I have a 97 f150 xlt 4x4 long bed 4.6 3.55 ls with 92,000 mi. I've bought the truck with 38,000 mi on it. My tire size has been 265/75/r16 the entire time. I've noticed a problem with the truck that I've been trying to get rid of for years. I've done things recommended from this site and they've helped, but its still there.

When I accellerate, the rpm's *sometimes* stay the same, reguardless of how much pedal I give it. It doesn't matter of its city, highway, incline or decline. I'll floor it and I stay at around 1700 rpm's in drive, not OD. It's worse with overdrive. It will also lag at 3000 rpm's. With the pedal to the floor, once I'm in 3rd the needle climbs to three, goes down to 2100, then climbs again. These symptoms are more prevalent off road. When it goes into the next gear, it takes a very long time to wind back up.
My power and accelleration is ok, it just digs too deep into the powerband when it shifts.

No one can help at 3 dealers and 2 garages. No codes, mechanically sound, but has a mind of its own.

I've changed:
Plugs
Wires
coils
Fuel filter
4 O2 sensors
Valve body (baumann)
programming (superchip)
intake (k&N FIPieceofshizat)
exhaust (Flow 40 2.5 si/so)
AND, I disassembled the entire intake to the heads, cleaned and replaced, seafoamed, etc, etc.

Will replacing cats and changing gears to 4.56 help?

 

Throttle positioning sensor? I have noticed this lag with my 97 4.6, too. Not really a nuisance, but when entering the Interstate, the truck pulls like the beast that it is, but right after the shift to 3rd gear, it gets really sluggish and take 10-15 seconds to get the next 10-15 miles an hour. I would like to know what to do for this, though, even if it isn't the exact same problem, I bet that if we figure one out we will have a good basis of where to start on the other one.

 

Guys,

Try checking the rear brakes for binding.
Do a compression check on the engine. The lowest readings should be within 75% of the highest. Clean the MAF and finally check the cats for obstructions. If they melted that is a sign of running rich so you will have to find out why the truck is running rich.

Regards

Jean Marc Chartier

 

Thanks guys. Back brakes aren't binding, they barely work. I cleaned the maf and cleaned my k&n and tried it w/o oil and noticed no change. How can I check the cats for restriction without cutting them open? My tip is sooty but I thought this may be from the chip. The cats look lousy from the outside and tick when I shut down, but they don't smell really bad. Do I really have to page Dr. Sawzall to the Operating Room?

 

My 4.6 does it too on occasion. I found it happening after I drive in 'Granny Mode' for a while. When I reset the computer and drive aggressively for a 1/4 tank the PCM relearns differently and the hesitation is gone. It takes at least 6 months of easy driving before the hesitation comes back.
So try it. Disconnect the battery to reset the PCM and then drive like you're at NASCAR for an hour and see what it does.

Fritz

 

No dice, unless I am in 4x4, I always drive NASCAR-style, and it didn't make a difference, even after resetting the PCM.

 

Shrike,

A service station can check for a plugged cat with a exhaust back pressure guage. it screws into the O2 sensor bung and reads the pressure. Don't start cutting yet. And if the cat is plugged you have to find out why and cure that too.

JMC