87gt 2.8 one bank of injectors not firing? (Page 1/1)
Dwayne FEB 04, 01:06 PM
orignal post

Posted a little while back about my sons 87gt not starting after sitting for a few days. after changing the distributor rotor the car starts and runs but running on 3 cylinders (3,5&6)...I believe one bank. here is all the troubleshooting I have done so far to try to find the problem.

new distributor cap
new rotor
new ignition module
new ignition coil
new pick up coil
used replacement ECM
all fuses checked good
tachometer moving when cranking
placed cyl #1 at tdc and checked for rotor at plug wire 1 position
45psi at fuel rail
healthy spark on all 6 wires with spark jump tester
cleaned and tested all6 injectors for spark, spray and 16 ohms
no fuel in vacuum line from regulator
swapped around injector and plug wires...still same cylinders/injector wire running bad.
compression checked out all cylinders about 130-140 psi

sounds like a injector wiring issue. I not sure how to troubleshoot it but I got 12v at all 6 injector connectors and 12v at ground with key on. I wanted to test with noid light to see if I get a pulse while engine was running but cant with the intake off or in the way of accessing connectors. So I inserted the noid light into each injector connector and with key on or off and i cant get the light to come on at all? tried cranking engine with fuel pump fuse pulled and no lite or pulse to noid. I hear that the ECM grounds the injector wires to fire them...How do I check for that? I'm not very handy with electrical issues. is there a layman's guide to troubleshooting wiring issues or step by step guide for this situation? ..any suggestions?

Thanks
theogre FEB 04, 01:31 PM
If injectors have power to them then iffy wire(s) to ECM or ECM is bad.
ECM fires by switching Ground wire to them. (Look up Arduino and N channel MOSFET turn on anything. Work about same.)

Discon all in same bank. Install noid light and try to start. Should blink when doing that.
Other injectors in parallel can/will "short out" the noid and won't blink.

------------------
Dr. Ian Malcolm: Yeah, but your scientists were so preoccupied with whether or not they could, they didn't stop to think if they should.
(Jurassic Park)

The Ogre's Fiero Cave

[This message has been edited by theogre (edited 02-04-2020).]

Raydar FEB 04, 05:27 PM
I know you checked your fuses, but...
The EGR solenoid runs off of one of the injector fuses. If it shorts out, it will take out that fuse, and the associated bank of injectors.
With that said... it's either the entire front bank, or the entire rear bank. (I forget which.) It won't be just one or two from either bank.

[This message has been edited by Raydar (edited 02-04-2020).]

Patrick FEB 04, 06:28 PM

quote
Originally posted by Raydar:

The EGR solenoid runs off of one of the injector fuses. If it shorts out, it will take out that fuse, and the associated bank of injectors.
With that said... it's either the entire front bank, or the entire rear bank. (I forget which.) It won't be just one or two from either bank.



Yes, it can be!

Raydar, we've been all through this with Dwayne previously. Have a look Here.

[This message has been edited by Patrick (edited 02-04-2020).]

pmbrunelle FEB 04, 07:33 PM

quote
Originally posted by Patrick:

Yes, it can be!

Raydar, we've been all through this with Dwayne previously. Have a look Here.




By the bundles of wires, it may appear that 1,2,4 and 3,5,6 are grouped together. The conclusion you jumped to by the external appearance of the harness is false.

The service manual schematics show 1,3,5 and 2,4,6 grouped together. That's how it actually is. If you were to wipe the crud off your injector harness, you would see that the 1,3,5 injectors each have a green wire leading to them, while the 2,4,6 injectors each have a blue wire.

Trust me, I know... I had to untape my injector harness while converting my present V6 Fiero from batch fire to sequential fuel injection. When I started, my harness looked exactly like yours, with the misleading-looking bundling.



If you want to confirm on your Fiero, you can pull the TBI INJ 1 or TBI INJ 2 fuse while the engine is running. If I am correct, the engine will run smoothly (as an even-fire three-cylinder engine) running on just one fuse at a time. If you try to run the engine on cylinders 1,2,4 or 3,5,6, it won't run correctly.

On my previous V6 Fiero, which was equipped with batch fire (as the factory wired it, but with an ECU that had independent control of either bank), I implemented "Camel Mode" on my engine... operation with loss of coolant by alternately operating each cylinder bank. While one bank ran the engine, the other had no fuel injected and simply had air flowing through. The banks switched roles every so often.

This was inspired by the Cadillac Northstar which had such a feature. Camels can survive without water for some time.

I never tried Camel Mode for real... probably if my Fiero ever suffered a loss of coolant, I'd pay for a towing and not want to risk scrapping the engine. My automotive hobby budget won't permit me to test Camel Mode

I may try it if I had little choice in an emergency, such as a nuclear bomb going off and I wanted to leave the fallout zone ASAP.

[This message has been edited by pmbrunelle (edited 02-04-2020).]

Patrick FEB 04, 08:08 PM

quote
Originally posted by pmbrunelle:

By the bundles of wires, it may appear that 1,2,4 and 3,5,6 are grouped together. The conclusion you jumped to by the external appearance of the harness is false.

The service manual schematics show 1,3,5 and 2,4,6 grouped together. That's how it actually is. If you were to wipe the crud off your injector harness, you would see that the 1,3,5 injectors each have a green wire leading to them, while the 2,4,6 injectors each have a blue wire.

Trust me, I know... I had to untape my injector harness while converting my present V6 Fiero from batch fire to sequential fuel injection. When I started, my harness looked exactly like yours, with the misleading-looking bundling.



Forgive me for not going out in the snow tonight to wipe the crud off my injector harness. I'll take a closer look next time I have my upper intake plenum off.

I understand what you're saying, but since it looks like it is physically possible to route the injector harness more than one way, I'll reserve judgment on how mine is actually connected.