Electric Fuel Pump ECU Ground Path

[Hunter#1]

I have a VZ250LTR that the VST Electric Fuel Pump is not kicking on at key on, or will kick on intermintely. I suspected that the electric fuel pump relay was faulty, but after further troubleshooting that is not the problem. I have 12V on the pumps red lead when I ground directly to the negative battery terminal, but when I put my ground lead on the blue wire on the pump leads the voltage goes to zero. So as I understand that blue lead is path to ground through the ECU.

Anyone have a tip as to what might be the problem with no ground? I did remove the stop laynard and reconnect it to rule that out. Doesn't mean something isn't wrong in the alarm circuit though. I didn't try cranking with the stop laynard removed to see if I got an audible alarm while cranking. I ran out of day light but will try that tomorrow...........

[Hunter#1]

Anyone......?

[rodbolt17]

the pump blue wire is the ground path, it goes to the ECU.
make sure all the connections are good.

[Hunter#1]

the pump blue wire is the ground path, it goes to the ECU.
make sure all the connections are good.

And if the connections are good on that blue wire? Bad ECU?

[Hunter#1]

While standing there scratching my head wondering what is going on, after about 5 minutes with the key on and literally not touching anything the electric fuel pump kicks on all by its lonesome.

I am really at a loss as to what is going on with this thing. I had 12v up to the electric fuel pump on the red lead side, and no ground on the blue wire so the pump would not kick on as described in the OP. Then, poof its on after sitting for a while with key on. Is that thing timed or something to cycle on and off if the key is on and motor is not started? This is driving me nuts.

[Hunter#1]

This is really becoming frustrating. Yesterday at the end of the day the electric fuel pump was coming on with key on (although I did nothing to fix it from not having come on). Now, this morning after sitting overnight it no longer is getting a ground on the blue wire, again. So I once again have no electric fuel pump at key on. This thing is doing all this on its own without being touched. One time it works, the next it don't. How in the hell are you suppose to troubleshoot something like this. It's maddening.

[rodbolt17]

not madding.
its you aint gotta clue.
drop a dime and buy one.

that ECU is sitting there all alone in the dark.

then some one turns the key.

the ECU gets a wakey wakey call and supplies a 3 sec or so pump ground.

go find your bad connection.

yea learning how to use a multi meter suxs.

yea I have been beat on by both civilian instructors and military instructors.

but if ya don't know how and what to check. your simply sunk.

that's the whole key to trouble shooting, know whats supposed to happen and what does.

[TownsendsFJR1300]

IE, disconnect the blue wire on both ends and attach a multi-meter for continuity. Start at one end and follow to the other end until you find a bad connection/the meter shows no connection.

You may have to jiggle, bend the wires some but as bad as yours is, it shouldn't be hard to find..

I've found bad wires where the external insulation looked fine but we had a bad connection. Started moving the suspect wire and found one short spot, roughly in the middle that was the issue(no connectors there, no crimps, straight wire). Cut that section out and opened it up. Corroded out completly although the outside looked fine.

[rodbolt17]

without having the harness diagram in front of me I cant say if the keyswitch powers up the fuel pump relay or the ecu powers it up.
but until the ecu wakes up(gets that 12v signal from the switch) that pump remains off.

[Hunter#1]

not madding.
its you aint gotta clue.
drop a dime and buy one.

that ECU is sitting there all alone in the dark.

then some one turns the key.

the ECU gets a wakey wakey call and supplies a 3 sec or so pump ground.

go find your bad connection.

yea learning how to use a multi meter suxs.

yea I have been beat on by both civilian instructors and military instructors.

but if ya don't know how and what to check. your simply sunk.

that's the whole key to trouble shooting, know whats supposed to happen and what does.

I have been looking Rod. I have a multimeter, and I do know how to use it. Your arrogant post was helpful, thanks. You do this crap everyday, some of us do not. Knowing what is suppose to happen, and what does happen is a lot easier when you have been doing this for twenty years and you have had formal OEM training provided to you. I guess you forget whats it is like to really need help with something and then have an expert in the field come along and just want to belittle you because you do not know how to do something. Thanks again for the help.

[Hunter#1]

without having the harness diagram in front of me I cant say if the keyswitch powers up the fuel pump relay or the ecu powers it up.
but until the ecu wakes up(gets that 12v signal from the switch) that pump remains off.

When the key is on I have 12V on the red wire at the pump. The blue ground wire to the ECU has an open somewhere which I haven't found yet. Hard to find it when it starts working again on its own.

[Hunter#1]

IE, disconnect the blue wire on both ends and attach a multi-meter for continuity. Start at one end and follow to the other end until you find a bad connection/the meter shows no connection.

You may have to jiggle, bend the wires some but as bad as yours is, it shouldn't be hard to find..

I've found bad wires where the external insulation looked fine but we had a bad connection. Started moving the suspect wire and found one short spot, roughly in the middle that was the issue(no connectors there, no crimps, straight wire). Cut that section out and opened it up. Corroded out completly although the outside looked fine.

Thank you for your patience with my ignorance and the suggestion. It's helpful. I'll go try that.

[TownsendsFJR1300]

Thank you for your patience with my ignorance and the suggestion. It's helpful. I'll go try that.

Yep, if you have 12 volts there, you need a ground for it to go to which apparently your loosing.

For the meter, find a setting where you hold the probes together and it registers/beeps, etc. That's the setting you want.

It would be easier if you had another set of hands to help hold the probes and watch the needle/digital screen as you work your way from the pump.

Good luck, you'll find it...

[Hunter#1]

Yep, if you have 12 volts there, you need a ground for it to go to which apparently your loosing.

For the meter, find a setting where you hold the probes together and it registers/beeps, etc. That's the setting you want.

It would be easier if you had another set of hands to help hold the probes and watch the needle/digital screen as you work your way from the pump.

Good luck, you'll find it...

That blue wire isn't but a foot long. I really think there is something telling that ECU to not allow the ground path to close. I just jumped the electric fuel pump wire terminals on the VST to the battery to ensure the pump is still operable. It is. Now after having done this and with the jumper wires removed the pump is again now coming on with key on. Besides stating the obvious, can anyone tell me the function of the fuel pressure sensor and if it were faulty would it prevent the ECU from allowing that electric fuel pump from kicking on? This problem with an open in the electric fuel pump circuit is intermittent. At the end of day its operable, but by following morning after sitting overnight or other long periods it is not. I'm curious about that fuel pressure sensor and what exactly is its purpose in the circuitry.

[TownsendsFJR1300]

IDK, someone else, Boscoe or RB will have to answer that..