Hello, I recently bought a 1999 Ford f150 Reg Cab Short bed truck with the 4.2 V6 Engine in it. with 53,000 miles on it. I am gettin 11-12 mpg. It is an automatic. I am scheduled for a tune up on Friday. I am not sure what to do, any help would help me and my wallet!!! Thankyou.

 

Check some of the obvious things:
Air Filter, Plug wires for cracks, Plugs.
This time of year the Gas is not that great so there are some side affects to that.

If your driving with low air pressure that can have an affect.

Time for an Oil Change

While I doubt it, might check the Cat...
could be clogged up.

I bought a used Lumina and the cats were toasts, after replacing mileage went back to norm...

 

Thanx a lot, what is the CAT?? I am not to good with car lingo. The pressure on the tires is ok. It just seems that everyone else is getting much better. I am getting a tune up on Friday will they look at the CAT? and so on? I am gettin all the plugs and wires replaced and puting a K@N filter in it. Has anyone gotten better milage with this same 4.2 V 6 engine?

 

Catalytic Converter. If the Cat is plugged the increased back pressure will reduce your mpg. Adding the K@N won't hurt either.

 

What about the o2 Sensor? I heard that might help my mpg.

 

I just recently got it with 110,000 miles on it.
I live up by San Francisco, the truck was just south of Los Angeles.
I ran it home up I-5 at 80-90 MPH, I got 16MPG doing that.

Gave it a tuneup right away when I got it home.
New plugs (the original plugs were still in there) new wires, new K&N air filter, new fuel filter, Redline synthetic oil in the engine, same for the gearbox, fresh oil filter. I also cleaned the air mass sensor in the intake tract with carburateor cleaner and gentle wanding with a piece of rolled paper torn at the end for a brush effect. Got lots of crap off the sensor, you really need to be careful doing that too, as it's really easy to screw one of those up.

Ran the truck yesterday on the highway for seventy or so miles and got 20.9 MPG on crap California 87 octane el cheapo gasoline.

The truck is a '99 with the 4.2, 5speed manual transmission, and the high 3.08 ratio rear end.

After all that, the truck is quicker, more responsive, and runs in overdrive with much less effort.


Something else you should have looked at is the condition of your oxygen sensors in the exhaust system.
You could have burnt sensors there. That or bad wiring to one or more of them. Hopefully your mechanic is good enough to be able to deal with all this and get your truck running right.

 

You haven't mentioned if you are running stock size tires, or what rear end is in your truck. A 3.73 rear end and tall tire will kill your mpg. The axle code on the door post will give you the code for the rear end: (18=3.08,19=3.55,26=3.73,27=3.31,H9=3.55LS,B6=3.73 LS)
The door post will also give you what size tires the truck came with, as opposed to what may be on it now.

 

Check your brakes also. If they are sticking, it will reduce your milage considerably. Just a thought.

 

If there is a problem with your cat's and you have less then 80,000 or 8 years it should be covered under warranty for any repairs, labor, and/or replacement so check with your dealer.

If the O2 sensors are bad they can and will effect gas milage. They sense the oxygen level in the exhaust and then give feedback to the computer, thus affecting the fuel air mixture. If there bad, or not working your truck will always be running rich or richer then it should be (more fuel).

It is highly recommended to change the O2 sensors (upstream) the one ahead of the cat's at approx. 60,000 miles as normal routine maintenance.

 

I get 15 to 16 on mine.

 

I have a basic question about the CAT's. A friend of mine told me that he had to replace his after just 60K and the reason being was because of the
so called SunoCo (ECONOMY) fuel grade. he continued to buy

I'm somewhat concerned about the fuel quality myself, but what can you do about it unless you buy Shell Premium all the time or some quality variant

 

I have the 4.2L with the auto and a supercab. I was getting appprox. 13-15 miles to a gallon, depending on driving conditions. I had Flowmasters put on and now I am getting about 15-16 mpg. I used to only be able to go about 75-90 mile for every quarter of a tank, but now it is up to close to a 100 mile for every1/4 of a tank. When I first got the exhaust I didn't reset the PCM and was getting bad gas milage. After reseting it, The mileage is pretty good.

 

OK, I've just read 3 threads about poor milage. I don't suffer from this problem. I thought mine was bad, but listening to you guys, mine is great. I have a 2001 regular cab 4.2, 5 speed, 3.55 gears, and the stock 275/60/17 (30") tires. My highway mileage is in the 19-22 range, that's cruising at 80 mph. City will range from 16-18.5, depending on how much right foot I use. I usually drive around with a bed full of tools (approx 500 lbs) and have a hard tonneau cover.

When I was in the people's republic of california for work, my milage dropped. The lowest I saw was 12 mpg city and 16 mpg highway in the 3 months I was there. When I returned to America my milage went back up.

Most of the mods I've done helped the efficiency of the truck, or at least seemed to. Check my sig to see what's been done.

Mods like larger tires, lifts, giant light bars in the bed, very low gears, etc. will definately hurt milage. I also have an 87 Bronco, and it got 16 mpg on the highway at one point. It was stock with a 302, 32" tires, 3.55 gears, and some basic mods. I added a 4" lift, 35" tires, and 4.10 gears and watched the milage plummit to 11 on the highway. Same everything else, and the milage dropped 5 mpg. I did run it for a while with the 35" tires and the 3.55 gears. It was not that noticable of a difference in milage when I got the gears done. At higher speeds the wind resistance affects the milage exponentially.

Mitch

 

I tested the milage today. 129.5 mile trip, 90% highway at average 82 mph, took 6.33 gallons of gas = 20.46 MPG.

Mitch