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Old 03-11-2009, 01:28 AM   #1
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Default AEM Variable TPS Question

Hey folks, so I put a variable TPS on my 1990 throttle body, which sees .080 to 3.2 volts, depending on how the pedal is depressed. I went through the AEM pro software and did the tps calibration, and it recognizes properly under the TPS Volts tag. However, my TPS% still only shows zero or 100 percent. It shows zero all the way up to about 2.8 Volts, and then switches to 100 percent. Am I missing something here?
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Old 03-11-2009, 04:46 AM   #2
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The "Throttle Analog Input" option should be set to whatever analog input of the EMS you're using to feed the TPS signal - i.e. "TPS Voltage" for the standard TPS input in the 1710 box.
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Old 03-11-2009, 10:51 AM   #3
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The "Throttle Analog Input" option should be set to whatever analog input of the EMS you're using to feed the TPS signal - i.e. "TPS Voltage" for the standard TPS input in the 1710 box.
I have that set up, and the EMS recognizes the change in voltage, but does not variably change the Throttle % field...
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Old 03-11-2009, 01:54 PM   #4
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Strange. Can you post your calibration?
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Old 03-11-2009, 02:06 PM   #5
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No problem. I've attached my calibration file to this post. I should also mention that the TPS I am using is new, and it's for a 1991 nissan 240sx. It has a 3 wire lead coming off of it. The wires were black, red, and white (White was in the middle). I originally assumed black was the ground, red was power, and white was the signal. When wired up this was, the EMS recognized a voltage change still (different range though, like .01 to 2.53), but the throttle % was stuck at 100%. I then switched the red and white wires, and am left with what I have now - a voltage range, and a throttle % that reads 0 or 100%... Like I have the strange feeling that the original way I had it wired was correct, but I couldn't get it to not read anything less then 100% throttle, even though the TPS voltage was changing as I pressed the throttle pedal (while car was off or running).

Thanks for the help btw. I appreciate it.
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File Type: zip 2009-03-10.V1.19.zip (1.8 KB, 79 views)
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Old 03-11-2009, 02:38 PM   #6
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No problem. I've attached my calibration file to this post.
What about the Idle Switch Input option? Your calibration has it to "Switch #5 Ground = OFF". That is used with the digital TPS (the idle switch) to control the idle engagement. Maybe it is affecting the TPS calculation in the software? Can you set it to "Switch is always OFF" and try again? That's how you should have it with the variable TPS anyway.


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Originally Posted by dustinb View Post
I should also mention that the TPS I am using is new, and it's for a 1991 nissan 240sx. It has a 3 wire lead coming off of it. The wires were black, red, and white (White was in the middle). I originally assumed black was the ground, red was power, and white was the signal. When wired up this was, the EMS recognized a voltage change still (different range though, like .01 to 2.53), but the throttle % was stuck at 100%. I then switched the red and white wires, and am left with what I have now - a voltage range, and a throttle % that reads 0 or 100%... Like I have the strange feeling that the original way I had it wired was correct, but I couldn't get it to not read anything less then 100% throttle, even though the TPS voltage was changing as I pressed the throttle pedal (while car was off or running).
The TPS is just a potientiometer. You better wire it properly though. Do you have a multimeter (which can check resistance) around? It is very easy to figure out the 3 wires using one.
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Old 03-12-2009, 12:52 AM   #7
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Woots! Thanks j man! Switching that input to always off fixed the issue!
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Old 03-12-2009, 01:20 AM   #8
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Woots! Thanks j man! Switching that input to always off fixed the issue!
Nice!

Now let's figure out the wiring just to make sure everything's stable. Do you have a multimeter? If not, go buy some cheap one from your local Sears, Lowes, Home Depot, etc. - you should be able to find some cheap one for $10.
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Old 03-12-2009, 12:26 PM   #9
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Nice!

Now let's figure out the wiring just to make sure everything's stable. Do you have a multimeter? If not, go buy some cheap one from your local Sears, Lowes, Home Depot, etc. - you should be able to find some cheap one for $10.
I have two - an analog one and a digital one.
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Old 03-12-2009, 01:42 PM   #10
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I have two - an analog one and a digital one.
Ok, set your multimeter to measure resistance and unplug the TPS connector.

Then start measuring between each two of the 3 wires of the TPS.

You have 3 combinations to check.

The goal is to find the pair with constant resistance - the one that stays the exact same number (doesn't change) while you rotate the throttle body.

So, you found that pair - let's call those two wires X and Y and the constant resistance between them R (should be few KOhms).
One of those X and Y is the +5V the other one the Sensor Ground.

The third wire (the one which is left out - let's call it S) is the TPS signal.

What's left is which between X and Y is the +5V and which is the sensor ground. To find that out you have to measure between S and X or Y.

If the resistance between S and X is closer to 0 with the throttle closed, and rases up closer to R when you fully open the throttle. Then X is the Sensor Ground. Y is the +5V and if you measure between S and Y it will behave the opposite - the resistance between the two will be closer to R when the throttle is closed and decreases down to close to 0 when the throttle is fully opened.

That's it.

Note tha above I said Sensor Ground - it means that TPS wire should go to the Sensor Ground pin of the ECU and not to its regular ground pins.

Ah, and also if your multimeter is auto switching units (between Ohms and KOhms) don forget that 100 Ohm on the display is a smaller resistance (closer to 0) that 5 KOhm. (1 KOhm = 1000 Ohm)

You can use both multimeters to back your findings up
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