How Long?

[Dan F]

I can concur with this as I have had 2 calibrated bleed offs on my C70 and even the more benign one eventually threw a CEL.

If it had worked, I would not have got a remap. On these later cars with the Drive-by-Wire throttles, you simply cannot use bleeds because at the end of the day the ECU will see it and compensate in a ways the older cars can't. Even if if you don't get a CEL, the ECU will simply alter the angle of the throttle butterfly to decrease boost if all else has failed, i.e. extra duty on the solenoid or ignition retardation etc.

Cheers,
Dan.

Yep, absolutely correct.

Adam.

OK, thanks for the replies all.

[sholtby]

In summary then if you have an 850 T5 or very early S70 with the same ecu as the 850 you can use a bleed valve. Although a Dawes type valve gives even better performance. The boost limit is 15 psi at which point the ecu cuts the engine.
For later cars your only option is a chip upgrade.

I remember on the old Audi Quattros Superchips modified the ecu by putting a zener diode across the MAP sensor so its output never went above engine cut off level and then fitted a stiffer wastegate spring. You could do all this yourself for about £20.

Simon

Basically yes - the Bosch Motronic 4.3 ECU (850 1993-1997) and 4.4 ECU (C/S/V70 1997-1998) will allow you to adjust boost using a bleed valve without fault codes, within certain limits. Problem is that it still doesn't address the issues of fueling and ignition, and overboost. It is true that there is scope within the stock paramters for reasonable gains on the 4.3 and 4.4 ECU with a bleed valve, but it's at the expense of fuel economy because when the ECU detects load beyond certain paramters, the ECU overfuels for safety, again within preset parameters. The ignition also isn't optimised.

The Bosch ME7 ECU won't allow any sort of mechanical messing. You can't use a bleed valve, you can't fit a de-cat pipe, you can't even use an "inferior" race-cat because if the efficiency is wrong you'll get a CEL. So the only way to increase performance reliably and to retain all ECU safety features on the 1999 and later cars is by reprogramming the ECU.

Adam.