87 R10 TBI injectors will not spray

[IROCmenace]

I am at a loss. Sorry this will be long.

This truck sat for a few years but ran before. My Dad gave it to my son so I am trying to get it running again.

Ultimately here is where I am. A mouse, or several, chewed some wires up. I have all the ones I can see reconnected.

Truck still would not start. I tested a bunch of things which led me to replacing both fuel pumps. They now both run.

The truck will run on starter fluid or if I hotwire an injector open. So I have fuel and spark.
Fuel pump relay is good
Pumps good.
All wiring for those items good.

I hooked up my scanner to the truck that can read OBD I live engine data. TPS is in range and responsive.

I understand the purple/white wire coming out of the ignition module sends a reference pulse to the ECM ground the injectors. I put a test light on the wire with my Dad cranking the truck and the test light flashed consistently.

I pulled the ECM and checked the 2 grounds, or at least what I felt were the grounds with the ECM unplugged. I tested them with a test light and they lit up.

The power side of both injectors shows 12V

I bought a Cardone ECM at Advance and replaced the ECM. No luck. Still no injector pulse. Talk about frustrating.

I replaced the dizzy as a unit 8-9 years ago. When I looked at the module today there is very little signs of wear. Truck never had much mileage put on it at any time. Just a hauler and tooling around vehicle occasionally. I pulled the module and put a different one in. It is an older GM module, I think the original one to the truck so it may or may not be good. Still no start.

I am going to get both modules tested. But from what I understand the testors only test the ignition side, not the reference side. I don't want to drop another $60 after the ECM but I may go ahead and buy another one.

I have triple checked the fuses, pulled, tested with a test light on one peg and the car battery on the other. All good.

My questions are:

Where exactly are the engine grounds. I can't find anything on them. Are they behind the heads? The ground strap from the firewall to the head is there and tight. I cannot get my hand behind the heads to feel for any other wires.

What else could this be? I tried starting it with out the TPS plugged in. Without the ECT plugged in and nothing.

TIA, I cannot think of anything else to do

 

[Cuba]

I know you have use of an OBD1 scanner, but have you tried checking for codes via the selftest method with just jumping the 2 A&B points? See if you at least get the code12?

Another thing, do you have access to the wiring schematics? Since the injectors are a ground side switch activated circuit (via the ECM), I'd verify that the ground side of the injector to ECM is intact. I know you verified the ECM grounds themselves, but it's possible the mice cut through the switch side of the injectors, since you know they do have power. You also have the neccessary pulsing for spark/injector...

 

[Honky Kong jr]

You could also spike into the ground side of the injector plug Seth another wire and pulse the ground your self, with the key on to feed power to the other side of the injector,quick like to verify the injector will work. If that makes sense all your doing is bypassing what the ECM should be doing and doing it manually.

 

[Georgeb]

I would take cuba's advice and verify the integrity of the ground pulse wires. The testing of the injectors as Honky Kong suggests is also a good idea.

 

[IROCmenace]

Thanks for the replies guys.

I have hot wired the injectors already to make sure fuel will flow through them. Basically held them open and fuel came through and the truck ran shortly.

I did some more tests after posting this with my son. I have the computer plugged in but still out so I tested a lot of wires. at the ECM and TB.

At the ECM:
ECM ground good
The blue and green injector wires are grounding/ flashing the test light... More than I got before with the old ECM. So I probably had a bad ECM too.
The fuel pump relay wire and pump reference signal are good
***The purple and white is not giving a signal. I had the test light grounded expecting it to flash like the module did but it did not. I made sure I could see copper at the ECM plug to make sure I had contact. Nothing but the injector wires were still flashing. Should I have had the test light connected to power and test for ground? Didn't think it worked that way But I wonder if the older module is bad.

At the TB:
**** Now I am really confused
Both the green and blue will flash the test light at the TB now.
The injector red and white still light the test light unless you try to start the truck. When ever the starter is spinning I get nothing from the power side of the injector but I have power there when the key is off.

