i'm new here, trying to find a fix for my ride. its a '99 f150, has the 4.6L, auto trans and it's rear wheel drive not 4x4. I'm not sure how to describe what it's doing really. when i'm driving along it does great but when i try to accelerate it seems like it's "fighting" itself like it has pre-ignition in a cylinder or 2. when i pull up to a stoplight and let it idle i can't take off without it acting up plus it's drinking more fuel than i can keep in it. when i bought the truck it's exhaust had been stolen and they cut the pipes off above the O2 sensor and i haven't had the money to fix that, it has some "exhaust" under it but it's just kinda rigged up, not sure if that has anything to do with it but it didn't start acting like this til recently. i'm a delivery driver and this truck is my only means of making money so i need to fix it asap, and ideas or suggestions would be greatly appreciated. oh, and i tried unplugging the MAF sensor to see if that would help but it didnt change anything so i'm pretty sure it's not that. i really need some diagnostic suggestions...

 

Have you tried to pull codes? How many miles? Take it to an auto parts store to check for codes. That would be your first place to start.

 

Above the upstream or downstream o2 sensors?

 

Sorry you got into this problem.
Do you have cats in place?
Are the OX sensors in place?
If not, this is a reason for poor fuel mileage.
Until you get this issue repaired, other issues there may be won't be the total answer.
At this point it's your first thing to do.
Did you know the exhaust was gone before you got the truck?
There is an old saying that goes like this, 'even if I get something for nothing it's not free if I have to spend money fixing it'.
Don't know if there is any help beyond getting the exhaust back to stock, at this point. They were likely stolen for their scrap value.
Full cat assembly for each side aftermarket is about 300 per side not counting labor and the OX sensors.
Good luck.

 

i didn't plan on taking it back to stock, i don't really have the money for that. i've been trying to find a shop where i live that will do it without going completely back stock, i just need exhaust i'd rather not have cat. converters on it. i'm just trying to fix it as cheaply as i can but not poorly like it is now. i let a family member do it how it is now, just so it would have enough back pressure to keep it from burning a valve hopefully cause i didn't have the time or $$$ and they did it for free.

 

on they codes, the only code it pulled up was for the o2 sensors, and the exhaust was cut off about 4" short of the manifold on both sides so yeah it has absolutely no o2 sensors. i'm pretty sure it's not the MAF sensor, i looked up a diagnostic check list and tried for the MAF but it had no effect. it has a 4.6L, XLT package 2wd

 

it rolled 250000 tuesday afternoon actually

 

You need to know a few things by your replies.
First you need the forward OX sensors in place to control fuel correctly.
Without them, the computer goes to 'rich' fuel tables to service the motor.
This has a devistating effect of fuel mileage.
Next, you are not looking for/wanting back pressure in any exhaust system.
The less the better because leftover exhaust lowers power output. It has no purpose, does not burn the second time, and contaminates the new incoming fuel mix to the cylinders by not being expelled enough due to excess back pressure.
Next, if you have emissions, you have at least a code P0402 from missing rear sensors and cats.
You would have codes from the fuel tables being out of limits, as well.
I get it's a difficult problem for you but some how the truck has to be repaired correctly if you expect it to run up to par.
There are no short cuts to all this.
If your putting a lot of gas in now per tank, you would save a lot of that money if repaired correctly, over the longer term.
I believe if I were you I would try to find a way to trade it off for a smaller car or other truck that is all complete and needs less expensive repairs.
It's going to get you sooner or later either way..
Good luck.

 

thanks, i appreciate it

 

Man...that's too bad. But without forward o2 sensors on both banks, it must run terrible. You just have to get the exhaust fixed to run right. Don't let someone tell you MIL eliminators will solve this....

 

I would goto a junk yard to see if i could get the complete y pipe from another truck that is the same as yours, and install the o2 sensors. even if you dont have any pipe after the y pipe it should start to run ok. then pull codes to see if there are other problems. with out the o2's in place you will have other codes that will should be fixed by the catts, and 02's. that will probley be the cheapest way to get it right. you should be able to unbolt from the manifoled, and then from the mid pipe and drop it out. you may be able to find one here where some one has put on headers, and a new y pipe, and have the old ones left over., good luck

 

I appreciate it man, all i know is i gotta do something.

 

I had a 04 Mustang that the weld broke right above the passager side upper catt next to the manifold from jerking it around lol. i drove it on home, but it was dumping so much gas fumes i thalt i was going to pass out. lol. i think if you just replace the y pipe, and cats you will get it in alot better shape. The car probly used over 1/4 tank in like 15-20 miles. i know your pain

 

it's horrible man, and i drive it all day everyday. to class durning morning traffic then home then completely across town during 4 and 5 pm traffic and deliver pizza all night. it eats me up