Oxygen sensor and high speed stumble

[Bruce Plecan]

Just a couple of my thoughts, here.
You seem to be having problems, and experimenting with chips.
First you need to gather good data.
  Good data generally means having a diacom, or some such
  disgnostic ability that records.  So diacom+

Base line the car to stock stock/fiming/fuel pressure/TPS etc.
  Record things in fine detail.
  Note complaints in fine detail.
  Try better gas/or an addivitive.  This is the time of year where in some
  areas they change from summer gas to winter brew.
Now look at the D+ runs looking for any numbers jumpimg around,
ie loose connections.

  Now plug in chip #2.  Clear the computer (unplug it for a min or 3).  Then
drive for 10-15 minutes, and reconnect dia+.  Repeat driving as done
earlier.
Now look and see the differences.
  Now you should be better able to see what they did by doing a frame by
frame
looksee.  If you have no egr apply and higher O2, with knock, that would
tell
me they had deleted the. the egr. apply, but for somereason the fuel, and
timing corrections are being applied. THey may have done lots of things (+
maybe some wrong).  ie delleted the egr fuel tables, or egr timing
corrections,
with out turning of the egr apply seletion option.

     I don't know you level of experience but, sounds like you might be
just a tad ahead of yourself.
Cheers
Bruce

>The Thibodeaus wrote:
>>
>> I have an 90 Vette with a L-98 which above 4000 RPM loses performance and
>> it has been suggested it is starving for fuel.  The fuel filter has 500
>> miles on it.  I pumped some fuel out of the tank tonight after shaking
the
>> car to check for any sediment and the fuel looks fine.  I am running an
>> adjustable fuel pressure regulator set at 48 psi.  I pulled the oxygen
>> sensor tonight and it had some black soot on it indicating a rich
>> condition.  Here is my question, by upping the fuel rail pressure to 48
psi
>> am I starving the engine at high RPM because the pump can't flow enough
>> fuel at that pressure?  Does this seem logical?  I increased the pressure
>> compensate for a ported plenum and also to overcome a pinging problem
>> (several prior posts made to this board and Vettenet on this nightmare)
but
>> it hasn't worked.  I am working with the chip programmer to resolve some
of
>> the pinging problems because I have found that they completely shut of
the
>> EGR function.  So, should I lower my pressure?  Any suggested value?
>> Thanks for any suggestions.
>>
>> Bob T
>Raising the fuel pressure will not "cause" the engine to run lean at
>high RPMs. It could cause it to run rich. If the pump cannot deliver the
>fuel volume at that pressure, the pressure will just drop off. This
>means it would have been lean even at lower pressure. Put a FP gauge on
>the rail and see if the pressure drops off when you lose power. If it
>does, get a bigger/better/meaner fuel pump.
>