[Fwd: New member needs help]

[Walter Sherwin]

Yup..................this procedure is for the small 90mm external coil  GM
EFI distributor.  This affects both TBI applications and TPI applications.
The 90-93 distributors were particularily suspect.   A new ( and improved )
drop in replacement assembly is available under GM P/N 1103952.



-----Original Message-----
From: Bruce Plecan <nacelp at bright.net>
To: diy_efi at efi332.eng.ohio-state.edu <diy_efi at efi332.eng.ohio-state.edu>
Date: Wednesday, November 18, 1998 7:10 PM
Subject: Re: [Fwd: New member needs help]


>
>-----Original Message-----
>From: Walter Sherwin <wsherwin at idirect.com>
>To: diy_efi at efi332.eng.ohio-state.edu <diy_efi at efi332.eng.ohio-state.edu>
>Date: Wednesday, November 18, 1998 8:18 PM
>Subject: Re: [Fwd: New member needs help]
>
>Is this the procedure for the small cap HEI TSB?
>Bruce
>
>
>>Jason...........You might want to examine your distributor very >closely.
>The early 90's distributors of that style were prone to a >number of
>maladies which tended to create the exact symptoms >you have described,
>since their "Reference Signal" is the >heartbeat of the entire fuel
>injection system.
>>
>>In this order..............1) run the car with the EST timing connector
>>disconnected and note whether or not an improvement exists.    2)  examine
>>the timing mark, with a timing light,  both with and without EST
connected.
>>Is the timing stable?   3)  with the EST disconnected, and while watching
>>the timing mark with a timing light, look for an ever so slight timing
>>advance with increasing RPM.  Then look for a gross timing shift of +6
>>degrees at 2000 RPM or less.  If the timing initially retards,  or
>>experiences the gross shift at more than 2000 RPM, then your distributor
is
>>bad.   4)  if all of these checks are okay, then your distributor is okay,
>>and your problem is elsewhere.
>>
>>Stay in touch..............
>>
>>
>>
>>-----Original Message-----
>>From: David A. Cooley <n5xmt at bellsouth.net>
>>To: diy_efi at efi332.eng.ohio-state.edu <diy_efi at efi332.eng.ohio-state.edu>
>>Date: Wednesday, November 18, 1998 3:12 PM
>>Subject: Re: [Fwd: New member needs help]
>>
>>
>>>Jason,
>>>The popping was definitely from an extremely lean condition.  The High
TPS
>>>could have been a problem, but without having a GM cal for that vehicle
in
>>>front of my, this is only an educated guess based on what I have seen in
>>>other cals... The TPS has a high and low limit.  Exceed either limit and
>it
>>>goes back to closed loop because it thinks the TPS may have a problem.
>I'm
>>>surprised the ECM didn't set a TPS voltage too high code.
>>>
>>>What did diacom say the TPS voltage was when it started popping?
>>>
>>>Also, a fuel pressure guage OUTSIDE THE CAR you can see while driving
>would
>>>help... Could have a bad conn. to the FP making it cut out and go lean as
>>>FP drops.  Also, some smart a$$ may have dumped a raw egg into your gas
>>>tank... when you accelerate hard, it slides around until it covers the FP
>>>pickup and cuts off fuel.
>>>Later,
>>>Dave
>>>
>>>
>>>
>>>At 02:22 PM 11/18/98 -0500, you wrote:
>>>
>>>>Hello everyone:
>>>>
>>>>    I am new to this list and I am looking for some help.  I have been
>>>>having a problem with my 89 Corvette L-98 6 speed.  For months now I
>>>>have been battling a problem that has been really frustrating.
>>>>Sometimes, when accelerating the car has no power at WOT and I have a
>>>>rapid popping/backfiring/missing thing going on.  I finally broke down
>>>>and got a Diacom and recorded the event.  When it happened at WOT, my O2
>>>>reading dropped to 0 and my integrator climbed to 180 while my inj.
>>>>pulse width was 9.5ms or so.  Now there was two thing I immediately
>>>>noticed.  One why the extremely lean condition and two, how come my Int.
>>>>and BLM were not 128?  I found the answer to number 2 last night.
>>>>
>>>>    My TPS voltage was .55 at idle and 4.98 at WOT.  The ECM will not go
>>>>into open loop PE mode at this high of a voltage.  At this high setting,
>>>>the ECM was trying to maintain a 14.7:1 air fuel ratio.  I readjusted
>>>>the TPS to 4.63 volts max and BINGO!  The ECM goes into open loop rich
>>>>condition.
>>>>
>>>>    Now, the million dollar question is could the high TPS voltage at
>>>>WOT cause the lean condition I am experiencing?  The fuel pressure is
>>>>fine (37 psi at idle 45 psi at WOT) but I never had an opportunity to
>>>>check it while the seemingly lean condition was occurring.  The fuel
>>>>filter is new, the injectors were leak tested and balance tested and the
>>>>O2 sensor is new.
>>>>
>>>>    I have Excel sheets I send if anyone would be nice enough to view my
>>>>data and try to help me.
>>>>
>>>>Thanks again,
>>>>
>>>>Jason Norris
>>>
>>>===========================================================
>>>           David Cooley N5XMT           Internet: N5XMT at bellsouth.net
>>>     Packet: N5XMT at KQ4LO.#INT.NC.USA.NA   T.A.P.R. Member #7068
>>>       I am Pentium of Borg...division is futile...you will be
>>approximated.
>>>===========================================================
>>
>