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m50b30 spark/fuel, cranks no start

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    m50b30 spark/fuel, cranks no start

    Hey all,
    I have had this swapped build for running for like the past 3 years. I havent driven it in a few weeks, tried to start it up and it cranks over but no start. Fuel, and spark is present, I tried a new battery, plugs but nothing, a couple of pops but no start. I then tried a compression test but I am getting 0 psi in all cylinders. I took of the valve cover and cams are turning, crank is turning and pistons moving, used borascope into the cylinders and there is not markings so I dont think valves have made contact/bent. I'll test timing to see if it randomly jumped a tooth, but all tensioners/chains etc were all replaced when I did the build and the car is only a weekend car.

    Any other things I should be looking at to diagnose this. Could it be a relay or something?

    Cheers,

    Adrian
    sigpic

    #2
    If you have 0 PSI on all six cylinders, that would be the first place to start.....

    if you cranked it over with a weak battery, you could have potentially washed the oil off the cylinder walls. Drop a bit of oil down each spark plug tube, crank it with the main DME relay unhooked and then try to fire it up. Good luck.
    Autobahn Motorsport - Portland, Oregon
    @autobahnmotorsport
    '88 M5 | '88 325i | '88 325is | '88 330is | '91 325is | '91 M-Technic 325ic | '93 740il | '03 325it

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      #3
      ZERO psi compression test? All six? Valves have to be hanging open. Even an engine with no rings will build a few psi.

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        #4
        Hi all,

        Thank for the responses, it seems the vanos/vanos solenoid was broken/stuck and had the intake cam advanced all the time, I re did the timing and put in another vanos unit and it fired up straight away, blowing a bit of smoke but thats from the oil I put in the cylinders to see if that would build compression.

        I havent done a compression test yet to see if any of the valves are bent, but will do that and update with my results accordingly.

        Compression is 180 PSI across the board cold. I'm satisfied with that to know there isnt anything bent.

        Cheers,

        Adrian
        Last edited by almostacrayon; 11-21-2019, 05:11 PM.
        sigpic

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          #5
          I didn't realize that the Vanos could change the timing enough to give you 0 psi compression at low speeds.

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