Thread: Possible vacuum leak

Originally Posted by ytt105

1993 RR 3.9 V8. I think I have a permanent vacumm leak. You can hear what appears to be a leak on the passenger side, but as the petrol and LPG intake are on that side I'm not completely sure.
An old trick that worked for all BMWs was to pull the dipstick out while the engine was idling and if you DIDN'T have a leak the revs would change. If you DID have a leak then the revs wouldn't change as you already had too much air going in.
Is this the same with the V8.
Pulling the dipstick or removing a vacumm hose makes NO difference to my idle.
The only thing that I can think that could be leaking on that side of the engine is the dipstick tube. Is there a seal at the bottom of the tube where it goes into the block?
Any other suggestions.

Buy yourself a Vacuum Tuning Guage, not expensive, the best diagnostic tool in the mechanics box, connect it to a manifold vacuum source (not ported) and read the Guage it will tell you many things, from late or early ignition to sticky valves and Vacuum leaks, Regards Frank.

The dipstick tube is only a push in fit, there is an o ring around the top of the tube that the dipstick shroud seals against - well there was on my 81 & 85 rangie so should be the same.

I had a vacuum leak on my 3.9 Disco V8. I couldn't find it anywhere. It used to whistle and you could hear it from the driver's seat and really ****ed me off. It turned out to be a leaking intake manifold gasket. It was like all my Christmases came at once when I found it.

Originally Posted by Utemad

I had a vacuum leak on my 3.9 Disco V8. I couldn't find it anywhere. It used to whistle and you could hear it from the driver's seat and really ****ed me off. It turned out to be a leaking intake manifold gasket. It was like all my Christmases came at once when I found it.

Could be what Utemad said, you could try to locate a manifold leak using Aerostart by carefully sraying around gasket joint and listen for a change (up) in revs when, if there is a leak it will suck in the Areostart causing an increase in revs, don't spray anyhing electrical or HOT, Regards Frank.

i would be using the good ol WD40.........its much safer to use and you will notice the change as soon as you hit the leak.........

Have a look at the plate that the stepper motor screws into. It is held by 4 allen screws, and they can come loose.
Then maybe have a suck on the vacuum advance pipe and stick it to your tongue.

Then have a look at the hoses to the brake booster, and the other vacuum hoses. the brake booster one can get hard near the manfold.
Its more likely to be a hose than hardware.
Regards Philip A

It can also be the injector seals. We had a 3.5 doing that here a few months ago.

Is it from within the cab, you can hear the leak or under the bonnet? I have a vacuum leak from WITHIN the cab which comes from the heater controls. Bloody annoying and do you think it's easy to get that damn switch out?! (Which is why I still have the leak!)