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TPS problems (Got 2 sensors, same problem)

mattbred

NAXJA Forum User
Location
Canada
I have a 1989 Cherokee 4.0L Manual transmission.

Here's some backstory:

When I got my cherokee, its TPS was at 0.25 volts.

When I changed it up to 0.80 volts, the thing would start up and immedietley rev to 3000 RPM's.

So I changed it up by 0.05 a volt at a time, starting up engine each time, and slowly got it to 0.80 volts.

When driving, if I come to a stop, it'll idle at 1300 RPM's. If I unplug the TPS, it doesn't change. If I stop the engine and restart it, it goes back to 900 RPM's.

I changed the ground from the TPS to go right to the battery instead of the computer, and the exact same problems happend.

I put a different TPS I had laying around, in, and it has the same problems as before. Also, I noticed that the volts will not be the exact same at each time I start up the jeep. IE one time it might be 0.80 volts, next itll be 0.815 idling, then after revving it'll be 0.821, then shut it off itll be 0.805. Very confusing.

I changed the volts to 0.67, and now the engine revs up to 3000 RPM's each time it starts. If I unplug the TPS and start up the engine, it idles at 900.

Also, here's the ticker. If I put the TPS back to 0.25 volts, it runs good again. But that's obviously not good right? If it's supposed to be 0.80 volts and all. hm..
What gives?
 
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I have have an '88. I went through this same deal. My tps is adjusted somewhere around .5v and runs fine.

What's the voltage at wide open?
 
I have an 88 and replaced the TPS. all was fine for awhile and the high idle returned. of all times in the winter. I had to ride the brakes and the rear wheels would push me down the road while the front tires slid on the ice. I took it to shop to see if they could tell me what was going on with it. they told me that they could not get any codes from it since it was a transitional year. Old style diognostics to new style. any way the seem be leaning towards the Idle air control
 
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Interesting. Well I set my TPS to 0.820 volts and disconnected the batt for 40 mins. Reconnected it and now it starts up and idles better when its cold. however after driving it for awhile it idles at 1300 still, and my voltages for the TPS are all wrong. Sometimes at idle it'll be 0.825, then itll b e 0.832, etc etc, which increases idle speed ofcourse. I don't know if this is the TPS's fault (I tried two, they could both be defective..), but simply restarting the jeep makes it idle at 900 again.. Which is turning me off from buying a new TPS. If I restarted it, shouldn't it idle back up to 1300 again?
 
Two things, test the voltage in to the TPS should be 4.5 to 5 VDC.

The slight changes you noted would not make any difference unless the throttle was not returning to the closed position.
 
I originally did what you did, adjust to the spec, and got the high idle. I simply backed off until my idle was "normal" and tightened everything down. It's been this way for a while now with no apparent ill effects.

Check this procedure out that I found later on. Turns out mine is spot on using this.

http://arizonaxj.com/tech/RENIXTPSAdjustment.html
 
First of all, make sure you're adjusting to voltage ratio between input voltage and output, not to a specific predetermined number. If you don't have the specs, do a search. I've posted the specs from the factory service bulletin a number of times here, but I'm not at home, so I don't think I have a copy to repost.

Second, make sure that there is no problem with your throttle linkage that might be causing intermittent differences. Disconnect the linkage from the throttle body to make the adjustment if there's any question, and make sure that the accelerator pedal pivot is free, and also the bell crank on the side of the engine, which can wear and bind.

Finally, make sure that all contacts and plugs are clean and not causing any resistance, and that the idle air control valve is not sticking due to carbon buildup.
 
Matthew Currie said:
First of all, make sure you're adjusting to voltage ratio between input voltage and output, not to a specific predetermined number. If you don't have the specs, do a search. I've posted the specs from the factory service bulletin a number of times here, but I'm not at home, so I don't think I have a copy to repost.

What Matt said. The link in my preceeding post points that out. It may be a slightly different proceedure that what Matt has but states the ratio is .82.
 
That's for automatic transmissions though. Mine is a manual, and the initial voltage is <=0.83. I think the ratio is 16% or 17% though?

Also, it is not my throttle linkage. I moved the TPS lever ITSELF, completley free of the throttle lever, and watched my voltage. If I let it go really fast, the voltage would drop to around .820. If I did it slowly, it would settle on around .830. Also, while idling high, I checked the voltage and it was .860. Dont know if thats accurate though since the engine is running.
 
Anyone else know why simply restarting me engine resets me TPS down to a respectable level until I move it's lever again?
 
Sounds like you may have a loose conection (causing a voltage drop) between the ECU's apx. 5 volt output to the TPS and the input to the TPS itself. Try testing the voltage coming into the TPS at the same times you are getting these different output volatges from the TPS. If it is also going up and down about the same amount as the TPS output at idle does, you will know where what is causing it.

Have you solvent cleaned and tightened up the TPS female connector pins on the TPS harness connector yet? They can be loose and dirty. The female connectors can be tightened to grip better with a gentle squeeze using small needle nose pliers and a very small flat blade screwdriver.
 
The voltage coming into the TPS is a constant 4.93 no matter what.

I havn't tried any solvent / electrical grease yet either. Dont think thats the problem..

