Throttle Position Sensor (TPS) voltage range

[mmasse]

I recently installed an intercooler to my TPC Supercharged engine ('97 993 Engine with 964 throttle body). I went to two trackdays already and the different is substantial. Before i could clearly feel the Unichip ECU retarding the timing after 7 or 8 laps. With the intercooler, this will not happen during the entire session (40 minutes). After the runs you can clearly feel the difference between the SC side of the cooler and the intake side. I am in the process of installing an intake temperature sensor to be able to read the difference.

Now, to my TPS issue. Which I need to understand before daring to take the care for tuning with a smaller pulley.

I got the tuning software for the Unichip and was able to download the maps currently on the Unichip. According to this maps, the Full Throttle Maps would be trigger when the TPS voltage reads 4.35. THe problem is that my TPS range goes only from 0.41 to 3.98, when pressing the gas pedal. I also checked the range when manually pushing the throttle body butterfly and I got the reading up to 4.31.

Can anyone tell me what's the normal reading range of the TPS? I though it was 0-5v, but it seems that this is only in theory.

My concern is that the Full Throttle Maps will never be activated with this TPS readings.

Anyone knows whats the TPS trigger point for Full Throttle on the stock ECU?

Thanks

[JJ 911SC]

It would be 5 volts if, you got 5 volts on one pin and the TPS get fully deflect.

Did you Ohm out the TPS from rest to full deflection?

[mmasse]

No, can you explain how to measure and which readings should I get?

Thanks

[JJ 911SC]

Mario

Basically the TPS is a variable resistor that output between 5 Volts and 0 volt depending of its position.

Check Para G2 on page 87 of http://www.electromotive-inc.com/pdf_files/TEC-GT%20Users%20Guide.pdf

[K Sykes]

There is usually some ability to loosen the TPS and rotate it some to get the right voltage range.

[mmasse]

Kinsley,

I tried that but the maximum voltage i got was 4.31. I also tried by disengaging the TPS (keeping is connected to the wires) and by moving it with the finger the maximum I got was 4.73. I tried with a spare TPS that I have and same thing?

Thanks

[Dr J]

Go to radio shack and buy a diode. Cut the wire from the tps to ground and put the diode there with the stripe pointing towards ground. That should up your voltage about 0.6V throughout the entire range of operation.

[mmasse]

Thanks Dr J
I will test this. Which of the three wires should I tap into?

[al lkosmal]

There are typically three wires connected to the TPS. One of them is the voltage source (input). one is ground and the third is the variable voltage output. Have you measured the voltage between the voltage source (input) and ground to ensure that there is a full 5V between power and ground, at that point. If the input/source voltage is low...............the output will also be low.

Regards,
Al

[mmasse]

Thanks Al,

I havenīt measured it the way you mentioned. I will do that.

What I did noticed is that when I disconnect the TPS, I do get a 5V reading on the Unichip Software

I will double check the way you suggested.

[K Sykes]

Originally Posted by mmasse

Kinsley,

I tried that but the maximum voltage i got was 4.31. I also tried by disengaging the TPS (keeping is connected to the wires) and by moving it with the finger the maximum I got was 4.73. I tried with a spare TPS that I have and same thing?

Thanks

One question then - and I am not familiar with the software/hardware you have - is there a way to calibrate the TPS in the software? In Megasquirt for example, there is a step where you move the accelerator from none to max and in essence "tell" the software that's WOT and No throttle. What you did to test by pulling it, gets you all that what I was originally suggesting..

[mmasse]

Kinsley,

Yes, from what I saw the software gives you the capability to do that. The issue is that I am not an expert at all in tuning and will not dare to make any changes to the maps myself, for the time being. What I am trying to address is to secure that the throttle is calibrated as good as possible before taking it to the tuner.

My concern is that the Unichip is a piggy-back type ECU. I understand theat I can calibrate what the Unichip considers full throttle, but not what the OEM ECU considers as full throttle. I might be wrong here, but my assumption is that there might be wasted power if the OEM ECU is not working on the full throttle maps, even if I tune the Unichip to consider a lower voltage as Full Throttle.

I am not sure if I am explaining myself, but what the Unichip does is correct the OEM maps. So it will add or detract from whatever the stock maps give.

Does anyone knows whatīs the trigger voltage of the TPS for the OEM ECU ( on 993 engine)to work on Full Throttle maps?...or does it even take TPS info into account for this or uses only the MAF sensor to activate full throttle maps?

Thanks agains for all the inputs

[JJ 911SC]

Mario,

Do you have a schematic of your set-up, if so post a pic of it.

Where does the 5 Volts for the TPS comes from and what is your actual measurement?

[mmasse]

JJ 911SC,

I donīt have the schematic, but it is a stock 993 wiring harness coming from the 993 ECU
Does this help?

[JJ 911SC]

and the Voltage is?

[mmasse]

JJ 911SC

I donīt have access to the car now ( I am at the office). Are you refering to the volage input to the TPS? If so, I will measure this afternoon and post

Thanks again

[JJ 911SC]

Yes. As mentioned below in a few posts, the maximum output (middle connector on a 3 prongs TPS) should be equal to the input voltage.

Take 2 Voltage measurements, with the TPS plug in:

* one between the TPS input and its local ground (the two outside TPS prongs), and

* one between the TPS input and the battery negative.

If you do not get 5 Volts on the second measurement, re-do it with the TPS unplugged.

PS: Post a pic of your spare TPS

[mmasse]

I tested the voltage with the TPS connected and disconnected. In both cases the reading between input and ground was 5Volts.
So there seems not to be an issue with voltage input. I manually moved the TPS and took measures and it went from 0.25 to 4.75. So it seems the issue is that the throttle body's butterfly is not providing enough movement to use the entire range of the TPS voltage.

[JJ 911SC]

That is "kind" of good news.

Unless you can get more travel from the throttle, you might need a different TPS that provide the full output for less traveling.

If you have the TPS model, see if you can find out what the range for the full output ie. 270 degrees of travel. You may have a mismatch.

[mmasse]

Originally Posted by Dr J

Go to radio shack and buy a diode. Cut the wire from the tps to ground and put the diode there with the stripe pointing towards ground. That should up your voltage about 0.6V throughout the entire range of operation.

DrJ

I have been trying solve this issue without success and decided to try the diode method that you suggested. Could you please give me specifications on which type of diode should I get?

Thanks