'86 MJ 2.5L ECM....good?

[eaglescout526]

Well with key on, I don't suspect there to be any voltage going through 87 until crank sequence. So O.L. would make sense to not be seen there as the relay isn't energized. I wonder what the second splice feeds then. Most if not all black wires in the harness are ground. But why would there be voltage there?

[SoCalManche]

6 minutes ago, eaglescout526 said:

Well with key on, I don't suspect there to be any voltage going through 87 until crank sequence. So O.L. would make sense to not be seen there as the relay isn't energized. I wonder what the second splice feeds then. Most if not all black wires in the harness are ground. But why would there be voltage there?

Well the one black wire that splices into four black wires shoots back into the harness towards fuel pump relay. The only solid black wire coming out of the harness over there is to a three pin connector that plugs into the ICM.

 

Don't know if that helps.

[eaglescout526]

So I wonder if that ground and the one that goes to the ICM come back to the dipstick ground. The one with the four splices is ground splice "D" that probably goes to the dipstick. On that second splice is a 20, 2 18's and 2 14 guage wires with a 14 going to the grounding point. Meanwhile the ICM ground and O2 sensor come together on probably the same eyelet at the dipstick. 

[SoCalManche]

17 minutes ago, eaglescout526 said:

So I wonder if that ground and the one that goes to the ICM come back to the dipstick ground. The one with the four splices is ground splice "D" that probably goes to the dipstick. On that second splice is a 20, 2 18's and 2 14 guage wires with a 14 going to the grounding point. Meanwhile the ICM ground and O2 sensor come together on probably the same eyelet at the dipstick. 

Wow, so I am extremely confused. I went to go play with the grounds at the dipstick tube, and two wires just popped off. The eyelet they were attached to has vanished. I verified these were connected a couple days ago, yet now they are detached completely, with no eyelet in sight.

 

I will re-crimp after I eat and cross my fingers.

[eaglescout526]

Maybe, just maybe. I'm crossing mine too.

[SoCalManche]

29 minutes ago, eaglescout526 said:

Maybe, just maybe. I'm crossing mine too.

Can't get the nut back on because the tip of the bolt is jacked up from me trying to use vice grips to rotate it out. I need to re-tap the bolt. Does it happen to say what size the bolt is in that book you have? For the dipstick tube stud.

[eaglescout526]

Neither TBI or electrical book says. Let me go look at the  2.5L and FSM.

[eaglescout526]

Good thing I got that Jeep/Eagle bolts bolts book. PN J0273573 is 5/16th in diameter, 18 in thread distance from tip to tip, 0.620 in shaft length and its made of steel.

[SoCalManche]

2 minutes ago, eaglescout526 said:

Good thing I got that Jeep/Eagle bolts bolts book. PN J0273573 is 5/16th in diameter, 18 in thread distance from tip to tip, 0.620 in shaft length and its made of steel.

You're a saint.

[eaglescout526]

1 minute ago, SoCalManche said:

You're a saint.

Just short of a miracle worker lol.

[SoCalManche]

15 minutes ago, eaglescout526 said:

Just short of a miracle worker lol.

Alright, unfortunate no-go. Still reading 7.9V at fuel pump connector without pump connected, and 4V with pump connected.

[eaglescout526]

Relay or jumper in? Cranking or key on? 

[SoCalManche]

1 minute ago, eaglescout526 said:

Relay or jumper in? Cranking or key on? 

Relay in. KEY ON.

 

Just went out and watched the voltage while cranking: drops from 4V to ~3-something V.

THERE IS A NEW DEVELOPMENT. So I'm currently running my fuel pump in a 5-gal bucket of fuel to hear things better (as well as took the opportunity to clean out the tank. I can hear it prime a bit when I flip key ON. I can actually keep getting it to FIRE briefly by continually cranking, without re-adding fuel to TBI. I hear fuel returning to the bucket and dripping out briefly when key ON aka somewhat prime.

 

This is wild. First time I've witnessed this in over a year.

[eaglescout526]

Alright we are getting somewhere. Now we just need the fuel to get to the TB and keep the engine running. Pressure at the rail with this new development?

[SoCalManche]

Just now, eaglescout526 said:

Alright we are getting somewhere. Now we just need the fuel to get to the TB and keep the engine running. Pressure at the rail with this new development?

I don't know. I had to return the fuel pressure gauge. I need to go buy a little one.

[eaglescout526]

Oh ok. Makes me wonder if the fuel pump runs, but its not putting out enough pressure weather it is resistance in the wiring and connectors or the pump genuinely failing. But that's good that it primes, that takes care of that wonder.

[SoCalManche]

2 minutes ago, eaglescout526 said:

Oh ok. Makes me wonder if the fuel pump runs, but its not putting out enough pressure weather it is resistance in the wiring and connectors or the pump genuinely failing. But that's good that it primes, that takes care of that wonder.

Any tests now that come to mind that may lead us to the issue?

[Ωhm]

That bucket of fuel, now this getting scary. Can you run battery straight to the fuel pump?

[SoCalManche]

Just now, Ωhm said:

That bucket of fuel, now this getting scary. Can you run battery straight to the fuel pump?

I took that page out of someone else's playbook on here. Can't remember where I saw it. Oops.

 

I can pull the pump from the assembly and bench test via battery, if that's what you mean.

[Ωhm]

1 minute ago, SoCalManche said:

I can pull the pump from the assembly and bench test via battery, if that's what you mean.

No, run battery voltage or use another battery straight to the pump connector in the bucket.

[SoCalManche]

The only "wires" I would have long enough to complete that task are jumper cables.

[Ωhm]

This is extreme testing. CAUTION is needed everywhere. Danger Will Robinson Danger.

[eaglescout526]

No little baby alligator clips laying around? Something like this makes me want to get a bunch of the weatherpak connectors and just make test connectors for power and ground like for the sending unit.

[SoCalManche]

1 minute ago, Ωhm said:

This is extreme testing. CAUTION is needed everywhere. Danger Will Robinson Danger.

The pump is setup in the bucket like it would be in the tank. The connectors are not submerged in the gas, and the bucket top is sealed off besides where the fuel lines and wiring comes out. 

 

I can't tell if you're being facetious or not, but if you want me to run batt power to pump, I will.

[SoCalManche]

1 minute ago, eaglescout526 said:

No little baby alligator clips laying around? Something like this makes me want to get a bunch of the weatherpak connectors and just make test connectors for power and ground like for the sending unit.

No, just the jumpers. I have a smaller set of jumpers, but they aren't baby alligator clips or anything.