Okay I know old cars but not this new stuff....

My daughter has a 1999 Durango 5.9 & it will run well for about 1 hour & then it starts to stumble & won't go
over 10mph, almost like it's not getting enough gas. If you let it set for awhile to cool down...1-2 hrs it will start
and run like nothing ever happened & then start stumbling again after being driven about 50 miles & then will only
run about 10mph & pop & backfire.

Could it be the fuel pump?
Fuel Filter?
Something with the ignition?

I was assuming the fuel pump was getting hot but I am not sure, it acts like it's running out of gas. I hate to spend $250
on a new one & then still have the problem.

Also one of the O2 sensors is unplugged & it is running in closed loop mode but has been that way & running fine for over
a year now.

Any ideas would be greatly appreciated...

scottieo@***.net

 

O2 sensors
Fuel filter
Spark plugs
Fuel injectors

Could be a lot of things.

 

I would think if it were the injectors it would do it all the time as with the sparks plugs....

O2 should not matter in closed loop mode I woudn't think....

Fuel filter is possible but why only when it gets about an hour of time driving?

I'm sooooooo confused...thanks for your input....

 

Sounds like a fuel pump. Auto Zone has one for $189 lifetime warranty. Also it could be the intake manifold gaskets or the belly pan gasket on the bottom of the intake manifold. Take off the throttle body and look inside the manifold and see if you see oil, if you do the belly gasket is surely bad. Give it a full tune up also. OEM Champion plugs and OEM wires. The plugs are only $1 and the wires at the dealer are $45.

 

Thanks for the reply, I am kinda leaning towards
the fuel pump but I am still waiting for it to happen
while I am driving it that way I can check the fuel
pressure while it is happening. I am also planning on
doing the plugs, wires, cap & rotor too it is definately due
for a tune-up it has 101,000 miles on it.

Do these have an access in the floor for the fuel pump
or do I have to drop the tank?

 

I've heard about the access panels before, but I think they are in the 2000's and up. The tank is plastic so it's not too heavy anyway. A new pump has a max shut off pressure of 95 to 115 psi if that helps. Checkers stocks them but they want $225 but if you tell them that Auto Zone has them for $189 they will match the price and beat it by 10% and they have it in stock. It is the same pump.

 

You may want to also think about the Idle Air Control Valve. Mine was the opposite ran good warm but in the cold acted like a 30 year old truck with a bad carbeurator. Your IACV could be stuck in the opposite position that mine was. After you replace it if you choose to do so, unhook the battery cable for 10 mins. to reset ECM. It ran about $45 at Advanced Auto Parts. Easy to replace just two screws that are star drive on back of throttle body. Let us know what your actual fix turns out to be.

 

Well....I drove it for 2.5 hours last night & it never stalled or died like it has been....
it ran just like it normally does, however I attached a fuel pressure guage to the fuel
rail & stuck it to the window so I could watch it while driving & here is what it read...

Turn key on 45psi
Start Engine first time 56psi
Drove for two hours & it started vibrating the guage in between 56 & 62psi....
Started it this morning & it was still vibrating in between 56 & 62psi...

so I am leaning towards the pump is going out but it is so cold here right now that it
may not be getting as hot as it did in the nicer weather... (the pump) the engine gets
up to temp just fine.

 

Normal operating pressure should be 339 kPa ± 34 kPa (49.2 psi ± 5 psi) per the service manual

 

Thanks for the pressure readings....

I just got finished changing the pump assembly & now the fuel pressure is reading
correctly, not 60psi anymore & it isn't irradic anymore, also when you give it
throttle the pressure increases 5psi now instead of drops 15psi so I am guessing
this will be the fix I needed.

When I got the tank out I also discovered about 1/4" of sugar coating the entire
bottom of the tank so therefore the screen was imersed in sludge. I cleaned it out
real well with the water hose & dried the excess water out of the tank & now it
looks brand new inside.

It took a few times of turning the key off & on to get the pump to force the air out
of the lines but it finally did & seems to be working great with steady pressure
reading of 49.5psi

Thank you all for all of your help it is very appreciated & if it decides to act up again
I will let you know but I am pretty confident the fuel pump was the culprit.

Thanks again guys, Scott