the brass restrictor is clean.It might be a good place to start on your car

HTH Andy

NM

Hi Andy

Have u a photo of the exact place the restrictor is on a MY98. As you said I have been spraying brake cleaner down every tube and sensor in that area to clear the problem.

Cheers

Neal