I have a 2001 Supercrew 4.6L 4x4 with 62K miles and my gas mileage which sucked from day 1 at around 15mpg has been slowly declining to now <13mpg. Does anyone have any ideas on how to improve or what engine components may need replacing?

Some answers to probable questions:
1. Yes my tires are of stock diameter and my odometer is working properly. (I verifed speed with my GPS)
2. I have a K&N intake and filter which is clean.
3. I recently changed my fuel filter. (not that it matters for mpg)
4. I recently changed the spark plugs (OEM Motorcraft)
5. I tried some redline injector cleaner fuel additive.
6. No change in driving style.
7. I run 87 octane.
8. I change the oil around every 4K or so (5W30).
9. I changed the trany oil at 30K, but never changed the diffs or transfer case oil.

 

try using seaform in your gas and brake booster. i let it suck up the booster til the engine dies then let it sit for about 10 min...then run it again for about 5 min before driving. also use mobile 1.

 

Your using the wrong motor oil for one thing...use 5w20...set tires at 35psi...I get 16-19 mixed driving...I always use 87gas...I have 265-70/17's on truck...they are goodyear rs/t's and they suck...Can't wait to get Bridgestones Revos...Oh I have a K & N filter as well...

 

You could change your upstream O2 sensors. I have read and talked to a few Ford mechanics and they mentioned changing them out around 50K. You are also getting to the mileage range to clean your EGR Ports in your throttle body plenum(the elbow that connects the body to the intake). If you do a search for egr ports you will find a lot of information on the subject and how to do it. I also have an 01 4.6L and recently cleaned mine and they were about 85% clogged.

 

Im not sure what your temperatures are like there in CA, but when it gets colder outside, you can expect a drop in mileage. If you do alot of city driving, its going to be even worse.

I drive a mix of city and highway driving, and I've gone from about 13.5-14 MPG to about 12...and it's going to get colder still.

 

I second that motion concreteguy. The RT/S sucks. I've had Bridgestone Dueler ATs and they were an awesome tire. (pre-revo)

 

I will look into getting a new O2 sensor cleaning the EGR port.

5w20 wt oil seems a little thin for a non high performnce V8 with 62k Miles on it.


I kept getting flat tires while wheel'n with the Stock goodyear tires the truck came with. So I changed to ProComp M/T and 16" rims which have been great. They have the same overall diameter as the stock tires.

 

the mud terriens will give u alot more rolling resistance then your older tires. that could be your problem right there:santa:

 

Agreed.

Also, O2 sensors tend to slowly deteriorate. At your MPG, you may want to replace the upstream sensors as general tune-up/preventive meaintenance.

 

Im on my second set of the M/T and there wasm't any significant difference in mpg when I first got them.

I will look into replacing some sensors starting with the O2.

 

You might want to check your MAF (mass air flow) sensor. The oil used on gauze filters has been known to travel from the filter to the MAF sensor causing it to give the computer a false reading which will cause problems with peformance and mileage. Also just for fun if you drive in much dust with your K&N pull the plastic plenum off on the clean side of the air filter and shine a light down it. You might be suprised at the amount of dirt that is getting past the filter. Heck you might be able to write you name in it.

 

My mileage started going way down a couple of weeks before my my MAF died. Apparently it had to go a while until it finally died and triggered the check engine light. 02 sensors is another good start. Both items are relatively expensive to replace, unfortunately. Cleaning the MAF may help though.,,,,98

Some areas have a different gasoline formula for colder months, I've heard.

 

Is the MAF that sensor just dowstream from the filter that sticks through the rubber duct?

How much does the O2 sensor cost, around $30? I haven't checked yet.

 

02 sensors run about $50 to $60 a piece. MAF was over $200 to have replaced at the dealer. What teed me off was getting charged full labor for the install. I had a K&N intake, a LOT easier to R/R. The MAF is right behind the filter box. When you pul,l the filter out, it's the aluminum piece right behind the plastic plate.,,,,98

 

MAFs pretty much don't die. You should clean (properly) your K&N, remove and clean your MAF, replace the upstream O2, reset your computer, clean your EGR, etc. Just basic work. Also, on mod motors it is a good idea to use copper plugs (I dunno if the ones from Ford are platinums on the truck motors, too). And, of course, higher flowing exhaust allows for better mpg. I'm still new to trucks, but I've been working with mod motors in Mustangs for four years. My N/A 01 Cobra ran mid 12s and got about 23 mpg average (mostly city driving).