8 cylinder front engine iconic vehicle
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By Dawid van der Walt
#108106
While my intake is off my car, I'd like to test my TPS.

Noting the values in Worf's inspection guide when testing the sensor at the LH Connector, should the same values apply when testing resistance across the pins in the sensor?
So less than 1ohm with the micro switch activated (throttle closed) - measures a cross pins 2 and 18, then infinite resistance while turning the rotator, till again less than 1 ohm (WOT) measured across pins 3 and 18.

Thanks
Dawid

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By worf
#108131
Dawid van der Walt wrote: Wed Oct 06, 2021 2:43 am While my intake is off my car, I'd like to test my TPS.

Noting the values in Worf's inspection guide when testing the sensor at the LH Connector, should the same values apply when testing resistance across the pins in the sensor?
Yes. The only hard part is figuring out which pin is which on ender. IIRC middle pin is ground.

If you have the wiring diagrams is shows pin numbers on the sender.
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By Dawid van der Walt
#108288
Measuring across 3 and 18, I randomly get a resistance reading. I can't seem to get any reading across 2 and 18.
What are the symptoms of a failed TPS when driving?
My car ran well on partial throttle, with a slight hesitance around 4500 rpm onwards.
I suspected the distributors, but could it be the TPS?
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By Mrmerlin
#108316
the way to test the unit requires it to be turned you should put it back onto the throttle shaft adjust it per the click then test it. the idle test is one then the throttle open to 3/4 to full is the other,
if you get any deviations replace it with a new unit,
the usual fail mode is it fills up with oil. put the unit face down so the shaft opening is laying on a white paper towel leave it sit for a few hours to drain.
If you do find oil or not you should replace the throttle shaft bearings with the upgraded versions these have double sided O rings.
Roger sells these you need 4 of them for an S4 intake,

NOTE the new unit will fill up with oil if the shaft bearings are not replaced
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By worf
#108360
Dawid van der Walt wrote: Thu Oct 07, 2021 3:16 am Measuring across 3 and 18, I randomly get a resistance reading. I can't seem to get any reading across 2 and 18.
If you are referring above to pin numbers on the ECU connectors then you are using my text and diagrams incorrectly. For the LH connector the operative pins are 2, 3, and 17. For the EZK they are 8, 18, 26.

And you should test both.

Go back and look at the pictures on page 41 again.

It's best to use the "blanks" (absence of pins) to make sure you have the right pins for the test.

If, as per thread title, you are bench testing the unit, then pin 2 is ground, pin 1 is WOT, pin 3 is idle.
Dawid van der Walt wrote: Thu Oct 07, 2021 3:16 am What are the symptoms of a failed TPS when driving?
Two basic failure modes: Idle switch, full-throttle switch.

If the idle switch is not closing due to either cable setup or because the switch unit has failed the symptoms are basically 'bad' idle. The exact manifestation depends upon the health of everything else on the motor. If everything else is perfect, the idle will, once the engine is warm, oscillate up and down in time with the oxygen sensor sweep. If motor has other issues then the idle might oscillate wildly, or the engine might just die every time it tries to return to idle from higher RPM operation.

When the full-throttle part of the switch dies, there's no easily observable manifestation. You'll only "see" this failure if you are measuring air/fuel ratios when you are at full throttle. When that part of the switch dies you are, essentially, running "lean" at full throttle.
Dawid van der Walt wrote: Thu Oct 07, 2021 3:16 am My car ran well on partial throttle, with a slight hesitance around 4500 rpm onwards.
A number of things could cause poor operation at 4500+ depending upon the exact definition of "poor."

This is an '89+ right? Do you have access to a Bosch Hammer or "Theo Tool?" If so, look for knock and/or hall sensor codes.

If not, when were your knock and hall sensors last replaced? What about the crank speed sensor?

Fuel filter health?
Injector health?
Resonance flap operation?
Cap/Rotor/Plug age?
Condition of coil and plug wires?

MrMerlin will next ask you for a picture of the engine bay. And I'd agree.
Dawid van der Walt wrote: Thu Oct 07, 2021 3:16 am ... but could it be the TPS?
Highly unlikely. The only thing I can think of, off the top of my head, is if the idle switch is always closed.

Idle switch failure of the TPS unit is very rare in my experience. Idle problems associated to the unit are usually cable setup. It's the full-throttle part of the unit that dies mostly.
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By Dawid van der Walt
#108404
Thanks for the replies.
My car is a '87 auto - RHD that I treat as a running project. It shows just under 100 000 miles, and the engine inside looks about that. I don't have much early history on it.

I started doing the head gaskets after a slight overheating due to a failed water pump. Happy to report no warping, and minimal pitting.

