30RH torque convertor refuses to lock up

[Leigh Berger]

Hi All - First Post Here!

Working with my daughter to fix her '97 up to get ready to ship to Hawaii for her daily driver over there.
Fair bit of rust underneath that we're scraping, wire-brushing, and treating with POR-15.
Flushing and filling Trans, Diffs, etc. New Diff Covers. Replaced the tank shield (was like Swiss cheese!), Dropped the belly pan shield and cleaned that up and treated as well. Will also be replacing the brake lines shortly.
Having some trouble with a Torque Converter that refuses to lock up.
3 Speed auto with the 2.5l 4-cylinder. Trans shifts fine through the gears, both up and down.
But once it gets to cruising speed under steady throttle, the TCC doesn't lock up and she's pushing 3000 rpms going anywhere near 50 mph.
Originally discovered this when the Check Engine Light pulled a P0740 code "TCC, No Revolutions per Minute Drop at Lockup".
Want to get it resolved. What I've tried so far:
Checked all related fuses, all OK.
Dropped the pan and drained and changed the trans fluid a total of 3 times, and filter once.
Including the last time when I replaced the TCC Solenoid, thinking that was the next likely (and easy) culprit.
No luck - still no lock up.
CEL is staying off after all the above, and after clearing the codes with battery disconnect. But haven't driven it much at higher speeds.
Anything else I can try before concluding the actual Torque Converter needs replacing?
Based on the attached (really cool) picture of the Trans Pan Magnet, and all the collected particles, does it look like this would be enough to kill a TCC?

Thanks,

 

[Chris]

Sounds to me like your torque convertor may simply need to be replaced.

You didn't mention how many miles are on it, but it if has well over 100k miles, that around the time that automatic transmissions need to start being serviced. Everything you've done already is everything I would have suggested had you not mentioned already having done it.

 

[Jerry Bransford]

The torque converter lockup solenoid is engaged when the computer provides a ground to it, the other side has +12v on it. I'd connect a volt meter with a long lead to the ground side of the lockup solenoid electrical connector on the rear of the transmission. It will show 12v volts when the it is not locked up. When the computer grounds that lead to lock the torque converter lockup solenoid, that 12 volts should drop to 0 volts. See if that is or is not happening.

 

[Leigh Berger]

The torque converter lockup solenoid is engaged when the computer provides a ground to it, the other side has +12v on it. I'd connect a volt meter with a long lead to the ground side of the lockup solenoid electrical connector on the rear of the transmission. It will show 12v volts when the it is not locked up. When the computer grounds that lead to lock the torque converter lockup solenoid, that 12 volts should drop to 0 volts. See if that is or is not happening.

Thanks Jerry - But how would I go about getting the computer to send the lock-up signal to the solenoid? Doesn't that happen only when driving at higher speeds?

 

[Jerry Bransford]

Thanks Jerry - But how would I go about getting the computer to send the lock-up signal to the solenoid? Doesn't that happen only when driving at higher speeds?

Just driving it at a fixed speed for more than a few seconds would cause the computer to lock the torque converter. I don't know the minimum speed, but if you're at a normal cruising speed it will lock the torque converter.

 

[Leigh Berger]

Yeah - I got that - That's where my problem is - it's just not locking up at normal cruising speeds.
What I don't get - is how to measure voltage at the solenoid when it's supposed to trigger the signal.

 

[Jerry Bransford]

Yeah - I got that - That's where my problem is - it's just not locking up at normal cruising speeds.
What I don't get - is how to measure voltage at the solenoid when it's supposed to trigger the signal.

What's wrong with what I suggested in post #3 above? I.E. run wiring up into the passenger compartment connected to a volt meter to see what is happening at the transmission's electrical connector for its torque converter.

 

[Leigh Berger]

I see now.
Wasn't thinking of running wires up to measure while driving - thanks!

 

[Leigh Berger]

Jerry - while I've got you:
Any chance the brake light switch could be a culprit here?
I had seen some schematics that routed the brake light circuit through to the TCC signal as well.
Even if the brake lights are not remaining on, if the pedal/switch are partially depressed, could that be telling the computer to NOT lock up the TCC?
Same question goes for the 4WD? - Even though I don't see any electronics in the 4WD on/off, is there some internal switching that would prevent TCC lock up if it thinks it's in 4WD?

 

[Jerry Bransford]

The brake light switch has nothing to do with the lockup circuit, neither does the 4x4 switch circuit. The lockup solenoid receives 12v directly from fuse 11 on one side and its ground connection on the other side is connected directly to the PCM for when it decides to lock it up.

