I have a possible vacuum leak

[Russell]

I have a possible vacuum leak on my car. I thought that on most or all BMWs when you remove the dipstick or oil filler cap while running, the idle will drop or the engine runs rough.

Is this true on a 95 M50? My idle does not seem to drop. I am trying to track down what I believe are vacuum leaks. After all the car is 10 years old and the PO records did not indicate any repairs in this area. I found the larger hose that connects to the valve cover had a leak. Fixed that and no change in idle.

As usual, TIA.

[ryan roopnarine]

I have a possible vacuum leak on my car. I thought that on most or all BMWs when you remove the dipstick or oil filler cap while running, the idle will drop or the engine runs rough.

Is this true on a 95 M50? My idle does not seem to drop. I am trying to track down what I believe are vacuum leaks. After all the car is 10 years old and the PO records did not indicate any repairs in this area. I found the larger hose that connects to the valve cover had a leak. Fixed that and no change in idle.

As usual, TIA.

i think that might be the m30 that that occurs on. mine has never "dropped" it usually just drops about 50-100 rpm for about 3/4 to 1 second, and stabilizes again.

[shogun]

Is is blowing or sucking when you open the oil filler cap?

First do a test by mounting a supermarket plastic bag membrane across the oil filler opening (after cap is removed) while engine is idling.
The membrane should appear being sucked into the valve cover if your PCV (positive crankcase ventilation valve) are working properly.

[Russell]

Will do, Great idea - Thanks

[Russell]

Does this mean all components of the crankcase ventilation sytem are working properly?

I am specifically wondering about the carbon vapor canister (never changed) and the fuel tank breather valve, also never changed. OR are these items not part of the crankcase ventilation system? Even so, I suspect they are due for replacement. How to you check? Bentley is no help in this situation.

Thanks for your help

Is is blowing or sucking when you open the oil filler cap?

First do a test by mounting a supermarket plastic bag membrane across the oil filler opening (after cap is removed) while engine is idling.
The membrane should appear being sucked into the valve cover if your PCV (positive crankcase ventilation valve) are working properly.

[jj7]

Does this mean all components of the crankcase ventilation sytem are working properly?

I am specifically wondering about the carbon vapor canister (never changed) and the fuel tank breather valve, also never changed. OR are these items not part of the crankcase ventilation system? Even so, I suspect they are due for replacement. How to you check? Bentley is no help in this situation.

Thanks for your help

I just parked the car after some driving,i did open the oil filler cap and as ryan said the idle drops a bit and for short period of time.I tried the dipstick and i think not much difference their either.But,russell,is there any hesitation or any other matter with the engine?in terms any symptoms that could help you out??the canister and breather could cause hesitation if thats what you are after...

[Russell]

I may have a rich condition based on and oil analysis that shows 1 percent fuel dilution of the oil after just 3,700 miles on mobil 1 0w40. Just in the process of eliminating potential issues.

Thanks

I just parked the car after some driving,i did open the oil filler cap and as ryan said the idle drops a bit and for short period of time.I tried the dipstick and i think not much difference their either.But,russell,is there any hesitation or any other matter with the engine?in terms any symptoms that could help you out??the canister and breather could cause hesitation if thats what you are after...

[shogun]

A defective fuel tank breather valve usually causes problems when engine is started (needs longer reving). Takes a while till engine runs.

Remove the fuel tank cap. If it is hissing and that shows a vacuum, then something isw wrong.

[Russell]

Engine running or off when I check gas cap off?

Thanks again. Your posts are most informative.

A defective fuel tank breather valve usually causes problems when engine is started (needs longer reving). Takes a while till engine runs.

Remove the fuel tank cap. If it is hissing and that shows a vacuum, then something isw wrong.

[shogun]

or on. Maybe when you arrive back home from work, open the tank and then it might hiss. Have read about some cars which even stopped during driving, especially with fuel tank almost empty.
I think the breather valve might have something to do with the vacuum system in/for the intake system and changes the parameters.
As for tanks, there were a lot of problems on the E38 series that tanks even cracked because of too high vaccum inside the tanks. As far as I know the tank airation system has been modified on that cars.
Some people also drill abt. 1,5 mm holes in the tank lid to avoid this problem of vacuum.
Not one of the greatest engineeering ideas, but it helps in emergency.