Oxygen sensor and high speed stumble

[thergen at svn.net]

What does the Auto X-Ray tell you about the O2 voltage when you think it
might be starving for fuel?

On Fri, 30 Oct 1998, The Thibodeaus wrote:

> Have done what you suggest but with an Auto X-Ray rather than a Diacom.
> Difference between stock and PR chip for low speed ping appears to be the
> deletion of the EGR function.  But the problem alluded to below, i.e., the
> high speed loss of power happens with either the stock chip or the PR chip.
>  The car appears to be starving for fuel almost like the fuel filter is
> plugged but I recently changed it.  That is why I pulled some fuel from the
> tank to ensure that I didn't get a load of crap or my tank wasn't dirty.
> So my question still remains, how marginal are the stock fuel pumps and if
> I boost the system pressure will it starve at higher RPM because the pump
> can't meet the demanded flow rate at the higher pressure.
> 
> Bob T
> 
> At 10:20 AM 10/30/98 -0500, you wrote:
> >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.
> >>
> >
> >
>