No TCC lockup, interesting scenario

[SammyM00782]

Good evening everyone. Boy do I have a doozy for you today So last weekend, I noticed my 94 XLT wasn't applying the converter clutch after doing some lighting upgrades. It was suggested to me to remove everything I did and try again. So I did that, to no avail. Now here's the real problem I can't figure out. If the truck is jacked up in the rear, freewheeling, the PCM will send 12v and command lockup . Put the truck on the ground, no PCM command. I had a DPFE code that I took care of, OHM tested the ECT sensor which is working fine, BOO switch is working fine, replaced the VSS sensor because when I went to go test mine it was filled with trans fluid. Also found I had a bad set of plug wires so I did that too while it was in the garage, could have possibly been messing with the PIP signal.... I'm literally out of ideas here as to what the hell is going on. I noticed tonight though after a coffee run to Wawa, I jacked the truck back up and this time I got no command for lockup. It seems to just work when it wants to, as long as I'm not actually driving. On a side note, I was getting the lockup command when the truck was still pretty cold so I don't think it could be a temperature issue. Thanks everyone.

 

[natenkiki2004]

Sounds to me like you know where to look for 12v power, follow where that wire goes. See if it's grounding out or broken. Go to the source and apply your own 12v power, see if it locks up. You'll know then if it's a control issue or a wiring problem.

 

[SammyM00782]

I'm probably going to have to pull the PCM out again and probe at the connector, right now I have it probed at the trans. I do have continuity in the wires though, tested that STAT. It's times like this when I wish I'd bought the power probe, makes life so much easier. :-\

 

[Albino 94LTD]

If, for some reason, it's running in Limp Mode, the TC won't lock up. Do you have any codes?

Make sure the MAFS plug is good and secure and check all other plugs near where you were working.

 

[SammyM00782]

If, for some reason, it's running in Limp Mode, the TC won't lock up. Do you have any codes?

Make sure the MAFS plug is good and secure and check all other plugs near where you were working.

I did have some codes when I got started, some of them didn't really make any sense but I've taken care of those in the meantime. 117 and 118 ECT sensor above/below min/max range, 327 EVP below min range (my fault as the wires don't stay seated in the connector and I had them backwards :-\ Gotta find a new connector for that, 332 insufficient EGR flow, 336 EGR sensor voltage higher than expected and 558 EGR valve regulator solenoid circuit failure. All have been remedied and I no longer have any codes popping up. Computer has been completely reset as well. Anything I could find related to TCC operation has been tested sensor wise so all the connectors should be seated properly. It seems to be intermittent but only when the truck isn't actually moving. On the ground, driving, I get nothing. I read somewhere that the ECC relay also has a hand in TCC lockup and I'm wondering if I have a problem there. I wiggled the relay yesterday and it seemed to me like there was a response. Like when you end a KOER test and the engine responds with a gust of intake air and and RPM increase, that's what I heard.

 

[SammyM00782]

Just a little update. I went to Wawa to get my coffee this morning so I decided to take the Exploder. Believe it or not, I got TCC lockup. It works moderately normal with the exception being I think it's commanding later than normal. I could've sworn I had lockup at and over 35mph. It just seems to me like it's waiting longer than usual, kinda odd. Could also just be that I left that battery unhooked for hours and the computer is just getting itself together. I'll have to wait and see right? I'll drive it over the weekend and see if everything pans out. I hope it does because I am WELL overdue for a fluid exchange, filter and VB refreshing. Whole bunch of Sonnax parts and a Transgo kit just sitting in the box....

 

[natenkiki2004]

I'm not a transmission mechanic so I could be wrong but isn't TCC the last "shift" that happens up around 50mph or so? The lower RPM shifts you see at lower speeds I believe are OD kicking in in 3rd & 4th. I think anyway... You wouldn't want the TCC lockup at 35mph, you could stall the engine and you often need the torque multiplier that the torque converter gives at lower speeds. TCC bypasses the torque converter so you have lockup all the way through for better MPG. The TCC lockup should also happen in D, just earlier.

 

[Rhett]

Could also just be that I left that battery unhooked for hours and the computer is just getting itself together. I'll have to wait and see right? I'll drive it over the weekend and see if everything pans out.

I think you're onto it here. Give it a couple of days (mine takes even longer than that after unhooking the batt) and see how it is doing. My truck will run wonky and TCC lockup will be off for literally days, maybe a week after a reset.

And about the fluid/filter change, it's always a good time for that. Hopefully it's just the PCM relearning and you won't have to mess with the valve body.