Fuel pump going out? - Ranger-Forums - The Ultimate Ford Ranger Resource


4.0L OHV & SOHC V6 Tech General discussion of 4.0L OHV and SOHC V6 Ford Ranger engines.

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Old 06-08-2015
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Fuel pump going out?

I have a 2003 Ford Ranger Edge 4.0 v6 SOHC and after it sits for over an hour it is really hard to start again. It will just crank for a long time then finally fire up. Once it starts there's no issues. Before the starting issues started happening when the temperature is below freezing as soon as it started cranking the doors would lock. Any one have suggestions on the problems?
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Old 06-08-2015
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Reads like you are loosing fuel pressure when it sits.
'03 is a returnless system so unless your MPG has gotten really bad or you smell gas, then the problem is probably in the fuel tank.
Fuel pump sits at the bottom of the tank, on its output port is a Check Valve, it is part of the pump, this valve allows fuel to flow out but not back in.
So when the pump is off this valve would hold pressure in the system, 65psi of pressure in an '03.
Connected to the Check valve/port is a rubber hose that goes to the top of the tank, and connects to the access panel of the tank.
This hose can crack or connectors can leak, either would cause pressure to drop after pump is off.

First a little about how Ford(the computer) runs the fuel system then a test you can run.
When you turn on the key, the fuel pump will run for 2 seconds and only 2 seconds, this is to Prime the system, but it only adds about 15psi of pressure, that is more than enough if there are no leaks.
The fuel pump will not come on again until engine RPMs are above 500, so not until engine starts, you can crank the engine until the battery dies, the fuel pump will not come on again...................unless you turn the key off and then turn it on again.

Try this test:
Turn key on, count to 3, turn key off
Repeat 2 more times, you should have about 45psi now, then try to start engine.
If it fires right up then you will need to go into the tank to see what the problem is.

You can also test fuel pressure with a gauge, to see if it is dropping down to 0 after key is off for awhile.

The 2 second thing is a safety precaution, if a fuel line should break, engine would stall out and fuel pump would shut off, RPMs under 500.
Fuel line could break in a fender bender or ????, but no matter why it broke, continuing to pump fuel out onto the ground is NEVER a good idea, lol.

Last edited by RonD; 06-08-2015 at 11:06 PM.
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Old 06-11-2015
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Yeah it does lose fuel pressure fast. It will drop from 62psi to close to 0psi in less than 10 seconds
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Old 06-11-2015
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If you are not burning alot of extra gas, MPG in the toilet, then it is the check valve in the fuel pump, or leaking fuel line in the tank.
Either way you need to pull out the fuel pump assembly to check it out.
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Old 06-12-2015
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OK thanks. Do you have any reasons why when the temperature is below freezing as soon as the truck starts cranking the door locks go crazy?
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Old 06-12-2015
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I would assume that would be a voltage issue.
Car batteries use a chemical reaction to store and release amps, when temp drops this chemical reaction slows way down so the available amps for the starter goes down.
This will cause voltage to the rest of the systems to drop below 10volts, and as low as 8volts while starter motor is being used.
Relays and the possessors that run them get intermittent when voltage gets low, door locks are run by relays and a processor, especially if you have wireless(key fob) lock/unlock.

New battery should have 12.7 or 12.8 volts with key off
3 year old battery about 12.5volts
5 year old battery about 12.3volts

As time passes the chemicals that hold a charge are getting used up, 5-7 years is expected car battery life

At 12.3 volts a cold morning could cause what you described, at 12.2 volts, or less, you can get the dreaded "click, click, click" of a dead battery if the temp is cold enough.

If your battery voltage is 12.5 or higher then remove and clean the battery terminals, available amps for starter motor is also effected by the connections.

Last edited by RonD; 06-12-2015 at 10:54 AM.
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Old 06-12-2015
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I put a brand new battery in it and it still does it
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Old 06-12-2015
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Then it will be in the wiring/connections.

You can do a Load test with volt meter at battery, disable spark by unplugging coil or disable fuel by unplugging fuel pump relay(in engine fuse box).
Crank engine for 10-15 seconds
It shouldn't get below 9.5volts warm(above 32 deg F), 9volts cold(0deg F), while cranking
If it does it could be starter motor is drawing too many amps, either from wear or failing cables, assuming new battery is 12.7volts.

As electric motors wear they draw more amps as the wiring inside generates heat instead of turning motion.
Same happens to battery/starter motor cables, if they start to get corrosion at connections or under insulation they heat up which requires more amps from battery.


You could hook up volt meter in the cab fuse panel, might give you a better reading of cab voltage when cranking, which is where I think the problem would be, but just guessing.

Last edited by RonD; 06-12-2015 at 12:09 PM.
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Old 06-12-2015
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OK thanks. I'll have to go look at it
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Old 06-13-2015
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Just found this thread and it describes what you have exactly and the voltage issue I was guessing at.
Doors Locking on Ignition - Ford Truck Enthusiasts Forums

But their(2 of them) issue was resolved with new battery
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  #11  
Old 06-29-2015
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would consider replacing fuel filter too
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