[Diy_efi] 928/749

[Mike]

If it was an oldie carby engine with the old world conventional ignition Id say corroded/damaged connections on ballast resistor,

mike


At 11:23 AM 8/16/07, you wrote:
>I've been chasing a long series of problems with my 928 since I installed the new motor this spring .  Right now it won't start,  it's having some weird electrical problem. 
>A little background...
>I ran it in a similar configuration for 3 years... Porsche 4.7L v8, Vortech supercharger, GM ignition module, sensors, throttle body, and 749 ecu.  Ran great,  had loads of fun flogging the crap out of it on all the road courses in the northeast.  Last fall it ate 2 spark plug tips and scored 2 cylinders at Lime Rock.  New motor was in the works so I finished it up and got it in the car.  The new one is a 5.0L Porsche v8, '87 big dish pistons,  16 valve ported & extrude honed heads all adding up to about 8.5:1 cr,   bigger cams, bigger throttle body, bigger exhaust.  It ran pretty good for about 2 days,  good enough to set me back in my seat and put a grin on my face,  then it all went to he!! again.
>I've swapped ECUs, ignition modules, plugs, cap & rotor, been through all the plug wires with an ohmmeter, wrung out the wiring harness from the sensors to the ECU.  I'm getting fuel,  I can hear all the injectors clicking,  and have 43 lbs of fuel pressure.   The REF signal from the distributor makes it through the ignition module to the ecu and the ecu is putting out EST pulses, verified by o'scope.  #1 is firing at TDC with bypass unplugged.  Everything is great,  it just won't start.  
>Tonight we checked the cam timing and retensioned the timing belt.  I've been through all the basics I can think of, all is good but no fire in the hole. I've reverted to my last known good bin while doing all this testing.
>
>The only weird thing I can put my finger on is with spark.  I move my inductive timing light from wire to wire checking for spark on all 8.  
>I'll find one not firing (it changes some times),  pull the wire off the spark plug,  insert another spark plug in the wire and ground the tip on the block and it will fire,  the timing light will light up.  Move the wire back to the plug in the block and it won't fire.  Pull the plug from the block,  put it in the plug wire and ground the electrode on the block and it will fire again.  WTF???  This is driving me nuts.  I've pulled one plug wire off 3 times to check resistance, wiggled both ends and the whole wire looking for an intermittent break,  everything is great,  3.1k ohms per spec.
>
>I'm running out of ideas.  Anyone have a thought??
>
>Thanks,
>
>Bill
>928s 5.0L Vortech/749
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Regards from


Mike
Perth, Western Australia
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