I've had my truck for a few months but ever since day one, the truck has been running rich. The truck itself has been serving its purpose in hauling stuff around for me but at about 8-10 mpg, I gotta think it can do better.
Any clues as to what I should start with and proceed with when trying to fix this problem?

 

2WD or 4WD?
What axle ratio?
What trans?
How many miles?
Any drivability issues?
Have you pulled any error codes?
What do your plugs look like? Are they all the same?
What does your exhaust pipe look like? Sooty?

Without some idea of what mileage you should expect and some idea of why it's guzzling gas, you're going to end up throwing parts at it and hoping. That's not a very efficient way to fix things.

 

I'll answer your questions as well as I can.

The truck is a 2 wheel drive
Not sure about the axle ratio or the transmission. The engine is a 302 on a 1994.
The truck has about 116K miles.
No driveability issues with the exception of the truck idling a little rough as I'm out in it for long periods of time (over an hour).
I haven't pulled error codes or looked at the plugs.
The exhaust pipe looks a little sooty (not bad though).

I bought the truck at the beginning of November last year. The truck pretty much had not gone over a couple of miles in a day for a period of 3 years before I bought it. Drove it off the lot and the valve cover was springing a leak (not the gasket) all over the place. Had that taken care of. The oil pan was also leaking (rusted to the point that it had a hole in it) and I had that fixed. Changed the solenoid, starter, had some radiator work done. The rear tank does not work. Can't hear a fuel pump running in either the front or rear.... for all I know it could be bad gas (what would I do about that) because this truck was used as a wash truck at a dealership and literally did not leave the dealership lot for 3 years.

My thought was that I should change the plugs and wires (I replaced the air filter and it didn't look bad) but beyond that I'm wondering what I could be looking at next.

 

Could be a leaky injector from the sounds of it. Also check your axle ration in your door jam. I cant remember the codes but i do know that if the code for the axle is h19 you have an open dif with 3.55 gears.

 

Pulling codes is necessary to begin the diagnostic process.

The spark plug reading is critical to spotting if there is a problem with only one cylinder, for instance the leaky injector that Titanium suggested.

As to the tranny, surely you know whether it is a manual or an automatic. There is a trans code on the ID sticker on the door jamb right next to where the axle code is listed.

 

The transmission is an automatic. I thought with so many transmissions on vehicles, you might be looking for the exact transmission (rather than automatic or manual). Tried to get the local auto parts store (Autozone) to pull codes today but they don't work with vehicles older than '96. Any recommendations on a brand to buy for a '94 F-150?

Bought a distributor cap and rotor and I'll put them on tomorrow.
I'll leave it up to someone else to replace the plugs. I did that one other time with a vehicle that hadn't moved in a while and it stripped the area and I had to get the darn thing helicoiled.

 

Don't do anything before you pull codes. Even if you don't have a CEL.

 

I can wait til I pull the codes. I guess I come from a different line of thinking because I rehab houses. So, if something looks ugly I just replace it. I bought this truck sorta along the same lines. It was $1500 and I knew it would need a lot of work to do what I'm asking it to do. But, it has now hauled kitchen cabinets, sinks, vanities, lumber, etc... and has more than paid for itself (plus it is a business tax deduction) in the couple of months that I've put it to use.

 

You might also what to check your o2 sensor. Alot of times if an o2 sensor fails it will tell the computer to feed the engine more fuel because it isn't detecting any fuel in the air stream so it will tell the computer that the air to fuel ratio isnt what it should be. Air to fuel ratio should be around 15:1 of somewhere around there.

 

Titanium, thanks. I have not yet pulled the codes but I did change out the rotor and distributor cap and that in itself has smoothed things out a bit. The plugs and wires will be changed out this week. I know that I need to pull codes to see what they might tell me but I'll do a little bit of research regarding the o2 sensor. Thanks a bunch!

 

Replacing parts before you've diagnosed the problem more often causes confusion than anything else (including fixing anything).

 

Steve, I'm not causing confusion to myself. Was going to replace the parts anyway because this truck sat for nearly 3 years without ever going more than 3 miles in one day. Things just weren't working when I got the truck and I replaced the battery, voltage regulator, solenoid, starter, oil pan (had rusted through), had a valve cover epoxied because it was leaking like there was no tomorrow and more recently the distributor cap and rotor. Ahhhh I replaced the windshield washer motor this weekend too (it rusted through). Money is not an issue, every fix is a business expense, and I would normally do this stuff anyway. Most likely I'll put in plugs (Autolite Platinum) and wires (dunno which kind yet) this week and change out the fuel filter.... and I'll look into the o2 sensor.

Like I said in the title, the engine seems to be running rich. That is the only thing that is bothering me about the truck. Otherwise it is serving its purpose and I couldn't be happier. I'm a real estate investor and rehab houses for a living, so fixing things on this truck is just another form of rehab for me and I really dig it.

 

Normally I'd say don't waste your money on platinum plugs. You don't have a waste spark ignition, you don't need them but since you're determined to waste money anyway go ahead.

What exactly do you have against doing a simple diagnosis by pulling the codes to find out exactly what the problem might be?

 

I figured I might get a comment or two about either using platinum plugs or the brand that I've chosen to use. No prob. Like I said, money is not an issue. I just haven't gotten around to pulling codes yet. Autozone didn't have the correct card reader as well as one of the NAPA stores I visited. I may end up doing a self test on it.

 

It's good that money isn't an issue to you because you're going to be wasting a LOT of it. Either by burning more gas to go the same distance, or by throwing away platinum plugs with a thousand miles on them to put in normal Autolite plugs, which run MUCH better in these engines.

Stay OUT of the zone - most of those morons know less about vehicle repair than they do about flipping burgers, and they're underqualified for THAT job, too. You don't need any scantool or card reader to pull pre-'96 codes. It only takes a paperclip (any jumper wire) and about a minute of your time. It'll take you at least 10x as long to read how than to actually get the codes, and the jumper wire is MUCH more accurate & reliable than any scanner. Here's one place to read how:
http://www.fordf150.net/forums/viewtopic.php?t=71346
There are plenty of others.