Sudden loss of lockup

[LifeRunner]

Hey again guys. 

Picked up a '99 2500 today with a few issues, chief amongst which is the converter not locking up. Overdrive works just fine. I began troubleshooting today, but I could use some input. 

It had a bunch of codes before I began measuring, most seemed to be related to the previous owners lockup switch because once I removed the jump between the relay 30 and 87a pins, and installed a relay in its place the codes could be reset and wouldn't come back. Now, according to the previous owner the lockup suddenly stopped working, not gradually. Solenoid assembly is new, and I've checked the contact at the transmission, it looks good and clean. When I measured the TCC cable from the PCM I read 12v at pin 11, contact A2, this didn't make sense so I removed the lockup switch thinking this could be throwing it off due to poor routing and bad handiwork, after this I no longer saw 12v while measuring from pin 11 on A2 to B+. Resistance from pin 11 in contact A2 to B+ was about 0.9k ohm iirc. Oddly enough, measuring from pin 11 on receptacle A2 on the PCM to B+ also results in 12v, which doesn't make sense in my mind. The resistance value from the PCM receptacle was very high, so it doesn't seem like a short circuit. 

If for some reason the converter is the problem, I just want to be 100% it's that, to avoid wasting $1000 on a new converter. 

 

Is there any way to see whether or not the PCM is trying to command lockup? If I wire up a new lockup switch and splice it into the orange/black TCC wire as close to the transmission as possible, shouldn't the converter lock regardless of the PCM? 

[IBMobile]

The PCM grounds the torque converter lockup solenoid via the orange/black (OR/BK) wire when commanded.  With the key on there should be battery voltage at the PCM connector C2 pin #11.  If you ground the OR/BK wire the OD solenoid should be energized and torque converter lockup achieved. I don't see how the B+ terminal is involved with the torque converter lockup.

[LifeRunner]

5 hours ago, IBMobile said:

I don't see how the B+ terminal is involved with the torque converter lockup

 

That's where the supply for the solenoids comes from, yes? Measured this to see if anything might have short circuited to B+. 

[IBMobile]

The power for the solenoid comes fro terminal 87 of the transmission control relay.

[Mopar1973Man]

@IBMobile is correct. This is controlled by the PCM and will be hot after tach signal is seen. So you should do your testing with the engine running.

[LifeRunner]

2 hours ago, Mopar1973Man said:

@IBMobile is correct. This is controlled by the PCM and will be hot after tach signal is seen. So you should do your testing with the engine running.

Okay, noted. 

Is there any way to see whether the PCM is commanding lockup or not? 

Also, if I wire up a lockup switch for troubleshooting purposes, shouldn't the converter lock regardless of PCM state? 

[IBMobile]

3 hours ago, LifeRunner said:

Is there any way to see whether the PCM is commanding lockup

Ohm meter to see if C2/11 is grounded when above 45MPH.  Cut OR/BL wire, splice new wire on to end that goes to the PCM,  run wire into the cab and attach it to one side of an ohm meter, ground the other led of the ohm meter.  Now drife the truck and when the speed is 45+ the ohm reading should be close to zero.

 

3 hours ago, LifeRunner said:

if I wire up a lockup switch for troubleshooting purposes, shouldn't the converter lock regardless of PCM state? 

Yes.  Leave the transmission control relay installed, splice a wire to the OE/BL wire, on/off switch, and ground wire.  You may need to install a about a 1000 ohm resister between the switch and ground to get it to work.  

[Evan]

Wouldnt you pull relay and run a jumper in its place.

 

Ive never quute understood relay. U currently run a jumper no relay and no toggle switch to lick converter. 

My truck functions as a normal oem truck minus the relay.

 

I used to pkay with a converter lock switch but have found for my use the converter swutch isnt needed.

 

I lock 3rd comming off hills without switch.

 

I do think the toggle switch coukd be used to test but i feel id go in and put a new converter solenoid and all under pan eletronics in because of to many un knowns. 

The connector that goes through the case next to tv cable is known for being problematic. If you unplug that connector and its soaked in fluid its no good.

 

Im currently running the kde manifold and gm solenoid the borge solenoid on oem manifold is suposed to maybe be better. 

Ive had two borges on this truck and am on my 2nd gm. Havent had gm solenoid fail yet. Put all new eltronics in when i refreshed the trans.

If unknown on eltronics id recomend all new harness solenoid, tranducer and plug through the case. Its a coyple hundred bucks will eliminate a few possible issues right of the bat.

 

The battery cables(all) and grid heater cables can all affect tourge converter lock and 3 -4 shifts.

