ecm electrical gurus

Have posted before about my power to the fuel pump problem, takes 2-3 minutes once the key is on for the fuel pump to start sputtering on. So I have replaced everything in the fuel circuit and same thing continues. Been searching and performed the fuel pump relay voltage test and here are my results.

Battery reads 12 volts
fuel pump relay
Terminal 86 + at 12 volts when ignition immed turns on.
Terminal 85 is not grounded with ignition on....
I jump 30 and 87 and the pump turns on immediatly.

So I put the negative lead for my volt meter on 85 and positive on 86 and turn the key to on. I wait 2-3 minutes as I hear the ASD start to click. It slowly and painfully builds up to 12 volts over the 2-3 minutes.....


So either the wires from the ECM to 86 or the ECM itself is bad...Does this sound right? Thanks in advance for any help

Yeah man, find that wire directly coming from it's source(86)...reference the voltage from there.

Wht year was it?

Sorry 92 xj 4.0 auto

One thing to get out of your mind is the ECU is not bad. You have a bad ground or connection somewhere. Check the red wire coming from the positive battery post and the ones on the starter relay.
I would also look for a bad ground on the ECU or a bad connection in one of the plugs.
That coming on slow is caused by a connection thats bad and when power goes through it it gets hot, it just keeps getting hotter until it finely makes connection.

I have replaced the battery cables and ground on the back of the engine yesterday, I ahve checked the grounds on the side of the block and have continuity through all of them. I am going to follow the dkblue/yellow wire that runs from the ecu to the fuel pump relay at terminal 85. Maybe there is something in that line that is bad. I know its rare that ecus go on these vehicles, but this one does have 300k miles on it. Things happen

DVM04 said:

I have replaced the battery cables and ground on the back of the engine yesterday, I ahve checked the grounds on the side of the block and have continuity through all of them. I am going to follow the dkblue/yellow wire that runs from the ecu to the fuel pump relay at terminal 85. Maybe there is something in that line that is bad. I know its rare that ecus go on these vehicles, but this one does have 300k miles on it. Things happen

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Solid state outputs either work or they don't so coming on slowly is not the ECU
Looking at the schematics I would suspect a bad ignition switch.

Ok there is 950ohms of resitance from terminal 85 to pin 51 on the ecm the dark blue/yellow wire that runs between them. Sounds a little high, going to check that wire and see what I can see.

Delete the previous post the resitance is zero from the ecu connector at 51 to the fuel pump and asd relay. pin 51 to terminal 85, the line is working correctly. SO I have power to 86 and the line is working to 85, but still takes time to build up power at the fuel pump relay, so I am going to wait until it gets cold and try the resistance again.

Langer, thanks for the replys. So far I have replaced the fuel pump, fuel pump and asd relays, the bypass relay, the fuel pump ballast, ignition switch, the firewall to engine ground, positive and negative cables, the postive cable to the pcm, and all the fuses in the pcm. same thing happens, turn the ignition to on, only when its cold, and it takes time for the fuel pump relay to start getting power, I could have sworn this was a ground problem but I cant think of anything else, hence the reason I moved to the ecu....ecpecially cause last night I had power to 86, but when I connected the volt meter from 85 and 86 I could watch the volts rise to 12 as the fuel pump powered on in the background. If I have power to 86, it leads me to 85 being the problem, if the wire for 85 checks out, the only ting before that is the ecu....

There is no relay in the ecu that needs to warm up? Its far fetched, but hell I am out of suggestions.

You do know that the ECU grounds the DK blu-yel wire to turn the relays on?

Yes I realize that, that is why I am asking if the ecu could have a relay in it that is slow to close. If I have power at 86 with the ignition on and still nothing between 85 and 86 it leaves me to believe that the problem is between before 85, ie the wire that goes to pin 51 or the ecu. The wire checks out, so that leaves me with a ground issue or the ecu, I cant find anymore grounds to replace.

There's no relays in it.

As for bad grounds you really need to remove and clean them, you may not catch them with a meter, also clean the one from the head to the firewall.

Just replaced the firewall to the engine ground yesterday, I have been sanding the contact area and applying dielectric grease. The +/- cables are new as are the grounds from the battery to the body. The only ground I have not touched is the ecu ground to the body...

Well cleaned the ecu ground and pulled all the tape off the wiring at the ECU and the PCM. So all the grounds are new or clean...Same thing happens.

Today its below freezing and I waited 7 minutes for the fuel pump to start powering up. All the wires grossly look normal at the ecu and pcm. 2 questions...

Where are the ignition fusible links located? They are not clearly marked on diagrams. I have looked at the 3-2 blue colored wire bundle that powers terminal 85 and 86 of the fp and asd relays, looks good, I am just going to start replacing them cause I am not getting anywhere.....

What about a problem with the starter solenoid or the ignition key tumbler? I am running out of theories here and I refuse to take the jeep somewhere for someone to fix this problem. I would rather pay one of you for a lucky guess.

I wonder if the ECU is waiting for somthing to reset?

Thats why I am wondering about the fusible links, maybe the ecu is slow to power up. All the wires look grossly normal that is why I want to start replacing stuff.....

I am going to look at the starter solenoid wiring first. I am runnign out of thoughts here....

DVM04 said:

Thats why I am wondering about the fusible links, maybe the ecu is slow to power up. All the wires look grossly normal that is why I want to start replacing stuff.....

I am going to look at the starter solenoid wiring first. I am runnign out of thoughts here....

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A couple of questions.
Do you have the Bypass relay?
What codes do you have?

ballast bypass relay?, yes, brand new from jeep. And no codes of course, that would be easy....

DVM04 said:

ballast bypass relay?, yes, brand new from jeep. And no codes of course, that would be easy....

Click to expand...

Do you have keyless entrey or Anti-theft?