TPS response...

[Schrade]

Vettetech1, throttle position sensors are famous for off idle sag. They can be tested with a ohm meter to see if there is a dip in the resistance just as the sensor starts to move off idle. Its a potentiometer and varies the voltage to the ecm.
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edit:
There are NO problems with the engine, no codes, nothing.
There is only the 'off idle sag' / slow response in rpm's.
5V Voltage FROM THE TPS, back to the ECM, is LINEAR; half throttle = approximately 2.3V.
TPS resistance, in mine, is exponential / logarithmic, as snappics show here.
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What's the solution to this? Is it common also in '90?

And do you mean a SPIKE in resistance; not dip??? edit: ain't no SPIKE in mine; it's just VERY LITTLE CHANGE, as the arm swings to midpoint!!! Then it GOES. See snappics below

I give mine SLOW pedal, and rpm's still respond slowly, until it GOES...

Exactly which is the lead to test / procedure?


Alright - I pulled the TPS, and put a multimeter to the signal feed, and signal return pins.

Here are results:

BASELINE

https://lh6.googleusercontent.com/-BRmm_H5cMKI/Ue7Ntl4JqAI/AAAAAAAABko/1f4ZG0fjKHc/s1280/IMG_5541.JPG

RANGE OF MOTION PEGGED

https://lh6.googleusercontent.com/-EDR_rrwfO9A/Ue7N9K5_E8I/AAAAAAAABk0/G9WgROeosJg/s1280/IMG_5542.JPG

AT LEAST HALF ROM

https://lh3.googleusercontent.com/-cahZaWI9uGU/Ue7OL301HuI/AAAAAAAABlA/RCrohjDVFbs/s1280/IMG_5543.JPG

This gives at least 1 NEGATIONS...

1) Impedance of MY TPS is not linear (is it broken, and IS supposed to be linear??? )
this could account for the delay in rpm increase with a SLOW pedal

If my TPS IS working, then it is safe to assume that the 5V REFERENCE signal INPUT, FROM the ECM, is inversely exponential, and is calibrated for the non-linear resistance of the internal potentiometer. OR, it is calibrated AFTER the 5V REFERENCE signal RETURNS TO the ECM.

:confused:

[Franke]

Schrade, since the TPS is a potentiometer it has 5 volts and ground from the ecm on the outside leads with the center lead as the signal wire. TPS signal voltage varies from about .54 volt at idle to approx 5 Volts at WOT.
According to the FSM the Blk wire is sensor ground from the ECM, the Dk Blu is the TPS signal, and the GRY wire is the 5 volt reference from the ECM. As you know the resitance should be linear so any spike/dip in Ohms is a problem as the voltage back to the ECM will fluctuate with the resistance. The solution is to replace the TPS as you probably cannot replace the guts of the TPS potentiometer. This is all from my 1990 FSM. Wire colors may be different on later years. Hope this helps.

[Schrade]

Thanks...

Is there a TSB for '90 TPS?

Do I need an osscilloscope to test it? Or just a multimeter?

[Schrade]

OK - if the TPS potentiometer response is LINEAR, then there should be a way to rig an arm of a sort, get a range of motion for the arm, then to confirm impedance at 1/4 range, half range, etc.

That is, as long as it is LINEAR...

[Franke]

Its a sealed unit from what I can see so as to protect it from the enviroment. A voltmeter or Ohm meter can be used to check it. Since it is attached to the throttle shaft then it could be verified off the car with an "arm" to watch the resistance change. Most of the defective ones i've seen are bad just off idle position. The FSM doesn't state that it is linear, that is my assumption. If it was logarithmic then the throttle response would be somewhat erratic I think.

[Schrade]

deleted to post #1...

[We Gone]

I may be wrong here but I have always tested them on the car with a jumper. they sell a test jumper to hookup so you can watch the voltage as you cycle the throttle.

http://www.ecklerscorvette.com/assets/pdf/corvette/A8906.pdf

http://www.mamotorworks.com/corvette.html?frame=3.900&searched=tps%20test%20jumper

You can also watch it on a scan tool if you have one.

[Schrade]

Went to Advance to test a new TPS; they didn't have one.

Tested a '90 'K' platform [V8] TPS (new, off the shelf), and got almost identical results.

THis calls for some modification to the throttle body / linkage cam pulley...
Which is of course, the answer to the :
Vettetech1, throttle position sensors are famous for off idle sag.

Ideas???

[Franke]

It appears not to be linear based on your arm positions. Please remember I assumed it may be linear but the FSM doesn't state one way or the other. It just states the voltage will vary with throttle position from .54V to approx 5.0 V WOT. Also, I always use a analog ohm meter to check the ohms from the potentiometer wiper so that I can actually see if there is a dip/spike in the resistance. The problem with digital meters testing pots is that they don't respond fast enough to a very small ohms change and is very dependent on how fast or slow you move the wiper arm. Usually the problem with a defective TPS is a bad spot on the pot just after you go off idle.
I know your TPS is not shorted or open as you would get a code 21 or 22 set.

