Throttle Position Sensor (TPS) voltage range
 

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

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?

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

Thanks

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

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

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

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.

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

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

Thanks Al,

I haven´t 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.

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..

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 what´s 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

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?

JJ 911SC,

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

and the Voltage is?

JJ 911SC

I don´t 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

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

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.

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.

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

The exact kind of diode is not very critical. You can try an IN4001 which is pretty common. It is good for 1 amp. I don't know how much current the TPS sinks but sensors should be relatively low current. If you have an ammeter, you can disconnect the TPS ground wire and put the ammeter in between the ground wire and an actual ground surface on the vehicle to see the current. If it's higher than 1 amp, just source the diode to handle the current, as that is the only real specification you will need to meet.

A diode is a basically a check valve for electronic current. If you're looking to increase ohms of resistance you will need a resistor. Getting real rough you would simply add a resistor (not a diode) of the value difference from 5v to your real world wot reading. Ohms law...

Ohm's law - Wikipedia, the free encyclopedia

The OP is trying to go up in voltage, not down, hence the diode suggestion.

Having said that, mmasse, still would urge that you look at a software solution. It should be a pretty trivial exercise. Also, are your tables only based on TPS? Or do they also use MAP? In many cases, TPS only drives acceleration enrichment and the VE table is driven off of MAP. In any case, the tuner you are planning on using should be able to calibrate the TPS in a minute or two. Last suggestion, have you checked with the manufacturer? They might be able to point you to a calibration tool in the software.

Kinsley,

Thanks for your input. Regarding the software solution, it will not solve the problem in my case. The issue is that I am using a piggy-back Unichip which modifies the base maps on the Motronic. I can modify the value for TPS on the Unichip, but this will not make the Motronic work on the WOT maps.

Do you know if the OEM Motronic for the 993 uses the TPS at all in order to trigger the WOT maps. If it is only MAF/MAP based then TPS will not be an issue at all.

Thanks again

Yep, I thought of that this morning. The 5v source is constant from the ECU. I would put a multimeter on and read the voltage across each pin. Might be a bit of corrosion in the harness or at the wire connections between the feed pin and the ecu.

Input is 5 volt as per multimeter, so that not the problem
I also tested a spare TPS and same thing