ECM question
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Joined: Apr 2010
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ECM question
Hello again, wanting to enquire as to whether or not a malfunctioning ECM could cause the electric fuel pump on a 1999 f-150 4.6 not to operate? Also would appreciate if some one has the wiring diagram of the fuel pump circuitry?
Senior Member
Joined: Jul 2004
Posts: 6,200
Likes: 39
From: Easton, Pa.
The fuel pump is 'activated' by a slave relay. through a crash sensor.
The slave relay is operated by the PCM.
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The slave relay has separate fused power to supply the pump.
The circuit goes through a crash sensor located at the top area of the passenger side kick panel. Check that it is not tripped.
.
The PCM operates the slave relay from an internal timing circuit.
It is easy to tell if this is working providing the rest of the circuit is not in fault.
When you turn on the ignition, the pump should run about 3 seconds off the timer then stop. A pressure gauge on the fuel rail would also show the build up of fuel pressure with 3 key on cycles.
.
At cranking, the timer re-operates the fuel pump full time when the crank sensor sends it's signal; to the PCM.
So you have a relay, a fuse, Sensor and a PCM power relay to check out before considering a PCM, wire or pump fault.
Look in your owner manual at fuse and relay assignment locations in the engine bay box.
Using logic from above operations you should be able to see what part of the function is at fault without an electrical schematic to start with..
Good luck.
The slave relay is operated by the PCM.
.
The slave relay has separate fused power to supply the pump.
The circuit goes through a crash sensor located at the top area of the passenger side kick panel. Check that it is not tripped.
.
The PCM operates the slave relay from an internal timing circuit.
It is easy to tell if this is working providing the rest of the circuit is not in fault.
When you turn on the ignition, the pump should run about 3 seconds off the timer then stop. A pressure gauge on the fuel rail would also show the build up of fuel pressure with 3 key on cycles.
.
At cranking, the timer re-operates the fuel pump full time when the crank sensor sends it's signal; to the PCM.
So you have a relay, a fuse, Sensor and a PCM power relay to check out before considering a PCM, wire or pump fault.
Look in your owner manual at fuse and relay assignment locations in the engine bay box.
Using logic from above operations you should be able to see what part of the function is at fault without an electrical schematic to start with..
Good luck.
Technical Article Contributor
Joined: Jan 2007
Posts: 10,636
Likes: 264
From: Vernon, NY
A key tool to be using is is a digital multimeter to see if you are getting the correct voltage.
For all we know you could have a wiring issue, such as a bad ground or a broken wire.
Start following wires and carefully check.
Good luck.
For all we know you could have a wiring issue, such as a bad ground or a broken wire.
Start following wires and carefully check.
Good luck.
Senior Member
Joined: Oct 2002
Posts: 7,295
Likes: 125
From: St. Louis (Out in the woods)
There's a reason that troubleshooting is necessary.
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Member
Joined: Apr 2010
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Thanks for all the replies!! I found the problem to be a broken wire right at where it enters the white plastic wire retainer on the top of the fuel pump assy.. There is barely enough wire exposed to solder a wire on and no room to solder if there was. Going to drain the tank, drop it and install a new pump from ebay.