Mint87RX7

ok i know that you are supposed to set your tps using the leds and then check to see that its at 1k ohm at pins A-B but nobody ever says anything about pinsA-C, in the fsm it says that A-C should be at 5k ohm at both idle and WOT. i just checked mine, A-B is perfect. A-C is at 5k ohm at idle and smoothly drops to 0 ohm at WOT. is there any way i can trick the ecu with a 5k ohm resistor since A-B is fine? and if i can how do i connect it?
I think i would just find the C pin wire at the ecu and cut it, connect it to a resistor then what do i hook the other end of the resistor to?

Turbonut

iTrader: (1)

Delete-Sorry what I posted was for an S5

Mint87RX7

ya forgot to say its an s4 tps, heres a pic to show you what im talking about, the fsm says the resistence on pins A-C should not change

Kenteth

This sounds like a bad idea. :/ Might work.

Did you use this writeup: http://fc3spro.com/TECH/HOWTO/TPS/tps.html ?

EDIT: actually yeah that is what the fsm looks like it says. I guess I never noticed that. Its not techincaly blown open though. Were you having problems with the TPS before, or just getting it set right? I'd test and see if it works the way it is before manipulating it.

Mint87RX7

its been running weird. i probly check the tps once a week to make sure its still right. also im having some bucking at high rpm and thats what i think this is related to, its not affecting the idle because at idle it reads 5k ohm like it should, but like i said it smoothly goes down to 0 ohm as you let the plunger out.
i think the resistor would work fine but i dont know exactly how to wire it

HAILERS

Goodness. Or as White FC would say * Getcha hand off it*.

Here is the DEAL. The TPS has an output. At idle the output is one volt approx. As you move the throttle the voltage goes up until it max's out around 4.5 volts.

As you apply throttle, the voltage should go up smoothly. There should not be any *opens* as the tps goes through its full travel. The voltage should not go to a lesser figure as the throttle goes towards full throttle.

The idea of using an ohm meter to troubleshoot a tps is to look at the value and notice if the reading goes *open* during the travel of the tps from fully depressed to fully extended.

An erratic reading is what you SHOULD be looking for, if you have a suspect tps. The resistance should be smooth when going from one end of the tps to the other.

Mint87RX7

ya i understand that it should be smooth, thats why i said it was smooth when testing pins A-B. look at the attachment i posted, im not worried about pins A-C being smooth, The resistance is not supposed to change at all!

a7r

I think that diagram is wrong. The TPS is just a potentiometer used as a voltage divider. What you're seeing at A-C as you move your throttle, is just the approximate inverse of what you'd see at A-B. Measuring B-C should get you an unchanging ~5k.

BTW, not to sound like a dick but: since you don't understand the basics of how these sensors work, please either educate yourself or take your car to a professional mechanic that has a clue about semi-modern EFI systems. You won't have a 'Mint87RX7' for long, if you do **** like this.

a7r

I think that diagram is wrong. The TPS is just a potentiometer used as a voltage divider. What you're seeing at A-C as you move your throttle, is just the approximate inverse of what you'd see at A-B. Measuring B-C should get you an unchanging ~5k.

BTW, not to sound like a dick but: since you don't understand the basics of how these sensors work, please either educate yourself or take your car to a professional mechanic that has a clue about semi-modern EFI systems. You won't have a 'Mint87RX7' for long, if you do **** like this.

Mint87RX7

well you did sound like a dick... i have a good amount of knowledge of how the sensor works, i just wasnt sure on how the ecu took the signal. and im trying to educate myself by asking questions here. thanks for the first response
does anybody know for sure that the FSM is wrong? or can somebody confirm whats written in the FSM?

Mint87RX7

so, there realy is nobody that knows what the tps is supposed to read? I searched for this for a while and never heard anyone dispute the information in the FSM.

Charlie

I had the same problem and posted. https://www.rx7club.com/2nd-generation-specific-1986-1992-17/tps-readings-388005/
I even took a spare apart and sketched it and posted it. The FSM does say there is not supposed to be a drop and the way I sketched it there shouldn't be a drop but my measurements showed that the resistance went from 5 K ohms to .6 K ohms. Hailers went out and measured his and posted his results too. At the time I was having problems with passing emissions and suspected a bad TPS based on what was in the FSM. Other comments (Ted) on the forum say the FSM is wrong.

After changing my cat I passed emissions so I gave up on trying to reverse engineer the TPS.
I am not sure if the A-C leg does anything and suspect that it may be used to tell the ECM that the TPS is connected. BoB _the_Normal also posted a TPS that he took apart. Look for that link too.

