EFI musings

[John Faubion]

> -> Well Dave with some prudent shopping you could have done it cheaper
> -> too. I picked up a GM #730 ECM, harness and most of the sensors from
> ...
> -> especially if you can adapt factory parts. Ford and GM already spent
> -> the money to make them reliable, why not use them?
> 
>  What do you intend to do about reprogramming the ECM?
>                                                                          
                                            
Actually very little. The programming for the '90-'92 F-bodies is a speed
density system. By sizing the injectors correctly you can adjust for the
size difference between the engines. For example, the factory 5.7L used a
Lucas #5207011 injector that flows 20.73 lb./hr at 44 psi of fuel pressure.
My 427 is 427/350 = 1.22 or 22% larger. If I maintain the same RPM range of
idle-5000 RPM that the factory used, then I would need to use an injector
that flows 22% more fuel to maintain the same injector pulse width. So my
injectors need to be 20.73 x 1.22 = 25.29 lb./hr. in this case I could use
the injectors from a Nissan 300ZX (Lucas #5206004) and adjust the fuel
pressure. These flow 24.73 lb./hr at 37psi. To get 25.29 lb./hr I need to
use 25.29/24.73 = 1.02 x 37 = 37.84 psi of fuel pressure. By sizing the
injectors this way and maintaining the same injector pulse width, the ECM
fuel maps should be close. With the learning ability built into this ECM,
it should be able to compensate for the small variances. 

If you are using a V8 that had the same type injection you want to use,
(i.e. your going to TPI and running a 350 small block) then your
programming is easy. Even if you have modified the engine with aftermarket
pieces such as a cam, headers, better heads etc., just contact someone that
already programs PROMs for these. Get information from them about their
chips on a version that would be close to what you have already built. If
like me you are building something the factory never even considered like
port EFI on a 427 big block, this could still be an option. You only need a
chip that will support the gear ratios, rear axle ratio, approximent
weight, type of injection (TPI, MPI, TBI) and most importantly RPM range.
Since I will probably not maintain the same RPM range (my 427 is built for
1500-6500 RPM) I would need a stage 3 or 4 chip from Hypertech. This will
also require an increase in the size of my injectors to support the
horsepower level of this engine. Even if I buy an aftermarket chip, I'll
still be under $400 for my total project.

The factory systems are much easier to adapt than to build your own
controller. I like to idea of building my own but I just don't have the
money to sink into the project. I'm also trying to decode the factory ROM
as well. I have access to the hardware to do this but as I'm sure everyone
knows, this is not a simple undertaking. Until then though, there are
several options open.

John Faubion
jfaubion at beaches.net