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

[SoCalManche]

Just now, eaglescout526 said:

RPMs fluttering would be a possible MAP sensor issue or something with the EGR and its solenoid.

I mentioned the RPMs fluttering to paint a better picture of how the engine is responding to the jumper wire versus the relay.

[eaglescout526]

Well its doing something. But we couldn't get a clear picture on why the ground has an open circuit.

[SoCalManche]

Just now, eaglescout526 said:

Well its doing something. But we couldn't get a clear picture on why the ground has an open circuit.

I don't really know how to explain this since, as I've mentioned before, I'm bad with circuits and wiring and stuff. But if the jumper is only connecting two of the five pins in the relay circuit, thus pushing a direct current to the pump, would that mean there's an issue with one of the other pins, since all five are connected with the relay itself? That probably makes no sense, but it's a thought that came to mind.

[Ωhm]

One more question, does the fuel pump motor run with the fuel pump relay installed? With KEY ON fuel pump will run for 2-3 seconds only and during CRANK fuel pump motor will run all the time.

[SoCalManche]

1 minute ago, Ωhm said:

One more question, does the fuel pump motor run with the fuel pump relay installed? With KEY ON fuel pump will run for 2-3 seconds only and during CRANK fuel pump motor will run all the time.

No, with relay installed, fuel pump does not engage.

[eaglescout526]

Ok so the component diag section states this

 

Fuel pump will not operate for one second with the ignition switch on

Possible Cause: Open circuit or fuel pump ballast resistor defective, which Jeep didn't get the later till 87 from the factory. 

 

So you have already done the first part, connect a jumper wire across the fuel pump relay

 

If the pump operates, check for battery voltage at the relay. Check the continuity betwenn the relay and Pin 6 at the ECU. Repair the wire harness as necessary. Replace fuel pump relay. Test ECU with MS-1700.

Test for continuity between the fuel pump and relay contacts(long enough leads much?)

Check the pump ground circuit.

Repair the harness as necessary. 

[SoCalManche]

35 minutes ago, eaglescout526 said:

Ok so the component diag section states this

 

Fuel pump will not operate for one second with the ignition switch on

Possible Cause: Open circuit or fuel pump ballast resistor defective, which Jeep didn't get the later till 87 from the factory. 

 

So you have already done the first part, connect a jumper wire across the fuel pump relay

 

If the pump operates, check for battery voltage at the relay. Check the continuity betwenn the relay and Pin 6 at the ECU. Repair the wire harness as necessary. Replace fuel pump relay. Test ECU with MS-1700.

Test for continuity between the fuel pump and relay contacts(long enough leads much?)

Check the pump ground circuit.

Repair the harness as necessary. 

So can you explain that to me like I'm five so I do the test properly? I can do that tomorrow after I pick up my 64" lead extensions from Napa. Well...hopefully they're long enough...

 

[eaglescout526]

15 minutes ago, SoCalManche said:

So can you explain that to me like I'm five so I do the test properly? I can do that tomorrow after I pick up my 64" lead extensions from Napa. Well...hopefully they're long enough...

 

Lol fair enough. I just typed what the book has.  But I am not great at explaining things to others in simple formalities but here goes.

 

So when you turn the key, the pump comes on and primes. Common knowledge with Renix. 

Since its not coming on there probably an open circuit somewhere in the fuel harness between the pump itself, the ground and the relay to the ECU. Or possible corrosion of a contact or wire.

 

So you already jumped the relay harness and still got nothing which means there is something going on in the harness. Which makes me wonder the condition of the starter relay connectors.(not entirely related but apart of the start up procedure per the ECU)

 

Since the pump doesn't operate we can't check for voltage. Well you still could to see if there is any power at the relay contacts. 

Checking the continuity of the circuit to see if there is any power between the two ends. As for checking continuity between the pump and the relay, if I had the wiring diagram for the pump to relay, they probably mean for you to check each connection so like the fuel pump to its first harness connector, then from that connector to the next one until you reach the fault or relay contact.

 

Then checking the ground circuit would be the same deal, making sure there are no breaks or corrosion between the connector and the ground behind the lamp. 

