Can't adjust TPS

[bcjjones]

Trying to adjust my TPS but it seems like the voltage doesn't change. From the red/green wire to the black green it reads 4.97 volts. I know its supposed to be 5v and when trying to adjust it the voltage never changes. I can push the TPS from one side to the other but it will not change at all. Sign of a bad TPS? I also checked from the white/green to the red/green and got a steady 1v. Which I know its supposed to be from. 48 to. 52 but that will not change either. Anyone have any idea?

 

[syndr0me]

Trying to adjust my TPS but it seems like the voltage doesn't change. From the red/green wire to the black green it reads 4.97 volts. I know its supposed to be 5v and when trying to adjust it the voltage never changes. I can push the TPS from one side to the other but it will not change at all. Sign of a bad TPS? I also checked from the white/green to the red/green and got a steady 1v. Which I know its supposed to be from. 48 to. 52 but that will not change either. Anyone have any idea?

Don't quote me on this but the 5v-ish your seeing is your reference volts. That tells your your TPS is receiving proper electrical draw. This shouldn't fluctuate.

On the other hand, the .5v or so your seeing SHOULD fluctuate. It's how the ECU knows the ThrottlePosition%. Idle reading should be .63v (Base Setting) and could fluctuate well above 4v at WOT if I am not mistaken.

 

[bcjjones]

Okay well that makes sense. I must have read it wrong when I looked at the how to.

And since I did that, I am checking it correctly right? The white/green to red/green should be the one that is .63v at idle?

 

[syndr0me]

Okay well that makes sense. I must have read it wrong when I looked at the how to.

And since I did that, I am checking it correctly right? The white/green to red/green should be the one that is .63v at idle?

Talking color wires, at this point someone else needs to chime in. Although if you are checking the right ones, then yes, 0.63 idle.

 

[DSM1G90]

We don't do voltage, but resistance to adjust a TPS. Car has to be OFF.

The TPS is like a volume control of a radio-a variable resistor.

You use a VOM set to Kohms and you need to read across 1 and 4-which is ground-, 3.5 to 6.5 Kohms is needed.

You put the red lead on pin 2 and the reading should change when you open up the throttle plate.

If you don't get the the above resistance readings, loosen the adjuster bolts to rotate the TPS til you can get the resistance reading.

If still no correct readings, then a good chance that the TPS needs replacing...

 

[Calan]

We don't do voltage, but resistance to adjust a TPS. Car has to be OFF.

You use a VOM set to Kohms and you need to read across 1 and 4-which is ground-, and with throttle plate closed, 3.5 to 6.5 Kohms is needed.

You put the red lead on pin 2 and the reading should change when you open up the throttle plate.

If you don't get the the above resistance readings, or no change when opening the throttle plate, then the TPS is a goner.

Measuring the resistance is a good quick check to see if the TPS is working, but setting the output voltage for .63v with the throttle closed is more accurate, and the preferred method for adjusting it.

Even if the resistance is perfect, the output could be off due to an improper input voltage (low ECU reference output, resistance in wiring, etc.). So it's better to make sure the output is at the correct voltage.

EDIT:

I should add that the .63v is for a 1G only. The 2G is a different beast, and I believe it is set by adjusting the idle switch point.

More detailed info from Steve can be found here.

 

[DSM1G90]

Great, thx for the info.

When I had to do a TPS on a Nissan Pulsar with the 1.8DOHC, I had to do voltage, which that vehicle TPS requirements were set for .5 VDC at throttle closed.

Kinda odd that Chilton's doesn't mention voltage requirements, but just resistance factors when adjusting a TPS for a DSM ...

 

[syndr0me]

We don't do voltage, but resistance to adjust a TPS. Car has to be OFF.

The TPS is like a volume control of a radio-a variable resistor.

You use a VOM set to Kohms and you need to read across 1 and 4-which is ground-, 3.5 to 6.5 Kohms is needed.

You put the red lead on pin 2 and the reading should change when you open up the throttle plate.

If you don't get the the above resistance readings, loosen the adjuster bolts to rotate the TPS til you can get the resistance reading.

