I’ve been chasing an intermittent issue with lockup not engaging at highway speeds. I know there are general conditions that the ECU needs to see to enable lockup such as speed, oil and and ATF temperature, but maybe 50% of the time lockup does not happen when these appear to be met. When lockup does happen, lockup function remains normal at all speeds, engaging and disengaging as it should until the next engine off/ on cycle. In other words, if it works, it stays working for the rest of the trip. I have a temp sender in the pan, and when lockup does occur, it seems to be at around 130F, but when it does not lock, the temp can be well above this, up to 180F without locking. Goes into O/D normally- mentioned because I read in a manual for a later model 343F application that both O/D and lockup are disabled below a certain coolant temp. No O/D flashing light to indicate a fault. I just replaced all of the electrolytic capacitors in the ECU (Thank you Tigris for your guide) hoping it would help, but it does not seem to have made any difference. The caps were all visually intact, no leakage or trace damage. I am thinking of replacing the lockup solenoid next. Can anyone help with other suggestions or provide more specifics on the lockup parameters? Thanks!
TC lockup troubleshooting KZJ78/A343F (1 Viewer)
- Thread starter AVL KZJ78
- Start date
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I had a very similar lockup issue in my first LJ78, installing a new lockup solenoid in the transmission solved the problem. (I replaced all three solenoids while I was in there.) It is a fairly easy and straightforward job, here are some photos of when I did it:
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Builds - 1990 LJ78 in Montana
Those aren't rattles .... That's simply the land Cruiser having a conversation with you. :)
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- Thread starter
- #3
Thanks for the data point. I will replace the solenoids next, and report back.I had a very similar lockup issue in my first LJ78, installing a new lockup solenoid in the transmission solved the problem. (I replaced all three solenoids while I was in there.) It is a fairly easy and straightforward job, here are some photos of when I did it:
Builds - 1990 LJ78 in Montana
Those aren't rattles .... That's simply the land Cruiser having a conversation with you. :)
- Thread starter
- #4
Problem resolved- the thermostat was stuck open. Replaced it, and I have stable temps, plenty of cabin heat, and the TC locks up reliably at 80km/h. Before, I found that I could achieve lockup only by exceeding 110km/h. Seems that the ECU needs to see sufficient temperature at the cylinder head, and short of this a sufficiently high speed can also cause lockup.
