Converter randomly unlocks

[LCAM-01XA]

Well, dunno if tis really random, but it sure seems like it - say I'm cruising at 52-53mph, no load on truck, cruise control on, then the thing all of sudden will unlock, the a few seconds later lock up again, then a few miles down the road do it again... I've noticed it never unlocks when I'm climbing hills, but only when I'm on level ground or descending. Don't remember it unlocking when I'm actually driving it (cruise off). Tis always been doing that, ever since I've had the truck, never figured it out - any ideas/suggestions please?

 

[towcat]

disconnect your brake light switch and take it for a short drive. don't forget to plug it back in after tho.

 

[Shadetreemechanic]

I solved that on mine with a new tach sensor.

 

[dakotajeep]

I had the same symptoms with my pickup and ended up wiring a switch that would groung the Torque converter to avoid the locking and unlocking while at speed.

I checked/replaced the FIPL, all electrical connetions, replaced my Tach sensor, checked all elec connections on the brakes and ended up just wiring in a switch....it seemed easy enough for me.

thad

 

[dbarilow]

i would guess on the tach sensor you can try to clean it off it the connections are good, it is a ford part only. located on the front of engine near oil fill its a large bolt looking thing with 2 wires coming out of it.

 

[LCAM-01XA]

If tach sensor was bad, wouldn't that mess up the lockup when I run without the cruise on? Cause that one is always locked when it should be locked, and only unlocks when I back off the throttle completely.

Towcat, what does unplugging the brake switch achieve? And by take it for a short drive, do you mean just like around the block, or do I have to pick up speed so I can use the cruise too?

 

[dbarilow]

the tach sensor feeds signal to the computer when to lock and unlock. if your tach bounces at all it will effect when it locks up. The brake switch also sends a signal to the converter when depressed to unlock the T/C. try it while you are cruising in OD just tap the brakes and listen and watch the tach.

 

[LCAM-01XA]

Yeah, I know that - my tach don't bounce one bit, never-ever. Brakes unlock the converter, off throttle unlocks it too. Really, everything seems to work perfectly, tis just that random unlocking when I use the cruise...

 

[Shadetreemechanic]

My tach never bounced either. But mine also didn't seem cruise related. Also from time to time mine would remain unlocked for 20 minutes or so on the interstate. It remained an intermittant annoyance until it unlocke and my od light started flashing while towing the tractor up the mountain. Replaced the tach sensor and reset the computor the next day and had no further problems.
Your relation to cruise seems to make the brake circuit seem more likely to me, though if the cruise received signal that the brakes were applied it should need manual reset before resuming and re locking the tc.

 

[tradergem]

I had the same problem with my truck awhile back. It turned out to be a bad FIPL that was giving a intermitant signal only while the engine was running. It would pass the Key Off Engine Off code test, and the Key On Engine Running code test. But it produced a continuous memory code after letting the engine run for 10-15 minutes. I tested the FIPL with a digital VOM and it would pass the minimum and max volts but seemed to have a little hitch in the middle of its movement. I replaced it with a new FIPL and the T/C started working properly again. Good luck and hope this helps.
Jim

 

[LCAM-01XA]

Well I towed a big 2-axle enclosed car trailer last night, 200 miles to the delivery point and 200 miles back, converter didn't unlock even once! But I had my foot on the throttle most of the time, as we all know how stupid cruise control gets when it encounters hills and you're nicely loaded. So tis definitely cruise-control related, whatever it is...