'747 top end fuel leanout

[nacelp]

I've looked thru all the calibration stuff I have and don't see a reason
there, You sure about all the sensors?.  ie, TPS settings, CTS, MAP?.
I have seen a improper set TPS screw up WOT, without setting a code.
  When it this start?.
  Might try a different prom, or reburing your cals, on a different BCC.
Running out options here
Grumpy


> Thanks for the suggestions. Unfortunately, all the items you've mentioned
> have already been checked. The in-tank pump and filter have been replaced.
> The fuel pressure remains at a constant 12psi at all RPMs when at WOT. The
> problem doesn't seem to be from the fuel system, but rather, the injection
> system. The injectors won't go higher than 57% duty cycle.
>
> Nick
>
> >Lots if not all fuel pumps lose there ability to supply volume, before
> >completely dieing.   Try rigging a Fuel Pressure guage, and see if it
> drops,
> >at extended WOT.  If that shows bad try a new fuel filter before
replacing
> >the pump.   I've seen the gm TBI pumps die with as little as 25K miles on
> >em.  Also, be advised fuel contaninated with water can immediately screw
up
> >a paper filter element.
> >Grumpy
> >
> >
> >> Vehicle in question:
> >> '93 GMC pickup, 5-speed
> >> 1989 '747 TBI ECM installed
> >> 350cu in, ported iron heads, mild cam
> >> ported alum intake, Holley TBI unit, headers, dual exhaust
> >>
> >> The part throttle driveability is very good, with a smooth idle and
good
> >tip
> >> in acceleration. WOT acceleration is also good, but only up to 4600rpm
or
> >> so. Using a Diacom, we've seen the O2 put out 950mv up to around
4600rpm,
> >> and then it drops to 500mv or so (and the power dies out). Obviously,
> it's
> >> running out of fuel.
> >>
> >> So I installed a Fluke 88 today to see what the injector duty cycle was
> >> (maybe they're going static?). The DC peaks at 57% right around
4600rpm.
> I
> >> figured that there's plenty of DC time left, so I increased the
injector
> >> constant (BPW) from 108 to 130 as a test. I go for another drive, and
the
> >> max DC didn't change one bit.
> >>
> >> Any ideas? Is there some set limit in the control program that limits
the
> >DC
> >> to the injectors? How do I get more fuel in the upper RPMs?
> >>
> >> Thanks,
> >> Nick
>
>
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