GM ECM TBI Questions with more information

[steve ravet]

JET wrote:

> When I did the swap from 2.8L to 4.3L TBI I
> used all of the sensors from the 4.3L except
> the O2 because it was heated, I used the ECM
> and harness that was with the 2.8L.

Someone more knowledgeable than me will weigh in on this, but it doesn't
seem like the 2.8L ECM would run a 4.3L engine very well, without at
least a prom swap.  My schematic shows an unheated sensor also  (one
wire)...

> I have tried to get the Check Engine light to come on, but it will
> not. I checked voltage at the between A and D of the ALDL connector
> and could not detect any?
>

It sounds like your ECM is either missing power/ground, or is dead.  Or
the check engine light is out or disconnected.  On my '86, there is a
small connector under the dash, near the ECM, that sends wires to the
instrument panel (check engine light, ALDL wires, VSS, etc.  Be sure
it's connected.

OK, just looked up the schematic:

Fused power comes from the fuse box to the fuel pump relay (orange).
When the ECM turns the relay on (tan/white, black/white), it makes the
connection back to the fuel pump(pink).  The pump is grounded at the
frame somewhere.  The other wire that goes to the tank (tan) is for the
gas gauge.  There is also a fuel pump prime near the pump relay.  This
is a short piece of wire (couple inches) with a connector on the end.
If you apply 12v, it should turn the relay (and the fuel pump) on.

But, I think you've got ECM problems.  Make sure it's getting power
properly.

Here's what I show for the ALDL:
A-gnd
B-diagnostic input
C-AIR solenoid
E-serial data

Two more have wires, but I can't tell what the hell they are because I'm
looking at Chiltons, not the factory manual.

Anyway, good luck.

--steve