 

Also curious if its locking convertor in 4th or not 

 

[LifeRunner]

On 8/21/2023 at 8:30 PM, IBMobile said:

Yes.  Leave the transmission control relay installed, splice a wire to the OE/BL wire, on/off switch, and ground wire.  You may need to install a about a 1000 ohm resister between the switch and ground to get it to work.

Will check this, thanks. 

 

On 8/22/2023 at 6:53 PM, Evan said:

If unknown on eltronics id recomend all new harness solenoid, tranducer and plug through the case. Its a coyple hundred bucks will eliminate a few possible issues right of the bat.

 

The battery cables(all) and grid heater cables can all affect tourge converter lock and 3 -4 shifts.

 

Also curious if its locking convertor in 4th or not 

 

OD and TCC Solenoid assembly including contacts is new. 

Got some things to check this weekend now. 

[Great work!]

When people install a tcc manual switch there is usually a resistor of a couple hundred ohms connected to the orange black wire at the PCM side and the relay power pin that supplies the tranny. The purpose is so the PCM sees a good connection  and electrical path through the resistor that is simulating a solenoid. With out it the PCM will throw a bad solenoid code.

[LifeRunner]

Right, I've done a little testing and redid the wiring for the lockup switch, this time with a resistor. The guy who sold it to me didn't use one so I figured I'd implement one; the lowest I had was a 1kOhm resistor, but I suppose that'll do? 

Regardless, still no lockup. Absolutely no reaction at all from flipping the switch. 

 

Unless there's something that's suddenly gone wrong inside the VB, I'm slowly realising I might be looking at a new converter, unless there are more checks to do before shelling out? 

[Mopar1973Man]

Or possibly the torque converter clutch is wasted and slipping. Just the possibility. 

[LifeRunner]

1 hour ago, Mopar1973Man said:

Or possibly the torque converter clutch is wasted and slipping. Just the possibility. 

Yes, as previously mentioned it's slowly setting in I'll have to put a new one on order.. 

While I've got the transmission out it'll probably get some upgrades done as well. 

[Great work!]

Try to make all the wires normal and then tap a 6 to 8 ft piece of wire into the tcc wire. Run it through the window.

 

Connect a test light probe to the wire and the the alligator clip from the light to ground ex the outer lighter socket shell or the key. 

 

Light should be off. Now turn on key light should remain off. Start engine light should be on.

 

Go about 25mph  at least 2nd or 3td gear, with your wire still on the light probe touch it to ground ( gator clip) the clutch should lock and the light turn OFF. Remain at 25 mph.

 

Take probe off ground, clutch should unlock and light turn on. Accelerate to 45+ the light should  turn OFF and clutch locks.

 

If something seems wrong repeat the test with the overdrive wire tapped C2 pin 21 brown wire. It works exactly the same way.

Edited August 27, 2023 by Great work!
Clairty

[IBMobile]

I had a torque converter clutch go bad.  I would have 4 gear but the trans temp would run very hot, 260°F.

[LifeRunner]

5 hours ago, IBMobile said:

I had a torque converter clutch go bad.  I would have 4 gear but the trans temp would run very hot, 260°F.

I sadly don't have a trans temp gauge, it's on the "to-do" list, amongst a whole lot of other things. 

I'm just puzzled by the sudden loss of lockup, always imagined it would start slipping worse and worse before going bad. Placed an order for a new billet heavy duty single disk converter this morning, so we'll see next weekend. 

[Mopar1973Man]

On 8/26/2023 at 9:50 PM, IBMobile said:

I had a torque converter clutch go bad.  I would have 4 gear but the trans temp would run very hot, 260°F.

This is due to fluid thrashing from the torque converter. The clutch locks the the torque convertor solid which stops the fluid thrashing which makes lots of heat.

 

Another example I've seen fire truck pump tests. Now pumping 1250 gallons a minute under a load of a measuring device at like 300 psi will heat 40 degree water to over 140 degrees in just a mere hour. The test tank is 2000 gallons IIRC. 

[Evan]

Transmission will produce the least amount of heat with the convertor locked and functioning correctly is i think what  he was trying to say.

 

Even working correctly in 1 2 3 tourge converter unlocked driving on fluid coupling the transmission will produce more heaat. But healthy shoukd have no issues staying under 165ish

Pulling hard in 2nd id let it hit 180 collant temp if it sustains there id keep trucking. If it walks passed id shut her down.  

The heat exchanger should sustain it dumping transmission heat. If it cant dont keep driving.

 

Trans temp might be more important than fuel or exhaust temp

 

3rd locked is the best place to be towing will produce the least heat. 

suspensionsn is tourqe convertor is actually locked when trucks in  4th.

 

Was this issue ever figured out?