Fuel pump voltage

joeb1300

Member
Can someone tell me if the ecm has anything to do with voltage to fuel pump?
I have a hot wire kit which i have 13 volts. My main voltage to from relay reads 9 volts. I have 13 volts going into relay under hood. Changed relay still no fuel pressure. 3 month old walbaro pump so I don't think that is it. Relay at take does not switch. Is this because of lack of voltage? Going crazy . added data logger lost my fuel gauge reading and the next day 0 fuel pressure.

Is the white wire next to the ac compressor my fuel pump check wire?
 

gunzandgearz

gearzandgunz
That's not exactly correct, you can have voltage all day long down to the load ie fuel pump blower motor anything that carries a load ,light bulb injector whatever. if you take the ground away you still have voltage it just wont operate the that load.This is what messes a lot of even good technicians up is the ground side. T he first thing that I would want to determine is if the new pump is bad, it happens more than it should. check for voltage as close to the pump as possible, I like to use a bed of nails which has small little needle type nails made for this type of electrical diagnosing so it doesn't expose the wire to moisture, which will haunt you later.if you have voltage to the pump then either the pump is bad or it is a bad ground.now you can run a jumper wire from pump ground side [wire] as close to pump as possible, over to the battery negative post and see if pump turns on,if it doesn't the pump is bad if it does its a bad ground.If you don't have voltage down to pump you need to do a voltage drop test back towards source until you find where you lost your voltage.
 

gunzandgearz

gearzandgunz
Sounds like dynoman has you headed in right direction, something else you can try is checking the voltage on the ground side with a meter, if you have more than half of a volt on ground side with meter reading then you have a bad ground.
 

gunzandgearz

gearzandgunz
I agree with that nick, the ground side always gets least amount of attn.. and is always first to screw everyone up.
 

bison

Moderator
Staff member
That's not exactly correct, you can have voltage all day long down to the load ie fuel pump blower motor anything that carries a load ,light bulb injector whatever. if you take the ground away you still have voltage it just wont operate the that load.This is what messes a lot of even good technicians up is the ground side. T he first thing that I would want to determine is if the new pump is bad, it happens more than it should. check for voltage as close to the pump as possible, I like to use a bed of nails which has small little needle type nails made for this type of electrical diagnosing so it doesn't expose the wire to moisture, which will haunt you later.if you have voltage to the pump then either the pump is bad or it is a bad ground.now you can run a jumper wire from pump ground side [wire] as close to pump as possible, over to the battery negative post and see if pump turns on,if it doesn't the pump is bad if it does its a bad ground.If you don't have voltage down to pump you need to do a voltage drop test back towards source until you find where you lost your voltage.
If you take away the ground path you have no electron flow and nothing happens. Try it sometime.


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gunzandgearz

gearzandgunz
so if I cut the ground wire in a working circuit and I check for voltage on positive wire running to that circuit I lose that too,HMMM.
 

bison

Moderator
Staff member
so if I cut the ground wire in a working circuit and I check for voltage on positive wire running to that circuit I lose that too,HMMM.
Hmmm. If you are checking voltage you are completing the circuit with your meter. Holding the lead on the positive wire without grounding will show the big donut. No ground, no electron flow. Sorry but you can't change physics.


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achalmersman

Well-Known Member
What Bison is saying is correct, and what gunz is trying to say is technically correct.

If you open the ground path there will be 0 potential across the load. If you measure from the ground side of the load to actual ground you will measure voltage (potential due to open ground).

This is the same principle that screws with people that say you "can't get shocked by the neutral". In a 120VAC application if you open the neutral and measure from the load side neutral to ground you will measure 120V and will get shocked if you touch it
 

gunzandgearz

gearzandgunz
The problem that were getting into here is if you are trying to tell someone how to check for something that's not working and they aren't that savvy with electricity and you tell them they will have no voltage to the load ie fuel pump, if there is a bad ground and he checks the power wire will he have power down to the pump, your dang right he will. what bison is saying isn't correct because he is talking about electron flow which is not the same thing as voltage and not even measured the same way.now if he said there would be no current flow then that would be correct but it wouldn't even be measured with a voltmeter it would be measured with an ammeter.
 

achalmersman

Well-Known Member
Instead of measuring positive lead to ground they should measure at the load, or as close as possible across the load. You are correct. Measuring the positive side of the load to the frame or body will throw some people. But if the ground was open and you measure across the leads for the pump you will measure 0V unless the open is in the tank in which case your pulling the tank anyway. Verify continuity when the tank is down at that point and replace pump if bad.
 

dynoman

Well-Known Member
This is why I sent the OP to the other thread where I explained how to check for power & bad grounds . I have beven doing this for 43 yrs and assume that the people asking don't know the proper way to troubleshoot , so I try to keep it simple.
 
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gunzandgearz

gearzandgunz
I agree with both of you,when you have guys that aren't that familiar with troubleshooting electrical it has to be kept simple.
 
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