Hey guys,

I just got off the phone with my friend who has been working on my car for the last 3 weeks at his shop. We have both gone over this thing a million times and come to the same conlcusion. This thing should run, but the injectors will not fire. If we put a noid light on it, it does nothing. There is 12volts ignition on one side, but the computer will not ground the other side of the plug. We have tried replacing the ECM as well as the distributor, but did not change anything. Anyone have a problem like this before? Any suggestions other than to tear apart the harness or replace it with a new one as well? Any info would be great, thanks in advance!!

Ryan Smith
Kamloops, BC
Canada

Did you check the circuit from the injectors to the ECM?? Could have a bad connection at one of the connectors or a broken wire(s).
Is everyting else OK? (Thinking about ECM grounds).

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Mick
1986 GT

I would check the fuses and all the fuse links if you haven't already.
Other than that, try a different ECM.

I would also check TBI INJ 1 and TBI INJ 2 fuses as they will stop the injectors from firing. Also, check the ignition module and pick-up coil as the ECM needs to see the engine turning over before it will fire the injectors.

Yeah, have tried new ECM already, no change. From what I understand, all injector plugs exhibit the same problem. Is it a common wire from the ECM to trigger all injectors or are they all separated? Also, if anyone could enlighten me as to the wiring and common workings of this mpfi system, I would greatly appreciate it. I know fuel injection, but is the distributor the only trigger for this system? The computer fires all injectors at the same time if I am correctly informed, is this true? If so, why so many wires in the fuel injection harness? Also, why no codes, would there not be a DTC if the ECM sees an open or a short to ground in the injector circuit? Maybe I am giving GM too much credit, but I dont think that would be a difficult failsafe to build into the system.

Check the Ignition Module and pick-up coil too. The ECM will not fire the injectors til it sees the engine pulses from the distributor. Autozone (et al) can test the module for free. An ohmmeter can check the pick-up coil.

If you look at the ECM pinout here: http://home.att.net/~subzero350/ you will see that the ECM has 4 outputs to the injectors. The power side comes through the TBI INJ 1 and 2 fuses.

EDIT: There are no fusable links in the injector wiring. Check the fuse holder itself for power on one side with the key in RUN. Then ohm the fuses to verify they are good. A visual check may not be sufficient. If everything above checks good then you need to check continuity on your injector wiring.

[This message has been edited by Hudini (edited 04-02-2008).]

Are the plugs firing? (If not do the checks Hudini suggested)
Got fuel pressure and an unrestricted filter?
Fuse link F feeds power to the ECM. (@ C-501))

If you have power TO the injectors, check the ground path to the ECM.
Unplug the ECM and ohm out the ground wires to the injectors to eliminate it as a possibility.
Troubleshooting is all process of elimination. Easy stuff first. These wires and connectors are OLD.
If the continuity is good, then find out why the ECM isn't triggering them.
For the BLU/BLK at the injectors, go to C1 and D14 (LT GRN) and D15 (LT BLU) at the ECM.
For the LT GRN at the injectors, go to C1 and C15 (LT GRN) and D16 (LT BLU at the ECM.

The ECM fires one bank, 3 injectors at a time.

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Mick
1986 GT

Does the Check Engine light come on when you first turn the key ON for the bulb test? If not, the ECM isn't getting power. There are 2 orange wires that feed 12V to the ECM, one on each corner of the plugs into the ECM. Make sure they both have 12V or the ECM won't ever come on and fire the injectors.

Here's some troubleshooting steps listed in this thread: //www.fiero.nl/forum/A...0924-2-009156-2.html

OK, lets do some steps.
First off we need the service engine light to work.
1) Check for a good ground at pin 'A' at the serial port. (ALCL Connector)
2) Check the 'gauge' fuse in the fuse block.
3) Make sure that both the fuel pump relay and the oil pressure switch and relay are connected and good.

At the ECM connectors (not the ECM)

4) Pin (row) C16 +12 volts (battery, from Fuse link)
5) Pin (row) B1 +12 volts (for memory from Fuse link)
6) Pin (row) A6 +12 volts (Switch ON! from Fuse block)
7) Pin (row) A12 (ohms) to ground, 0 reading.

" Does engine start?
Your answer would be "No"

1.Is ecm battery feed ckt 240 and ecm fuse ok?
Now the battery feed ckt 240 is coming out of your ecm in two locations C16, and B1. Both of these wires are orange, and splice togather at the insterment panel connector. ECM fuse is the Pink/Black wire at A6 on the ecm. It is also called circuit 439. So now you have to answer the question "are they ok?"
Yes- Ign. off, disconnect ecm, ign. on, probe ckt 240&439 with test light to ground. Is the light "on" on both circuits? Yes move on to set 2. No repair open in circuit the did not light the test light.
No- Locate and correct short to ground in circuit that had a blown fuse."

[This message has been edited by Formula88 (edited 04-03-2008).]

if you have power and a good ground, check the line from the dist to the ecm, called dist reference. don;t have the 86 pinout handy, btu the link above should have it. that line is best checked with a scope, but a high quality analog meter might show the pulses.
no pulse on this line, no injector firing.

First things first: Do you get a tach signal (tach comes off base peg) when you are cranking the car?