HAILERS

The fsm is correct. Yours should reflect what is stated in the fsm. Been there, done that. The resistance should change as the plunger is moved.

An example is a throttle body I just this last five minutes took off the shelf. It reads 1Kohm on A to B and 4.4K ohms on A to C at the same time i.e. idle position. That's within the 5K plus or minus 1K.

The voltage output to the ECU is the only thing that really matters as far as I'm concerned, allowing that the tps has no opens or irregular voltage movements.

a7r

Stop deluding yourself. If you knew anything about the basic concept of how semi-modern EFI systems measure throttle position using voltage dividers, you wouldn't ask a completely idiotic question like 'can you subsitute a resistor for X'. Remember .. Vout = Vin * (R2)(R1+ R2). If you don't have voltage drop across B and C, there can be no voltage drop between A and C.

My S4 FSM is right. That diagram has a typ-o; which FSM did it come from?

HAILERS

It's from the 1987 series four factory service workshop manual. It's from the section 4A for the non-turbo. In the same book, but in the section 4B, they get it right. They forget about A-C and just do A-B at idle and then full throttle.

RotaryEvolution

iTrader: (30)

his problem he was concerned with was that the readings dropped at pins A-C when the throttle changed positions, the FSM states that the readings should always be ~5k ohms between those pins.

my question is, was the connector connected while the test was performed? if it was, it will throw off the results as the resistances go through the ECU.


personally, i measure the ohms at the signal wire to the ECU and the voltage on the signal wire to the ECU. if both of those are correct then i see no problem with the complete circuit.


you could also be testing the connector with the wrong pins since the resistance drops on the one circuit as it should on the A-B circuit and stay the same through the resistor circuit A-C.

edit: look at your chart and look at your original post again, you will see the error you made. reverse your readings and you should have your answer.

HAILERS

A to C at wide open throttle will read apporx .5K ohms. The manual is wrong as far as A-C goes at full throttle.

Or this thread from several years ago where I think I got it right https://www.rx7club.com/forum/showth...&highlight=A-C

Mint87RX7

so it doesnt actually say what A-C should be then? in your last post hailers you said the fsm is correct then controdicted yourself by saying that the resistance should change. I wish somebody knew for a fact if the fsm was wrong or not lol.
also, what exactly does the tps influence? does it effect how much fuel is being sent? right now my car is running very lean unless at WOT and dont know whats causing it

RotaryEvolution

iTrader: (30)

i thought i answered this question at the top of this page...

it shouldn't go all the way to 0 ohms but it could go under 1k ohms depending on where you have the TPS set at. if it is sweeping smoothly from 0 to 1k ohms up to 5k ohms then the TPS is fine and you will need to set it at 1k ohms at the idle position.

Mint87RX7

sorry i didnt realize there was a second page already

Mint87RX7

when i test it i unplug it and check the resistance at the plug just cuz thats what the fsm says but its a better idea to do it your way karack, never thought about the resistance from the 6 feet of wire going to the ecu.
I am checking the rite pins:
A-B is 1k ohm at idle, smoothly sweeps to 5k ohm at WOT
A-C is 5k ohm at idle, then smoothly sweeps to 1k ohm at WOT. (it is supposed to stay at 5k ohm)
regardless if i checked the right pins, one of them should not change resistance. but Im sure I checked them rite.

so now i have to figure out if karack is right thinking the fsm is correct. or if hailers is right thinking the fsm is incorrect

HAILERS

No. The FSM is wrong. The 87fsm that I was looking at reads just like the jpg you attached. The non turbo fuel section. The Turbo section is much better and ignores the A-C all together.

I took a tps connected to a throttle body and set the idle to 1K ohm on A-B. Then went from A-C where upon at full throttle (fully extended tps plunger), it read 460 ohms or approx .5K ohms. This was on a seventeen year old tps. It works just fine. It's output is set at one volt at idle when the engine is fully HOT. Just like each and every other RX that I own.

ON a non-turbo it easy to just fully heat the engine up, then put the meters negative lead on a good ground and the positive up the back of the green/red wire on the tps connector, leaving the connector fully connected up. Then adjust the tps screw til the meter reads one volt give or take .05 or so. The fsm states in the CONTROL UNIT, that when the car is at idle, pin 2G should read approx.........1 volt dc. Your doing the pin 2G at the tps connector instead of at the ECU. The green/red wire at the tps goes to pin 2G at the ECU.

Mint87RX7

ok ive rechecked it and if the fsm is wrong then my tps is set within spec. thanks for the info, im just trying to rule out different things that could be causing my car to run like crap