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Old 01-04-2012, 01:25 PM   #10 (permalink)
drmiller100
Master EcoModder
 
Join Date: Dec 2011
Location: Boise Idaho
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The MPGUinno is ACTUALLY only looking at how long the fuel injectors are open.

Lets say your fuel filter is partly clogged. You start your car, and it starts out with 40 psi pressure at the fuel rail.

After a while crud inside the fuel filter stirs around, and partly plugs the filter. Pretty soon your fuel pressure at the rail is only 32 psi.

Your O2 sensor says the engine is lean, so the computer compensates by leaving the injectors open longer. Longer injector time means the MPGUino says you are getting less mileage.

FWIW, I am a mechanic, and see a LOT of fuel pump issues. Plugged fuel filters cause the fuel pump to work VERY hard, and plugged filters end up burning up fuel pumps. Fuel pumps cost 100 to 300 dollars, and I charge 200 bucks to drop a tank and put it back up because it is a MISERABLE job.

All for a 20 dollar fuel filter. I tell my good customers to regularly replace the filters, and my best customers I don't even ask them, I just do it every year or 3 when I see the car.
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