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TPS Diagnostics

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This question pertains to a 250X so pardon me if the specs are different, but I've seen threads in this forum that makes me think things are similar, if not the same.

My manual gives me a a standard of 4 - 6 kohm and a formula to check TPS at idle. Is 4 -6 kohm = 4000 - 6000? And what is supposed to be 4000-6000? Is A in the formula supposed to be 4000-6000?

The formula:

A (resistance between blue and black terminals (the outer ones on the plug). I get about 3000.

B = TPS resistance at idle = A X (.13 - .15). So...if A is 3000, the range is 390 - 450.

My manual says to adjust the resistance between the yellow and black (middle and black) to the calculated resistance. So adjust to what??? 390-450?

I'm no electrician and the manual wasn't written for someone like me.

I posted here because more action in this forum than 250 and trying to get bike right before Memorial Day weekend.

Thanks for any help.

Dave

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The manual is telling you to check the overall resistance of the TPS resistor between the blue and the black. Should the measurement be in spec (4-6K resistance 5k ideally being what they're looking for) you want 650-750 ohms at idle.

If you find the over all between blue and black to be different but still in spec they give you a formula to correct the adjustment so you can get the TPS set properly to the spec the ignition is looking for at idle.

So, your assumption is correct. BUT>>>>

The issue is this; The 3k your measuring isn't high enough. Your TPS is dirty or something because your not getting enough resistance across the blue and black.

That is going to end up causing an idle lead timing issue. In other words, the lead time for the ignition will be incorrect because the TPS will be sending the wrong info to the ECU.

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The manual is telling you to check the overall resistance of the TPS resistor between the blue and the black. Should the measurement be in spec (4-6K resistance 5k ideally being what they're looking for) you want 650-750 ohms at idle.

If you find the over all between blue and black to be different but still in spec they give you a formula to correct the adjustment so you can get the TPS set properly to the spec the ignition is looking for at idle.

So, your assumption is correct. BUT>>>>

The issue is this; The 3k your measuring isn't high enough. Your TPS is dirty or something because your not getting enough resistance across the blue and black.

That is going to end up causing an idle lead timing issue. In other words, the lead time for the ignition will be incorrect because the TPS will be sending the wrong info to the ECU.

Thank you! I've loosened the screw and slid the sensor from one end to the other and that has no effect on the 3k. I guess maybe that not going to surprise you because it sounds like the adjusting part is for yellow - black resistance at idle (i.e. throttle closed).

I also removed the TPS from the carb and looked at it and don't know how to clean it or anything. It seemed clean inside the o-ring but I didn't move it far from the carb so I could make sure and put it back on exactly as it came off.

Should I try to fix it somehow or get a new one?

Thanks again!

Dave

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If you can get the sensor apart and clean it maybe you can save it. The thing about it is this. Its a sweeping variable resistor. There is a piece of resistor wire thats is wrapped around a core that is then swept by a conductor that is attached to the yellow wire. If the contactor that sweeps the wire has rubbed off and is shorting the wires the overall resistance will fall.

If you can clean the swept area of the resistor you may be able to save it, but its probably not worth saving.

Now setting that stupid thing Ive got some experience in too. When I set the one on my 426 (it did the exact same thing on the Yamaha) I got the idle perfect before plugging it in. Then I set the TPS to where I had zero bog when I wacked the the throttle open but the engine still returned to the same idle.

The ECU only has so much timing built into it. Where you start that timing is pretty key to preventing engine laziness and detonation. You want as much timing as you can get without it pinging or detonating. If you do this by ear, you'll probably be perfect. Then check it with the meter just for shits and giggles...

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Cool! Thanks for the help! Good gas for you if I can.

Another question...with the TPS unplugged, how did your bike run @ idle...accelerating....and if you turned off the gas did she decelerate promptly?

Dave

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Update -

Turns out my volt/ohm meter that I've had for like 35 years has gone south. Checked my son's bike and his too had an out of spec reading for A. I was like...hmm... So...went and got a new digital multimeter and rechecked. My TPS is in spec for A but was out of spec for B. Adjusted to be in the middle of the range for B. All is well. :smirk:

Thanks.

Dave

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Cool! Thanks for the help! Good gas for you if I can.

Another question...with the TPS unplugged, how did your bike run @ idle...accelerating....and if you turned off the gas did she decelerate promptly?

Dave

ya, once I got the TPS set properly it'd return to idle correctly.

One of the hanging idle issues is the idle speed and fuel screw settings. If you don't have the fuel screw set right and end up with the carb slide higher than it should be, you end up telling the TPS to start to advance the timing before you should really. Thats why its fairly important to get the fuel screw and the idle speed correctlt so the TPS can accurately tell the ECU/CDI whats really going on.

3D ignition maps are bitchen...when in focus. :smirk:

One way of setting the TPS is this (Its not described anywhere..but I did it by thinking about it a bit)

I set the idle speed and fuel screw to perfect. (burned the shit out of myself more than once)

Then I plugged the TPS back in.

Idle speed went up...

I backed the TPS off until the idle speed went back to normal. I advanced it till it sped up again...then backed it off just to where the idle would be normal and tightened it up.

Basically, I set the TPS to advance the timing with the smallest amount of throttle input I could adjust into it.

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Good tips Shawn! I'm getting an understanding of how it works. Thanks!

On my 250, the TPS is totally behind my frame so I can't access it to adjust it while the bike is running. I can barely see it...let alone get a tool on it to loosen it.

Dave

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