Why would my truck experience a sharp, sudden decrease of fuel mileage? My last tank of gas netted 100 miles less than usual under standard driving conditions.

'99 5.9 with 170k miles

[IMG]local://upfiles/49168/26DBBFB16B7C478B85968BAAC80165CF.jpg[/IMG]

 

Has the performance dropped off as well?
With a sudden drop in mpg I would suspect something like the coil, cap/rotor or ignition wires. Could be a bad computer as well. My 99 V10 the mileage dropped quickly right before the computer died.
Are you getting any codes?

 

170K miles, it could be the fuel pressure regulator is clogging and can't deliver at the proper pressure; the internal fuel filter is clogged; the fuel filter screen is clogged; the catalytic converter is plugging, meaning there is a deeper problem with your truck; the O2 sensor(s) are bad. Check your air filter too.

 

Thanks for the input....
I haven't experienced any performance issues. Even though I don't have any shimies or shakes, it sounds like it may be a fuel regulator issue. I know it's also due for a fuel filter change.
I'll change the fuel filter first (any recommendations for brands?) and see how the fuel mileage goes from there, then post the results...

 

You can't change the filter. It is integral to the fuel pump assy. You can change the pressure regulator, and beyond that change the entire pump assy. There is also a screen at the bottom of the pump assy that can be changed as well. How old are your plugs, pug wires, cap, and rotor? Those all can affect mileage.

 

theres no inline filter on these trucks? its all in tank?

 

Check it outright here:
https://dodgeforum.com/fb.asp?m=609276

 

You sure someone didn't help themselves to some of your gas?

 

were you riding the gas realy hard resently




97 1500 5.9L v8 magnum 4x4
slt larimme long box
flowmaster 40 seris dual exit
pilot fog lights
k/n airfilter (coming soon)

 

Thanks for the pics of the fuel regulator assy...
You're right about no external fuel filter. I thought these trucks were installed with at least two (you and haynes manual showed me otherwise).
I'm going to see how this next tank of gas goes before pulling that fuel pump assy. I may have gotten some bad gas...

PS-My plugs and plugwires are new, less than 5k miles on them... Checking out the other info., I know it's also time for a new exhaust system as well...