[Diy_efi] 928/749
Bill Shaw
b.shaw
Thu Aug 16 15:50:51 UTC 2007
That's good to know. I have the parts in stock to do that test :-)
Best,
Bill
Rick McLeod wrote:
> A poor mans tester:
>
> gap a plug at about 0.175 and test free air
>
> a .025 gap under compression relates to about a .166 gap in free air IIRC from my engine technical training classes
>
> this has worked reliably for me in the past
>
>
> ----- 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
>>>>> _______________________________________________
>>>>> Diy_efi mailing list
>>>>> Diy_efi at diy-efi.org
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>>>>> Main WWW page: http://www.diy-efi.org/diy_efi
>>>>>
>>>>>
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>>>>
>>>>
>>>>
>>>>
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>>>
>>
>>
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