Viable Option for TPS Replacement

[Tom]

Back to the TPS... @johnb can you tell what logic/criteria the KLR uses to trigger the WOT signal/maps?All the literature says it triggers at ~65%, which is fine, but the factory spec for the TPS pot is 2.7k to 4.7k ohms at full throttle. With such a wide range, ~65% of what? Assuming the KLR is using the pot as a voltage divider and doing an ADC on the resulting voltage, it seems like that could be a big swing -- with some cars triggering at 60% (or less) and others at 70% (or more) just depending on how high their particular pot goes. I need to test to make sure the pot is linear too, but either way it will be helpful to know the actual trigger logic to make sure any replacement TPS will work right. Any insights?

[johnb]

Back to the TPS... @johnb can you tell what logic/criteria the KLR uses to trigger the WOT signal/maps?All the literature says it triggers at ~65%, which is fine, but the factory spec for the TPS pot is 2.7k to 4.7k ohms at full throttle. With such a wide range, ~65% of what? Assuming the KLR is using the pot as a voltage divider and doing an ADC on the resulting voltage, it seems like that could be a big swing -- with some cars triggering at 60% (or less) and others at 70% (or more) just depending on how high their particular pot goes. I need to test to make sure the pot is linear too, but either way it will be helpful to know the actual trigger logic to make sure any replacement TPS will work right. Any insights?

It is indeed wired as a voltage divider, but that means that it always divides the supply voltage according to the ratio of the 2 resistances. So in theory the overall resistance of the TPS pot can vary without having any effect on the relationship between wiper position and output voltage, as long as the supply is constant.

Actually though, the supply isn't constant because the TPS resistance isn't that high, so there is a voltage drop on the supply that varies by throttle angle. The KLR reads both the supply voltage and the wiper position through separate ADC channels, and always calculates throttle position as a ratio of the two. So it's always 65 degrees regardless of the pot variation. That's actually around 72% of the available 90 degrees, so sources that say 65% are mistaken.

I wrote about this recently: https://jhnbyrn.github.io/951-KLR-PAGES ... ssing.html

...but it might have too much detailed info for practical purposes

[danmartinic]

If the goal is to replicate the TPS... due in part to it being out of production and extreme cost etc... could we not just buy the more readily available units for BMW and others and transfer the inside parts into our original housings?

I am assuming of course that those printed boards are the same inside and the incompatibility lies with mounting or number of output pins etc

[Tom]

If the goal is to replicate the TPS... due in part to it being out of production and extreme cost etc... could we not just buy the more readily available units for BMW and others and transfer the inside parts into our original housings?

I am assuming of course that those printed boards are the same inside and the incompatibility lies with mounting or number of output pins etc

It's possible, but finding a BMW part with the same internals would be the trick, if such a thing exists. If you know of one, I'm all ears. The pot traces on the 951 TPS look designed in place for that case, and the idle contact switch is either NLA or not off the shelf. Bosch may have used the same parts in other units, I really don't know, but without opening a lot of units, I wouldn't know where to start. My plan was to find off-the-shelf parts that are electronically compatible with the originals, and design a new case around them... That seems like the path of least resistance unless someone knows of another TPS with internals that would transfer over like that...

[danmartinic]

The trace board has a part number on it.. and there are only three connections to it? Perhaps one of the 3-pin connection TPSs have the same board (if any work as potentiometer like the 951s)

img_2362_b4775e683b667bf476600d0455c22d6a0e127ca5.jpeg (85.44 KiB) Viewed 270 times

How about a call out to BMW and Bosch car owners from the 80s & 90s to open up their TPSs

And I suppose there is no way to re-plate those traces?