I'm having a problem with my 99 F350 Crew 4x4 94k. On long drives it seems like the engine disengages from the tranny on downhills. What happens is with the foot off the accelerator as soon as there's a bit of back pressure there's a ZZZZZZZ zippering noise and the RPM's drop to zero. As soon as I step on the pedal, everything's fine. It's not an everytime thing, but has become more frequent.

If I keep light pressure on the pedal on downhills it doesn't happen.

Any ideas?

 

That would be the torque converter unlocking. You can get a different pcm code to keep it locked, wire in a switch to lock it manually or install a 4-page chip programmed to keep it locked.

 

Do the RPMs drop to zero or does it drop back to idle RPM? If your loosing the RPM signal, maybe the cam sensor is starting to go bad.

 

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Sounds to me like thats what it is doing. mine will stay locked for about 30 seconds if I try to coast down a long hill using only the engine. then it wil unlock and the rpm's drop to idle and I just coast down, slowly gaining speed. here is a link to the converter lock mod I did, works well. http://www.forgotton.net/mods/tclock/index.htm


Diesel Rod

 

Thanks for the insight.

Do the RPMs drop to zero or does it drop back to idle RPM?

I believe they do.

This may be unrelated, but I also have a serious "clunk" when starting from a standstill. It's almost like something that's stuck for a few feet and then let's go. Seems to be coming from somewhere in the front end.

 

Do you have shift on the fly 4X4?

 

Do you have shift on the fly 4X4?

Yes it has the shift on the Fly 4x4.

 

why is it good to keep the torque converter locked up while going down hill?? if your towing a trailer i can see that because you want engine braking, but if your not towing anything, then you will just coat down, and probably help with mileage.. but i heard that when its unlocked it builds alot of heat which kills the tranny. any help is appreciated

 

Yes, when the converter is unlocked the shearing of the oil in the converter creates a lot of heat, when you are going down hill the vehicle is moving, and the engine is slowing down, there is no load on the converter so it doesnt make as much heat as if it was unlocked and going up hill. the only real advantage to locking it when goin down hill is the engine braking effect, it is comonly used with the EBPV mod too.


Diesel Rod

 

thanks diesel rod

 

I'm just grabbing in the dark here, but try manually locking the hubs to see if it has any affect on the zipper noise or the clunk. I don't think they are related to the transmission disengaging.

 

Found the culprit at my Ford Dealer today: Torque Converter is shot