Computer Diagnostics and Tuning Technical discussion on diagnostics and programming of the F-body computers

Need Some Help

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Old Sep 1, 2005 | 12:54 AM
  #1  
CRCDUDE's Avatar
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From: Valpo,IN
Need Some Help

WHat I have is a 96 Maro 383 cc 306 ported heads headers Bla, bla, bla.
The PCM is a OBD1 and has been reprogramed with Tunercat.

Car has run good in the past and recently started dropping cylinders at random. Every time it is started (cold or hot doesnt matter) it drops a different cylinder and usually 1 dead completly and 2 others mis firing intermitent. If you rev it up a lil, it doesnt seem to help.
If you shut it off and restart it will have differnt dead cyl's and the 1's that were dead will B fine.

So far I have tried
Compression and leak down test
Swapping injectors from good cyl's to bad 1's = no diff
fresh plugs / verfied spark condition
Verified fuel supply and pressure
checked for vacumm leaks
adding and subtracting fuel in the individual cyl trim (idle and off idle) tables
recalibrated MAF tables (added fuel) = seams to help

and I'm sure a few others my toasted brain has forgotten

I am at a loss here and need a direction to go so if any 1 has 1 i will gladly listen and try
Old Sep 1, 2005 | 03:23 PM
  #2  
2QUIK6's Avatar
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From: Ft. Worth, TX
Re: Need Some Help

Maybe a dying opti spark or bad crank sensor? Doesn't sound like it would be PCM/program related.
Old Sep 6, 2005 | 11:08 PM
  #3  
CRCDUDE's Avatar
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From: Valpo,IN
Re: Need Some Help

Well it has an OBD1 PCM so there is no crank sensor..
WE did try a good opti with the same result, also tried a new PCM with a diff program. and that mearly changed the dead cylinders

Next is new injectors and or a wiring harness.

Good thing for the donor car
Old Sep 7, 2005 | 09:02 AM
  #4  
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From: Little Rock, AR
Re: Need Some Help

How have you verified it is spark or injector related?

Are you actually seeing the injector pulses go away with a noid light?
Old Sep 7, 2005 | 11:17 AM
  #5  
CRCDUDE's Avatar
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From: Valpo,IN
Re: Need Some Help

No I dont have the noid light, kinda why I am gonna swap inj's next.

Maybe I'll hunt around and see if I can borrow 1
Old Sep 7, 2005 | 12:42 PM
  #6  
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From: Little Rock, AR
Re: Need Some Help

You have to pinpoint where the problem is before you can fix it.




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