If still no correct readings, then a good chance that the TPS needs replacing...

Sure, if you want to get technical the ECU reads it's sensor "Data" with an resistance check. ECULink just reads TPSVolts though. Comes to the same.

 

[Calan]

After reading a bit of Steve's info in that thread, the .63v only applies if you are running ECMLink...which I wasn't aware of (and I'm not sure why, unless it has to do with Link's built-in auto adjustment tool). Otherwise, it's between .48v and .52v.

Sure, if you want to get technical the ECU reads the data Ohms.

Not sure what "data ohms" is, but the ECU reads voltage, not resistance. That is why you adjust the output voltage of the TPS potentiometer.

 

[rvaughn]

I agree with the above statements, a little more detail, if you care:

Ohms Law: V=IR

If you assume a fixed current, as the resistance rises, you will see a voltage increase. Conversely, as the resistance drops, the voltage decreases.

Another way to look at this circuit is as a voltage divider circuit (with a little imagination): You can look at the TPS as a bunch of little resistors in series (or physically as one big resistor that is divided into partitions), as the TP is changed, the arm ('tap') moves up and down on the resistor set, and produces a voltage from the arm, through the ecu and to ground. This reference voltage is what the ecu is programmed to reference for your TPS.

When you get down to it, you could measure either resistance OR voltage, but for DSM's the published data is in resistances.

 

[Calan]

When you get down to it, you could measure either resistance OR voltage, but for DSM's the published data is in resistances.

Which is meaningless on an 18 year-old car where the harness resistance, ECU output, and TPS itself may have degraded, causing a lower than ideal reference voltage across the divider (potentiometer). That is the main reason for adjusting the TPS based on the actual output voltage, rather than resistance from input to output.

Good info on Ohm's law and how a voltage divider works.

 

[rvaughn]

I ment not to call anyone out, only to explain the circuit and why the data is published as it is for different vehicle types. I agree with your statement, there is two cases to consider:

1. A degradation of those components would cause an increased contact resistance, or increase in total resistance, which when referencing ohms law, once again, would cause a higher voltage reading. The published data does prove that, if the resistance has increased beyond the engineered tolerances, it is likely that your TPS has become faulty as it has a contact surface that is being changed while under load, IE destructive to the contact.

2. A degradation of those components, specifically a component contacting ground directly ('ground fault'), would cause a direct short and therefore a parasitic loss or full fault, giving a faulty TPS reading as all voltage would fault to ground. A quick continuity check between ground and the wire in question, while disconnected from its reference ground, would prove whether or not the wires insulation has 'failed'.

And with that degradation, you would see a total resistance which was uncharacteristic for the published data regardless. It is still a valid test, its all in how you interpret the results.

 

[syndr0me]

I agree with the above statements, a little more detail, if you care:

Ohms Law: V=IR

If you assume a fixed current, as the resistance rises, you will see a voltage increase. Conversely, as the resistance drops, the voltage decreases.

Another way to look at this circuit is as a voltage divider circuit (with a little imagination): You can look at the TPS as a bunch of little resistors in series (or physically as one big resistor that is divided into partitions), as the TP is changed, the arm ('tap') moves up and down on the resistor set, and produces a voltage from the arm, through the ecu and to ground. This reference voltage is what the ecu is programmed to reference for your TPS.

When you get down to it, you could measure either resistance OR voltage, but for DSM's the published data is in resistances.

Good info and perfectly illustrating my point. Thanks.

I beleive the ECU reads Ohms to make the correct dicision. Measuring in Ohms makes more sense (Acts like a potentiometer, very coming way of reading things. * Analog controls in your Xbox 360 or PS3 * HINT HINT*.) A certain Volt comes to the same in Ohms any ways. ECMLink reads in Volts, it's a unit in Volts which could be expressed in Ohms by using Ohms law if "I" remains constant.However, the ECU will make a decision based on Ohms.

 

[bryanwheat]

Good info and perfectly illustrating my point. Thanks.

