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Old 06-15-2013, 03:06 PM   #1
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A tricky TPS Throttle Position Sensor

I've taken a not so great video of my testing of my 1990 2.5L Wrangler's TPS. If I am testing it correctly then I either have two bad TPS's or whatever device sends voltage to the TPS is causing an issue.



Does by the way anyone know which device sends and receives from the TPS? I figure its the Ignition control module or the Engine Control Unit. I'm pretty new the jeep and am pretty confused.

Either way my fluctuating voltage when working the TPS, as its pluged into my volt meter, is from 4.72 to 4.96. I am not getting anywhere near the 0.5 to 5.0 range that I understand I am supposed to get.

I have watched and read a bunch of videos on how to test the TPS but have been unable to be positive which wires are which coming from the TPS connecter.

If you've got any advice please do share, I am supposed to be setting out to Utah for vacation via the jeep on Monday :/ I've been trying all week to get my YJ happy and ready to roll........

I have a previous and on going post about my over all issue at:
http://www.wranglerforum.com/f8/plee...ml#post3862650
BUT basically I am running REALLLLLLLLLYYYYYYYYYY REALLLLLLLLYYYYYYYYY rich.

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Old 06-15-2013, 03:14 PM   #2
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The three wires (not sure which color is which) will be..... Ground, 5volt reference and signal

Ground should always be ground
5volt ref should always be 5volts with key on
Signal should vary from 0.5volts to 4.5 volts as you move the potentiometer.

Bad sensor ground is the most likely cause assuming you are on the signal wire. With a bad sensor ground the potentiometer cannot vary the reference voltage.

When testing components you should always verify that the reading is the same with the sensor ground and a chassis ground.

Good luck

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Old 06-15-2013, 03:44 PM   #3
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Quote:
Originally Posted by Tomdata View Post
The three wires (not sure which color is which) will be..... Ground, 5volt reference and signal

Ground should always be ground
5volt ref should always be 5volts with key on
Signal should vary from 0.5volts to 4.5 volts as you move the potentiometer.

Bad sensor ground is the most likely cause assuming you are on the signal wire. With a bad sensor ground the potentiometer cannot vary the reference voltage.

When testing components you should always verify that the reading is the same with the sensor ground and a chassis ground.

Thanks for the quick response...

My testing of other wire results are as follows:

RED:
(Tested by using positive probe on the wire and negative probe on engine block): 0 volts with ignition off. Steady 4.98-99 reading with ignition on. (This must be positive)

GREY: Tested by using negative probe to grey wire and positive probe to positive battery terminal): 12 volt reading with ignition off. 7.20-17 with ignition off.
(This must be negative?) I am wondering if the 3 volt drop with the ignition on is normal.

YELLOW/green: Described in the previous post.

When you say ground should always be ground I'm not sure I understand all the way. Would you please elaborate a bit on that?

Thanks much,
Dave
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Old 06-15-2013, 03:51 PM   #4
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Pm sent
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Old 06-16-2013, 03:05 AM   #5
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Quote:
Originally Posted by DaveHead View Post
Thanks for the quick response...

My testing of other wire results are as follows:

RED:
(Tested by using positive probe on the wire and negative probe on engine block): 0 volts with ignition off. Steady 4.98-99 reading with ignition on. (This must be positive)

GREY: Tested by using negative probe to grey wire and positive probe to positive battery terminal): 12 volt reading with ignition off. 7.20-17 with ignition off.
(This must be negative?) I am wondering if the 3 volt drop with the ignition on is normal.

YELLOW/green: Described in the previous post.

When you say ground should always be ground I'm not sure I understand all the way. Would you please elaborate a bit on that?

Thanks much,
Dave

For anyone who may also google their way here, looking for a similar issue resolution, Tomdata was right. The ground (Greyish wire on my jeep) was bad. This was preventing the TPS from working. I manually grounded it and retested the TPS sensor with a successful reading.

