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weird fuel pump problem


redneksoldier

redneksoldier

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Ok, so I'm a bit puzzled. I've got a '03 4.0. The fuel pump is good. When you turn the key on (koeo) the fuel pump doesn't prime. If you proceed to crank the engine, the fuel pump will come on and after a couple of seconds it will start and run as normal. No loss of power, stumbling dieing etc. Any ideas what would cause it to not prime before cranking?
 


cp2295

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Do you have any issue starting (ie long cranking time) or do you feel a quick power loss on the freeway then power returns within a second or two?
 
redneksoldier

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It takes a couple seconds of cranking to get it to fire, but no power loss once it's running. That's the main reason I noticed that there is a problem. It used to fire right up if you just barely bump the starter.
 

RonD

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I would reboot the computer(PCM), unhook Negative battery cable for 5 minutes.

Then retest.

Also pull out the Fuel Pump Relay(in power box) and visually inspect connections then reinsert it.

I think the '03 PCM connection is located in upper center of firewall(engine side), on some years they had water issues and add a cover plate, unhook battery and remove connector, check it for moisture.

Long shots would be the Battery Saver relay or Anti-theft system, not sure battery saver can cut power to fuel system??
Reboot of computer should reset anti-theft system.
 
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redneksoldier

redneksoldier

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Thanks for the suggestions. I will look into the Battery saver and anti-theft. First, I will pull the PCM connector, make sure it's clean and pack that sucker with some silicon electric grease to keep future moisture out. By the time I finish that, the pcm and anti-theft should be reset and then we will see what happens. Funny thing is that when you turn the key on, I can hear the relays cycle like they should but its too hard to tell which ones. I will look into this further as I go.
 

RonD

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There are two relays in the power box that should click with key on.
EEC(ECM/PCM) relay, it also provides power to Fuel Pump Relay coil.

Fuel pump relay, it is controlled by the PCM by grounding, EEC relay provides this relay's coil 12volts, PCM provides the Ground to turn fuel pump relay on and off.
PCM also monitors Fuel pump power, when fuel pump relay closes 12volts is sent to inertia switch(then fuel pump) and to PCM, so PCM will usually turn on CEL(check engine light) if there is a problem with this circuit.
 
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