A little too simple

[Onebil2mny at aol.com]

First, I would like to introduce my self..  I'm Bill, and I'm a caraholic.

I am currently working on a 56 BelAir conv with a production line LT4 using a
GM ECM from Howell, 700R4 tranny, and all kinds of other non list related
mods.   I am also building (for my self, the BelAir is for my Father) a 72 442
conv. LS-6 crate motor with a Roller Hydraulic cam, Wiand Team G with injector
bungs, Kinsler throttle plate and an Accel ECM. It also has several dozen non
list type mods. I think this list may be a little advanced for me, as I'm only
an ASE Master Tech, and don't have a Bachelors degree in anything.  I've been
following a couple of the posts lately, and I don't know a thing about burning
proms, much less building a device to modify OBD2 ECMs!

Anyhow, here is my query.....   I have installed a TBI motor from a 91 Chevy
Truck in to a 85 MonteCarlo.  The Monte was originally equipped with a TBI
4.3L.  I have installed a 91 Caprice ECM & Prom (ECM service # 16136965) and
on the monitor everything seems OK, except for the MAT as the Monte was not
originally equipped with one.  I will install on soon as I have the pin outs,
sensor and sensor pig tail....  I just need the terminal at the ECM.  My
problem is what appears to be a terrible lean condition.  I am using the 4.3's
throttle body as I was advised it should keep up.  It does appear to have the
same size throttle bores, and I can only assume injectors are ok....  at least
for Idle!  Anyhow, I have checked for the obvious, vacuum leaks, etc. but it
still runs lean, hesitates, backfires, etc.  That is until I dead head the
fuel pressure.   If I pinch off the return line, it runs fine.  I have 12 psi
at idle, in spec for a 85 car, but I don't know the proper pressure for a 91.
Could low pressure be my problem?  Does a 91 Caprice TBI require a higher fuel
pressure?  Or, is there something wrong with my choice of ECMs?  Any
suggestions would be great!


Thanks for the help. and sorry if this is a little too simple.
Bill (feels so uneducated) K