Hello gang from a new member. I'm on my second 97 F150 4x4 S/C with 4.6 engine and 3:55 rear end.The old truck (205,000 km) was getting around 20 mpg at 110km/Hr on the highway. This truck is the exact same including engine and rear end, with only 115,000 km, but is only getting 15-16 mpg (5.2 km/litre)at same highwy speed. Also has a K&N filter and flow through exhaust. Dealer mechanic did a check and says O2 sensor etc OK, however engine RPM's seem to be about 300-400 rpm too low, and stated it appears to be running under its optimal power range. Suggested this may be transmission RPM related, but says torque converetor OK. Another shop suggeste I change O2 sensor, plugs and wires etc to teh tune of about $600. Dealer mechanic says this won't do much to inprove mileage. Any suggestions that might help from those with similar experience. Most owners I know with this truck/engine/rear end combo are getting anywhere from 19-22 mpg.

 

Welcome to FTE!

Due to this being posted in the User Introduction forum ,the thread will be moved to a TECH forum.

The forum for this topic is the 97-03 Truck forum

 

I have a 97 F150 4X2 with the 4.6 engine and typically get around 18 on the highway and 14 in town, so I'm not sure that your mileage is that atypical.

 

Maybe I have the bad gas mileage here. I have a 97 4.6L 4x4 with a 3.55 rear end and I get about 15 highway and 8-10 city. Is there anything I should check first to see why I'm getting this bad of gas mileage?

 

clean ur MAF throttle body and change that Air filter and fuel filter. and u should notice a difference in performance and efficientcy

 

Is the odometer off, due to different tires? I installed a set of All terain tires and lost 2mpg US Gal. from the stock all season.

 

If they're the same size, the difference is probably the difference in the rolling friction between the two tires.

 

I do have a new set of M&S tires LT 265-15 10 ply that came with the truck. Didn't realize they could make a big difference in mileage. I believe stock tires from the factory are a bit smaller, and possibly not LT's, but P metric. Will also look at the MAF throttle body.

 

I attribute my 2mpg loss to both different size and rolling resistance. I believe the friction is the biggest cause, but when I looked up the specs for my OE tire and the replacement. Both 235/70R16 the OE tire was slightlly smaller diameter. Almost 1/2 inch.

 

I think you might be right on the tires. I had factory spec P235-16 r70's on the old truck. This one came(used) with 10 ply LT 245-16 R75's M&S which has both larger OD diameter and more rolling resistance as a fatter tire and more aggressive grip. They are Woosung tires which is a Korean knock off of the Hankook. The old truck tires were Brigstones.

 

If you have bigger tires than stock, your odometer is off, therefore you are going more miles than your odometer is saying (and going faster than what your speedometer says) so you are going further ever time the tire goes around. If the circumference of the tire is 20% bigger, for example, you are going 20% further than your odometer is registering. So if you are getting 15 MPG, then you are actually getting 18 MPG using these hypothetical #'s.