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1999 Ford Explorer XLT - Strange Fuel Pump Issue

jgalt1

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Year, Model & Trim Level
1999 Ford Explorer XLT
My wife's 1999 ford explorer was having trouble starting periodically. We changed the battery and ultimately had the same problem so started to look at fuel.

I listened at the gas filler cap to determine if I could hear the fuel pump energize while the car was cranked. I didn't hear it and it wouldn't start. I then opened the gas cap and tried again and heard it energize and it started right up. This has now been repeated a dozen times or so and opening the gas cap enables the fuel pump to energize and start the car.

I checked the fuel pump pressure and it seems good. Also replaced the fuel pump relay but it still behaves this way. maybe once or twice a week my wife has to open the gas cap to get the car to start.

I'm wondering if I should just have the fuel pump replaced due to age and hope that fixes it but don't really have the $$$ to get it done now. I'm hoping there may be a simplier/less costly fix.

Any help would be most appreciated.

Thanks!!
 



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Looking at the wiring diagrams, it appears that there is a fuel tank pressure sensor that is involved in the fuel pump operating circuit. It probably sits on top of the gas tank. Sorry to sound so vague - but I am just looking at a wiring diagram, not a full shop manual. Good luck.
 






Looking at the wiring diagrams, it appears that there is a fuel tank pressure sensor that is involved in the fuel pump operating circuit. It probably sits on top of the gas tank. Sorry to sound so vague - but I am just looking at a wiring diagram, not a full shop manual. Good luck.

Okay, thanks. I will do some research on that.
 






You need to check into the EVAP purge system. If you have pressure building up in the tank, the purge system isn't working right.
 






I'd wager the pump is on the way out, but you could check for voltage at the pump next time to rule out electrical such as relay, harness, connections, etc.
 






Thanks guys. How do I check the "EVAP"/"PURGE" system? I am planning to replace fuel pump/filter soon as a preventative due to age but want to buy some time if I can.
 






I'd wager the pump is on the way out, but you could check for voltage at the pump next time to rule out electrical such as relay, harness, connections, etc.

^ This. My money's on bad fuel pump. If you can do the job yourself (and you just replace the pump) you can replace the pump, strainer, hoses and filter for under $80. Next time it wont start, thump the bottom, rear of the fuel tank with a rubber mallet or piece of wood, rather than removing the fuel cap. I don't see why excess pressure in the fuel tank would prevent the pump from running.
 






Thanks. As of now we still have the problem but don't always have to open the fuel cap....if we don't hear the whine of the pump when the key is move to ON...we try again and on the next one or couple tries we hear it engaged and then crank it and it starts.

If the pump is going bad why would it ONLY give us issues on starting? No issues while running. Maybe It can happen like that though, I'm not that knowledgeable.

Wondering what typical shop cost would be to replace? Can't do it myself.
 






Thanks. As of now we still have the problem but don't always have to open the fuel cap....if we don't hear the whine of the pump when the key is move to ON...we try again and on the next one or couple tries we hear it engaged and then crank it and it starts.

If the pump is going bad why would it ONLY give us issues on starting? No issues while running. Maybe It can happen like that though, I'm not that knowledgeable.

Wondering what typical shop cost would be to replace? Can't do it myself.

Classic intermittent bad pump operation. I had the exact same symptoms on my 2000 Mountaineer. I don't know what a shop will charge you. Make some phone calls, but make sure they install a Bosch fuel pump. My guess is something around $300.
 






The purpose of the tank vapor pressure sensor is to alert the computer (PCM) to loss of vapor pressure within the tank. Loss of pressure could be caused by the fuel cap left off (vapor emitted to atmosphere, a no-no), cracked hose or other leak of vapor between tank and vapor canister, or failed solenoid(s) which control ingestion of canister vapor into engine, to be burned as "fuel".

The pressure sensor cannot in any way affect the pump being able to run or not. It is there strictly to detect vapor loss to atmosphere. imp
 






Classic intermittent bad pump operation. I had the exact same symptoms on my 2000 Mountaineer. I don't know what a shop will charge you. Make some phone calls, but make sure they install a Bosch fuel pump. My guess is something around $300.

Thank you for your reply. I think based on the responses, I will proceed to get the fuel pump/filter replaced. Thanks for tip on Bosch fuel pump.
 






......If the pump is going bad why would it ONLY give us issues on starting? No issues while running......
Just like with any electric motor, starting takes the most amperage. The fuel pump brushes wear out and lose
contact with the commutator and cause the intermittant
starting. Once the fuel pump is running, current draw is
less and the fuel pump will continue running...until the
next stop and start.

I too would install a new pump.
 






Just like with any electric motor, starting takes the most amperage. The fuel pump brushes wear out and lose
contact with the commutator and cause the intermittant
starting. Once the fuel pump is running, current draw is
less and the fuel pump will continue running...until the
next stop and start.

