Prove it with a picture
#1
01-02-2020, 01:52 PM
Prove it with a picture
I was wondering if anyone out there with a running 97 - 03 would be willing to put their truck in KOEO, pop the hood, run a multimeter from the neg battery terminal (good ground) to pin 87 on the fuel pump relay socket and snap a pic of the voltage reading. I've seen posts that insist all of the following: 0 or 6 or 6.7 or 6.8 or 10 or 12. Perhaps someone can put it all to rest with a pic.
#2
01-02-2020, 02:46 PM
Under your conditions of KOEO there will be no significant voltage to the fuel pump shown on an Analogue meter. A DMM meter might show something that is of no consequence in a fault free circuit. It's no different than any other circuit such as Brake lights, Heater motor etc.
Reason:
12 volts from fuse 10 goes to the fuel pump relay contact.
From the relay second contact to the Crash Sensor contact then to the Fuel pump.
This relay is NOT operated under your specified conditions therefore no operating voltage will be present at the fuel pump.
A lead, in the pair, from the fuel pump, is the ground and terminates to ground point in the Cab behind the driver kick panel. If this ground is corroded, the pump may not run reliably.
If the Crash Sensor has been tripped, is faulty or leads unhooked, the pump will not run under any conditions by design so the pump can not feed a fire under accident conditions.
.
Further; the relay will operate under control of the PCM Timer circuit for about 3 seconds at ignition turn on, then open the relay by the time you do any measurement.
If there is a second person or a voltmeter is hooked up, you will see the voltage come On for the duration of the Timer, then go off when the Timer times out and the relay contacts open.
This is normal operation under 'initial' key on only conditions each time. You can prime the fuel rails/engine this way if the tank runs out of gas, then fuel is added.
.
When you begin to Crank the engine, the Crank Sensor signal will cause the PCM Timer to 're-operate' the fuel pump relay, powering up the fuel pump 'full time'.
This is the minds picture you need of the operation.
Good luck.
Reason:
12 volts from fuse 10 goes to the fuel pump relay contact.
From the relay second contact to the Crash Sensor contact then to the Fuel pump.
This relay is NOT operated under your specified conditions therefore no operating voltage will be present at the fuel pump.
A lead, in the pair, from the fuel pump, is the ground and terminates to ground point in the Cab behind the driver kick panel. If this ground is corroded, the pump may not run reliably.
If the Crash Sensor has been tripped, is faulty or leads unhooked, the pump will not run under any conditions by design so the pump can not feed a fire under accident conditions.
.
Further; the relay will operate under control of the PCM Timer circuit for about 3 seconds at ignition turn on, then open the relay by the time you do any measurement.
If there is a second person or a voltmeter is hooked up, you will see the voltage come On for the duration of the Timer, then go off when the Timer times out and the relay contacts open.
This is normal operation under 'initial' key on only conditions each time. You can prime the fuel rails/engine this way if the tank runs out of gas, then fuel is added.
.
When you begin to Crank the engine, the Crank Sensor signal will cause the PCM Timer to 're-operate' the fuel pump relay, powering up the fuel pump 'full time'.
This is the minds picture you need of the operation.
Good luck.
Last edited by Bluegrass; 01-02-2020 at 02:49 PM.
#5
01-02-2020, 09:15 PM
This certified Ford tech with 30 years experience says it should be 12v. https://www.justanswer.com/ford/424g...rate-fuel.html. I found a LOT of other posts that don't match what Bluegrass wrote. I'm not getting zero when I test it.
A picture taken by someone who knows what they are doing would probably help a lot of people because it would be definitive proof that it should be zero and not 12 or 6 or 6.7 or 6.8 or 10.
Take a pic and show me, and I'll return the favor and upload a pic of mine that shows it's not zero. Then we can discuss it, and the thread might turn into something helpful for more DIY-ers out there who are lost.
A picture taken by someone who knows what they are doing would probably help a lot of people because it would be definitive proof that it should be zero and not 12 or 6 or 6.7 or 6.8 or 10.
Take a pic and show me, and I'll return the favor and upload a pic of mine that shows it's not zero. Then we can discuss it, and the thread might turn into something helpful for more DIY-ers out there who are lost.
