1987 injectors no power

doublearrow · Jun 5, 2022

I have a 1987 5.7 all stock tbi. I drove this truck for several years. Parked it for about a year and then got it running again. I ran it a few times then the last time I started it it fired up and ran for about 15-20 seconds and died. It will crank but not start.
I can hear the pump prime in either tank when I turn the key.
I can jumper from the battery to the connection by the fuel pump relay and get them both to run.
I'm not getting any spray to the injectors. I have a weak battery but got it to start momentarily with carb cleaner.
I know no spray is common, and replacing the ignition control module fixed alot BUT....
My understanding is the with the key in a test light should show ONE wire on each injector as having power, I show nothing. Seems most threads/research I have down shows to have power to the injectors and the ecm sends pulse to spray. But with no power to start with this doesn't happen.
But where are they getting power? All of the fuses I think could control injectors are good and I get power to both sides of the fuse. None are labeled as injectors. Wires are bundled up well and but I'm afraid to start pulling on something and have more electrical problems by pulling a splice out.
I cannot find a wiring diagram that shows which fuse should give power to the injectors with key on.

yevgenievich · Jun 5, 2022

I believe it should be two fuses labeled ecm

gmbellew · Jun 5, 2022

check the driveability manual in the Reference Library for the no start condition for the full suite of things to check. but if I were to replace 1 part without testing anything for your symptoms, it would be the Ignition Control Module.

1987 GMC Jimmy · Jun 5, 2022

When did you replace the ICM, and what did you replace it with? ECM sends 12/14V injector voltage via pins D14 and D16. If you don’t have a pinout for the 1227747 ECM, downloaded and/or printed, I would do so now. And yeah, you can check the two ECM fuses. Can’t recall which one for sure, but I think it’s ECM-I. Wouldn’t hurt to check ECM-B also. My money’s on the ICM, but you can also use a little 9V battery touched to the two injector pins to do a aural pulse test. Not precise, but you can gauge good pulse/weak pulse/no pulse with this test. A good injector will give you a nice, loud click.

doublearrow · Jun 5, 2022

Ok it is the ECM-1 fuse. It was good but with battery charging yesterday I never could get it to light up at the injector. This morning I did.
Before today it had been several years since I replaced icm. I was hesitant to do so before getting power to the injectors. This afternoon I went ahead and replaced icm and no change.
I did the 9 volt battery test yesterday and they both click..
I guess I've got more research to do. I was convinced once I had power to injectors it would be solved. I don't have noid lights to check pulse just had a test light to test for 12v key in power to one side of injectors.

gmbellew · Jun 5, 2022

if it sat for awhile, you could have some rodent chewed wires somewhere causing issues...that is not easy to track down.

doublearrow · Jun 5, 2022

gmbellew said:
if it sat for awhile, you could have some rodent chewed wires somewhere causing issues...that is not easy to track down.

Not sure where I would start there. I have power to injectors, I have spark. It ran 20 seconds or so before shutting down. I bought a guage to check fuel pressure, both pumps prime depending on tank selector. The guage I bought from cfm tech many years ago and is going to take some re plumbing to fit. Going to have to do more research.

yevgenievich · Jun 5, 2022

Would Need to check the pulse signal getting to ecm

jimmy87 · Feb 6, 2023

I have been a lurker for a while, this is my first post. I have a mystery and hope I can get some help from the good folks on the forum.
I have an all stock 87 Jimmy with a 350 and 700r4.
I had to replace the wiring for the tbi due to wires missing insulation and bad connectors. Funny thing is the truck ran good with the old wiring. I replaced it with a Painless tbi wiring harness.
After installing the truck ran, I stopped the truck after a few seconds, something about running trucks in closed garages.
So I tried to crank it up again after a couple of months (life got in the way) the truck would not run. I have a good spark (after finding a week coil and replacing). I have good fuel pressure (during the prime cycle I applied 12v and ground to the injector and got a good cone of fuel spray), so the injectors work too. The tps works as expected. The map sensor works as expected. The egr solenoid is new. Oil pressure switch and temp sensor work. The fuel pump is running while cranking. While cranking if I ground the injector it will pulse. I ran through the driveability manual and concluded it was either a bad icm or ecm. I got two different new icm and a referb and pull from a truck ecm. With that I still don't have any injector pulse. I checked continuity of all the wires and they are good. I checked for any shorts, none foumd. I get grounds where I should and the correct voltages at the ecm connector. I also get a pulse on the purple/white wire back to the ecm from the icm. So I am at a total loss here. Anybody run into this problem or have any thoughts or sugestions?

gmbellew · Feb 6, 2023

jimmy87 said:
I have been a lurker for a while, this is my first post. I have a mystery and hope I can get some help from the good folks on the forum.
I have an all stock 87 Jimmy with a 350 and 700r4.
I had to replace the wiring for the tbi due to wires missing insulation and bad connectors. Funny thing is the truck ran good with the old wiring. I replaced it with a Painless tbi wiring harness.
After installing the truck ran, I stopped the truck after a few seconds, something about running trucks in closed garages.
So I tried to crank it up again after a couple of months (life got in the way) the truck would not run. I have a good spark (after finding a week coil and replacing). I have good fuel pressure (during the prime cycle I applied 12v and ground to the injector and got a good cone of fuel spray), so the injectors work too. The tps works as expected. The map sensor works as expected. The egr solenoid is new. Oil pressure switch and temp sensor work. The fuel pump is running while cranking. While cranking if I ground the injector it will pulse. I ran through the driveability manual and concluded it was either a bad icm or ecm. I got two different new icm and a referb and pull from a truck ecm. With that I still don't have any injector pulse. I checked continuity of all the wires and they are good. I checked for any shorts, none foumd. I get grounds where I should and the correct voltages at the ecm connector. I also get a pulse on the purple/white wire back to the ecm from the icm. So I am at a total loss here. Anybody run into this problem or have any thoughts or sugestions?

run through chart A3 and then A4 if the fuel pump is priming and you have spark. did you put a noid light on the injectors?

jimmy87 · Feb 7, 2023

Thanks for the reply,
Yes, put a noid light on both, no flash. I did check the return wires from the injector to the ecm and I have 12v at the ecm connector. It appears the ecm is not grounding the circuit like it is suppose to. Also when I check for a code, all I get is code 12. I did check both the grounds for the ecm, connected to the intake. I cleaned the intake for the grounds.

Thanks

gmbellew · Feb 7, 2023

jimmy87 said:
Thanks for the reply,
Yes, put a noid light on both, no flash. I did check the return wires from the injector to the ecm and I have 12v at the ecm connector. It appears the ecm is not grounding the circuit like it is suppose to. Also when I check for a code, all I get is code 12. I did check both the grounds for the ecm, connected to the intake. I cleaned the intake for the grounds.

Thanks

go through this. could be a bad ECM if that is where you land on this. they are available for about $150 I believe.

jimmy87 · Feb 18, 2023

I wanted to provide and update to my issue. After buying a new ecm and icm, I found the problem, the ecm was loosing power on the ignition input to the ecm while cranking. I found this while probing the injector wires while cranking.
I re-wired the whole truck with a Painless chassis harness kit (so dont have an oem harness to work with). I tied into the fuel pump circuit to provide power for the ecm ignition in. So I have now corrected that and have power with ignition on and while cranking. With that it is pulsing the injectors.
I see a lot of these threads just sort of die off with no resolution, I wanted to provide that much for the next guy.
Thank you gmbellew for you help.

1987 injectors no power

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