I too would install a new pump.
This in depth description of why it doesn’t work at startup but does while driving is so helpful. I’m having this exact issue and I wasn’t sure why it was doing this. Thank you!!
 






Just like with any electric motor, starting takes the most amperage. The fuel pump brushes wear out and lose
contact with the commutator and cause the intermittant
starting. Once the fuel pump is running, current draw is
less and the fuel pump will continue running...until the
next stop and start.

I too would install a new pump.
This being true, have you given much thought to the "returnless" fuel system in which the pump SPEED is continuously being varied as needed to maintain volume sufficient to maintain expected pressure?

At first, I thought this was nonsensical. Dead pump every few months, but know what? 170,000 miles on my original pump! 2004 Explorer 4.0L. Can hardly hear it "prime up" even!
 






This being true, have you given much thought to the "returnless" fuel system in which the pump SPEED is continuously being varied as needed to maintain volume sufficient to maintain expected pressure?
In my 99 the pump don't vary speed just a pressure regulator in the tank
 






Just listening to a pump does not mean it is good or bad per say with 0% margin for error, some times the louder the pump the worse off it is. Just like a motor, one going going clang pop ping is not going to last as long as one that is quite. I just replaxed my pump in my x a few months ago it was the oe factory pump with 268k miles on it and it gave no signs of failing other then being obviously loud when priming and being able to hear it "run" the whole time. I had just dropped off my kids at the grandparents house and made it i dont know 4 miles from there house down a dirt road and it just gave 2 small hiccups and shut down, fuel pump just quit. Made it easy to figure out because it was silent. I got a high pressure pump from jegs for 90$ i think. Installed it hit the key an ready to roll. The new pump is almost silent, when priming it primes so quickly it almost hard to catch. Myself i would replace the pump, fuel filter, check you filler neck tubes and your evap system along with pressure sensors on tank there easy to get to. all the plugs can be seen by removing your driver side rear tire and looking on top of tank and in frame in the same area. You can do this job yourself it seems way harder than it is, its more labor than it is tech hard. If your safe about it you dont have to drop the tank. You can make you a door under the driver side rear seat, pull your seat lift carpet and cut the top out of that hump there and all you plugs and pump are right there. However use your BRAIN!!! wrap tank in water soaked welding blanket have a empty tank and dont cut too deep. I like doing this on all my vehicles because parts fail. They all do at some point just depends when. This way if im 20 miles out on the hog lease in mud and the family with me the worst i have to do is wait to have a pump brought to me and can change it in a matter of minutes vs a nightmare. I know this is very long im sorry just thought the info was help! I hold no responsibility to personal or other damage/injury :)
 






before dropping the tank to replace the pump it is a good idea to make sure your intermittent pump running issue is not electrical
Nothing sucks worse then dropping the tank, replacing the pump and strainer only to find the truck is still doing the same thing.
Nobody here would ever do anything like that now would they? hehehehehe

So after having that happen to me a few times I finally learned to do a thorough check of the fuel pump power wires before I drop the tank
Check for power and ground at the fuel pump connector where it plugs into the tank
Inspect the wiring plugs and pins very carefully
I have fixed a couple of trucks just by doing this

Next is the fuel pump relay and fuse followed by inertia switch....make sure all the contacts are clean and free from corrosion
Now I also do a fuel rail pressure test, try to do when truck is warm.
Also know what a healthy pump sounds like through he filler door is a good idea, after a while you can start to hear the ones that are whining, struggling, having a hard time pushing fuel when compared to a healthy new Bosch pump
The relay can be bench tested or simply swapped out for another relay, this way you know the fuel pump is the actual issue

Bosch BLUE ONLY and make sure its a real Bosch pump not a fake from Ebay or Amazon...check item description and seller credentials
 






Hmm the fuel pressure regulator could also be shot unless this is just new enough to have the fuel rail pressure sensor. Either could possibly cause the same issues. More so the sensor version of it.
 






99 has an in tank pressure regulator, no fuel pump monitor, not until 2002+
There is no rail pressure sensor on these trucks not 98-01 as we are discussing here
 



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In my 99 the pump don't vary speed just a pressure regulator in the tank
I believe Ford used a returnless concept, to which you refer, for several years, finally going to the speed-controlled pump to maintain constant pressure at the engine. In '99 version, the pump put out maximum volume at all times, dumping the excess back into the tank, constant pressure being maintained at the fuel regulator.

I MO, the return-type concept is best, though it has drawbacks: fuel is being circulated from tank to engine and back whenever it is running: this heats the fuel some, and ensures that ALL crap in tank is pushed to the filter real quickly. Pump has to work at design max all the time. Problem I pictured for the later speed-control deal was, what if the Fuel Temperature & Pressure Sensor quits working? Stranded along the road? No, Ford thought of that: under loss of FT&PS data, PCM runs pump at MAX, excess being dumped in tank, eng. runs very rich. Happened on my 2004.
 






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