So I am going to get a new module to begin with. I am going to try and trace or at least test the continuity of the reference wire at the ECM to see if mice cut it somewhere between.

What should I look at for the loss of power at the injector while cranking?

Thanks again guys

 

[Honky Kong jr]

To test the ground if it's an incandescent test light hook the clamp to positive and poke the negative wires with the pointy end.

 

[MrMarty51]

Another way to test the ground.
Hook Your probe wire to a good grounding source, probe the negative terminal at the injector connector while they are connected, crank over the engine, if the light shineth, it then is a grounding issue.

 

[IROCmenace]

Well. Put a new module in. Nothing. Checked fuses again. All good
Checked wires at the injectors flashing on the ground side with a test light. Just to do it I checked fuel pump reference, icm reference and a bunch of others with a dvm and test light at the ecm. Crawled under the truck and heard the pump run. Hot wired another injector and it sprayed. It is almost like the injectors themselves are getting power but won't open unless I hot wire them but that doesn't make sense. I even pushed the contacts inside the injector plug closer together to make sure the are contacting the injector. Is there some fuse somewhere not in the box that is not in the books?

One thing of interest or not. The voltmeter does not work. It used to before truck was parked. Don't see how that could be related but hey, full disclosure

 

[Honky Kong jr]

Are you getting proper voltage to the injectors threw the ECM. Could be a lower voltage that isn't enough to open them but enough to light a test light. Then when you hot wire it they get full voltage and open. Takes more amps to open or close a solenoid then it does to light a bulb. Just throwing it out there.Food for thought.

 

[IROCmenace]

Are you getting proper voltage to the injectors threw the ECM. Could be a lower voltage that isn't enough to open them but enough to light a test light. Then when you hot wire it they get full voltage and open. Takes more amps to open or close a solenoid then it does to light a bulb. Just throwing it out there.Food for thought.

Yes on the power side I get 12v iirc. when not cranking but I will double checkI was so frustrated i forgot to write everything i did down. Should I not be getting proper voltage where should I look next? I am thinking of pulling the whole harness out and replacing it but.... ugh....

 

[Georgeb]

I would try forcing a ground at the ecm plug and see if the injectors open. If they do The harness is probably good.

 

[Honky Kong jr]

If the 12v is constant and the ground is pulsed for ***** and giggles feed the injectors with 12 directly from the battery and ground pulse from the ECM and see what you get when you try to start it. I believe you said they open when you read direct power and ground. Worth a shot. It could be a low 12v signal under load threw 30 year old wire.

 

[IROCmenace]

If the 12v is constant and the ground is pulsed for ***** and giggles feed the injectors with 12 directly from the battery and ground pulse from the ECM and see what you get.

Good idea, I will try that

 

[Honky Kong jr]

Good idea, I will try that

Lol you commented I added more to my reply.

 

[IROCmenace]

Update, I got it. Strange chain of events.

Truck would run on spray or gas down the TB before but wouldn't today.

I tried starting it with gas down the TB yesterday and it only puffed out of the TB. It would bump maybe once.

I rented a noid light today. It flashed but was dim. I had my Tahoe jumping battery at this point so there was plenty of juice. Wouldn't fire with starter fluid either.

With all the wires checking out for ground and current I tried spark again thinking the dim noid light was weak signal through the ignition system not giving a strong enough signal to the ECM. My test light is LED so it us on or off, not dim like the noid light was.

Timing light on 1 and 3, nothing.

So evidently those last few seconds of running were it for the cap and rotor a few weeks ago.

Coil checked out.

Put a new cap and rotor on it boom. Started right up. Only running on one injector but running. Already swapped plugs on the injectors. One is shot.

So basically new problems arose while figuring out the pumps and ECM. All in all I don't think I needed an ICM but now I have a good extra.

Man these things don't like sitting.

Thanks for the replies