91 F150 5.0 V Auto 4x4 84,000 original miles.

Ok... i've somehow lost 170 miles to a tank in the past year and a half. I use to get 300+ miles to a tank now I'm nown to 120 if i'm LUCKY!! Recently installed K&N Intake, replaced O2 Sensor, Fuel Filter... I noticed the echaust smelled REALLY RICK!!! I plugged in my code reader, it passed the self tests with engine off and it gave me the following codes with the engine running:

- RPM @ Idle out of range/High
- Cooling Temp Sensor out of specified range or ECT out of range

I'm not beilieving that these 2 codes have much to do with me loosing 170 miles to a tank.... the tires didn't make much of a difference.... what would cause my exhaust to smell so rich?

Thanks!!!

 

You mentioned tires. Did you up your tire size? If so your speedo and odometer will be off unless you recalibrated them. It would take a fairly large tire change to do that, but depending on gearing it's possible to lose quite a lot of fuel mileage.

If that's not the case you can start checking the sensors.

Just my quickie try it suggestion here, but if you got a faulty or wrong O2 sensor it could make the truck get an improper signal. If you still have the old one and it was in working condition it might be just as quick to put it back in as it would to start troubleshooting other sensors and problems.

It's possible that the engine is running in open loop due to the O2 being off. This could cause a slow warm up and throw the ECT code.

 

Pull the red line off the Fuel Pressure Regulator (FPR) & check for the smell or presence of gasoline. If so, replace the FPR.

 

I went from the 27" tires to 31X10.50 bfg all-terrains... I live in Bakersfield and I've gone trough the phonebook numerous times and no one ic alls anc re-callibrate my speedo, they only have the programmers to do it and mine takes that little gear... is that enough of a difference to need to re-gear the back end? The mileage is no better and no worse since I put the new O2 sensor on...

 

That small of a change shouldn't kill your mileage so bad, but your indicated 120 miles is actually around 137 miles.

Either way, sounds like you have either a fuel or spark problem. I'd start checking things out one by one. The TPS (throttle position sensor) would be a place to start for your idle issue.

If the coolant temp is out of range to the low side you might not be getting enough heat in the chambers for good combustion. First verify that the sensor is working. This leads me to think you might have a weak spark or a problem with the fuel pressure regulator, as either or both could make the truck run rich.

 

Get a Haynes manual (PN 36058) & a cheap digital multimeter, and test the ECT & IAT. The book shows exactly how.

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