TC Locks Up at 45 MPH

[Extreme1]

Since I bought the truck in '97, the TC has locked up under part throttle acceleration at 45 MPH.



First I tried reflashing the PCM, no change.



Piers said I should have 1. 2v @ the idle position. I carved up the TPS (Piers said he's had to also) and got 1. 0v, any more and I get into the interior of the sensor. Before I started it was 0. 4.



There was no change in shift point with this change in idle voltage. (The cruise works nice again though). The voltmeter (analog) sweeps nice and smooth from idle to WOT.



A few weeks ago at Goerend's, Dave lent me a new TPS (still in the box). Idle voltage went up to 0. 6. I didn't drive it with Dave's new TPS because it was still so far off.



The WOT downshift from TC lock does work (it didn't until I started messing with this).



Supply voltage is 5v, resistance from the TPS ground pin to the negative battery terminal is less than 1 ohm.



Has anyone else gone through this?



Does anyone have any ideas on what to check besides replacing the TPS?

 

[Wally19]

Buy a Manual!

Hey Eric, buy a manual transmission for that truck, and no more TC problems. You can thank me later for my advice.



Jason

 

[LSMITH]

Have you tried a variable voltage regulator hooked to the TPS? I am thinking if you hook a variable voltage supply up to the TPS you can get the appropriate voltage out of the TPS. Feed it 6 volts and get 20% higher voltage out kinda thing. If you could do that and drive it you would know that the TPS voltage was in fact the problem you need to tackle or not. You should be able to pick up a simple regulator at Radio Shack for a few bucks.



Just an idea, hope it helps.

 

[Cummins Corvette]

Mine does the exact same thing. It actually makes the turbo bark when it locks. It is annoying to say the least, and I think a DTT smart box is going in mine if it will help.

 

[shendren]

just a thought... ... . with the tps being so far off, is the throttle cable adjusted correctly. you should be able to get 1. 0 volt with relatively no problem... . ?



scott.

 

[Extreme1]

Thanks for the replys. Jason, can you help a fella out? Let's swap you 6 speed in just to try it...

Originally posted by shendren

just a thought... ... . with the tps being so far off, is the throttle cable adjusted correctly. you should be able to get 1. 0 volt with relatively no problem... . ? scott.

Yes, according to the service manual it is. I did try adjusting the linkage rod before I modded the TPS but it didn't change the voltage enough and I ran out of throttle movement.



The 5" measurement (+/- 1mm ) is right on. I have the "break-over" at the end of throttle pedal travel (although not as much as before the throttle cable update).



Piers did say he's had to carve up the sensors to get them to rotate far enough to work. The bolts are almost outside the sensor! He's been there, done that, so I think the method I used to get the idle voltage up is OK.



What else controls the TC lock? Everything is working and there are no codes stored.



I might try an adjustable regulator like LSMITH suggested. I could use it on both ends of the TPS. I will probably have to wait a couple weeks as Wednesday is the surgury.

 

[RJ2]

My transmission locks up at 45 just cruising but if you

get on it ,the thing just hangs in there till about 55.

What can be done to lock it up faster. Thanks RJ

 

[Strick-9]

Extreme1,



Loosen off on your governor springs 1 click each. When you crank the motor, it will idle lower than before.



Then you can increase the idle speed with the idle adjustment the and TPS voltage will come up as the throttle linkage moves forward.



The truck will start better and have a stronger idle as well.



-Chris

 

[WyoJim]

My TC locks up at 45. Has done so since new. If I bury my foot in it it locks up at 65. 75000 miles.



My son has one, locks up at 45. 40000 miles.



We been driving these things for four years and didn't know they weren't right. Where are they supposed to lock up?



I probably won't sleep tonight.

 

[JIM S.]

We been driving these things for four years and didn't know they weren't right. Where are they supposed to lock up?

In stock form they lock up at about 45mph in over drive under light throttle, mine did and still does after ajusting the TPS. what did change was the lockup in just (drive) under light throttle it would lock at 30 MPH now it more like 34-35MPH.





wyojim... . dont sweat it. . its normal

Jim

 

[rjones]

Mines doing the same I adjusted the TPS from 1. 0v to 1. 387v And it didn't change anything, how high can you go in voltage before you start getting into the limp mode? Rick

 

[Blakers]

Mine locks up at 45 too. What's wrong with that? Why adjust the tps if doing what it's supposed to do?



Blake

 

[Extreme1]

When discussing the lugging I HAD locking up at 45 with Piers, he said to adjust the TPS voltage to 1. 2 and it would lock up around 52-54 mph. His does and it's a '94.



With the 181 delivery valves, the shudder is gone but the convertor clutch is still having bad things done to it due to the speed differential. At 55 it is only 100 or so RPM difference at lock up so it's a lot easier on the TC clutch.



Thanks Chris, I'll try to play with the springs tonight if I have time.



RJ2 - Governor spring kit. It won't hang at 55, it will have the power to pull past 55 and upshift. I know exactly what you're talking about, a GSK will fix it. So will a convertor but a GSK is a lot easier and cheaper to install.

 

[Todd T]

I have to agree with Chris on this one. here is what is going on to help you understand what your doing.



idle voltage is . 5 to 1. 5 volts. we all know that. the PCM controls lockup from the TPS & VSS voltage. we all know that too.



you have installed governor springs, probably a plate or slid the stock one forward. what has happend, is your engine now takes less throttle to keep it at highway speeds and less to get it there. take a scan tool and monitor your TPS and VSS while going down the road. take measurements in 5-10MPH increments. you will see that at 40-50MPH your TPS voltage is so low the truck thinks you are idling. the only other reference it has to go by is the VSS. we know the transmission controls shifts from the TB cable. if you dont have it adjusted right your shift points will be affected. lockup is the PCM. dont forget to re-adjust this after you move the throttle position.



do what Chris said, adjust your G springs to idle you down farther then adjust more throttle onto your TPS. ideally you should have 1. 2 volts "solid" at idle. this gives the truck both its reference points back determine lockup. moving the TPS in its slots should only be done to fine tune your idle voltage. forget what the book says about throttle rod length you have to have a good sweep of the TPS voltage first and full throttle travel second. remember the governer really doesnt let you ever go to full open on the throttle, unless you are heavily modified. watch the lever movement next time your in the AFC housing. about two inches of throttle lever travel on the outside of the pump is enough.



Extreme1, if you dont have a scan tool you can use straight pins through the jacket of the wires on your TPS and set your voltmeter under the windshield wiper for a road test. watch that TPS voltage, I bet you have about 1. 7 volts at 50MPH on level ground that is not good.



when i put my 0 plate, 370's, 191's and 4K gsk in, i had to put in about 1 1/2" in my throttle rod to get the TPS and TB settings good again I still short shift in 4th at light throttle, but i have to live with that until i go through the transmission.



let us know

Todd