I beleive the ECU reads Ohms to make the correct dicision. Measuring in Ohms makes more sense (Acts like a potentiometer, very coming way of reading things. * Analog controls in your Xbox 360 or PS3 * HINT HINT*.) A certain Volt comes to the same in Ohms any ways. ECMLink reads in Volts, it's a unit in Volts which could be expressed in Ohms by using Ohms law if "I" remains constant.However, the ECU will make a decision based on Ohms.

The ecu just reads an input voltage. That is it, it isn't reading ohm's. It doesn't work like that. Ohms is just a word used to describe how hard it is to push electrons thru the circuit.

 

[bcjjones]

Damn y'all really know yalls stuff. Okay I had read between. 48 and. 52 from another one of Steves posts. I just re read it and realized its from the green/white to the green/black so I was checkin the wrong wires. Got it properly adjusted now. Thanks for all the time and help!

 

[Calan]

I beleive the ECU reads Ohms to make the correct dicision. Measuring in Ohms makes more sense (Acts like a potentiometer, very coming way of reading things. * Analog controls in your Xbox 360 or PS3 * HINT HINT*.) A certain Volt comes to the same in Ohms any ways. ECMLink reads in Volts, it's a unit in Volts which could be expressed in Ohms by using Ohms law if "I" remains constant.However, the ECU will make a decision based on Ohms.

What Bryanwheat said ^^.

************

An ohm is a unit of measure for resistance to current flow.
Current is the actual flow of electrons through a conductor.
Voltage is the electrical "pressure", or potential for current flow.

The ECU does NOT measure the resistance of the TPS circuit; it simply supplies a reference voltage to the TPS, and then measures how much voltage was dropped across that circuit (input at pin 19 on a 1G, pin 84 on a 2G).

For a very simple example, let's assume that we are supplying 5v to a 200 ohm resistor, connected in series to a 100 ohm resistor going back to ground (a simple voltage divider). Using ohm's law, we can calculate the current draw in the circuit as:

I = V/R
I = 5/300
I = .017a

Now that we know the current, we can use ohm's law again to find the voltage drop across the first resistor:

V = I * R
V = .017 * 200
V = 3.4v

So we are dropping 3.4v of the supplied 5v across the first resistor. If you were to measure the voltage between the resistors referenced to ground (which is basically what a TPS output would be), you would see 1.6v:

Measured voltage between resistors = 5v supply voltage - 3.4v drop across the 200 ohm resistor = 1.6v

Now lets assume that for some reason, our 5v supply isn't what it should be, and we are only supplying 3.5v to those same two resistors. Doing the math again, we get:

I = V/R
I = 3.5/300
I = .012a

and:

V = I * R
V = .012 * 200
V = 2.33v

Measured voltage between resistors = 1.17v

In both cases, a resistance measurement shows 300 ohms and looks fine. But the output voltage is not what is expected in the second example, because the input voltage wasn't accurate.

Use a resistance check to verify the TPS is working, and use a voltage measurement to adjust it.

(someone feel free to verify my numbers; I've indulged in a few cold ones tonight. )

EDIT:

Since I'm sure someone will bring it up, there is an easier and much faster way to calculate voltage drops in a series circuit that ignores current altogether. I purposely did it this way to avoid confusion in this example.

 

[rvaughn]

^+1

I agree completely, it couldn't have been said better.

 

[DSM1G90]

Current is the actual flow of electrons through a conductor.
Voltage is the electrical "pressure", or potential for current flow.

Aren't these supposed to be reversed?

(Ohms is right though - the resistance of current flow.)

Voltage is the diameter of the garden hose.
Current, measured in amps, is the pressure of water going through the garden hose.

Solid copper wire takes lots of volts to send a set current value
Stranded wire doesn't take as much volts to send the same current, and more wire strands in the wire gauge, the easier current will flow under less voltage.

Why you see both battery connection cables with very small strands in the gauge set - get that current flowing easily.

...............................................

