I have twin Suzukis 1996 140s. They run great but the port motor tach doesn’t work. It is a simple three wire tach. The yellow wire is the signal, the grey is the power from the switch, the black is ground. I bought a new tach and plugged it in and nothing (all three come to the tach from the motor harness). I put the other motors tach on it and no reading. I have 12v on the grey wire and the black is a good ground wire. The harness is in good shape and where it plugs in at the motor looks great. The Pole setting is on 5 which is where it calls for it. 2 questions
Don’t know about 'zukes, but OMC/BRP and Merc drive the tach off of the voltage regulator / rectifier assembly. Check to see if the output of the charging system is correct.
The rectifier/regulator was my choice to be tested today as well and I took the one off the other motor and put on it and tach still not working and the yellow tach wire comes from under the flywheel into the rectifier and leaves the rectifier heading up to the gauge. I believe that the problem is whatever produces the yellow wire tach signal under the flywheel is the problem. I have eliminated the tach and the rectifier by swapping with the know good motor. How would I check the tach signal wire with a meter?
the tach signal is generated by the charge coil the tach pole setting is determined by the # of magnets under the flywheel(6 magnets- 12 poles) if this is a DT 140 you could have a issue with your ECU. The yellow wire come from the charge coil thru the rectifier to the ECU and on to the tach it has nothing to do with the #1 plug firing. You need to also check and see if your engine is charging your bat.
Know it all,
You are dead on! I have learned there are two “battery charge coils” under the flywheel and I see the yellow tach signal wire does go from there to the rectifier and in and out of the ECU. Through part swapping, i know the tach and rectifier are good. I hope it is not the ECU as it is expensive. I quess I could swap the ECU on the other motor and see if that makes the tach work. The batteries appear to be charging because when i throttle the motor up a little, I do see the voltmeter move slightly up. Everything runs excellent and everything works but that tach.
cheapest and easiest way to diagnose without a DVA meter, would be to swap the ECU. If its not the ecu, then you need a charge coil, and a flywheel puller.
not to sound to basic, but have you verified that teh harness is good?
also, you say the batteries are charging, does the volt gauge increase when only the 1 motor with the bad tach is running
Chris,
Your thoughts are exactly what my next steps were going to be. I have a flywheel puller also, But I am going to swap ECUs and hope that doesn’t fix it
If it doesn’t fix it, then the only thing left in that circuit is the battery charge coils. I hope it is a $106 charge coil vs a $900 ECU. I do have a good ECU off of a 1994 DT 140 that someone gave me awhile back and might get lucky and it be interchangeable with my 1996. The volt gauge (i have one for each motor/battery)on the non tach working motor moves up when i accelerate it. I feel pretty sure that motor is charging. Does that make you think it will be the ECU more likely?
Thanks as always for your advice.
Rick
How could i check the continuity of the yellow tach signal wire from the motor to the gauge? I know how to use my multimeter in the ohms position for continuity checks, but the leads on the meter wont reach from the motor end of the harness to the console and harness runs under the deck. Is there a trick, maybe run a separate wire from motor to gauge to see?
It was the ECU unit. Swapped it today and the tach reads perfectly now. I had one that was in a box of misc parts for the DT 140 Suzukis that i bought months ago off eBay. I hope I am not doing something to hurt the motor, the numbers on the ECU I put on were only off by one digit and the wires and plugs were identical to my original one. Mine is a 1996 carbed and the ECU I put on was from a 1994 carbed. The motor cranked right up, idled great, throttled fine, charges fne and all gauges work. Am I good to go? It seemed to smoke heavier but I don’t think the oil mixing is controlled by ECU, but by linkage and I have a mechanical oil pump.
