Guys/Gals, a fellow tried to tell me the other day that when his fuel filter gets stopped up he gets bad fuel milage. I didnt understand that one at all. Maybe im an idiot but i would think that the vehicle would just run like crap.

After I started thinking of it though, i guess you would have to mash on it a little harder to make it do what it normally would do otherwise. I dont know and I hate to sound stupid but what do you all think about that?

 

If your fuel filter gets "stopped up" or is dirty, so as to block the fuel from flowing through as it is supposed to, it does not affect the gas mileage. It will stop the vehicle from running properly due to lack of fuel....

If the engine can't get the fuel is sure does not burn more of it!

 

Those are my thoughts exactly, but if you have to push harder on an accelerator pedal....
I dont know i agree with your thougths but the guy swears it makes his burn more fuel.

 

Even if you push harder, if the fuel can't get through, it can't get through....

Hey, tell him to keep driving on his fuel filter and NEVER change it. Sooner or later, he will be PUSHING REALLY HARD!!! hahahahahahahahaha

 

Yeah, but once he has to get out of the cab and start pushing the truck, his gas mileage should improve again. :-)

 

It's actually more complicated than no fuel flow, no go... computers and all make it that way.

Your filter slowly gets stopped up, but the amount of flow alters even when the pressure remains constant....yet the same amount of air is still getting in. The truck runs lean, O2 sensor says need more gas... injectors get told need to increase your pulse width, so they put a longer injector pulse of gas in.

It's either the amount going in decreases with velocity remaining constant
- or -
the amount going in may not change but it's velocity drops.

Either way, it's this longer pulse that's the key. Instead of a relatively quick pulse where the spray is well atomized... the longer pulse doesn't allow good atomization. A nearly clogged fuel filter can kill fuel mileage and power.

-Kerry

 

Nice work KSPIL! I knew there was a reason but could't quite get it altogether in my my head.

Let me ask this thought, how many clogged filters have you seen and what causes it (dirty gas is not a good answer). I've been working on my own cars for 25+ years and never replaced a fuel filter. Also, I've emptied out a number of tanks and never saw any nasties come out. Let me make one exception, friend of mine in highschool worked for a fuel delivery company (20 y/o) and he'd get the dregs from the tankers. He was the only one I ever saw clog a filter. Is it all or just cheep fuel? Have I just been lucky?

 

You've been lucky. The stuff is in all fuels.
The filters may catch large objects, but they were designed for the really fine stuff. I have replaced the frame rail filter on my 2000. It's a difference I can feel at 75K miles. The filter media is not a clean white on a used filter. It is brown or gray, that's the stuff a gas filter was designed to keep back. It's that fine suspended solid that clogs up fuel filters.

-Kerry

 

Maybe I've been lucky or maybe I've just not noticed any change in the operation of my vehicles. Are you changing filters based on performance or simply based on maintenance schedule. As you said earlier, the pressure may remain constant even with a slow (clogging) filter, is there something else I can check to know if I should change my fuel filter? Other than lubes I hate changing things without a logical reason (read cheap).

 

But, wouldn't you throw a code if you didn't have enough fuel flow? I just tuned my 97 4.6 135k and it still studders slightly, but sometimes smooths out. I can't figure it out??? Could it be a clogged fuel filter? I probably have 30-40k on this filter. Thanks.

 

Injectors or carbon built up on the valves which prevents them from sealing properly.

 

I figured it was about time (75K) as the performance was seemingly lacking and the truck had not had it changed since I bought it...at 46K miles. Was the performance change that noticeable? Probably more of a placebo. But my mileage (and I have a pretty much constant routine) slightly improved from the range of 13.29 - 13.47mpg for the three tanks before to 13.83-13.91mpg for the the three tanks after.

The only way to tell if you're getting the fuel delivery is to meter it, that is how much is going through for a certain time... of course that requires us to know what the flow rate is of the stock pump, and whether you have a set up and the time to gauge the flow rate. We're not worried about the pressure, yet.

It's a maintenance item that, like auto transmission fluid/filter changes, gets ignored and performance suffers and things break... The price for a fuel filter is probably $5 and I picked up a set of fuel line disconnecting tools for $10. I own enough of these newer cars that I needed to pick it up anyway just to have.

In the end it's just cheaper to chance whether a filter is spent and spend a few dollars than to spend more time and more money trying to find out what your flow rate is. That test is better left to when you need to determine if you have a bad pump.

-Kerry

 

I imagine the truck would eventually give you a code, it seems like there's a sensor on everything. I do not know if a sensor exists on the actual fuel system, though. It does have sensors on the evap side, though.

I'd say Johns9163 is right on about the injectors and carbon buildup. The truck has a lot of mileage. Might want to do a fuel system and intake cleaning. A bit expensive, but the mechanic essentially pressure washes the inside to clean off the valves and seats and the fuel rail/injectors. Long term solution is to use a higher detergent gas or a good FI cleaner in a bottle to help keep deposits off.

-Kerry

 

Well regardless of what people think, I just talked to a few local mechanics here in my town and they claim that a stopped up fuel filter can actually decrease fuel milage. So I guess it is true that you could possibly get bad fuel milage with a clogged or restricted fuel filter.

 

Newer vehicles (at least Ford's- those are the ones I work on) use a FRP (Fuel Rail Pressure) sensor, which is part of the electronic returnless fuel system. There are only 3 ways I know that it will set a code: 1) if the filter is completely clogged, and no fuel pressure can be developed (which isn't likely), or 2) the filter is restricting enough to cause a detectable driveability concern- random misfires under load, or 3) if the fuel trims (pulse width) increase to a predetermined point then lean codes will set.