Now, I'm going to add a little "kink" to this conversation on TPS settings after leaving for a while when the wife hollered for dinner and thinking about it while eating:

Let's go back to the "voltage" thing: (now, Glad to see what I'm used to seeing-the .48 to .52VDC with the throttle plate closed since I don't have any of that add-on "DSMLink" goojazz logging stuff attached to my Laser.. That .63VDC sorta threw me a while.."where did that number come from?")

Now, if the comment mentions that measuring voltage is the more accurate way to go instead of resistance, let's pick on these two numbers then:

Let's say the resistance of the TPS falls within the 3.5 to 6.5Kohms to be a normal variable resistor since these readings come from putting the VOM probes on each end of this resistor. NOW, we check voltage across one end of the resistor and the "wiper", - the movable part of a variable resistor - and the voltage FALLS below the .48 to .52 VDC required voltage reading with the throttle plate closed.

We roll the TPS around to see if voltage rises up to these recommended setpoints.

If it does, we're good..and if not, then...

"Houston, we got a problem."

Now, is it the TPS acting up, or does the ECU have a problem that needs to be addressed to get us the voltage out to get our system in a proper and correct closed loop again?

How much voltage does the ECU put through the ends of the "variable resistor" (TPS) to begin all of this action - this is the beginning factor in all of this. This is were we need to begin with before any adjustments (or possible replacement) are processed.

But first, we need to get that throttle plate adjust correctly where it supposed to be before we even begin with all of this. Otherwise, with an out of adjusted throttle plate, we will never get things where they supposed to be.. (I learned all of this when doing the two idle setpoints on my 1.8L before I could even think of doing the TPS- in which I managed to get it all dialed in correctly..)

thx - DSM

 

[Calan]

I believe the ECU supplies the common 5v sensor reference (and sensor ground) to the TPS. I would think with the TPS off of the TB (no mechanical stop), you should be able to get close to a full 0v to 5v out of it... but I never actually measured it that way.

If the TPS is like most potentiometers, the most common failure mode would be dead spots along it's travel.

Aren't these supposed to be reversed?

Nope.

Solid copper wire takes lots of volts to send a set current value

Ehhhh..... what?

Voltage does not really "send" current through a conductor. Current is drawn through a circuit based on the amount of resistance to electrical flow the circuit provides. Voltage is the electrical potential that a power source provides to a circuit.

Think of it this way (just think about it... don't actually do it!):

Put on thick rubber boots and rubber gloves, stand on a dry floor and stick your finger in a light socket. Now strip down and cover yourself in salt water, stand in a puddle and try it again. Take a guess as to which one will get your attention faster.

There is always 120v sitting at the light socket, but you may not feel anything at all in the first case because there is a lot of resistance to current flow (rubber is a good insulator). The second scenario is likely to kill you though, as you basically form a short circuit to ground and should glow nicely.

Stranded wire doesn't take as much volts to send the same current, and more wire strands in the wire gauge, the easier current will flow under less voltage.

It all depends on the cross-sectional area and conductivity of the metal being used. Stranded wire is usually used to provide more flexibility.

 

[DSM1G90]

dead spots along it's travel

(too bad we can't pop them open and spray them down with contact cleaner, or similar...done that numerous times with noisy volume/tone controls on radios and such...)

thx again - DSM

 

[syndr0me]

Out of all this, have we came to an agreement on the best way to adjust the TPS? Resistance check or Voltage check?

And just out of curiosity, how does the ECU read/interpret the sensor data? Any solid text book or FSM references?

This was a sweet and very intuitive debate none the less.

 

[Calan]

I didn't realize there was a debate...or anything to agree on.

 

[syndr0me]

I didn't realize there was a debate...or anything to agree on.

Lol. Well someone was saying to measure in Ohms to adjust the TPS and some in Volts. Going through these threads and long posts I've managed to get lost on what is going on. I just remember it starting with one person talking adjusting it "X" way and the other adjusting it "Y" way. So now alot has been said...

... What is the best way to adjust your TPS?

 

[Calan]

Well here is how I do it, and why. Anyone else can do it any way they freakin' want to....it's a free country.

 

[DSM1G90]

Looking at what Calan posted definitely does make sense when one puts it to the test..