[Diy_efi] 928/749

[Bill Shaw]

Well,  a new coil helped some but didn't cure the problem.  It will 
start and run now but is still dropping spark intermittently in a couple 
of cylinders.  The pulses from the ignition module to fire the coil are 
nice and steady,  don't miss a beat.  Using the timing light on a couple 
of the plug wires shows erratic firing. It's starting to look like 
something in the distributor now,  but I can't imagine what.  The rotor 
and cap look find and check out OK with an ohmmeter. 

I was thinking about changing to a different ignition controller,  maybe 
something like a MSD 6.  Multiple sparks might be of some benefit,  but 
the MSD really won't give me a stronger spark than using the GM 7 pin 
module,  will it?  The spark is generated by the coil,  not the module,  
so I'll get the same voltage won't I?

Bill
Still not sparking on all 8
>>
>>
>> ----- Original Message ----
>> From: Bill Shaw <b.shaw at comcast.net>
>> To: diy_efi at diy-efi.org
>> Sent: Thursday, August 16, 2007 10:12:12 AM
>> Subject: Re: [Diy_efi] 928/749
>>
>>
>> Yep,  swapped the coil with a spare I had in inventory (forgot that 
>> one,  and a few more I'm sure!).  I need to go back there and double 
>> check,  the spare was used.   No ballast resistors,  I took them out 
>> when I did the 749 conversion.  I'm off to buy a spark tester today.
>>
>> Thanks for all the input guys.
>>
>> Bill
>>
>> Steve Ravet wrote:
>>  
>>> good point, it takes more energy to fire the plug under compression 
>>> than
>>> in the air.  You didn't mention testing/replacing the coil.
>>>
>>> --steve
>>>      
>>>> -----Original Message-----
>>>> From: diy_efi-bounces at diy-efi.org 
>>>> [mailto:diy_efi-bounces at diy-efi.org] On Behalf Of dgilbert78 at juno.com
>>>> Sent: Wednesday, August 15, 2007 10:49 PM
>>>> To: diy_efi at diy-efi.org
>>>> Subject: Re: [Diy_efi] 928/749
>>>>
>>>> Hello: Had a problem like that , everything was there , but would 
>>>> not run. final fix, spark wasn't hot enough. Go buy chep spark 
>>>> energy tester at parts store. If it does not troow a healthy gap, 
>>>> fix that. I went absolutely nuts. I had spark, everything, just not 
>>>> enough and the damn thing would not run.
>>>> good luck
>>>> Darryl..
>>>> On Wed, 15 Aug 2007 20:33:37 -0700 "Steven P. Donegan"
>>>> <steve at donegan.org> writes:
>>>>          
>>>>> Only takes 3 things to go bang - gas, spark and compression       
>>>>>         
>>>> - you've          
>>>>> verified 2 of the 3 below. Compression seems to be the only thing 
>>>>> left.
>>>>>
>>>>> On Wed, 2007-08-15 at 23:23 -0400, Bill Shaw 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
>>>>>>