This problem does not seem to have an answer DESPITE in depth investigation.

THE PROBLEM: My 1997 4.6L, 5 speed manual tranny, ExtCab F150 CHUGS AT 82mph. I get to that speed on the interstate and it chugs as if it is coming out of gear then going back in.
It chugs at 82mph in 4th gear and at 82 mph in overdrive. I even tried 3rd gear with the same result.

THE INVESTIGATION: My mechanic has always been a genius. He has detected and fixed problems that have stumped others. I drove the truck to 82 while he checked the COMPUTER for ANYTHING. NO PROBLEMS with fuel flow, etc.
He checked the tranny and found it to be sound. The fuel filters were changed. Over the past 2 months I have changed the VSS (variable speed sensor) and the both O2 sensors. I have replaced the plugs and the plug wires. I have had the truck tuned up. I replaced the fluids in the transmission, transfer case and both differentials and used the specified fluids for all.

CAN ANYONE SOLVE THIS ONE? Other than this 82mph problem, the truck is flawless.

------------------
1997 F150XLT 4X4 Supercab 4.6L Silver

 

Do these trucks have some sort of speed limiter programmed into the computer?

 

And/or have you changed tires/sizes recently?

------------------
Chuck 'Wyldman' Shelton
wyldman@houston.rr.com
Black 99.5 Lightning Build # 1273, DOB 5-14-99, NLOC #315
Best run to date 12.857 @103.48
CD Changer; Tow Pkg.; Lojack; Sal's custom nitrous chip; G-Tech/Pro; SnugLid; BedRug; Invinca-Shield, full kit; NOS KIT 100 hp shot (currently); Clear and smoke Lexan fog light covers; 3M Ti Window Tint; Bel radar detector (shouldn't be an accessory); PowerStack cone filter (a.k.a. supercharger waker upper); American Auto Designs ram air hood; Cal-Tracs traction bars; Bassani headers;Goodrich T/A Drag Radials; Muth Signal Mirrors, inbound

 

Wyldman,
The tires are the same size as the one that came from the factory.
d reyes
As for the speed limiter, aren't they set higher and how can you detect if that is the problem anyway?

 

There is a speed limiter on these trucks, Wyldman's question about tires is the most common one as well as an axle ratio change.
Go from 3.55 to 3.73 gears and the driveshaft is turning faster than before at the same speed. It thinks you are going 100 mph when you are doing 90, or something like that.
If you have not had any changes to the vehicle though, they may have put the wrong calibration in the PCM for your axle ratio.
I am not sure on the 5-speed trans, but the autos also have an OSS,output shaft speed sensor.
Another issue is the accuracy of your speedometer. Have someone pace you at speed and get them to concur with the speeds. If the output of the sensors is wrong it may also affect the speedo.

Good luck
Birdman

 

I've read from 1 hour to overnight. Try it. Its the cheapest & easiest thing to do. Having the chip reflashed might work too.

 

Disconnect battery.
Turn on headlights.
Wait 10 minutes.
Reconnect battery.
Drive it.

Sounds like a speed-limiter kicking in at 82, to me. Good luck.

Jim, I just noticed you were from Colorado. Check your fuel filter and add some Dri-Gas to your fuel tank. You are burning 10% alcohol in the winter in Colorado gasoline.
Since your problem shows up at the same speed in different gears, I'd still lean toward speed-limiter.

[This message has been edited by J-C (edited 02-16-2000).]

 

If I'm not mistaken, the speed limiter is not based on engine rpms, but on actual speed of the truck as reported by the speedometer/computer.

It definitely sounds like it's the speed limiter kicking in.

 

J-C,

Ok, maybe I'm just smoking crack but if you disconnect the battery, where are you going to get the power for the lights?

Not trying tto start anything, I just don't understand the electrical on these trucks yet.

Bones

------------------
2000 F-150, XLT, 4X2, Ext. Cab, S/B, 4.6L, 3.55 L/S, Tow Package, Premium Sound CD Player.

Future Mods: NONE, I'm broke.

 

No Bones thats not right, you are overthinking it man! He's just saying turn on the light *switch*. The lights will not come on but the cuircits will open and discharge the storage in the capacitors and such (internal thingies) quicker than just by letting the battery stay disconnected. Otherwise it takes from 20 minutes to a half hour. You don't have to believe me, this was per Mike T.

 

Thanks, that totaly makes sense now. I'm a little scared I didn't think of that.

Bones

------------------
2000 F-150, XLT, 4X2, Ext. Cab, S/B, 4.6L, 3.55 L/S, Tow Package, Premium Sound CD Player.

Future Mods: NONE, I'm broke.

 

Dennis and others,
If it is the "SPEED LIMITER", how do I fix that or can I? Will disconnecting the battery automatically reset it?

 

Superchip it!

 

Hey! if this turns out to be the problem does this mean we are all super genius level mechanics!

 

This is absolutely a speed limiter problem, and is probably due to a faulty ECM. You could try installing an aftermarket chip, but to correctly remedy this, Ford needs to post a TSB on it. I would keep checking with Ford and see if a ECM TSB surfaces for your year and model. Disconnecting the battery should have no effect on the speed limiter, but the truck will feel peppier for a while.
Take care,
~Chris

------------------
Moderator
MustangNet

'95 Eddie Bauer F-150 SC & '64 Falcon/Ranchero
-------------------------------------
Are you A.S.E. Certified ? If so, ask me about
iATN...the best tool you'll ever have ! ! And it's
free