Arne Posted July 30, 2006 Share #1 Posted July 30, 2006 OK, here's a new one on me. The tach in my early '71 240Z (4 wire) suddenly this afternoon started to peg the needle at 8000 RPM any time the key is turned to the Run position, whether the engine is running or not. I suspect a problem with the tach itself, not the wiring as the ignition appears to be working fine, since the car starts and runs normally. Any thoughts? Link to comment https://www.classiczcars.com/topic/20991-new-tach-problem-240z/ Share on other sites More sharing options...
a7dz Posted July 30, 2006 Share #2 Posted July 30, 2006 Wish I could read this diagram! Maybe you can and then send it to me. http://www.classiczcars.com/forums/showthread.php?t=21924&highlight=tachSounds like a bad tach. Mine is stuck a 1200 all the time. I have a least one four wire that does not work as well. I did buy one to replace it but, I am not sure is is any good either. Link to comment https://www.classiczcars.com/topic/20991-new-tach-problem-240z/#findComment-176468 Share on other sites More sharing options...
Arne Posted July 30, 2006 Author Share #3 Posted July 30, 2006 Well, I have a spare tach from the pats car, so if it's dead and can't be repaired easily... Link to comment https://www.classiczcars.com/topic/20991-new-tach-problem-240z/#findComment-176471 Share on other sites More sharing options...
EScanlon Posted July 30, 2006 Share #4 Posted July 30, 2006 Arne:Swap the tach, the 8k one is dead.E Link to comment https://www.classiczcars.com/topic/20991-new-tach-problem-240z/#findComment-176483 Share on other sites More sharing options...
Arne Posted July 31, 2006 Author Share #5 Posted July 31, 2006 Sounds logical, but before I install teh other one, can anyone think of anything in the car's wiring that could cause this failure? No sense in doing the same thing to another one, you know. Link to comment https://www.classiczcars.com/topic/20991-new-tach-problem-240z/#findComment-176535 Share on other sites More sharing options...
EScanlon Posted July 31, 2006 Share #6 Posted July 31, 2006 Age, someone trying to "adjust" and shorting the lower board to the upper, resistor (?) between two boards getting fried. That's just off the top of my head.Others?E Link to comment https://www.classiczcars.com/topic/20991-new-tach-problem-240z/#findComment-176536 Share on other sites More sharing options...
a7dz Posted July 31, 2006 Share #7 Posted July 31, 2006 Try this link for the diagram;http://www.classiczcars.com/forums/attachment.php?attachmentid=12516&d=1148842545 Link to comment https://www.classiczcars.com/topic/20991-new-tach-problem-240z/#findComment-176538 Share on other sites More sharing options...
ktm Posted August 3, 2006 Share #8 Posted August 3, 2006 The diode finally went south? I know (from this forum) that the 240z tach is susceptible to heat when the diode starts to 'wear out'. The tach would slowly climb and then peg itself until it cooled down. The fix was to solder in a new diode that is available from radio shack. Link to comment https://www.classiczcars.com/topic/20991-new-tach-problem-240z/#findComment-176966 Share on other sites More sharing options...
zKars
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