Hello, I have a 99 F150 with the 4.6L, I am having some major issues. The truck starts right up, but when I throttle it it has like a flat spot and starts to die then picks up....that's sitting still. When I drive it does the same thing and the worse part is getting on the freeway...it won't go over 40 mph no matter what I do....unless I am going down hill!

Had the o2 sensors replaced just before this started happening. After driving for a little while thinking maybe bad gas or vacuum leak the check engine light came on...I hooked up my scanner and got PO1131 AND PO1151 o2 sensor codes but they are new changed by Ford.

It cost me an arm and leg to get that done and not going back to Ford. The truck sat for a year or so after it was done.

I have drained the fuel, new gas with octane booster and fuel injector cleaner, no change, checked for vacuum leaks, none, no indication of misfire from the computer...Any ideas? Im running on a tight budget.

Thanks

 

Thoes codes are lack of switching on the rear O2 sensors (both sides). Given the other issue you have on the freeway I would bet on the cats being plugged.

Take it out for a run after dark for a few miles and give it hell. then look under and see if the cats are glowing red.

Here is a link that might help. http://www.aa1car.com/library/converter.htm

Good luck.

 

Thanks, I did take her out and gave it hell but didn't check the cats when I got back, I'll give it another shot tonight.
Thanks
Mark

 

Before you blow the engine from excess backpressure take it to an exhaust shop, they have the equipment to test for blockage.

 

I'd suggest checking the fuel pressure. Have you changed the fuel filter recently?

If it isn't fuel pressure, do what glc says.

 

I wouldn't do that. If it is running too lean, you just might melt a piston. It's running bad enough that finding the problem shouldn't be that hard.

 

Dude, you replied to a spammer! Go up the 2nd post and you can see he pulled that right out of my reply. I hate fricking spammers!

The codes are not for lean, the rear O2's aren't switching, most likely bad cats.

 

Well, if it is the cats, this would be the perfect time to slap on some magnaflow ones. They will be far cheaper and better than stock.

 

97 f150 4.6l 4x4 i swapped out transmission it shift all except last gear at 40 mph it starts bucking but will never go past no matter how much I floor it. I change plugs, wires, and coil packs. I also change intake gasket and valve cover gaskets. Along with timing chain and guides. Turn on and idles perfect takes off good it shift up 1, 2, 3 but will not upshift to 4. The truck sat two years. Would the fuel pump good bad. I checked the fuel pump pressure at idle it's within spec but I haven't checked it under load. Could I get some help please