What's new
CK5
Register an account today to become a member! Once signed in, you'll be able to participate on this site by adding your own topics and posts, as well as connect with other members.

Truck died after rough bump now no fuel!

dyeager535 said:
The 91 with 4L80E is wired differently I believe. That is a true PCM and not an ECM. Are you using the actual GM wiring diagrams for that year? GM makes mistakes in the manuals, not likely something that big though.

You've checked fuses?
Click to expand...

Just found a page that had numerous diagrams for 91 and did find the PCM diagram that matches, D14 on the PCM (mines 7060) was yellow for coolant temp.

I have checked and rechecked. Originally when the truck died I had a blown 10 amp ECMB fuse, but there was a fuse tap for a previous accessory in the truck that was removed before I bought it, the wire end was loose exposed wire under the carpet, I had assumed the bump put pressure on it and it grounded and popped the fuse. I replaced it but still had no fuel at injectors. I did have trouble with my distributor but now that’s replaced and one of the symptoms went away (no code 42 when unplugging the timing advance bypass wire), haven’t been able to get it to run to set timing.
 
This manual show the same info you are finding. Unfortunately I can't seem to find a 91 atm

IMG_20221202_140038.jpg
 
Wes Harden said:
Think this is it compare before doing things

View attachment 432623
Click to expand...
That is awesome! Thank you! I had read on another forum that if the ECM doesn’t see the feed signal from the fuel pump it won’t let the injectors run. Pin D7, the diagram I found shows that circuit is fused, and on this diagram it shows that circuit ties in to the oil pressure switch, as well as the fuel pump relay, which ties in to “F1”, I assume to be a fusible link? If so any idea where this particular link would be located in the engine comparment? If not, if this circuit is fused by a blade fuse in the fuse box, should I assume the fuse to be the ECMB fuse since this fuse is related to the fuel pump circut? I think the white/tan wire is what I need to look at.

If I pull the connector off the oil pressure switch and I jump the connection, this is would also help me eliminate my oil pressure switch as the problem too, right? I just found another post where a guy had the same problem and after several attempts the fix was the oil pressure switch.
 
Will it start on ether?
The engine should at least try and start normally with or with oil pressure.
The fuel pump relay and the switch are parallel, so if one works the truck will start and run.

Look at the fuel pump relay in diagram, find the red wire at terminal C. if you supply +12v to that terminal the fuel pump will run till you disconnect the 12v power.
I recommend printing that diagram out and marking it with notes to help.
 
Wes Harden said:
Will it start on ether?
The engine should at least try and start normally with or with oil pressure.
The fuel pump relay and the switch are parallel, so if one works the truck will start and run.

Look at the fuel pump relay in diagram, find the red wire at terminal C. if you supply +12v to that terminal the fuel pump will run till you disconnect the 12v power.
I recommend printing that diagram out and marking it with notes to help.
Click to expand...
Fuel pump primes with the key on, 12 volt power to the lead at the fuel pump relay runs the pump. It starts on ether. I previously had a weak spark condition but that went away with the new distributor. I’m definitely going to print that out.
 
Wes Harden said:
So inspect the hell out of the injector wires, esp where they connect to the tbi near the air filter stand off.
Click to expand...
I checked the injector wires and they look great, confirmed no power to the red or white injector wires in the run position, going to check at the pink/black wire and blue and green wires at the ECM and check for pulse while cranking tomorrow
 
Should have nothing to do with the ECM or distributor (spark). As I recall the injectors draw 12v off a fused ignition circuit. Need to check the wiring diagrams to confirm.

There will be no injector pulse because you don't have voltage at the injectors. The ECM might ground the circuit, but that's not the issue.
 
dyeager535 said:
Should have nothing to do with the ECM or distributor (spark). As I recall the injectors draw 12v off a fused ignition circuit. Need to check the wiring diagrams to confirm.

There will be no injector pulse because you don't have voltage at the injectors. The ECM might ground the circuit, but that's not the issue
Click to expand...

I didn’t get to mess with it yet but I’m gonna tonight. Fused as uh blade fuse or fusible link? Schematic I’ve seen doesn’t show it and I’m about to pull my hair out lol
 
UPDATE: it’s fixed, and I am PISSED.

When the truck originally died, I was pulling up to my work and found the ECMB fuse popped, a 10 amp. Knowing this is the fuel system fuse, and having zero 10 amp fuses in my truck or in my work truck or my shop, I took the 10 amp fuse for my transmission and put it in there and checked for fuel while cranking. I checked codes and had a code for trans solenoid a and b (81 and 82). All this is time I had assumed it was a no pulse problem, but after I did the noid light test and then checked voltage I knew that wasn’t the case. I checked the red and white wires as far up as I could and everything looked good. After reviewing the wiring schematic posted on this thread, the red and white wires trace back to the pink/black wire, which runs back to the circut for trans solenoids a and b. I’m sure y’all can see where this going… I checked 12 volt at the blue and green wires and had it. Popped a new 10 amp fuse in for the trans… fired right up. Not only did she fire right up, but she runs great. Think the timing is just about as good as it could get by eyeballing the distributor and by ear. Only code is code 42 for the Timing advance bypass wire being unplugged. Gonna hook the timing light up tomorrow after work and finish her up.

I’m so mad at myself… I never imagined a fuse for trans shift solenoids would control 12 volt to my injectors… but hey, she runs! Finally!

Now to go hide from my shame…
 
Make sense, the 91 has updated comp for trans. Iirc the 3 fuses together ecma ecmb and trans all work together. Glad you found this. lessons learned. I hope the new dist lets you get your est back, you really need spark advance to run high rpm.
 
Wes Harden said:
Make sense, the 91 has updated comp for trans. Iirc the 3 fuses together ecma ecmb and trans all work together. Glad you found this. lessons learned. I hope the new dist lets you get your est back, you really need spark advance to run high rpm.
Click to expand...
Thanks so much for posting that schematic, you saved my bacon and my sanity!
 
You must log in or register to reply here.

Latest Posts

Top Bottom