1988 DT55 voltage to tps

[cardinalmike]

Hi folks. Thanks in advance for any expertise.

Does anyone know what the voltage going from the CDI to the throttle valve sensor should be for a '88 DT55. I have the manual but it doesn't specify this voltage.

I had one tps go bad this summer, and bought a new one. I stupidly did not bench test it before putting it on the motor, but it seemed to me that the idle was back where it should have been for a few minutes before returning to the default high idle you get with a bad tps. I pulled the new one off, and it was fried. infinite resistance throughout the range of motion, just like the one I had replaced.

I sent it back, and the online retailer verified it was bad and replaced it under warranty, but I'm suspicious that my motor is frying my TVS's. I checked the voltage coming from the CDI, and it's over 19 volts. That seems off to me. Suspecting the CDI, I got my hands on another (used) CDI and swapped it out, but I'm getting the exact same 19+volts down the wires to the tvs. My rectifier and all 3 ignition coils are within spec doing ohms tests off the motor.

I guess it's possible that 19volts is correct, and I just bought a dud TVS. But I'm thinking it should be more like 5V, and I have an electrical issue somewhere else that's sending voltage to places it shouldn't be. Anyone ever come across anything like this?

Thanks again.

-Mike

[Solarman]

dt55, 88, tvs

Do you have a rectifier with regulator built into it? Or is your regulator separate on that model? Also, your motor has carbs, and the you're talking about the TVs? Not the tps, right? And your motor doesn't have an ECM (electronic control module), just a CDI (condenser discharge ignition) system? Do the wires off the TVs plug directly into the cdi unit?
I am not sure on voltage for the TVs on your motor. It does sound high, my tps plugs into the ecm and does vary the voltage to mine (3 - 5v approx).
Being an 1988, model you might verify your regulator if separate from your rectifier is ok. That's the only thing I think could affect the voltage on your unit? Sorry can't be of more help. Any chance of checking another regulator out? or, If a combined rec / reg ? Just thoughts.
Good luck, let us know what you find?

[cardinalmike]

You are correct. I should be saying throttle valve sensor. It attaches to the #2 carburetor, and returns a variable voltage to the CDI unit. 3 wires to the sensor; hot, ground, and return. The manual gives you voltages to check for at fully closed and fully open.

My two bad switches were returning no voltage (infinite resistance between hot and return) so it's the same as not having one. The motor seems to default to a higher RPM, and doesn't advance the timing when you throttle up so it runs like crap.

My new one does fine in my garage. I have yet to plug it into the motor cause i don't want to break this one until I figure out if that high voltage is correct or not.

The parts fiche just says "rectifier assembly" for 88-90. So maybe i need to find where the regulator is. I assumed it was a 2 for 1.

[Solarman]

dt55, 1988, tvs

See if your manual has a test for the regulator. It's the only thing I can think of that changes the voltage, other than the rectifier, put out by the magneto.

[Solarman]

dt55, 1988, TVs problems

Ok. I clicked on the rectifier for your motor, and the part description says rectifier & regulator assy.
My thoughts are, the regulator controls the amount of voltage through the electrical system. I'm thinking the voltage should be 12 - 14, the most 16 volts, unless your battery is dead, or shorted, causing a higher voltage draw through the regulator, and maybe caused regulator to go bad?
The tests for regulator in my manual say to replace my rectifier? Your manual may be different?
Good luck, keep us posted.