And yet another E4od post

[Magoo]

Ok. Narrowing down the mileage problem I have reported before. The truck runs down the road at 55mph and 2000rpm. I have counted the shifts many times and I get 4. Yesterday i hooked up the trailer, which weighs 1500 to 2000lbs and right out the driveway she shifts up quicker than normal and third and fourth are power robbers and damed if I wasnt rolling along at 65mph at 2000rpm. Started racking my brain all day on it. After driving an hour or so it started bucking. Shifting in and out of gear. I believe I know whats going on but not sure why or how to fix. I think, that unloaded it is not fully locking up in 4th gear. (does it also fully lock up in 3rd with the OD button on as well?) With a load the trans is fully locking up. And its locking up in both 3rd and 4th gear. Once fully up to temp on a long pull with a load it bounces in and out of full lock up. Now once I loaded the trailer (8000lbs. of doug fir beams) there was no way to drive it with the OD button on. With the button off it drove fine but it sure sucked the fuel. Roughly 8 to 10mpg. And She cruised 45mph at 2000 rpm. So--------------------

What controls the lock up?

These trannies have throttle position sensors and speed sensors which control shift points. Some say the Tach sensor as well but I am not sure thats true. Which is responcible for lock up?

Where is the computer?

Is it in the trans on the valve body or is it under the dash or something.


So in summary. Truck gets horrible mileage but runs great with out a load. Add a load and my shifting changes and my cruising speed increases with lower RPMs, but it bounces in and out of lock up which sucks to drive.

If it can be fixed I will fix it. If not, than its prolly getting parted out and I am buying another with a 5 speed. Already got my eye on one.

 

[Mr_Roboto]

The computer controls everything, the sensors just give the computer input. The computer is in the same place as a gasser PCM, under the dash.

I suggest replacing the Tach Sensor, it is the one sensor that will cause in and out lockup of the torque converter. Like any magnetic sensor, they will fail eventually. "Replace the tach sender on the oil fill housing a big 1" nut with 2 wires. Ford only part Engine RPM sensor E5TZ-17B384-A about $50."

Also reference the third post in this thread: http://www.oilburners.net/forums/showthread.php?t=12736&highlight=sensor it explains the various sensors..

 

[snatchal]

I was having the same problem. 10 miles per gallon.
I did the converter lock-up mod and now I get 16-18.

 

[Magoo]

Update. Read everything I could find on this trans. The RABS issue kept nagging me. I have had trouble with the light coming on since I got the truck. Never thought too much about it. Turns out that the RABS needs the stop light bulb resistance to tell the computer that brakes are being applied. There is a nominal amount of voltage that runs through the stop light wire whenever the key is on which is not enough to light the factory tail light but still makes the connection to ground which arms the computer. How this is read by the tranny computer is beyond me. So. This truck has LED lights. There is no path to ground and so no resistance to tell the computer anything. That nominal amount of votage "is" enough to light three of the LED lights in the tail light. So today I put truck light bulbs in and wala, problem solved. Almost

So here is what has changed.
Now I take off from a stop and it shifts 1,2,3 no lock, 3 lock, 4 lock. Its like a five speed tranny. 5 noticeable shifts. There is a big drop in RPM on the 3rd to 3rd lock change and it seems to come on quicker than I like. I know the FIPL controls that or at least I think it does, but mine is new and I checked it and it is within the proper range. So is the RPM sensor.

I am sure to get better mileage as now I can cruise 65 at 1900 to 2000 rpm.

It must have been the trailer lights that allowed the thing to shift into OD mode but not enough to hold it there so it jumped in and out of OD causing the bucking feeling. Going to hook up the trailer again and check it.

 

[Mr_Roboto]

The light issue is interesting. I read something a while back about tow trucks having problems because the wrecker bodies had LED lighting. I believe the solution was to wire in regular incandescent lights underneath the truck.