 

I think I explained it well enough. If not let me know.

[SoCalManche]

3 minutes ago, eaglescout526 said:

So you already jumped the relay harness and still got nothing which means there is something going on in the harness. Which makes me wonder the condition of the starter relay connectors.

Are you referring to the fusible links that attach to the starter solenoid?

 

5 minutes ago, eaglescout526 said:

Since the pump doesn't operate we can't check for voltage. Well you still could to see if there is any power. 

Couldn't we check for voltage if jumper wire took the spot of the relay?

 

7 minutes ago, eaglescout526 said:

Checking the continuity of the circuit to see if there is any power between the two ends. As for checking continuity between the pump and the relay, if I had the wiring diagram for the pump to relay, they probably mean for you to check each connection so like the fuel pump to its first harness connector, then from that connector to the next one until you reach the fault or relay contact.

 

Then checking the ground circuit would be the same deal, making sure there are no breaks or corrosion between the connector and the ground behind the lamp. 

So what is the best way to go about this? Basically slicing open all the split loom and chasing wires?

[eaglescout526]

1 minute ago, SoCalManche said:

Are you referring to the fusible links that attach to the starter solenoid?

Yes and no. I am not sure if any one of the fusible links is even apart of the fuel pump harness, but i was just thinking about the contact tabs and such on the starter relay as those can corrode too and cause resistance or loss of power.

 

1 minute ago, SoCalManche said:

Couldn't we check for voltage if jumper wire took the spot of the relay?

Yes you can.

 

1 minute ago, SoCalManche said:

So what is the best way to go about this? Basically slicing open all the split loom and chasing wires?

No, I was thinking more using the connectors as breaks in the harness. Rather than getting really long leads and putting one in the relay harness and the other at the pump itself, I was thinking of using the connectors as testing sections so that way you aren't trying to dig into the entire harness when hunting down the problem. So that way when testing from one connector to the next and suddenly an open loop comes up in one section between two connectors, the problem could lie there. Ohm will probably correct my thinking if I'm wrong.

[SoCalManche]

7 minutes ago, eaglescout526 said:

Yes you can.

So I know (A) on the harness for the pump is the ground since I soldered an additional ground to it, but do you have on hand which terminal (B) and (C) are?

 

8 minutes ago, eaglescout526 said:

No, I was thinking more using the connectors as breaks in the harness. Rather than getting really long leads and putting one in the relay harness and the other at the pump itself, I was thinking of using the connectors as testing sections so that way you aren't trying to dig into the entire harness when hunting down the problem. So that way when testing from one connector to the next and suddenly an open loop comes up in one section between two connectors, the problem could lie there. Ohm will probably correct my thinking if I'm wrong.

Are there that many connectors to make a distinction such as that? 

[eaglescout526]

One would send power to the fuel pump and the other is the fuel gauge wire. I think the fuel gauge was C. 

 

Well I did some looking at the electrical book and saw a couple things. First I saw is there is a fusible link tied to the fuel relay harness. Second the connectors would be at the tank(1), second would probably go into the cab behind the kick panel then probably into the engine bay wiring harness that routes back to the ECU. Well I am learning more about the diagrams but ill admit the last two after the kick panel are a shot in the dark.

[SoCalManche]

7 minutes ago, eaglescout526 said:

One would send power to the fuel pump and the other is the fuel gauge wire. I think the fuel gauge was C. 

 

Well I did some looking at the electrical book and saw a couple things. First I saw is there is a fusible link tied to the fuel relay harness. Second the connectors would be at the tank(1), second would probably go into the cab behind the kick panel then probably into the engine bay wiring harness that routes back to the ECU. Well I am learning more about the diagrams but ill admit the last two after the kick panel are a shot in the dark.

I probed all the fusible links when the issue first arose, and they all had battery voltage. I could check again though.

[eaglescout526]

I think that's why the book says to test T6 and the relay to make sure there is continuity there. T6 has the power to trigger the relay for that one second and then stop. While the relay itself waits for power from the start up procedure to run the pump.

 

I only saw one associated with the fuel pump relay and a couple other things.

 

Below is the top image split into four to see the words better.

First half.

