350TPI Fuel Consump Problem

[Dave Zug]

at first glance, and without knowing if you have gone thru the basics - it
may be that your o2 sensor isnt warm enough at idle due to perhaps too much
fuel, and the reading drops waay low from being cold. This will make the
BLM's try to richen up the mixture compounding the problem.

you probably have an o2 monitor and can see if the sensor is switching and
it IS and I am in the basics when you are beyond that. I tried anyway. a
heated o2 will help if you do have this condition.


160 IS the max yes.  Low FP voltage will increase injector PW but below like
11 volts only I think.  36 psi fuel pressure (yes, LOW) may make your blm's
go up and fuel consumption go up because PW will rise making more poorly
constructed droplets that dont burn as efficiently. as FP rises with
manifold pressure the droplets become more atomized and a better burn may be
the reason the BLM's are good at highway speeds.

Try removing the vacuum line from the FP regulator at idle and see if the
BLM's go down. thhey normally WILL even if there is no problem but also look
at the idle-pulse widths compared to the vacuum-off idle pulse widths - I
don't know how long it may take for the BLM's to adjust - get into cells
0,1,2 at least for a while.

----- Original Message -----
From: Don Burns <donburns at macconnect.com>
To: <gmecm at diy-efi.org>
Sent: Sunday, October 08, 2000 6:04 PM
Subject: 350TPI Fuel Consump Problem


> 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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