[Fwd: New member needs help]

[Walter Sherwin]

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.
>===========================================================