1993 Ford Explorer Fuel Pump/PCM Problem? | Ford Explorer - Ford Ranger Forums - Serious Explorations

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1993 Ford Explorer Fuel Pump/PCM Problem?

Robert3916

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November 8, 2007
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City, State
Ann Arbor, Michigan
Year, Model & Trim Level
1993
While driving through a construction area, My Explorer quit working. Tested for fuel
pressure with key on, no pressure. (New fuel filter) Removed tank, tested fuel
pump, powers on. Tested lead into fuel pump, 6 volts, not 12. Tested all leads
up to and including Fuel Pump Relay(replaced relay too) still 6 volts not 12. Fuel Pump Relay In, is 12 Volts, but Out to fuel pump is 6 volts. I discussed problem with a Mechanic over the schematics of the system, and that he said that the PCM that has a direct connection to the Fuel Pump Relay out connection may be causing a load to drop the voltage down to 6 volts.
Is there another component in system causing the PCM on another connection, to cause a load on the connection from the PCM to the Fuel Pump Relay to be 6 volt and not 12 volts. How can I test the PCM to see if it
is bad? (I am told scan tools will not catch this problem sense no check engine light is on. Not an emission problem?)

Thanks Robert3916
 


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BrooklynBay

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MrShorty

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I don't quite understand the details (I'm not familiar with solid state electronics), but that 6V is normal, and comes from the PCM via the fuel pump monitor circuit. If you need to confirm, this has come up many times here, and a quick search of the site should yield several hits.

Other than that, the fuel pump circuit is fairly simple DC electricity. Where the voltage drop is is where the problem is. So this:
Fuel Pump Relay In, is 12 Volts, but Out to fuel pump is 6 volts.
means that the fuel pump relay is open. Were these tests performed at a time when the relay should have been closed? When the engine isn't started, the relay is only closed for a couple of seconds, and then opened until the engine rotates. Again, this has been described in more detail previously.

My personal preference at this point would be to repeat those two voltage measurements, after grounding the fuel pump test lead (key on) which should close the relay. If the relay still doesn't close (no change in results), then investigate why the relay isn't closing. If the relay closes, continue searching elsewhere in the fuel pump circuit.
 












Robert3916

Member
Joined
November 8, 2007
Messages
10
Reaction score
0
City, State
Ann Arbor, Michigan
Year, Model & Trim Level
1993
I don't quite understand the details (I'm not familiar with solid state electronics), but that 6V is normal, and comes from the PCM via the fuel pump monitor circuit. If you need to confirm, this has come up many times here, and a quick search of the site should yield several hits.

Other than that, the fuel pump circuit is fairly simple DC electricity. Where the voltage drop is is where the problem is. So this: means that the fuel pump relay is open. Were these tests performed at a time when the relay should have been closed? When the engine isn't started, the relay is only closed for a couple of seconds, and then opened until the engine rotates. Again, this has been described in more detail previously.

My personal preference at this point would be to repeat those two voltage measurements, after grounding the fuel pump test lead (key on) which should close the relay. If the relay still doesn't close (no change in results), then investigate why the relay isn't closing. If the relay closes, continue searching elsewhere in the fuel pump circuit.
Thanks
 




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