WUZ

iTrader: (14)

Hi guys and gals,
I am surrering from a serious overboost problem on my MY97 UK turbo. It has K/N panel filter, Scoobysport B/B and Magnex C/S (with resonator).

B4 filling with Shell SUL,(car run on NUL), the car was boosting up to 1.0 bar and settld off at 0.9 bar (standard parameters?). Since filling up the car with SUL and resetting the ECU, (a la MRT) I went on a 10 mile blast to let the ECU re-learn the knock setting etc, only to find that on middle-throttle the boot raises to 1.1 bar and stays there but if I put the throttle to the floor in 3rd, 4th or 5th gear, the boost climbs up to 1.25 bar and overboost protection kicks in about 2 seconds later.

If this just because the ecu has not had enough time to re-learn and adjust knock, etc. to the new parameters or is it something more serious!!!!!!!!!!!

Help and info respectfully received!

Russell

[Edited by WUZ - 10/20/2001 12:43:40 PM]

john banks

Probably just the higher octane of SUL leading to quicker spool up with factory mechanisms that still operate at the same rate. Same happened with me when downpipe fitted. Need to change the size of the restrictor in the pipe that activated the wastegate actuator. Search in drivetrain for "restrictor" and you'll find many posts.

WUZ

iTrader: (14)

I tend to agree with you John.
The car is going in to AWD Motorsport in Perth for the annual service+HKS plugs and both Grant and Scott were talking about changing the restricter size but I also have a down pipe that I want to fit does this mean that i would be better off getting it fitted at the same time so that the same thing does not happen again (Scobysport D/P)

Cheers.

Russell

WUZ

iTrader: (14)

BTTT

DJB

I suffered from overboost a few months ago after the dealer replaced a rubber tubing t-piece connector with a material which melted. This caused a leak in the feed-back system which activates the waste gate and resulted in recurrent overboost.

I think in your case, reseting the ECU has removed all the restrictions imposed by the ECU that in the past prevented higher boost pressures. NUL will make the engine more prone to detonation and to protect the engine, the ECU has retarded the ignition timing to prevent det. The introduction of SUL and the ECU reset has then allowed the ECU to advance the ignition timing again without causing det and at the same time, boost pressure builds up to higher level. The ECU however will only allow boost to build up to a certain level. If this pressure is exceeded, the ECU driven overboost cut-out activates. You cannot alter the threshold for overboost cut-out unless you change the ECU or modify the signals it receives (Superchip method). What you can do however is to prevent the high peaks in boost pressure caused by a restrictor which is too small. The restrictor is there to allow boost to build quickly and is essential in preventing turbo lag. I think in your case that boost is building too quickly resulting in a high peak, activating overboost cut-out. A slightly larger restrictor should prevent the high pressure peak and will probably cure the problem.

In answer to your last question about the down-pipe, yes fit it first since this will another cause of high peaks caused by the turbo spooling up more quickly.

D.

D.

Bob Rawle

Its definately due to the ecu learning that SUL allows it to run more timing etc than with NUL, yes do get the downpipe changed at the same time as that will have the same effect. That way you only need to get the restrictor adjusted once.

WUZ

iTrader: (14)

Thanks for the info so far, please do keep it coming in as all info is appreciated!

The car seems to have stopped overboosting now - I can floor it in any gear at any speed and the boost winds up to 1.0 bar and stays there = suberb!!!!!!!!!!!!!!!!! This does not mean that it won't do it as the cold nights come in so keep the info flowing guys and gals!

Thanx.

Russell

GrahamF

I have experienced exactly the same 'problem' with my MY98 (PE phase 1 + T75 + ITG). After ECU rest and change to SUL, boosts to 20 psi (was 15). Occasionally hits the overboost cut, but only if I hit the throttle hard in 4/5th at about 4000 rpm. Mostly it stays below the cut-out point. I tried switching back to NUL, but the boost hasn't changed, so I think the increase was due to the reset. It's now been through 7/8 tankfuls of NUL, so the ecu isn't going to learn much more! Car was originally rolling roaded at PE @ 19psi on NUL, so maybe this is OK? I don’t think this is a restrictor issue, because once reached, the car will hold the 20psi right through to max revs. How long would I expect the peak to hold before the wastegate control brings it down? I assume the wastegate contro should bring the boost back to 15psi once it 'sees' >15psi on the low pressure side of the restrictor? If so, is my sustained 20psi because the ecu is not telling the wastegate to open, and is this what I would expect from a PE phase 1 ecu? In Russells case, though, this can’t be true, as I assume he has a standard ecu?

Graham

Just read the last post. What changed?

Graham

WUZ

iTrader: (14)

I think that the fault with my car may lie with the water temp sensor. The select monitor shows me that the ecu sees a water temp of 98 degrees centigrade before the fan kicks in but this cannot be because the water is not that hot (84) this means the sensor is shagged and could be confusing the ecu.

Result - new sensor on its way

(well done to AWD Motorsport for all their help and enthusiasm today)