Usual Suspects: the torque converter part 2
Not Guilty as charged:
As said before there are many causes that result in issues with lock-up. Some tend to look only to the converter while this may only be the result of a problem that is located elsewhere.
When your car has a strange shudder or vibration, make sure you first check the engine. Defective ignition coils or spark plugs can cause similar symptoms to lock-up complaints. Diesel engines with dirty fuel filters are a very common cause of vibrations.
Air mass flow sensors can be added to this list as well. If all of this is checked, then focus on the
valve body or mechatronic unit. Data corruption easily results in lock-up problems.
Also engine misfires caused through faulty ignition electrics or injectors will be more noticeable after lock-up engages. Drive shafts and/or propeller shaft should also be checked for balance.
After installation of a new or rebuild converter, it could happen that there is a loss of drive. In this case always check the mechatronic or valve body. Especially when you have a General Motors 5L40E BMW 1998 and up or Cadillac 2003 up or Mercedes 772.6.
The valve body of the CFT23 Ford Focus C Max is also very sensitive on contamination which can also cause this condition.
Jolts in shifting gears
This can often be related to (mechanical) problems in the engine, like faulty sensors, leaking injectors etc or a worn valve body. An adaption relearn can sometimes perform miracles as well.
Not enough acceleration
Make sure you check your exhaust catalyst, any restrictions in the exhaust system will seriously reduce power output.
Rumble or knocking when starting
When you hear this specific banging sound, be sure to check for broken engine or transmission mountings before you open up your transmission and bring out the converter to stand trial.
A final tip:
Once the converter has been rebuild or has been replaced, it is essential that the lock-up adaptation values are reset and the relearn process is done exactly according to the manufacturers recommendations, otherwise the lock-up will not function correctly creating drivability issues.
Lastly, do not forget to flush the oil cooler to prevent debris getting in the transmission!