I have a 88' F-150 4x4, 31-10.5-15 tires, 4.9L, 5-speed with either 3.50's or 3.55's gears. Lately I have been getting 130 miles to a rear tank of gas, also have a lund visor and running tailgate down. Just replaced air filter, fuel filter, plugs, rotor, distributor cap and wires. I was wondering if it could be the oxygen sensor sending a lean signal to the computer telling it to add more fuel? PLEASE HELP!!!!

Thanks,
Ryan

 

Yeah that could do it.

 

How "lately"? Did you do something right before the mileage dropped? What was it before? The tailgate should be up for best mileage & handling. How long ago did you "just" replace that stuff, and what plugs & wires did you install?

The computer would probably detect a problem with the HEGO, so pull the codes. Is your tailpipe turning black? Does it smell like gasoline? Does your oil smell like gas?

BTW Your rear ratio isn't 3.50. You couldn't get that ratio in an 8.8" axle. If you post the AXLE code from the door sticker, we can tell you what it is. If it's 19 or H9, it's 3.55; 18 or H8 is 3.08. The "H" means limited slip; "1" means open diff.

 

I've never heard of a truck getting better mileage with the tailgate up than with it down. Unless, of course, if it has a cap or a tonneau.


-=Whittey=-

 

I have a similar vehicle, see signature...

I have noticed a lot of soot in the exhaust.....

Anyway I've been getting about 175 miles to 20 gallons of gas, it is really sucking the gas right down...

Do you think its the exhaust?

I have replaced everthing the first poster mentioned except for the fuel filter & I DON'T run with the tailgate down.

Would it be worth a shot to put $60 bucks into an Oxygen sensor?

Also could my Oxygen sensor be bad EVEN if the Service Engine light WASN'T on?
If there is a code to pull the Light WILL be on, correct?
Thanks

I would like to get better mileage, I just put $62.00 worth of gas in the SOB filling both tanks & I may get about 400 miles total....

Garrett

 

No, the exhaust is just where you LOOK for info about how the engine is running. It's not a likely CAUSE of this problem.

Replace the filter.

My HEGO only cost ~$40 for a lifetime Bosch from O'Reilly, and I think it'd be worth it.

Yes, the sensor could be bad even if there's no code stored for it, but there CAN be codes stored that DON'T turn on the CEL, so pull them ANYTIME you think there might be a problem. It never hurts. Just be sure to CLEAR them after you write them down so you're not chasing your tail.

whittey
I've never seen proof that any truck gets better mileage with the t/g DOWN, but I've heard that Ford, the insurance research agency, and NTSB found that it affects handling adversely. I haven't read the articles, but I'm sure they're available on the net somewhere.

 

By HEGO you mean 02 sensor I take it????

Should I get a Bosch, Autozone, or OEM unit?

The Bosch from Autozone is probably the same one you have, right???

I am curious, how would FUEL mileage be affected by the filter?
You'd think if it let less fuel through you would just get better fuel mileage & worse(r) performance????

Thanks

Garrett

 

OH & when I said "Do you think its the exhaust?" I meant "Do you think its the 02 sensor, stupid me...

 

Looked at the axle code and it is 19 the 3.55 when I first posted i couldn't remember off the top of my mind. I went to napa and got a new oxygen sensor. Tried to get the old one off after I let the truck run for a minute or two so it warmed up. But no luck getting it to budge. Tailpipe is black on the inside and out side is fine. Lost my patience with it so I will take it to my dad's friend and let him deal with it since he charges hardley anything.

 

Change the fuel filter . If the engine isnt getting enough fuel more driver imput in needed : you have to push the gas pedle down more to make the truck move and stay at a consistant speed Besides you are supposed to change it every 15,000 miles anyway ..some people change them out at 30,000 miles ..what ever floats your boat..the point is it isnt perminent so I would go ahead and change it . A pluged up filter will also lead to a overheated and or over worked fuel pump which may cause premature failure of the pump(s)

 

I just replaced the fuel filter,cap and rotor in the last 500 miles every thing else was replaced in the last 1,500 to 2,000 miles. it still got the same crappy mile before I did any of this!