Effects Of Clogged Fuel Filter

[Doityourselfer]

dealer tells me that a clogged fuel filter can cause poor mileage.

while i can see why a clogged fuel filter should cause trouble like stalling, hesitation,etc(fuel is being restricted), why would it cause poor mileage???

[Three Fat Tigers]

city fuel economy in 92 940T is lower then normal. car is moderately in tune, (plugs,wires,air filter,02 sensor,no fuel smell in fpr vac line), dealer says a clogged fuel filter can cause poor fuel economy.

come to thing of it, car has the same filter for 100k miles and probably more,as i purchased it at 126k and the previous owner gave me a fuel filter that he hadn't had a chance to install am now at 162k.

so I've got the new fuel filter,am gonna install it. now, while i can see how a clogged fuel filter can be responsible for problems such as stalling, hesitation, intermittent engine cut-out,(-hey fuel is being restricted) I can't see how it can cause poor fuel economy. can you explain this?

A clogged filter can make a car run weak and generally poorly, how exactly that translates in to mileage is a subject I've never tried to explore before, and at the moment, not enough brain cells have showed up for work today to fully man the bridge, so not sure what to say, other than even combustion across the cylinder bank and optimum fuel to air ratios are key to economy.

Bad gas can also cause the filter to clog up, and regardless of that, cause bad mileage. So can a defective knock sensor, so can a good knock sensor where there is sufficient piston noise.

I'd also run a compression test on that engine, there may be a lot of ring/cylinder wall wear. Especially as, IINM, that was the car that had been run for a long time with the air box cover installed in a offset position where lots of unfiltered air made it straight in to the engine. If it's lost enough compression or it's really uneven, then that too could account for this.

Also if the valve clearances are off significantly, could be a factor, at least that is very easy to check.