I guess I’d understood from all the great info here that fusible links failed for mechanical reasons, etc., but hadn’t really understood they could fail in an intermittent way that would make them darn hard to troubleshoot.
Short story is my LX450 developed an issue where the engine bay got hot, and the engine would start stumbling once hot. But before all that it would start fine and let you start and drive just far enough to get in to trouble and require a tow. But then run just fine when you got it home and you tried to start diagnosing.
When it would get hot and start sputtering, I could hear the Circuit Opening Relay chattering in spurts so got curious about the power side to the relay coil and started tracing back. Made it to the battery looking for voltage drops, but saw no problems after the three fusible links, at least static, not running - even though I'd gotten it hot enough to fail and stall. But disconnecting F7 for FL AM2 (the one with the connector) and moving the wire around seemed to have broken the flaky connection for good. Bypassing it with an external fuse, I could never get it to fail again. New fusible link set in and many attempts to get it hot again, never a problem. Not sure whether it was loss of voltage to IGSW at the ECU causing it to command the relay closed, or the power to the relay that caused the circuit opening relay to start going haywire, but at least the sound got me looking.
Just in case someone like me gets stranded in the desert and is thinking that a quick voltage reading across the fusible links means they’re not the problem. In my humble opinion probably worth a change, upgrade, or at least mounting reinforcement, as other threads have mentioned.
Thanks to everyone for all the useful reading about the subject on this forum.
Short story is my LX450 developed an issue where the engine bay got hot, and the engine would start stumbling once hot. But before all that it would start fine and let you start and drive just far enough to get in to trouble and require a tow. But then run just fine when you got it home and you tried to start diagnosing.
When it would get hot and start sputtering, I could hear the Circuit Opening Relay chattering in spurts so got curious about the power side to the relay coil and started tracing back. Made it to the battery looking for voltage drops, but saw no problems after the three fusible links, at least static, not running - even though I'd gotten it hot enough to fail and stall. But disconnecting F7 for FL AM2 (the one with the connector) and moving the wire around seemed to have broken the flaky connection for good. Bypassing it with an external fuse, I could never get it to fail again. New fusible link set in and many attempts to get it hot again, never a problem. Not sure whether it was loss of voltage to IGSW at the ECU causing it to command the relay closed, or the power to the relay that caused the circuit opening relay to start going haywire, but at least the sound got me looking.
Just in case someone like me gets stranded in the desert and is thinking that a quick voltage reading across the fusible links means they’re not the problem. In my humble opinion probably worth a change, upgrade, or at least mounting reinforcement, as other threads have mentioned.
Thanks to everyone for all the useful reading about the subject on this forum.
