A couple of months ago, I was complaining about VERY poor mileage (12MPG) on my 97 F-150 4x4 SuperCab 4.6L V8 w/81000 miles. I tried changing the plugs and wires and such, but to no avail. I did find out that my engine ONLY likes Motorcraft plugs and will not run right with Bosch plugs.

The CEL light would come on intermittently, then clear, then after a couple of days it just stayed on.

It took awhile to schedule the time to take my truck to the shop s since I am in the Navy and I do have to go to sea. Finally I took the truck into the shop. They found that I had a bad DPFE (Differential Pressure Feedback) Sensor, which would not let the EGR valve function properly. Along with that, they had to clean the exhaust lines running to the EGR and DPFE sensor. They had carbon build up that had mostly closed the lines.

Now my truck runs GREAT. My mileage is backup to 17-21MPG.

$77.00 part and $170.00 in labor...

This was the first time I have ever had to take my truck to the dealer for repairs since I bought it. I don't count recalls...

 

Just out of couriosity did the valve stay open or not open at all. I would guess that if the EGR stuck open a bit that it would dilute the mixture and cause the computer to compensate with more fuel. My usual 16.1 has slipped ever so slightly to @ 14.6 or so. I am going to service my egr and see what happens. Thanx for posting, this site is always full of ideas.

 

I have the exact same truck setup as you...and perhaps the same problem. My milage is 12-13+ and didn't change after I replaced plugs and wires.

Is this a fix that I can do myself or that others have done? Fairly handy with a wrench provided I have decent di-wreck-tions and a bit of time on my hands.

I'd love to get my milage up to 17-21mpg.

Thanks...Scott

 

I am not sure if the EGR was open or closed. All I know is that the truck 'feels' better.

I am sure that you could replace the faulty DPFE sensor but I do not know what cleaning they did. I supposed I could have figured it out.

I have a Ford Factory Manual (on CD) and they talk about cleaning but do not go into it very deeply. I guess that is what "Factory Trained" means ...

 

17-21 mpg on a 4.6 4x4 extended cab? Is an auto or manual? 13-14 is the best I've ever heard of (or personally experienced) for a 97 4.6 4x4 extended cab. You might want to consider having your speedometer checked.

I have heard of shops changing speedometer gears to satisfy customers who complain about fuel milage.

 

I picked up my 97 in March of 96.

Stepside Supercab
4.6L V8
E4OD Transmission
Electronic Shift 4x4
AEM Cold Air Intake
Amzoil for engine, tranny, xfercase and both differentials

I have always gotten:
14-15 in city.
16-17 combination
18-20 Highway. (65-70Mph)

This was with the stock Goodyear RTS 265 70R16 tires (crap tires)
At 5K miles, I replaced those tires with Goodyear AT/S 305 70R16's (I do like to go off road) which has changed my Odometer/Tach readings.
After the tire change, my actual speed (GPS and mathmatically verified) is 5.5Mph faster than what is indicated in the speedometer, so my mileage is a little better than that above.

Now, my plan is to replace the catalytic converters and muffler with Magnaflow components and maybe a set of JBL headers.

I have never kept a vehicle this long. But I have never had a vehicle that has given me 100% satisfaction. Even my Wife likes to drive it.

I drive it everyday to work from Va Beach to the Norfolk Naval Base which is 26miles one way…

 

Must be all the hills around here that kept me from getting any better than 14mpg with the 4.6L

The '98 2x4 4.6L my wife had would get 18 going to CO every year, but we always had head winds in KS and western CO, and mountains past Denver. I always felt it could've approached 20 or better under perfect conditions.

The '02 4x4 5.4L I have now gets up to 16 on the same roads that the 4.6L gave me 12-14mpg and doesn't downshift as much.

Sounds like you have a handle on your speedometer accuracy. I see a lot of people fail to take that into account when figuring gas milage after they change tires. The speedo gear swapping story is true, a Ford service instructer was bragging about doing it in a class I was in a long time ago.

26 miles one way to Norfolk NS? that's what, about a 4 hour dirve?

BTW, I prefer ships that aren't designed to sink

GSM1 '86-'92

 

Since the 'Peace Dividend" in 92' there is only about 100 ships/submarines here in Norfolk anymore.

It only takes me about 35min to get into the base. But I leave between 0530 and 0600.

USS Oklahoma City (SSN-723) is my last boat. I am retiring in Nov. Stick me with a fork, I am done.

24 years active duty, 19 years sea duty.... Time for some of the younsters to do this for awhile.....

I am REALLY looking forward to retirement....