350TPI Fuel Consump Problem

[Bob Valentine]

At 09:04 PM 10/8/2000 -0400, you wrote:
>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?) 

Hmm.... ECM is adding fuel.     See lower down.

> 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.

Assuming you're running a pressure-referenced regulator, that's right.
The FP on mine does the same thing, sometimes runs at bat voltage,
sometimes a little less.   Haven't had any problems, so haven't really
checked it out.

>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.

You're rich (ecm pulling fuel out below 128BLM), then you're going lean
(ecm adding fuel above 128BLM).    

>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??

I have an unbaffled tank, and on sharp turns with less than 1/4 tank, BLM's
suddenly spike.  So yes, the ECM will try to compensate for fuel
starvation. Hook up a pressure guauge you can read while driving.    You
stated your regulator holds pressure when the pump is shut off, so you can
probably rule that out.  

Sounds like there's a couple of things which could be suspect, vague here
since you didn't specify any details of what you're running:

1.  Any chance it's the 02 cooling off at idle and screwing things up?  If
you're using a heated 02 (and it's working) this shouldn't be an issue.
2.  Is the 02 sensor good?   Is it a GM sensor?  
3.  Verified the 02 output with a DVM?  
4.  Injector size match the calibration?
5.  Calibration match the motor (at least 350 for a 350)?
6.  Does the pump have sufficient capacity for the motor?  

-> Bob Valentine
-> bob at tecmark.com

----------------------------------------------------------------------------
To unsubscribe from gmecm, send "unsubscribe gmecm" (without the quotes)
in the body of a message (not the subject) to majordomo at lists.diy-efi.org