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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.

        Cheers,

        Adrian
        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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