2.5i 6 cylinder technical problem URGENT
- Thread starter shawna
- Start date
All normally aspirated will force a small temporary rise in revs when the brake pedal is pressed because of the change in inlet vacuum, however modern cars inc the BMW have ECU sensors, pumps and valves to correct this. Most likely things causing the problem,
1. Leaking pipes/connectors from the master cylinder to manifold
2. Defective master cylinder seal/diaphragm leaking - basic test being - ignition OFF - pump brake pedal several times it should firm up at the top of travel and stay there, keep foot on pedal - Ignition ON (start engine) - pedal should slowly fall, suggesting the booster is OK.
3. or it's one of the sensosr/pump/valve systems that regulate the effect, although I'm guessing anything from MAF, exhaust oxygen sensor to crank breather could do it as well depending on operating temp, in which case checking for fault codes would be my next move once the above were eliminated.
Let us know if he sorts it?
1. Leaking pipes/connectors from the master cylinder to manifold
2. Defective master cylinder seal/diaphragm leaking - basic test being - ignition OFF - pump brake pedal several times it should firm up at the top of travel and stay there, keep foot on pedal - Ignition ON (start engine) - pedal should slowly fall, suggesting the booster is OK.
3. or it's one of the sensosr/pump/valve systems that regulate the effect, although I'm guessing anything from MAF, exhaust oxygen sensor to crank breather could do it as well depending on operating temp, in which case checking for fault codes would be my next move once the above were eliminated.
Let us know if he sorts it?
MrPT said:
Vacuum servos are a very simple principle (probably invented in the 1920's) enormously complicated by current emissions add-ons, so I confess that once the basics are eliminated and we are down to ECUs and sensors I take the default "I've no idea now" route used by dealers i.e. "check for fault codes"