 

[davecarlson98]

The brake light switch has nothing to do with the lockup circuit, neither does the 4x4 switch circuit. The lockup solenoid receives 12v directly from fuse 11 on one side and its ground connection on the other side is connected directly to the PCM for when it decides to lock it up.

Thanks Jerry, I am going to try this Voltage drop test. Out of curiosity, if you had to replace this solenoid, does it usually require changing of all of the solenoids? Thanks,Dave

 

[Jerry Bransford]

I wouldn't automatically replace the others, I'd replace just the TCC solenoid and see what happens.

Have you checked the solenoid's ground side connection to see if the PCM is grounding it which causes it to engage? It receives a constant +12v, it's the ground from the PCM that engages it.

I'd probably connect a ground connection with an on-off switch to the ground side of the connector wire and see what happens.

 

[davecarlson98]

I wouldn't automatically replace the others, I'd replace just the TCC solenoid and see what happens.

Have you checked the solenoid's ground side connection to see if the PCM is grounding it which causes it to engage? It receives a constant +12v, it's the ground from the PCM that engages it.

I'd probably connect a ground connection with an on-off switch to the ground side of the connector wire and see what happens.

Hi Jerry, I was just studying the manual(scary!) and I was comparing it to my driving experience. I have often avoided Overdrive because when in Overdrive, 4th gear seems to cause the engine to lug.....I assume not good for the engine and possibly the TCC.....I have often felt that in this condition the Overdrive should automatically shift to 3rd rather than stay in Overdrive. Is it possible that the PCM if defective for not recognizing this lugging condition and automatically downshifting?.....Other than the dealer telling me to get a new Torque Converter and the pesky P0740s, i dont really have any other symptoms...Thanks, Dave

from page 145TORQUE CONVERTER CLUTCH (TCC) The torque converter clutch is hydraulically applied and is released when fluid is vented from the hydraulic circuit by the torque converter control (TCC) solenoid on the valve body. The torque converter clutch is controlled by the Powertrain Control Module (PCM). The torque converter clutch engages in fourth gear, and in third gear under various conditions, such as when the O/D switch is OFF, when the vehicle is cruising on a level surface after the vehicle has warmed up. The torque converter clutch will disengage momentarily when an increase in engine load is sensed by the PCM, such as when the vehicle begins to go uphill or the throttle pressure is increased

 

[Jerry Bransford]

Hi Jerry, I was just studying the manual(scary!) and I was comparing it to my driving experience. I have often avoided Overdrive because when in Overdrive, 4th gear seems to cause the engine to lug.....I assume not good for the engine and possibly the TCC.....I have often felt that in this condition the Overdrive should automatically shift to 3rd rather than stay in Overdrive. Is it possible that the PCM if defective for not recognizing this lugging condition and automatically downshifting?.....Other than the dealer telling me to get a new Torque Converter and the pesky P0740s, i dont really have any other symptoms...Thanks, Dave
View attachment 287687

It's common for the engine to lug when it shifts into Overdrive if you are running larger than a stock tire size. Bigger tires produce lower engine rpms when driving than smaller tires do. Your Profile is incomplete on things like your tires size, what size tires are you running? If they are larger than stock there are only two fixes, go back to a smaller factory size or regear the axles to a lower ratio to raise the engine rpms back up to where they need to be to stop the lugging. That's what I did for my 35" tires, I regeared my axles from the factory 3.73 ratio to 5.38.

 

[davecarlson98]

It's common for the engine to lug when it shifts into Overdrive if you are running larger than a stock tire size. Bigger tires produce lower engine rpms when driving than smaller tires do. Your Profile is incomplete on things like your tires size, what size tires are you running? If they are larger than stock there are only two fixes, go back to a smaller factory size or regear the axles to a lower ratio to raise the engine rpms back up to where they need to be to stop the lugging. That's what I did for my 35" tires, I regeared my axles from the factory 3.73 ratio to 5.38.

great tip....let me find my tape measure!

 

[davecarlson98]

great tip....let me find my tape measure!

does long term lugging damage the TCC?

 

[Jerry Bransford]

great tip....let me find my tape measure!

Just give us the size molded onto the sidewall.

 

[Jerry Bransford]

does long term lugging damage the TCC?

No, at least not that I have heard of.

 

[davecarlson98]

No, at least not that I have heard of.

thanks

 

[davecarlson98]

Just give us the size molded onto the sidewall.

265/75R15