Oxygen sensor and high speed stumble

[Clarence L.Snyder]

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.