another similar 700r4 question

[libtec]

Hi. Thanks for looking.

I have a question that might go along with the problem Ryan Colley listed for his 700r4. I have a 90 6.2 suburban 4wd that has a problem getting the convertor to lock up. 99.5% of the time the convertor never locks up and for no reason at all it will start working.? I think it's a loose wire problem somewhere since the problem doesn't appear to be heat related at all. One situation that happens however is that when the convertor does lock up the tranny refuses to down shift when I mash the pedal to the floor. The only way to get it to unlock is to tap the brake or slow way down (5mph) and then the system resets and everything goes fine.

What I don't know is how is the lock supposed to function normaly? I know that the convertor is supposed to engage after you run at a constant throttle setting for over roughly 30 seconds and at or above 35 miles an hour. When is it supposed to disengage? I figure that they would set it up to kick out when you push the pedal far enough to get more power rather than stay on and lug the motor down. Similarly, wouldn't enough of a speed reduction turn it off so you can accelerate again.

Can I bypass the computer control that times out the 30 seconds and collects other inputs and set a 12v on/off signal straight to the tranny through a toggle switch? Is there a negative side to doing this? It seems like that computer is an extra that isn't really needed if a guy is willing to flip a switch every once and a while.
I don't have any info on testing or troubleshooting the elements that provide the inputs (TPS, speed signal generator ohm readings or voltage outputs) so I can figure out why the system isn't working all the time in the first place.

Last on the list. What are the two electronic modules under my dash by the steering column? one is a little black box clipped onto the metal below the radio, the other is a box with heat fins directly under the column?

Thanks in advance!

[Ryan Colley]

Hey Libtec...yes I have that exact same problem with the TC not unlocking until you slow right down and it seems to reset itself. The only other option is to manually shift it into "D", which shakes the truck rather violently.

If you have a Haynes GM/Ford diesel manual there is quite a detailed description of the TPS and how to adjust it. I quickly scanned it over last night but I have to take a closer look. It might be over my head!

FYI - I checked with my local GM dealer about the price of a TPS - he quoted me $210 (Canadian).

Let me know how things progress on your end...

[convert2diesel]

Libtec and Ryan:

Have just gone through the same scenario on my 6.2 Buick conversion.

Did some additional research after my original post and discovered that the computer activates the TCC whenever the VSS signals speed over 36 MPH (I assume GM figures that by that time you are out of 2nd gear). The 4th gear solinoid is used as a momentary disconect for the 3/4 shift and presumably 4/3 shift.

According to my information the computer needs only the following:

1. Engine heat over 110 degrees
2. VSS signal over 36 MPH
3. Steady state TPS signal over idle (>1.25 volts) or below 70% throttle angle.
4. Power through the brake switch

For now I think I will utilize the TPS from the diesel (same output as gasser), Install resister across the temp sender and leave the rest open ended except for the VSS. Hopefully the default programming for the computer will allow the TCC to function independantly. If not will have to invent dummy loads for the balance of the sensors.

Much of what I've done you guys already have installed in your trucks. There are three wires going into the TPS:

With ignition on, one wire will give you close to or exactly 5 volts. This is the five volt reference coming from the ECM. Normally this wire is the furthest forward on the harness going into the TPS. The wire normally at the rear is the TPS ground (through the computer). The one in the middle is the signal voltage. At idle it should read less then 1.25 volts. As you open the throttle, the voltage should climb to almost five volts at WOT. This is the way it is set-up on mine. Your harness may be different so check your manual.

In order for the TCC to lock up, the TPS signal voltage must be above 1.25 volts and be steady. If you move the throttle to any great extent the computer will see a non-steady state situation and unlock the TCC.

If the TPS is out of wack, it is possible the TPS never gets over 1.25 volts, thus no lock-up. Ryan I am doing some consulting for Auto Aces over on Coventry Road and can get an aftermarket TPS for about $175.00 (if my memory serves me correctly). Contact me through my email if you need one.

Hope this helps.

Bill

[libtec]

Bill

Thanks a bunch! Any info I can get is greatly appreciated. Having the voltage numbers to work with for the TPS is a great bonus. I'm going to do a bunch of fun work (radio, new carpet, high idle switch, resistor to extend glow plug time) in the near future and am going to dive into the TCC problem with everything I can based on inputs from the site members. If your listening in Ryan, I'll post my findings, Good or bad.


John.

[Ryan Colley]

Bill/Libtec

Thanks for the info, I will check my voltage readings to confirm the operation of the TPS and report back. I have checked all my TPS connections and they appear to be OK. Bill -my email is ryan_colley47@hotmail.com - let me know how I can get ahold of you, I would definitely be interested in getting a TPS from you if that turns out to be the source of my problems.

Good luck with the rest of your upgrades, Libtec.

Ryan

[convert2diesel]

Ryan:

You have mail. Glad I was able to be of assistance.

Bill