Is 15 inches of vacuum at idle typical of 535i?

[Robert K]

I just put a vacuum gauge on my 1991 535i and got a reading of 14-15 inches of mercury vaccum. I attached the gauge to the end of the little vacuum hose that attaches at the middle of the valve cover breather hose. The needle stayed fairly steady, fluctuating between 14 and 15. I was just wondering if anyone knew what the typical vacuum reading was for the M30 engine. I couldn't find a spec in Bentley or Haynes.

Grace and peace,

Robert K

[ryan roopnarine]

http://www.bmwe34.net/e34main/trouble/engine_diagnose.htm
bottom of page

[Jeff N.]

Mine, with long duration non-stock cam pulls about 16 to 17. Martin's car (better compression, stock cam), pulls maybe an inch or two more or so.

14 to 15 seems a bit low for an unmodified motor. Vacuum leak or low compression?

[Robert K]

I did my initial test with the engine totally cold and just started. I drove it around on the highway for 10-15 miles (it hasn't been run that much the past two weeks) and then checked it again. At the vacuum hose going into the fuel pressure regulator, it showed a rock steady 17 inches of mercury. That sounds a little better. Thanks for the link Ryan!

Grace and peace,

Robert K
1991 535i

[ryan roopnarine]

bruno is the one to thank in this case. everytime something breaks on this car, it seems that someone has already documented how to fix it on the internet. granted, m20-m70 don't have the ubiquity of the chevy 350 or nothing, but there's more information on the internet than there is for my mom's late model ford taurus. vacuum testing seems to have spotty info all round since the demise of the carburettor. i had to ask four or five people how i would go about using a vacuum pump to test the egr valve on aforementioned vehicle, ended up following the procedure two of the five (the other three gave completely different answers).