2009 Yamaha model YDRE Surge at Low Speeds

[LESSOR2]

Hello,
I am new to Electric carts. I have a 2009 Yamaha model YDRE/ JW2-F4236-30. It's 48V. The cart surges when slowly depressing the pedal from a start position or when the cart is slowly rolling. A very slight press of the pedal and the cart surges. I actually dumped someone off the back seat last weekend, fortunately wasn't hurt. I am by means an expert with carts but I do have knowledge in how speed controllers work as I use them in a smaller, lower voltage applications. I suspect the speed controller has a problem evenly adding voltage to the motor as needed. I am a long way from a qualified repair dealer so I am looking for any advice on if I am on the right track of diagnosis.
Any advice greatly appreciated.

Thank you,
Brent

[cgtech]

First, make sure the motor speed sensor is operating. Push the cart, it should beep at you & resist motion (should "push back").

[LESSOR2]

Roger that cgtech. Test complete:

When I push the cart I hear a relay activate and the cart definitely fights me. What to look for next?

Also I thought it might help to refine the symptoms a little. I used the cart today. From a dear stop or a very slow roll I experimented, a slight depress of the accelerator pedal results in the cart starting out normal (slow) but when the cart hits about 2 or 3 mph it surges. It doesn't do it every time, but it does it most of the time. The surge is pretty good too. Made me think that if we are ever crazy enough to have gold cart drag racing at our campground then that cart would definitely be a contender.

Thank you,
Brent

[cgtech]

Next, can we absolutely be sure the motor & controller are stock factory items? (If you give me numbers off each, or pics, I can verify). Many aftermarket controllers allow for easy diagnostics that may help.us.

[LESSOR2]

Do these tell us stock vs mod? I can easily take more.

[cgtech]

100% stock

[cgtech]

I've seen a couple throttle pedal sensors fail this way, but not many.

The real yamaha part (jw2-h5885-00-00) retails for $130.99, and several on the forum have wasted their money on the $50 chinese copy, only to have it not work.

[LESSOR2]

OK........I think I am beginning to get a better understanding of the engineering. Tell me if I am on track. There is a throttle sensor at the pedal location that transmits to the speed controller how much voltage to apply to the motor? If that sensor is failing then it is misleading the electronic speed controller. Sound correct.....more or less?

So, if the throttle pedal sensor is failing then it looks like I have to pull the floorboard up to gain access. Simple push pins like on my ATVs. I looked up the part and without seeing the pedal assembly, I'm assuming it's a pretty simple R&R? Any recommendations on where you like to buy parts so I can make sure I don't end up with a cheap Chinese counterfeit?

Again, thank you for all your help and guidance.
Brent

[cgtech]

Your assessment of operation, while simple, is correct enough. The floorboards are easy enough, but the space between the floorboard & TPS hardware is a little slim.

Don plowman (www.plowmanscarts.com) is a yamaha dealer, a site sponsor, and doesnt sell junk.

[LESSOR2]

Hey cg,


Well, TPS replaced, but the problem persists and the cart has failed run.

After I replaced the TPS, the symptoms disappeared and I thought, Great! But later in the day the choppy acceleration at slow speeds returned. At first (as I know a bit about electric motors) I suspected that the brushes may be bad. It acted as if the brushes were failing to make consistent contact with the armature. But on the way back to camp the cart started the slow and then speed up at mid-range to full pedal. That made me think speed controller. I barely made it back. Then the cart quite again. After I let it sit about an hour, the cart ran again, but all the symptoms remained

I then decided (based on my limited knowledge) to measure the voltage coming from the speed controller to the motor. My multimeter show voltage jumping all around and cutting out. I would think that the voltage to the motor at that stage should be pretty linear. Yes?