I am looking at changing the dump valve on a MY96 and have been told that if I have got a stanadard ECU or a piggy-back ECU I should not put a DV to atmosphere as there is a chance of running lean on motorway cruise as the ECU is still looking for the readings off the MAF sensor.
Is this correct and has anyone experienced running lean or encountered any other problems ?

Thankyou in advance

Gavin

 

The MAF sensor only measures "air flow", but the sensor concerned would be the 02 sensor, reading exhaust gases, so being as the engine is now dumping excess intake air to atmosphere instead of recirculating back into the system, so it will sense rich mixture due to leaner air mix, so yes may cause problem, although I appreciate the dump valve will encourage the turbo to spin faster, thus pushing more air in.
Sounds complex, you're right. Far too many pro's and con's to fit or not to fit dump valves, I just cant stand the silly noise they make when fitted to a road car. Only work there best when coupled with anti lag systems.

 

That doesn't sound right to me... Apart from a cold start, your MAF sensor should be doing it's job whether driving round town or on a motorway, irrespective of what type of dump valve you use. Don't forget, your dump valve only comes into play when changing gear, so if you're cruising along on a motorway in 5th, it won't be doing anything. And whether it dumps to atmosphere or recirculates, it shouldn't have any effect on your MAF... (of course, I could be totally wrong here, and if so, I apologise, and I'll get me coat...

 

Already metered air by the MAF sensor vented by the dump valve leads to a transient rich condition on lift off which can dilute your oil with fuel over time which is not good for oil quality and your engine. There is no risk of running lean.