I am trying to diagnose how bad my torque converter is. I believe it’s unlocked when it shouldn’t be or slips when it is locked.
What I’ve observed, in some situations the speed of the car increases from say 60 to 80kmh but RPMs literally do not move. This makes no sense to me.
In other situations when the transmissions is in 4th or 5h, the RPMs are at their lowest point which means locked torque converter, when I give it gas the expectation is that RPMs should not freely rise, when I give it more gas the RPMs suddenly rise by 500 or so as if the car downshifted, but you see I have a CAN datalogger and am logging the gears, the gearbox reports it’s still in 5th gear so it presumably just unlocked the torque converter which means the input speed from the engine can be higher than the input speed to the gearbox as the rotation is now fluid coupled and there is a net loss.
To summarize, what does it mean if the speed of the car increases by 20 or more kmh but the engine RPM is reported as not having moved or moved by just 100-200RPM? Intuitively I expect that RPMs should rise with the speed of the car in the case of a locked TC, and in the case of an unlocked one, RPMs should rise a lot faster than speed of the car, but then we have the third case where speed of the car increases but RPMs barely move if at all.
The only thing I can think of here is that one of the speed sensors in the gearbox has gone bad and reports incorrect data.
This all sounds like normal operation.
60 to 80kmh but RPMs literally do not move until say around 2300RPM
You’re likely in a high gear, so a small engine rpm change makes a big output change. Give it more pedal and you’ll force a downshift, which may be what it’s doing by itself eventually giving you the expect rpm rise.
the RPMs suddenly rise by 500 or so as if the car downshifted, but you see I have a CAN datalogger and am logging the gears, the gearbox reports it’s still in 5th gear
This is absolutely the converter unlocking.
Most vehicles will set one of many codes if they see any sort of transmission weirdness at all. If you’ve not go codes setting it’s almost certainly normal.