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Discussion Starter #1
Dear friends, hope you may help us becouse I`ve bought a 1998 TJ, and a check engine code Pop-up (P0123), probably the previouse owner couldn`t find the solution and sold to me the jeep, need help from the exprets.

what i have done checking until now:
1. replace the old TPS to brand new TPS!
2. replace MAP sensor, from working TJ!
3. replace the old ECU (main computer) to brand new!

holy JEEP god, tried to find the ground going from the TPS it self and can`t find it, but when conect pin 1-3 showing 5V.

any suggestions?

thank you in advance
 

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The TPS can be tested with a digital voltmeter.
The center terminal of the TPS is the output terminal.
With the ignition key in the ON position, check the
TPS output voltage at the center terminal wire of the
connector. Check this at idle (throttle plate closed)
and at Wide Open Throttle (WOT). At idle, TPS output
voltage should be greater than .350 millivolts but
less than 900 millivolts. At wide open throttle, TPS
output voltage must be less than 4.5 volts. The output
voltage should increase gradually as the throttle
plate is slowly opened from idle to WOT.
 

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Genius
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For starters I would check the engine/chassis ground for cleanliness and that they are secure. Also make sure you clean the terminals and posts on the battery. Next unplug the tps and ecm and check for continuity between the tps and the corresponding pins going into the ecm. After that I would back probe the tps signal wire with a tiny wire or small paperclip. Turn the ignition is on and engine is off to see what your min and max voltages are while slowly rotating the throttle plate from idle to wide open throttle.
 

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The TPS can be tested with a digital voltmeter.
The center terminal of the TPS is the output terminal.
With the ignition key in the ON position, check the
TPS output voltage at the center terminal wire of the
connector. Check this at idle (throttle plate closed)
and at Wide Open Throttle (WOT). At idle, TPS output
voltage should be greater than .350 millivolts but
less than 900 millivolts. At wide open throttle, TPS
output voltage must be less than 4.5 volts. The output
voltage should increase gradually as the throttle
plate is slowly opened from idle to WOT.
Dear lord. You've got to be a mechanic? Amazing knowledge!
 

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Discussion Starter #10
Firstly thank you for all participants that trying to help me,
this morning:

1. first check with probe and scheme of TJ Wires, the circle of phase 5V, the signal from TPS back to ECU, and the Ground pin on TPS to ECU ground, everthing has good contact and conaction.

2. As BM3 advised, checked with Voltmeter from the middle pin (signal one) the volts, those are the results:

on idle rpm: 4.5 volts stable.

on MAX rpm: the drops smooth to 1.9-2.0 volts.

any suggestions?
 

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For such tests I find an old-fashioned analog meter to be far better and easier to interpret results on than a DVM. DVMs are not a great choice for automotive troubleshooting when compared to an analog multimeter (VOM).

A bad clockspring can mimic a bad TPS and fool the computer into generating an erroneous bad TPS code since both connect onto the same databus. The clockspring is a coil of wires inside a housing residing under the steering wheel and is what connects the steering wheel's controls (horn button, cruise control, etc.) to the rest of the Jeep.
 

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Discussion Starter #12
For such tests I find an old-fashioned analog meter to be far better and easier to interpret results on than a DVM. DVMs are not a great choice for automotive troubleshooting when compared to an analog multimeter (VOM).

A bad clockspring can mimic a bad TPS and fool the computer into generating an erroneous bad TPS code since both connect onto the same databus. The clockspring is a coil of wires inside a housing residing under the steering wheel and is what connects the steering wheel's controls (horn button, cruise control, etc.) to the rest of the Jeep.

Yes I heard about the clockspring, would you say do disconnect it, erase the fault code on the ECU, and try to run/drive the car like that?
 

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Discussion Starter #14
The TPS can be tested with a digital voltmeter.
The center terminal of the TPS is the output terminal.
With the ignition key in the ON position, check the
TPS output voltage at the center terminal wire of the
connector. Check this at idle (throttle plate closed)
and at Wide Open Throttle (WOT). At idle, TPS output
voltage should be greater than .350 millivolts but
less than 900 millivolts. At wide open throttle, TPS
output voltage must be less than 4.5 volts. The output
voltage should increase gradually as the throttle
plate is slowly opened from idle to WOT.

Nothing helps:
disconnect the cables for the weekend, erase the fault code from the ECU,
the check engine with P0123 immediately pops up, when i push the pedal with high RPM. the volts are as metioned before in the post...

:atomic:

i am really confused, any suggestion what ealse to check???
 

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Discussion Starter #18
Keep in mind where sensors are concerned it's best to stay with the OEM when at all possible. Too many aftermarket sensors have crappy quality and sensors are just too important to proper engine operation to try to save a few bucks with them.
Really appreciate it, but the problem starts with the old OEM TPS, The same symptoms, same faul code.

I really would like someone if possible to forword me to a shop I may order from US to Europe, one OEM just to check this theory also.


if any has link to some type of shop?
 

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Firstly thank you for all participants that trying to help me,
this morning:

1. first check with probe and scheme of TJ Wires, the circle of phase 5V, the signal from TPS back to ECU, and the Ground pin on TPS to ECU ground, everthing has good contact and conaction.

2. As BM3 advised, checked with Voltmeter from the middle pin (signal one) the volts, those are the results:

on idle rpm: 4.5 volts stable.

on MAX rpm: the drops smooth to 1.9-2.0 volts.

any suggestions?
Unless I'm completely missing something, it looks like you have a problem with the TPS. From BM3 post, the voltage at idle should be less than 900 mv ( i.e. less than one volt ) and gradually increase as the throttle opens to something less that 4.5 volts. What you've describe is just the opposite.
 
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