I have a '91 F-150 with a 5.8. I tow my open trailer and race car with, about 5400 pounds. When I manually hold it in first it pulls well, I then shift to 2nd and it still pulls well until the converter locks up about 2 seconds later at which point it feels like power is cut considerably. My first question is if this sounds like normal operation? My next question is if there is a wire from the pcm to the trans that I can interrupt with a toggle switch so I can manually delay the lock-up to 3rd/OD when I'm up to speed?

Thank for any help!

 

My first question is if this sounds like normal operation?

I'd have to go with a no based on what you've said but a couple questions.

Sounds like its locking up the TCC before it should and maybe when it shouldn't to start with.

Does it lock up under 35 mph? Does it lock up/stay locked under heavy load/heavy acceleration and in any gear?

How does it shift otherwise, say just the truck by itself with none or just a light load?

Is the check engine light on or has it been on at any point/does or has the OD "Off" light flashed at any point? Have you checked it for trouble codes regardless?

My next question is if there is a wire from the pcm to the trans that I can interrupt with a toggle switch so I can manually delay the lock-up to 3rd/OD when I'm up to speed?

Yes there is but first perhaps a little trouble shooting is in order?

 

The truck shifts empty/with a light load fine. I can still feel the lock-up but it is not nearly as profound as when I am towing.

Yes it will lock up when towing a heavy load under 35 mph.

It shifts into second and still feels strong for a second then the converter locks up and it almost feels like another shift (with the lever in the 2 position so it is NOT going into 3rd.). It then stays locked up and when I shift into 3rd I don't feel the lock-up hit again so I am assuming that it is locking up in second and staying locked up all through 3rd and into OD when I let it go in.

No flashing of the OD light ever.

I'm pretty sure the trans is a rebuilt unit from JASPER and has about 16k on the rebuild, I found a warranty card in the glovebox, I'll have to dig it out again to verify. I bought the truck in it's way to the yard and saved it.

 

I have used these before, they do just what you are looking for.


http://www.kennedydiesel.com/detail.cfm?ID=193





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The ECU will command the converter to lockup after the second gear shift transition is complete, that is normal.
A locked converter will transmit more torque to the rear wheels, at the same RPM, as an unlocked converter. This also allows the transmission to run cooler and last longer under heavy load conditions. Try to refrain from towing in OD as well being that it is the weakest gear.

 

I'm wondering if your mistaking 3rd for TCC lock up, it does feel like a shift.

My 94 from a stand still, say taking off to accelerate up to and cruise at 55-60mph shift lever in O/D. starting in 1st, it will shift to 2nd then 3rd the tcc lock up then O/D.

It has never locked the tcc until after the shift to D and it never locks the tcc while under 35mph, if I'm slowing down the second I drop under 35mph it unlocks.

I have equipped that truck with a small light so I know when the computer gives the command to lock the tcc, that little light glows when the computer locks the tcc. (and a Auto/off/lock switch for the TCC)

I never tried it holding second gear, I just took it for a ride to see what it would do.

As long as I held second gear the tcc would not lock, it wouldn't lock regardless of how fast I went, accelerating or if I held a steady speed, (just over 35mph or well above that). The second I up shifted it locked the tcc, then unlocked it shifting to O/D and relocking it again. It always does that, unlock/lock for the shift to O/D, does it real quick. light goes out, shifts, light back on, light is only off for a split second for that shift.

I would suggest you check it for trouble codes, see if the computer will tell you any thing.
Sounds like you have a speed sensor problem of some kind. The computer just isn't getting the correct information on your speed at all times, if at all.

 

I also never saw my converter lock up in 2nd - it needed 3rd gear at least, not sure on the vehicle speed as it's been a while now. The way the converter operates also makes many people think they have 5spd transmissions - they get 1st free, 2nd free, 3rd free, 3rd locked up, and OD locked up, the converter locking up while in 3rd gear is often mistaken for an actual upshift. Then if you're in OD or 3rd and converter is locked if you floor the throttle the converter will immediately unlock, when you back off the throttle a bit it will reapply and lock again. When you completely let off the throttle converter unlocks again, which is why the E4OD generally sucks for engine braking. I have my converter on a switch, I can lock and unlock it any time I please regardless of what the PCM wants to do - really the only reason I did this mod is to be able to let off the throttle while going down a grade without the truck start picking up speed, basically converter stays locked and when combined with an applied coast clutch (achieved by canceling the OD and forcing a downshift into 3rd) it makes for some real nice engine braking...

 

I'm sure I'm not mistaking the third gear shift for the converter lockup as I am holding the truck in 2nd when the lock-up occurs. When I bump it up to D it shifts into third. Sounds as if I may have an issue. I will pull the codes and I may have a good VSS to swap in to see if it changes. Can either of you guys tell me which wire is the TCC circuit and in which plug it is? Keep in mind this is a 91 f-150 with a 5.8 if that matters.

 

PPL-YEL (Purple wire with yellow stripe), you should find it in a section of the harness on the drivers side front wheel well.

It will be in the main harness running from the trans to the EEC regardless how they run it for that model year.

 

A bad coolant temp sensor for the PCM can engage lock up in 2nd gear, if the PCM thinks the engine is very hot it engages lock up to reduce heat generation. I think they ohm out around 30 ohms cold.

 

Let me make a correction, it will lock after the 2-3 transition under normal driving conditions and it will lock after the 1-2 shift @ WOT. If the transmission downshifts to second gear from 3rd or OD, it should lock or relock.

 

Alright, I've got a new VSS and a new ECT sensors, I will install them this week and see what happens and post my results if any. Thanks everyone!

 

You 100% sure on this Matt? My observation has been that at WOT the PCM will keep the converter free the whole time the pedal is on the floor, which actually makes sense considering how pathetic the clutch in the factory TC is. Factory converter engaging behind a healthy engine running at WOT is just a recipe for disaster for that reason.

 

MY lock up on my 34' Rv comes out early. Just had the unit redone but going down the road it sees enough of a load that it comes out of lock up. If I let off the gas or go down a hill it locks back up. Just a very light amount of throtle makes it come out of lock up at speeds under 50 mph.