HOWEVER, The MAP sensor ground was also bad, I also manually regrounded the MAP sensor ground.

After regrounding both sensors the jeep no longer runs rich and idles perfectly again.

I now however have a great idle but when I give the jeep gas quickly it dies. I will investigate this further tomorrow and hope to post a final solution then.

I started trying to follow back the bad ground wires to the reason they were bad... They are running to a very difficult spot to reach near the interior passenger side. I am guessing I need to find and resolve this OR find perhaps another bad ground being caused by the issue that gave both the TPS and MAP Sensors bad grounds...

If anyone knows what other components share a mutual ground with the MAP and TPS please chime in. I looked through all the wiring diagrams and didn't find a clue.

Thanks in advance, and Thanks for Tomdata for getting me this far...
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Old 06-16-2013, 04:58 PM   #6
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Hey Tom, you were so helpful yesterday I can't help but pick on you today... Whenever you have some downtime if you have input on the next step of resolving my overall issue, I would greatly appreciate any input.

I'm guessing there may be a third device with bad ground to check, So far today I've run through, pulled , cleaned, reset, and tested all major ground wires. These are grounds I find coming from the negative battery terminal going to the firewall, to the block, and from the block to the fire wall and they test 0 volts. Seems plausible that the bad grounds must be coming from the ECU, unless I've missed something Maybe the ECU itself has a bad ground... I sit and Ponder ponder ponder.... Anyways the post is getting to long here...

I'm still poking around and plan to poke around all day till I track down the culprit.

The new post with new video is at: http://www.wranglerforum.com/f8/star...ml#post3866618

Retesting the TPS while installed it actually reads 1.18 to 4.98 I think that's just due to the idle setting and/or the way its bolted on. I figure that should be fine and surely NOT cause the dying when giving gas quickly issue. Once warmed up she idles at a steady 1000 again...

Also, lastly, I Tested the O2 Sensor voltage and that looks well grounded. Out comes the manual again... I've about read the whole damn book over the last week.

Thanks man,
Dave
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Old 06-16-2013, 07:46 PM   #7
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The tps sensor should read 0.5 volts at closed throttle and about 4.5 volts at wide open throttle. If you have the ground and reference wires backwards the tps will read 4.5 volts at closed throttle and 0.5 volts at wide open throttle. That would cause the symptom on your video.. Same goes for the map sensor.

Try unplugging sensors one by one (making sure to shut it off and restart in between sensors). If the symptom goes away then that sensor is probably causing the problem.

I bet you grounded the wrong wire for the map sensor.
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Old 06-16-2013, 09:32 PM   #8
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The tps sensor should read 0.5 volts at closed throttle and about 4.5 volts at wide open throttle. If you have the ground and reference wires backwards the tps will read 4.5 volts at closed throttle and 0.5 volts at wide open throttle. That would cause the symptom on your video.. Same goes for the map sensor.

Try unplugging sensors one by one (making sure to shut it off and restart in between sensors). If the symptom goes away then that sensor is probably causing the problem.

I bet you grounded the wrong wire for the map sensor.
The TPS and MAP are sharing the same positive cable so its down to just two wires to make sure get put in the right place, well a total of 4 between both sensors. Seems doable lol

The TPS is actually testing at 0.75ish with the engine on if I lower the idle screw just a bit I presume it will drop to.5 volts (when uninstalled it goes from .15 volts to 4.98)

Anyhow, I did swap the two wires on the map sensor trusting that yeah I must have done it backwards. This gets rid of the engine dying when giving it gas issue but brings back the engine running rich with lower ruff idle rpms. Tried a new map sensor and get the same results. I've been switching wires and retesting and wiggling harnesses and plugs for the last couple hours.

Going back out there but figured I'd leave an updated post incase you or anyone else reading may have further input.

Thanks for your time, I owe you a few beers or whatever you drink next time your in the Sac area.

-Dave

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