Re: '747 top end fuel leanout

["nacelp" <nacelp@bright.net>]

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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