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Old 08-09-2007, 08:34 AM   #1
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Default Determining pins on TPS

I know this should be simple, but I am seeing a discrepancy.

I picked up a BMW TPS, and am checking the pins to figure out how to wire it in.

Quote:
Originally Posted by Matt Cramer View Post
The easiest way to check a TPS is to unplug it and put an ohmmeter on its pins. Observe the resistance as the throttle opens and closes. Each pair of pins will behave differently:

The resistance between the VREF and ground pins will remain constant.
The resistance between the ground and signal pins will be low with the throttle closed and high with the throttle wide open.
The resistance between the VREF and signal pins will be high with the throttle closed and low with the throttle wide open.
Easy enough. But I found a listing of which pins were what online at a BMW forum

Quote:
Pin 1-black wire-5volt in
Pin 2-shielded wire-ground
Pin 3-yellow wire-signal out
Pin 4-ground
Pin 5-WOT switch
Pin 6-Closed switch
_
6 1
5 T 2
4 3
From testing it, it would seem that pin 1, which would have a black wire going to it, acts as ground, and pin 2 acts as the VREF.

Could there be something going on making Matt's testing procedure wrong for this instance? Or was it just the pin listing wrong? Seems odd to have a black wire as 5V, and a shielded wire being ground...

Thoughts?
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Old 08-09-2007, 08:50 AM   #2
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Hm, ok, I'm now rethinking. I don't have the car in front of me...so if somebody definitively can tell me if the throttle cable is on the top or bottom of the pivot, that'd help. I think I had my WOT and IDLE positions on the TPS mixed up.
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Old 08-09-2007, 09:21 AM   #3
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matt's description is for a tps with that decreases resistance (increases voltage) as throttle opens. Sounds like your beemer tps does the oppsoite--voltage is greater when the throttle is closed. I think if you wire it per the pin out, it will still be fine because you have to calibtrate megatune to work around the tps anyway. If megatune does not like greater ADC at low throtlle and lower ADC at open throttle, then try switching the power and ground. Most likely it won't be a problem. A potentiometer doesn't care which way power goes through it, but I have no way of knowing what other electronics could be in the switch. There are two grounding points, if you have to flip/flop make sure that second ground isn't hooked up anymore.

WOT and idle positions are irrelevent. Forget about em. All you need to do is apply power and ground, and scavenge the linear out.

the throttle cable grabs the throttle door wheel from the bottom. If you hold the thorttlebody in one hand, and pull on the wheel with the other, you'll understand the mechanics of it. If you connect to the top slot of the wheel, giving throttle will forcibly close the throttle, not open it. That is until something in the linkage snaps.
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Old 08-09-2007, 09:34 AM   #4
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Quote:
Originally Posted by Ben View Post
the throttle cable grabs the throttle door wheel from the bottom
That's what I needed. When testing the TPS, I was assuming the opposite (playing with the TPS at work on my desk...no car in front of me). TPS works just as Matt described, so should not be a problem. Thanks.
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