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I recently bought a 2004 Ford F-150 lariat, 5.4L. Currently sitting on 37 in tires with a 5 inch lift. I understand my gas mileage would already be low, but 7 MPG just doesn’t sound right. When I bought it I would have almost 400 miles to empty, now when I fill up I have about 250. Really costing the hell out of me. I’ve replaced the o2 sensors because they went out, but that didn’t help much at all. Any suggestions?
Agree with @glc . One or more of them could be very relevant and could even be causing the last two. If you are asking about the counter indications of 5 of 6 and 6 of 6 - - the IMRC valve (also known as CMCV "Charge Motion Control VAlve") could have vacuum hoses or wiring harness 'binding' on its linkage. If this device is NOT FUNCTIONING PROPERLY, it _will_ negatively effect power and fuel economy. Couple of important points.
The device & linkage are VERY difficult to see or check on. By removing the Throtle Body and the Fuel Rail - and climb/lay up across the motor, you can see it well enough to verify linkage is connected and not binding. (But hood latch will poke holes in your stomach !!!).
Interestingly, there are NO contacts or switches on either bank that can tell the PCM the CMCV butterflys are stuck open or stuck closed. The PCM figures that out by calculations from MAF / IAT / O2 Sensors / required or expected fuel trim adjustment corrections / etc. (What all else, I don't know). But this alone suggests it could likely effect fuel economy, and also that some of the other sensors could cause an erroneous report about 'stuck open' or 'stuck closed'.
