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Thread: 1996 M3 Hot Start Issue

  1. #1
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    1996 M3 Hot Start Issue

    I have a 1996 m3 that I supercharged about 4-5 years ago and restoring.
    Recently it developed a starting issue, only after driving it for a while 45 min + then when I shut it off and come back to it after 15 -20 minites and try to restart it ,takes way to long to start sometimes 3 x 3-4 seconds of cranking, but if i leave it over night it will start fine in the morning. Recently I replaced my fuel presure regulator, spark plugs and new siemiens cam position sensor, the cam position sensor I believe I replaced when I supercharged the car 5 years ago but I did it again recently anyway. I also cleaned the MAF. Fuel pump I bought used when I supercharged the car as well its a walboro. They are not known. to go bad and usualy if a pump goes bad its completly dead from my experience. Injectors (visually) dont seem like they are leaking, was thinking to have them cleaned/balanced and put new o-rings on. Any sugestions greatly appreciated Thanks!

  2. #2
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    Are there any faults stored I'd look at a the crank or camshaft position sensors because when there hot the windings inside could be coming apart from age and expansion with heat

  3. #3
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    replaced the cam shaft position sensor, the crank sensor im not sure about, need to locate it and check ot out

  4. #4
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    11/88 E32 750iL+98 E36M3
    Moved from E46 forum to E36 M3 forum
    Shogun tricks and tips for the E32 series are HERE!

  5. #5
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    If you bought the VDO “Siemens” cam sensor, that is possibly your issue. This is known to be junk. You must buy an original BMW Siemens sensor. VDO “Siemens” is not the same as Siemens. FCP and others listing it as OE doesn’t help.

    What fuel pressure regulator? If Bosch 3.5bar, I’ve had them arrive varying in pressure from 3.75-4.25 bar. Test it. It should be ~43-45psi at idle with the vacuum line attached and 51psi with the line removed (at idle). You need to buy an original Pierburg if out of spec.

    To get you by; blip the throttle to 2500rpm and kill the ignition at 2500rpm any time you park it hot. It will fire right up every hot restart. This clears the combustion chamber off all fuel.

    Confirm what sensor you used (and yes you must redo it if it is the VDO “Siemens” version) but I’m betting your fuel pressure is the issue. Mine was like this for years running a Dinan 4.0bar FPR with a 10psi pulley config. The ghetto way of not tuning for more boost. The engine is very sensitive to pressure issues.
    Last edited by Braymond141; 08-17-2020 at 11:33 AM.

  6. #6
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    could be also a defective check valve in the fuel pump, when engine is switched off, fuel under pressure flows back into tank, air/fuel bubbles start building up in engine bay. Years ago BMW had an extra check valve 16149068988 for such a problem to be installed above the tank in the fuel line, some info here http://www.bimmernut.com/forum/showt...highlight=fuel
    Shogun tricks and tips for the E32 series are HERE!

  7. #7
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    I bought a siemens sensor does not say VDO on it and I bought genuine FPR from bimmerworld as well, I also though about the check vavle in the pump but not sure if the walboro has one built in, this week im replacing the crank sensor

  8. #8
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    you can test the fuel feed line pressure loss when engine is switched off, there are instructions in the repair manuals what is acceptable and what not in a certain time frame.
    Shogun tricks and tips for the E32 series are HERE!

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