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Thread: Same pressure gauge for compressoon test AND manifold vacuum test?

  1. #1
    Join Date
    May 2015
    Posts
    65

    Default Same pressure gauge for compressoon test AND manifold vacuum test?

    Hello all together

    a few months ago I started servicing my E34 535i. The next thing on the list is measuring compressoon on each cylinder and also measuring the manifold pressure. Can I use the same tool for both procedures? I have noticed that there are special gauges with marked/coloured scale back plates. Do you have a good recomendation on what pressure gauge to buy?

    Thank you
    ----------------------------------------------------------------------------------------------
    1989 E34 535i
    M30B35 six cylinder, single overhead camshaft, 3.43 L, multi-point fuel injection

  2. #2
    Join Date
    Feb 2006
    Location
    Oldham, England
    Posts
    3,078

    Default

    Well, the manifold isn't under pressure as such, it is under vacuum. Vacuum specs are often quoted in inches of mercury but you could convert a negative psi reading to inHG. I have three separate gauges - compression, vacuum and fuel pressure. Plus a couple on the leak down tester. Accuracy and clear display are what counts for me. I couldn't have somebody else picking tools for me :-)
    Oct '00 E46 330i. Feb '92 525i (departed)

  3. #3
    Join Date
    May 2015
    Posts
    65

    Default

    Alright, and which vacuum line should I use? There is i) fuel pressure regulator, ii) idle air valve and iii) crankcase ventilation. Please excuse me if I am wrong
    ----------------------------------------------------------------------------------------------
    1989 E34 535i
    M30B35 six cylinder, single overhead camshaft, 3.43 L, multi-point fuel injection

  4. #4
    Join Date
    Dec 2004
    Location
    Sydney, Australia
    Posts
    4,374

    Default

    Just use a tee to tap into the FPR feeder line.

    Probably a good idea to install a little gauge so you can see how it behaves when driving/all situations too.

    Check Shogun's contribution (Today, 03:57 PM) to KJ's thread for an idea of how to test and observe the results.
    Last edited by genphreak; 05-27-2016 at 02:16 AM.

    Join the Aussie
    540i LE yahoo forum

    08/88 535i e34 M30+miller MAF, 'stiens, tints & teeth!

  5. #5
    Join Date
    May 2015
    Posts
    65

    Default

    Got it, thanks alot
    ----------------------------------------------------------------------------------------------
    1989 E34 535i
    M30B35 six cylinder, single overhead camshaft, 3.43 L, multi-point fuel injection

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