We're having problems with our motorhome. Its a 1989 Pace Arrow on a Ford F53 chassis with the 460. It was running fine until my father swapped the engine battery on it. Now the fuel pump is not getting power. I have not been able to find any fuses, or fuse links that are bad. The problem is the green fuel pump relay is not getting 12v switched power. I can jump power from the battery to the relay and the fuel pump will come on. I have traced the red 12v switched wire back to the computer and the wire is good. Like I said the motorhome ran fine before swapping batteries, so I'm assuming there was an arc that cooked something. Could the computer be dead? I also cannot get the computer to go into test mode with my OBD I scanner. Thoughts?
Ford fuel pump relay not getting power?
- Thread starter nwjones18
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The computer ECM or IRCM (engine control modules) or BCM (body control module) turns on power (PCM power control module) to relays and diag.
(I don't which specific computer is used on your motorhome).
The combination of symptoms ( no diag mode and and no relay power) is a symptom of failed computer module, computer power supply, or bad battery voltage.
Turn ignition key to "on" without starting. All warnings lights and gauges should be on. If engine warning lights are not lit, then this will also confirm a computer module failure or bad battery voltage.
Could be as simple as new battery is not fully charged, (computer will not turn on without correct voltage) so measure battery voltage or try different battery.
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1987 Toronado
1999 Olds GLS
(I don't which specific computer is used on your motorhome).
The combination of symptoms ( no diag mode and and no relay power) is a symptom of failed computer module, computer power supply, or bad battery voltage.
Turn ignition key to "on" without starting. All warnings lights and gauges should be on. If engine warning lights are not lit, then this will also confirm a computer module failure or bad battery voltage.
Could be as simple as new battery is not fully charged, (computer will not turn on without correct voltage) so measure battery voltage or try different battery.
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1987 Toronado
1999 Olds GLS
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I know the EEC relay (brown relay right beside green fuel pump relay) powers up and 'clicks' when the ignition is turned on. I have swapped both relay's with the ones on my bronco and they are fine. The engine turns over strong, but I have not actually tested tested the battery, but will do that. I wasn't with my dad when he put the battery in, but I doubt he would have hooked it up backwards..
If it's cranking strong you don't have a battery problem...
In the Ford systems I've worked with the PCM provides power for the F/P relay, but just because the PCM relay clicks, does not necessary mean the F/P relay will receive power or even provide power to the PCM... There is generally a fuse or fuse wire in the circuit the feeds the contacts that are independent of the coils... Some versions did place the inertia switch in the relay control(coil) circuit so possibly it could be tripped...
If you can ground the outer terminal on the test connector marked fuel pump and pump runs, you have a fried PCM or it's not getting voltage...
In the Ford systems I've worked with the PCM provides power for the F/P relay, but just because the PCM relay clicks, does not necessary mean the F/P relay will receive power or even provide power to the PCM... There is generally a fuse or fuse wire in the circuit the feeds the contacts that are independent of the coils... Some versions did place the inertia switch in the relay control(coil) circuit so possibly it could be tripped...
If you can ground the outer terminal on the test connector marked fuel pump and pump runs, you have a fried PCM or it's not getting voltage...
Originally Posted By: eljefino
Does this bus have the collision inertia switch? That might have tripped.
Exactly what I was thinking.
Does this bus have the collision inertia switch? That might have tripped.
Exactly what I was thinking.
There usually is an extra ground wire to the computer at the battery. Peek around for it - maybe left off or the connector not plugged in?.
Re clean and check the integrity of all connections at the battery.
Start from square one.
Re clean and check the integrity of all connections at the battery.
Start from square one.
Well I have tested the collision switch and it seems to be working, also grounding the fuel pump test pin will not turn on the fuel pump. I'm getting no check engine lights when the ignition is switched on, so I'm thinking the computer isn't getting power or is toast. I'll check to see if I'm getting 12v off the eec relay and report back. Thanks!
Got a 'box' with lots of relays on the vehicle? [A CCRM]
Bad soldered connections or a faulty relay are common problems.
Bad soldered connections or a faulty relay are common problems.
Originally Posted By: nwjones18
I'm thinking the computer isn't getting power or is toast. I'll check to see if I'm getting 12v off the eec relay and report back. Thanks!
If all the wiring, relays, fuses, etc are good, you can toss the computer into the street and the pump will run with the test point grounded... Keep checking...
I'm thinking the computer isn't getting power or is toast. I'll check to see if I'm getting 12v off the eec relay and report back. Thanks!
If all the wiring, relays, fuses, etc are good, you can toss the computer into the street and the pump will run with the test point grounded... Keep checking...
I just thought I'd update. It turns out the computer wasn't getting power. I do not know how its possible but something actually happened with the wiring when the new battery was installed, a short or something. I ended up rewiring power to the ECC relay and from the computer to the fuel pump relay and everything seems to be working.. Wiring is a nightmare on a motorhome.. Hopefully the fix works.
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