[Franke]

Schrade, Something else I just read in the driveability and emissions section states that..." voltage should increase at a STEADY rate as throttle is moved toward WOT about 4.6 volts. The ECM has the ability to auto zero the TPS voltage if it between .46 volt and .62 volt. This means that any voltage between .46 and .62 will be determined by the ECM to be 0% throttle". From that statement I gather that the TPS should be linear. Correct?

[Schrade]

Schrade, Something else I just read in the driveability and emissions section states that..." voltage should increase at a STEADY rate as throttle is moved toward WOT about 4.6 volts. The ECM has the ability to auto zero the TPS voltage if it between .46 volt and .62 volt. This means that any voltage between .46 and .62 will be determined by the ECM to be 0% throttle". From that statement I gather that the TPS should be linear. Correct?

I read that STEADY part too, just a while ago.

And the answer is, "Not necessarily does it mean the pot is linear."

It means - that IF my TPS sensor works properly, then what I drew as conclusion before, is correct:


if my TPS IS working, then it is safe to assume that the 5V REFERENCE signal INPUT, FROM the ECM, is inversely exponential, and is calibrated for the non-linear LOGARITHMIC resistance of the internal potentiometer. OR, it is calibrated AFTER the 5V REFERENCE signal RETURNS TO the ECM.

[Schrade]

Seems like many Dodge diesels have problems that are fixed with 'Linear-Taper Potentiometers' installed in the TPS.

Hmm...

[Schrade]

This appears to be the case... , again, IF my TPS is in order:

If my TPS IS working, then it is safe to assume that the 5V REFERENCE signal INPUT, FROM the ECM, is inversely exponential, and is calibrated for the non-linear resistance of the internal potentiometer. OR, it is calibrated in like manner, AFTER the 5V REFERENCE signal RETURNS TO the ECM.

I sure wouldn't mind if someone in the know would post up on this...

Or if someone would take 10 and replicate the measurement.


ed.:
The latter assumption is NOT correct, after observing a STEADY voltage increase, with everything plugged back in .

edit:
Throttle response is in sync with the potentiometer, NOT the voltage reading, which SEEMS linear, after observation.

This is eatin' me up here.

[Schrade]

Just got off the phone with Marc. He was at the bench, and did the impedance test.

First time, he said NON-linear. :thumbsup: Baseline 6,740 (units?); pegged 1,000, midway range of motion 4,220.

His cell cut off, he called back post 5 minutes. "It's linear - I did some calculations", he said.

:confused: :confused: :confused:

Do my snappics in the other thread look linear? Isn't the 'halfway sweep' reading that I posted AT LEAST HALFWAY???

We gonna' have to rig an arm extension of some sort, and get more reliable readings...


Might be moot however...

The original problem of 'off-idle sag', is attributable to the collapsed MAP sensor hose (yet to check)...

No one mentioned that collapsed MAP vac hose would make for this 'off-idle sag'???

[Franke]

Hi Schrade,
Somewhere in these two posts I thought I mentioned MAP and possibly fuel delivery but I can't find that post. Based on those above readings I can't figure it out. If the pots overall resistance is 6740? and midway is 4220 with WOT at 1000 ohms it would seem to me to be Logarithmic. Oh well. Iffan you do find the sag please post as it will undoubtly help others.

[Schrade]

Hi Schrade,
Somewhere in these two posts I thought I mentioned MAP and possibly fuel delivery but I can't find that post. Based on those above readings I can't figure it out. If the pots overall resistance is 6740? and midway is 4220 with WOT at 1000 ohms it would seem to me to be Logarithmic. Oh well. Iffan you do find the sag please post as it will undoubtly help others.

Yessir there Franke...

I missed your MAP issue post , being a possible cause of this sag in TPS response. Thanks!

I sure wish we could get somefeedback on this; everyone knows mods, but when it comes to common issues, or basic tune, either no one posts up, or no one knows ...

:confused:

[Franke]

By the way I did have a MAP sensor go bad on my Z. The car went nuts until the ECM took over and used a calibrated setting for MAP until I could get her home. I had very little throttle response and stalling. Some idle and then stalling (had to keep the rpms up but even then it was tough) until the ECM learned the issue.

[Schrade]

By the way I did have a MAP sensor go bad on my Z. The car went nuts until the ECM took over and used a calibrated setting for MAP until I could get her home. I had very little throttle response and stalling. Some idle and then stalling (had to keep the rpms up but even then it was tough) until the ECM learned the issue.

Marc said the common MAP issue is that the vacuum feed hose TO the MAP sensor collapses when you come off idle. He said this could cause 'off-idle sag'.

Knowledge is good. Sharing it is better yUP!!!

[Schrade]

Marc said the common MAP issue is that the vacuum feed hose TO the MAP sensor collapses when you come off idle. He said this could cause 'off-idle sag'.

Knowledge is good. Sharing it is better yUP!!!

So if I have a MAP response issue, it would show up in DataMaster, in a slow RPM increase, as an erratic change?