First, a little background. My wife's 2000 Explorer 4.0 V6 with 70K miles runs just fine EXCEPT... Last year she drove from Calif to Denver to visit family. During the trip, half way across Nevada, the car started stumbling on hills. Engine temps was fine, half tank fuel, it was summer temps outside probably 85-90F. She pulled over and let the Explorer sit for half hour, started it back up and it ran fine. She continued carefully until the next town and I recommended she have the fuel filter replaced. She did and the remainder of the trip was fine.

Today, same story, just east of Salt Lake City climbing to the top of the mountains, the Explorer did the same thing. Half tank fuel, truck started stumbling and she pulled over and let is sit for half hour and gingerly continued to the next town driving slowly. She didn't push the truck hoping it would run to the next town which it did. She will stay there overnight and probably have the fuel filter replaced again just as a precaution.

So, question is, why does this occur? Temperature, several hours of running before problem, fuel pump overheating? Bad gas or water in gas, she had filled up half a tank before the problem. Fuel filter again? Seems strange it runs just fine at home and also for many hours before this occurs. 2 times on the same trip, once last year and then today..... She loves her truck, but I am having a real problem trusting it on these trips she takes.

Thanks for any ideas
Woodie

 

This almost sounds like it has something to do with the altitude and maybe the computer isn't properly compensating for that? I dunno...if it's happening in the same area while climbing mountains, that's my first guess.

 

Quick update. New fuel filter as of this morning. Diagnostics say everything is fine except they found a very dirty MAF sensor. Drove about 5 hours today and then same thing happening except it will barely run now even after sitting for a while. Being towed to Ford dealership in Laramie, WY. Hopefully they can figure out what is going on. I am guessing fuel pump.

This is very stressful when my wife is stranded in the middle of nowhere and I can't help... ;-)

Woodie

 

Well, another day, another update. Dealership has the Explorer, worked on it for a couple hours this morning, can't find anything obvious. Wife says dealership found one code which isn't critical and shouldn't anything to do with current problem. Wife rented a car, drove on to Denver which was the destination. Left Explorer with dealership to resolve whatever the problem is....

Woodie

 

I had a similar problem. Would idle fine but lacked power. I found the fuel pressure was about 7 psi low out of spec and flow rate was really low. Replaced fuel pump and all is well.

 

That is what I am guessing also. Anyone have an idea of what it costs to get a fuel pump (in the tank) replaced on the 2000 Explorer at a dealership?

thx
Don

 

Expect $600-1000.

Mine was $600 at an independent.

 

I paid $300. for the pump and install at an independent shop.

 

Its a fuel pump. Replace with Motorcraft or Walbro only, most aftermarket pumps will do the same thing your faulty pump is doing now.

 

Quick update.... wife picked up the Explorer from the dealer in Laramie, drove it all day thru 90F plus temps with no issues. They did replace the fuel pump so we will see if that is the real cause (probably is), only time will tell.

Thanks to all for the info and suggestions.

Don

 

I noticed in your original post, that you wanted to know what is actually happening and why it does this.

Basically what is happening is that your fuel contains ethanol. Ethanol has a low boiling point. Your fuel system was not really designed for ethanol (it was from a materials standpoint, but not from a mechanical, operating standpoint). When you drive long distances, and the days are hot, the fuel int he tank heats up, bringing the ethanol closer to its boiling point. The pump picks it up and pumps it to the rail and injectors, where it soaks up heat from the engine compartment, which brings it even closer to its boiling point.

For short trips, this is fine, because things aren't as hot, and the fuel in the tank isn't as hot, as you drive longer distances, the fuel returning to the tank from the pressure regulator is hot, and that mixes with the fuel in the tank and that raises its starting temperature. Once the fuel starts to reach the critical temperature, the ethanol begins to boil, and that causes the pressure to rise rapidly. This rise in pressure makes the pump and the pressure regulator work harder. If the pump is getting old anyway, it will start to get louder, and won't be able to keep up. Once the pump starts to slow down the fuel rail begins to vapor lock, and boiling ethanol forces the fresh gasoline out of the rail, and replaces it with ethanol vapor. This leans out the engine till it finally stalls. The more fuel demand you need, the worse the problem gets.

Once everything cools back down, everything seems to work fine.

 

Thanks for the detailed explanation, it all makes perfect sense. What you describe fits our situation perfectly, that explains why there was never any problem on cooler days or shorter trips.

thanks
Don