 

Second half.

This is from the PDF electrical manual. Hopefully this will help give an idea as to what we are looking at.

[SoCalManche]

1 minute ago, eaglescout526 said:

I think that's why the book says to test T6 and the relay to make sure there is continuity there. T6 has the power to trigger the relay for that one second and then stop. While the relay itself waits for power from the start up procedure to run the pump.

 

I only saw one associated with the fuel pump relay and a couple other things.

 

Below is the top image split into four to see the words better.

First half.

 

Second half.

This is from the PDF electrical manual. Hopefully this will help give an idea as to what we are looking at.

Which pin do I check for continuity with T6? I'll go do it right now.

[eaglescout526]

5 minutes ago, SoCalManche said:

Which pin do I check for continuity with T6? I'll go do it right now.

So see where the relay is in the third pic of the second half? Looks like 86 jumps to 85 and goes into T6. I just realized I screwed up the pic alignment but where the relay goes down to the ECU in the diagram, it shows the EGR but it really goes to the area of the ECU diagram marked fuel pump relay which is T6.

[SoCalManche]

 

3 minutes ago, eaglescout526 said:

So see where the relay is in the third pic of the second half? Looks like 86 jumps to 85 and goes into T6. I just realized I screwed up the pic alignment but where the relay goes down to the ECU in the diagram, it shows the EGR but it really goes to the area of the ECU diagram marked fuel pump relay which is T6.

Yes, I see that now. So how do I accurately test that? With a jumper wire between 85 and 86, using that as a point to connect with T6?

[eaglescout526]

Looking at the diagram I think you are just looking for to see if there is a break in the line between T6 and relay terminal 85. So once you get your probes in place, that's when you would do the key on test and see what the volt meter shows for voltage if any voltage goes to the relay.

[eaglescout526]

Does your voltmeter have a continuity test setting? Should be a symbol represented as what looks like sound waves by the dial. That would confirm weather theres a break in the wire(no beep) or not(beep) by the multimeter. But testing for volts is a good thing to check too.

[SoCalManche]

5 minutes ago, eaglescout526 said:

Does your voltmeter have a continuity test setting? Should be a symbol represented as what looks like sound waves by the dial. That would confirm weather theres a break in the wire(no beep) or not(beep) by the multimeter. But testing for volts is a good thing to check too.

I will go check to see if it has that setting, which I'm sure it does. But are you sure it is pin 85? I checked pin 85 to T6, and it was 0V. I checked 86 to T6 and it was a bit wonky for sure, but mV showed up. 

[eaglescout526]

It should be pin 85. TBI book says to check for continuity not necessarily voltage but it didn't hurt to see if the ECU is sending any down the line. I think I have an 86 electrical manual.

[SoCalManche]

1 minute ago, eaglescout526 said:

It should be pin 85. TBI book says to check for continuity not necessarily voltage but it didn't hurt to see if the ECU is sending any down the line. I think I have an 86 electrical manual.

Checked continuity, and the multimeter beep was quite loud and constant, lol. (Sorry neighbors)

[eaglescout526]

Lol good we have continuity there which means no breaks in the harness between the ECU to the relay. Now my 86 electrical manual shows the same as the 88 above but a little bit different but still the same for T6 to the relay. 86 shows to go to the B splice and is triggered by the ignition switch. 30 on the relay is power from fusible link F. 87 goes to splice K which seems to power a few different things. I will have to get a good pic of it in the morn.

[SoCalManche]

3 minutes ago, eaglescout526 said:

Lol good we have continuity there which means no breaks in the harness between the ECU to the relay. Now my 86 electrical manual shows the same as the 88 above but a little bit different but still the same for T6 to the relay. 86 shows to go to the B splice and is triggered by the ignition switch. 30 on the relay is power from fusible link F. 87 goes to splice K which seems to power a few different things. I will have to get a good pic of it in the morn.

Sounds good. If you keep showing me which things to test, I'm sure we could find the gremlin. And I'd be more than happy to buy you a few Venmo beers to say my ultimate thanks.

[eaglescout526]

Lol no worries. We will find it. We will just keep running down the diag list until we get somewhere.