tps sensor

Michael Yount said:

the control-module programming compensates for any difference in sensors, readjusting to a base voltage when the throttle is closed."

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I've got this book somewhere, but I've never spent much time in it so forgive me for not bowing to Mr Probst just yet. I've got one curious question though(which I might have already known if I'd read the book ): How does the computer know that the throttle is closed? I thought the voltage output from the TPS was necessary to inform the computer of its current position? How does it know that the throttle is now closed and that it can go ahead and reset the baseline without a signal from the throttle position sensor to begin with? Does it assume that any signal from 1.2-0.6 is closed?

I'll be looking for the book as soon as I get home this morning.

SlowGT said:

I've got this book somewhere, but I've never spent much time in it so forgive me for not bowing to Mr Probst just yet. I've got one curious question though(which I might have already known if I'd read the book ): How does the computer know that the throttle is closed? I thought the voltage output from the TPS was necessary to inform the computer of its current position? How does it know that the throttle is now closed and that it can go ahead and reset the baseline without a signal from the throttle position sensor to begin with? Does it assume that any signal from 1.2-0.6 is closed?

I'll be looking for the book as soon as I get home this morning.

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that was a thought i once had too. stangs, unlike my eclipse, which has an independant sensor to note when the butterfly is closed, dont have such a sensor (that i know of). i figure it must have a way to know or uses previous readings (one reason why one clears the KAM after playing with the TPS base setting) and other sensor data (idle speed, etc) . here is why:
remember to clear a flooded motor, one floors the pedal while starting. well, the puter would think the baseline is 4+ volts if the puter could not have another means of establishing a baseline upon startup, etc. make sense? i am thinking aloud with you on this one.

i wonder if it does not go with previous notations of the TPS baseline and then adapt if the TPS setting has changed (which takes a bit of time - like numberous start ups or idling for a bit of time). so like if one artificially raised the idle setting with the set screw and did not reset the TPS (so now the TPS is reading high at idle), the puter would eventually adapt to this new setting - one reason that some people get a fight from the puter when trying to raise the idle permanently. the puter tries to lower it back down to spec by controlling other things (since it cant back the idle screw out).

ok, it is late and i hope that made some sense.

I don't know - but it doesn't bother me. I can think of a bunch of ways it could set the baseline - as y'all have touched on in your musings. The most logical is during startup - there's a brief moment during every start up that the ignition is on (tps is sending a reading) but rpm is zero. It could establish it there - and that would also account for all the warnings/counsel about not depressing the gas pedal during start up on efi cars. While running, it could compare rpm to flow through the mass air meter and determine when the throttle is closed - and do a tps baseline check then.

What I'm quite certain of is that our ecu's aren't still wondering.

Wow this thread is making us all think to hard. Here is my take on it, I don't claim to know even half of what people like Michael and Jrichker know about the EEC system. I do however repair electronic equipment for a living (Guitars, GuitarAmps, Sound Systems it ain't Nasa but I have a pretty solid understanding of electronic theories). I would think the TPS would have to have atleast a +/- 5 milivolt tolerance because most multimeters affordable to the average guy have such a tolerance. I would bet you that if you get three multimeters together and test your TPS voltage with all three different meters you will get three slightly different readings. I did this measuring voltage in an amp I was working on yesterday at work just as a test. Using two different meters there was a 4 milivolt difference between the meters. These were both Fluke brand meters so I would assume the difference could even be greater when we are talking about using a cheap meter from the parts store.

Now then when a TPS goes bad it is no different that the tone knob on a guitar or when the volume knob on your stereo starts to give you a bunch of static when you try to turn it up. The wipers in the pot get old, dirty, wet ect. and don't work smoothly. When my TPS went bad I had a bucking and missing problem at a ceratin RPM and otherwise it was fine. I hooked up an analog meter to it and watching the sweep of the needle as I opened the throttle you could see when you hit the "bad spot" the needle would jump around eraticly and then smooth out again when you got past it.

Michael Yount said:

While running, it could compare rpm to flow through the mass air meter and determine when the throttle is closed - and do a tps baseline check then.

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hey, what about us with no MAF? i bet you are right about the baseline (KOEO) and previous baselines or input (for flooded starts, etc). interesting.

TS, the puter can see accomodate a 25% range in the sensor input before it tosses codes (i.e. TPS should be able to be set at ~0.75 V to 1.25V and zero itself at start up).

interesting about the meter variances - i remember you talkin about it before. good thing we have a puter that can accomodate it.

JT - my guess is that's why Probst' comment in the book refers to 'since 88' (the CA cars were mass air beginning in 88; everything in 89) -- I'm gonna guess the SD systems deal with this baselining issue differently. It may even be that the basis for the old 'set it at .99V for increased performance' thinking comes from the SD days --- but I'm speculating entirely.

Michael Yount said:

JT - my guess is that's why Probst' comment in the book refers to 'since 88' (the CA cars were mass air beginning in 88; everything in 89) -- I'm gonna guess the SD systems deal with this baselining issue differently. It may even be that the basis for the old 'set it at .99V for increased performance' thinking comes from the SD days --- but I'm speculating entirely.

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Michael, thanks. that makes perfect sense.

JT - maybe you can do some 'sperimentin' for us. Since you've got an SD car - if you've got your voltmeter, maybe you can set yours at, say, .90V, .99V, and say 1.1V and see if it affects drivability, idle quality, etc. Easy for me to ask....

I have an '87 and when I first started hanging out here and read about the TPS I messed with mine setting it at different voltages and never noticed a difference. And as I said earlier in the thread when I bought the TPS that is on my car now I just stuck it on in the parts store parking lot and have never had an issue.

Well - there you have it.

Big J .

i have not messed with mine (if it aint broke......) - i do know that it sits at 1.2 volts which i have never liked. but it does not pitch a code so i have not messed with it (i should lower it down - just never get around to it).

This one of those things that probably isn't gonna have much effect either way. So I figure if someone feels better knowing theres is set at exactly .99 or whatever then go for it. Can't hurt anything. I am not prepared to say that just because I didn't notice any difference on my SD system it doesn't matter. It may like was said earlier be where the .99 theory originaly comes from It may come into play more with aftermarket throttle bodies as well, I don't know I am dealling with what I have experienced with my STOCK setup.