I have a 1997 ford f-150 xcab 4x4 with a 4.6 litre 5spd with 3.73 gears. The problem i'm having is that when i tow my bobcat trailer or any trailer , i'm having a power loss as soon as i shift into 4th and 5th gear. I can barely break 60 mph in 4th gear when towing. This is the list of things we've dont so far, new plugs, wires, fuel filter, air filter, swapped maf sensor, aic, temp and air intake sensor and tps. Checked for trouble codes with the fordstar tester, no codes. Checked for vacuum leaks, none. Checked fuel pressure with and without load, 38 psi. and fuel pressure regulater tested good. We also had the injectors professionally cleaned at the ford dealer with some expensive solvent ran through them. When i take off from a dead stop I have all kinds of power until I hit 4th, this is very wierd, it almost feels like the ac or some other kind of load in ******* out the engine when everything is off. PLEASE HELP !! I DONT WANT TO TRADE OFF MY MINT TRUCK. We've also moniterd all the sensors with the fordstar, like egr, tps,maf, etc.

 

You got me stumped.
I find no references to man. trans operation as a far as engine operation alteration manegement goes. If the involved dealer testing can't see anything then about the only thing left is PCM torque manegment going on.
Ask the dealer to try a PCM reflash and drive the truck at least 30 days after any PCM reboot occurrs so it re-learns operating parameters before making final decision as to any improvement has taken place.
Questions are has the truck ever pulled in 4 and 5 satisfactory?
Is the clutch slipping?
What is the GCW your pulling? It's a lot to ask 4th and 5th to pull like 10k of weight at any real rate of accelreration. There just isn't much torque in a 97 4.6 at low rpm.
You may be asking to much of the engine in those gears vs weight.

 

I have a similar set up, 97 F150 XL, 4x4, ext cab, 8 foot box, 5 speed with 3.55 rear grears. Its bone stock except when I bought it it has 1 size bigger tires than the OE's (255 70 R 16 vs the stock 235 70 R16.....aprox 1 inch taller)
Couple questions for you, how heavy is the Bob Cat and trailer? I know those things are heavy depending on the size. Have you been towing this with the same truck, and all of a sudden you had loss of power?
You have the 3.73 gears which is a good thing for towing, (I wish mine had 3.73's), better than my 3.55 anyway, was that stock? What size tires are you running? Any exhaust mods?
I tow a 1976 17.5 foot travel trailer that is probably 3700 lbs loaded, hat doesn't include the 5 people in the truck, plus approx 5-600 lbs of crap in the box, and it does OK, if you are on a steep hill or have a good head wind, you'll be shifting.
One thing I can tell you is the 4.6 does not have a lot of low end torq, so you'll have to get into the RPM's to get the power you need for towing. My XL does not have a tach, but I'm guessing it wakes up around 2500 RPM's or so.
I asked the above questions because bigger tires effect grear ratio which effects towing, opening up the exhaust can reduce low end torq as well.

Hope this helps

 

4th gear should be 1:1 on the 5-speed..... If you are having trouble towing that, then you have just reached the max amount you can handle with your truck.....

I assume, it all drives and performs fine when running solo, right?

Are those 3.73 gears stock?? The reason I ask is that I didn't think the 3.73's were available for the F150 in that year.... If you got the Light Duty F250 of that year, then you could have the 3.73... Do you have 7 lug wheels on it?

Anyway, give some more details on the weight you are hauling and that'll help diagnose the problem, but I'm gonna say that you are just maxed out on the power abilities of your 4.6...

Mitch

 

I do believe that, as others have stated, it is the lack of power in your 4.6l. I would never pull a bobcat with a 4.6 on a regular basis.... it just seems that you're putting alot of strain on a motor that was primarily manufactured to give the consumer the best of a fuel efficient V-8, not towing capability. If it just started then we may have a problem..... otherwise just drive it 'till it blows and then convert to a 5.4

 

THANX FOR THE FEEDBACK GUYS.. When I first bought the truck I could hit 100mph like nothing without towing anything, now even without a trailer on it I can barely hit 85mph, I've just noticed the huge power loss towing my bobcat & trailer that I think weighs around 3500 maybe a little more just guessing. My gear ratio on my vin lookup said 3.73's, but i have a 5 lug wheel so who knows if it's right. I can damn near get rubber is the first 3 gears. Now when i tow anything i can barely hit 60 mph. 1st through 3rd is normal with awesome power, as soon as i throw it into 4th, it's nap time. lol

 

If you're having problems under no load (no trailer) then do a compression test. Sounds like you are loosing it under load. Also, try changing the tranny filter. I had a 97 F150 4.6 that went to hell one day, shifting erratically and topping out at about 75. Drove it like that for a month, got pissed off and changed the filter, worked like brand new. And the old filter looked like someone took a dump on it

 

Could also be the fuel filter at the fuel pump inlet.

 

thanx for the input, it's a 5spd manual by the way.
I will try the compression test tomorrow to see what i get.
I'm not sure if the filter at the fuel pump inlet could be plugged since we've done a fuel pressure test and a bleed down test, at idle, running and under load, all within specs. I'll try anything though, thanx

 

i had a very similar problem with my jeep with loss of power...turned out to be a restricted catalytic converter...a piece of the material in the cat broke loose and restricted my exhaust flow. cant hurt to check it out.

 

yeah, i've thought of that, when i was going to drop my exhaust the bolts were kinda rusty and i've been through some broken bolts and head bolts on other fords, i kinda put it on hold for last resort, lol. My older work truck did the same there you were talkin about with the ceramics breaking up inside the converter and had severe power loss. thanx for the input

 

I have a 99 4x4 with a 5.4 Automatic and I tow a car trailer that weighs 1950# by itself I have towed my 05 Jeep Gr Cherokee on the trailer behind the Pickup and had no problem. Even going down the interstate at 80mph in overdrive but it sure is better for the tranny with overdrive locked out. I did however put 3500lbs of household furniture and crap on the trailer and towed that down the interstate 300 miles and had a hard time making 70 mph even with the 5.4L. The difference was the aerodynamics of the trailer. With dressers and crap on it that really made a big difference at highway speeds. Once you get up to speed it is HP and not so much the torque you need to go faster. The bucket on the front of your bobcat is nothing but a parachute your trying to drag down the road did you face it forward or rearward... Also I got about 16MPG towing the Jeep and 12MPG the furniture that resembled the Borg spaceship.(square)....

Just something to think about

 

I bet it is the cats. I had a Mazda 2200 automatic (powerhouse) that was bad doggy. We drained the cat & it really woke it up all the way to just doggy. With a truck that old, the cats could be the culprit. Let us know what fixes it.
Good luck

 

Checked Compression On All Cylinders, All Passed With Flying Colors. Heated Rusty Exhaust Manifold Bolts And Dropped Exhaust. Went For A Very Noisy Drive, Lol. Still Sluggish In 4th And 5th. I'm Thinkin Of Trading It In For A 2000 F-250 Super Duty Crew Cab 4x4 With The V10...... I Cant Wait......i'll Post Pics Of My New Beast Soon.