I'm waiting on head gaskets so doing what I can while I'm in there. Hence the TPS deviation.

For MrMerlin
My engine three weeks ago:
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My engine today:
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Testing my TPS:
The numbers 2, 18, 3 are on my sensor, above the pins. 18 is the center pin which is earth, as I understand.
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To test, I attached my multi meter to pin 2 and 18, and turn the rotator all the way from one stop to the other, expecting to have a reading at one stop, and non at the other.
I then did the same but with the meter attached to pins 3 and 18.
When doing this, I sometimes get a reading across 3 and 18, and none across 2 and 18.

I can hear the micro switch clicking at one stop which should be fully closed throttle.

The sensor is clean and oil free.

My distributors and rotors are worn, and will be replaced as the engine goes back together. The injectors were cleaned in January, and the plugs and leads are about a year old. Flappy is good. The bearings and seals was changed in January, along with new intake gaskets.

I'm also doing water pump, belt, oil pump and tensioner while I'm in there. And cleaning - lots of cleaning.
Mrmerlin liked this
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By worf
#108416
Mrmerlin wrote: Thu Oct 07, 2021 7:48 pm you might get confusing numbers,
I would mount that TPS on the throttle shaft and test in location,
that way you will see if its operating as it should
Can't fault that logic!
Dawid van der Walt wrote: Thu Oct 07, 2021 6:41 pm My car is a '87 auto - RHD that I treat as a running project.
I was wondering what those strangely routed lines were until I noticed that your brake booster is on the wrong side. LOL.

Helps to know that the engine is in pieces too.
Dawid van der Walt wrote: Thu Oct 07, 2021 6:41 pm Testing my TPS:
The numbers 2, 18, 3 are on my sensor, above the pins. 18 is the center pin which is earth, as I understand.
Well... the most-sure way to figure out the pins on the switch is to test continuity from the harness-side connector body to the ECU connectors. That way you can be sure you have the right pins and that your measurement of the switch is correct.
Dawid van der Walt wrote: Thu Oct 07, 2021 6:41 pm To test, I attached my multi meter to pin 2 and 18, and turn the rotator all the way from one stop to the other, expecting to have a reading at one stop, and non at the other.
You'll have either infinite resistance (no connection) or less than 1 Ohm resistance.
Dawid van der Walt wrote: Thu Oct 07, 2021 6:41 pm I can hear the micro switch clicking at one stop which should be fully closed throttle.
Correct. Once you hear the switch click, one set of connections should show < 1 Ohm and the other should show Inf. As soon as you turn the receiver and the idle switch opens you should see the previous < 1 Ohm reading go Inf. Then on the other set of pins as the receiver gets to about 90% you should see Inf go to < 1 Ohm.
Dawid van der Walt wrote: Thu Oct 07, 2021 6:41 pm My distributors and rotors are worn, and will be replaced as the engine goes back together. The injectors were cleaned in January, and the plugs and leads are about a year old. Flappy is good. The bearings and seals was changed in January, along with new intake gaskets.
Hall sensor.
Knock sensors.
Crank Speed Sensor.
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By Rdon
#108424
Dawid,

Maybe these pictures will help with your testing. My switch operated inconsistently due to failed solder joints as shown. When cold the switch tested normally but at operating temperature, not so much.

Take careful note of the electrical connections that I have highlighted, the WSM information is incorrect. With your meter connected, tap on the body of the TPS and verify your readings. In my case, due to the failed solder joints, continuity was lost when doing so.
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By Dawid van der Walt
#108437
Thanks Roger. It was your photos that send me on this detour.
I'll fit it to the throttle body and measure again.
My Hall sensor and knock sensors were also replaced in January. I understand the crank sensor is a pain to replace so to date I haven't messed with it.
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By Dawid van der Walt
#108453
I will admit I did not expect fitting the TPS to the throttle body to make a difference, but it did.
With it fitted and adjusted, I have less than 1 ohm at closed throttle, and just over 1 ohm at WOT.
Now I'll have to test it when fitted to the car. Can I test the resistance at the LH and EZK with the battery disconnected and most of the engine harness also disconnected?
Thanks
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By Mrmerlin
#108475
NOTE you absolutely will replace the crank sensor as this is the easiest time to remove it, no intake or heads HUH?

HINT the connector condition of the CPS will be the same as the knock and Hall sensors, if they are all original.

NOTE you can also use the continuity selection on your test meter to test the TPS,
its a switch .
its either working or not,
IF you had suspect operation then it would be wise to open it and resolder the connections and clean the contacts or replace it.
A good sign,
its not filled with oil.

Sean, I know…. It’s a tough call.

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