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HELP fuel pump relay 1993 expl

brandonf51780

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recently I had a problem with the fuel pump on my 1993 ford explorer. The pump did not kick on. After replacing the fuel pump it still did not start. When i played with the relays "ECC and Fuel pump". plugging the in and out with the power on, I finally heard a click in the relay and truck started. Moments later the truck is stranded again. I am unable to replicate the relay "kick-in".

Could this be a wiring issue?
I have swaped relays around in the box several times to no avail....
What should i look for?

voltage at relay is- North plug 12v - West plug 12v (when key on)

at inertia switch 7v ?????
 
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MrShorty

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The 7 V you are seeing at the inertia switch is a "ghost" voltage that is generated by the PCM for some reason (I'm not real good with solid state electronics so I don't know why it is there). Basically, it tells me that the connection between the inertia switch and the fuel pump monitor circuit is probably ok, but that power isn't getting beyond the relay. Whether that is because the relay is bad, or some other wiring problem is preventing the relay from closing, or other, I don't know.

I would suggest you get a wiring diagram (even the one in Chiltons is good enough for troubleshooting the fuel pump and EEC relays), then determine if power is getting to the fuel pump relay from the fuel pump fuse and from the EEC relay.
 
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MrShorty

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When the pump comes on, is it generating sufficient pressure (40 psi)?
 
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brandonf51780

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not sure, i will have to get a fuel rail tester to know. When i do so ill get back too you. I did code it again and instead of a code 556 *which is gone now
I get a code:
542 & 543
 
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MrShorty

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KOEO or CM codes?

542 and 543 both point to some fault (or faults) in the fuel pump circuit. If they are KOEO codes, that means the fault(s) exist(s) at the time of the test, if they are CM codes, that means the fault occurred during operation, but may not be currently present.

It looks to me like we are still looking at the fuel pump circuit.
 
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brandonf51780

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Well first i want to say thank you for the resulting posts.
The Fuel codes 542 and 543 were CM codes. I beleive these happened about when the motor ran after i switched the fuel pump. Shortly after this last startup, the no-start began again.

I recently cleared the codes and rechecked showing a two orginal codes 116 CTs and 114 IAT. No other fuel circuit related codes...... Still need to get a fuel rail tester...... after that, voltage tests round the truck?
Also,
I Just grounded the fuel pump connection. Relays and fuel pump started and ran continus. I tried to start the truck while this was grounded..... Hope it was ok to try, although the truck did not start.... any input?
 
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MrShorty

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KOEO 116 and 114 are to be expected in a no start - they indicate that the engine was cold, which is pretty obvious if it won't start.

If the fuel pump is coming on, then yes we will want to know if it is generating enough pressure.

Have you done anything to verify spark at the plugs?
 
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