350TPI Fuel Consump Problem

[Don Burns]

I posted to the DIY list a few weeks back about my mileage problem and then
left town for a while. Am surprised that someone didn't bite my head off
since the question really belongs on the GM list. Anyway many listers are
on both so you probably saw this before.

The car is an 86 Fiero with a crate 350TPI and 5-speed. Its closest
equivalent is probably a '90 350TPI in a F-body. Problem is the fuel
consumption sucks, expecially in traffic: 12MPG. On the road it does 20+.

At idle, integrator readings range from 130 to 140. Block learn seems to be
pinned at 160 (this is the mac, right?) Earlier somebody asked (I think
Shannen) about fuel pressure. I think I said 40 or 41 lbs, but I lied. So
much for my lack of thorough note taking (Bruce, you were right). The fuel
pump is seeing about 0.6 vplts lower than battery (my cutoff switch wiring
is probably responsible).

So today I started again from scratch. With fuel line pressured up and
engine not running pressure is about 42 lb. (and stays there... no leaks).
Started engine and pressure drops to 36 lbs and stays there. I think this
is much too low.

Took the car out on I75 this afternoon and found following at 65 to 80mph:
1. Integrator drops nicely into mid 120s.
2. Block learn starts dropping and even gets into 140s... nice sign. Also
found that when punching the gas the block learn quickly drops into the 120
to 130 range and then in a second or two begins to rise into 150s. I assume
this may be the ECM detecting a lean condition and then eventually trying
to compensate for it.

Getting back to the fuel pump, is my FI system starving because of lack of
high enough pressure and then trying to compensate?? Will appreciate some
feedback on this. Another question: If the FI is starving what is a quick
way to determine if its the fuel pump or prseesure regulator opening early??

Still have to answer Shannen's question about running with O2 disconnected.
Need to jack car with floor jack to get to connector but the sciatic nerve
suggested today was not the day to do this.

Thanks for the help!

Don



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