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Discussion Starter · #1 ·
I have been trying to track down a problem on my bike and decided to fully test the TPS in hopes that it was causing the problem. I know that it is basically a potentiometer and it drawn as one in the manual:

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The ECU puts +5V on A (Bn/G wire) and B (Bk/V wire) is the common. Then the signal is read by the ECU on C (orange wire). Of course as the throttle is twisted the voltage on C will change linearly on a PF2C TPS.

At first I started by just measuring the resistance. If this were just a basic potentiometer the resistance between A and B (Rab) would be a constant and the resistance between C and A (Rac) and B and C (Rbc) would be changing as the throttled is turned (one would be increasing and the other would be decreasing by the same amount). So Rac + Rbc would always equal Rab.

However this is not how it worked on this TPS. The resistance between A and B was 1.21k and remained constant while turning the throttle, as expected. The resistance from C (sensor signal) to B (common) started at 1.27k and increased linearly to 2.71k at full throttle. Then the resistance from C (sensor signal) to A (+5V) started at 2.32k at closed throttle and increased to 2.7k at about 1/3 throttle then decreased to 1.79k at full throttle. So obviously this doesn't work like a standard potentiometer.

I put the connector back on the TPS and removed the ECU connector and placed +5V across A and B and then read the C wire and it varied from aroound 0.3V at closed throttled to about 4V at full throttle.

It IAWDiag and JPDiag the ECU seems to be getting a good (linear) reading from the TPS as well. The only issue I have is that I will reset it and it will be at 2.6 and then I will open/close the throttle several times and it might read 2.4..so I reset again and it goes to 2.6, then operated the throttled and it might end up at 2.8. So it seems to vary around 0.2%, but I assume this is not significant and typical behavior?
 

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93 900ss,2019 Triumph 1200XE, 2017 CRF250L RALLY, 2003 F650GS DAKAR, 1993 KLR250, 1986 HONDA TLR20
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Your TPS is a voltage divider. Now I am not a ducati expert here but I can tell you most ECU' are not only looking for position but rate of change. Think of the rate of change as an accelerator pump.
If there is a tiny bad spot on the wiper inside the sensor it can cause a stumble. The only way to really pin it out is with an oscilloscope as it happens to fast to pick up on a volt meter.
I am speaking in general terms and not specific to ducati but most systems work like this.
the below is a bad tps wiper note the time frame that could manifest as a stumble on acceleration.

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JD
 

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Discussion Starter · #3 ·
Yes, a potentiometer is basically a varying voltage divider, but oddly the measured resistance didn't seem to indicate that. The impedance from the wiper to one end did not vary linearly as a normal potentiometer would. And the resistance from the wiper to each end didn't sum to the total resistance. That is what I found odd.

I have fairly nice Tektronix digital scope, so I will try to measure with that. Great suggestion. Thanks!
 

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Discussion Starter · #4 ·
I did this test several times doing it quickly (~200ms from closed to full throttle) and slow (>2 seconds) and both times the response, which was from about 0.3V to just over 4V, looked perfect.

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93 900ss,2019 Triumph 1200XE, 2017 CRF250L RALLY, 2003 F650GS DAKAR, 1993 KLR250, 1986 HONDA TLR20
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Looks like that is not your issue although there might be one other thing using the scope check it at the ecu end all 3 wires and wiggle the connector look for any signal change If you have a bad connector it should show up. If that proves ok I would start looking elsewhere for what ever the problem is.
 
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