Also here's something ineteresting. With the positive probe of my voltmeter in terminal C of the TPS, and the ground probe in terminal B, I reset the output voltage to 0.79 volts (16% of my input).

However, with the ground probe of my voltmeter on the engine block, I get 0.804 volts. With the ground probe on the firewall ground, I get 0.802 volts.

What's this mean? All my ground locations on the engine & firewall are clean and tight. Perhaps the ECU's ground is bad? Where is it?
 
That is only a difference of 0.014 volts maximum, and the other is a difference of 0.002 volts which is probably meter and sampling error only. I would not worry about that amount of difference (0.014 volts), it is insignificant.

I noticed for two years that mine would change idle speeds and slow back down to a lower idle speed after a restart sometimes, and other times it would not, for no apparent reason except that it possibly reset the computer (kinda like microsoft operatings systems, LOL!).

I do know that the renix can start and idle properly with out the TPS! It can also decide to ignor certain sensors if it desides they are giving it bad data.

have you tried rechecking all the sensor volatges while wigling the hell out of the wires?


mattbred said:
The voltage coming into the TPS is a constant 4.93 no matter what.

I havn't tried any solvent / electrical grease yet either. Dont think thats the problem..

Also here's something ineteresting. With the positive probe of my voltmeter in terminal C of the TPS, and the ground probe in terminal B, I reset the output voltage to 0.79 volts (16% of my input).

However, with the ground probe of my voltmeter on the engine block, I get 0.804 volts. With the ground probe on the firewall ground, I get 0.802 volts.

What's this mean? All my ground locations on the engine & firewall are clean and tight. Perhaps the ECU's ground is bad? Where is it?
 
the question here is the high idle right?
is there a certain reason were stuck on the TPS?
a vacuum leak can cause high idle. so can a number of other things
i know i read that when you start the jeep w tps unplugged it idles fine so maybe a vacuum leak on another computer controled silonoid that by passes w/o tps signal..
worth a shot if you ask me
keep us all posted
 
Yup ,sounds like progress to me with all this --newer better stuff --
Are these Cherokees crappers or what is it with them ?
Mine is THE most picky vehicle i have ever had ,just about had enough of it is all i can say , i have owned at least 12 jeeps and this version is starting to be a POS in every way.
One thing for sure , IT AINT NO JEEP not from where i am from ,but then again i knew that when i bought it and didnt expect that of it ,,but geez , at least do somethin like a 4 x 4 without doing wir=erd stuff. What a pile ,or should i say car ?
You guys that have never been --jeepers will be p.o.d but that is the truth
Eastern Washington state,come check it out somtime.
No offense to --ANYONE --intended whatsoever ,but i am beginning to think these things are crap.
Mine was intended for the Yukon,Canada,Alaska, but i dont think it willmake it out of the state ! 96 Cherokee
 
I drove a 96 cherokee from 98 till the end of 2001, 4 years total. All I did was change the oil, gas it up, drive the hell out of it and replace the A/C fan clutch in 2001. Oh and went through one set of tires.

Low Range said:
Yup ,sounds like progress to me with all this --newer better stuff --
Are these Cherokees crappers or what is it with them ?
Mine is THE most picky vehicle i have ever had ,just about had enough of it is all i can say , i have owned at least 12 jeeps and this version is starting to be a POS in every way.
One thing for sure , IT AINT NO JEEP not from where i am from ,but then again i knew that when i bought it and didnt expect that of it ,,but geez , at least do somethin like a 4 x 4 without doing wir=erd stuff. What a pile ,or should i say car ?
You guys that have never been --jeepers will be p.o.d but that is the truth
Eastern Washington state,come check it out somtime.
No offense to --ANYONE --intended whatsoever ,but i am beginning to think these things are crap.
Mine was intended for the Yukon,Canada,Alaska, but i dont think it willmake it out of the state ! 96 Cherokee
 
Probably time to check the ECU and look for another ground problem, or a bad wire from/to the ECU. The ECU is way up under the dash, right side of the steering column, to the upper right side nearly behind the A/C dash controls. It is difficult to remove by itself. Renix ECU failures are nearly unknown, but a bad wire that is nearly broken or another ground in the dash / ECU area might be worth looking for. It is possible to drop the ECU to a point where you can test the TPS input directly at the ECU to help isolate a wiring problem.

Have you tried letting it idle from a cold start to fully warmed up with the TPS disconnected to see what the idle does. Then very slowly give it some gas to 2000 rpm then slowly return it to idle? (do it slowly or it will probably backfire, hesitate and die with out the TPS connected). The idea being to see if the idle changes with out the TPS attached.

Also probably time to get an electrical physical layout and electrical diagram from an FSM.

Send me a PM with your email address if you need one.

One last thought, as I recall I suggested the TPS connectors might need cleaning and tightening, and I think you argued that they must be OK as the volatge and ground is steady, but you are not yet testing the low voltage signal back to the ECU from pin C! You are reading the TPS output voltage at pin C of the TPS, but the return wire and conector in the wiring harness side of pin C, might be loose and dirty enough to be sending a variable signal from there to the ECU while you are seeing a stable volatge at the TPS.
 
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Ecomike said:
Probably time to check the ECU and look for another ground problem, or a bad wire from/to the ECU. The ECU is way up under the dash, right side of the steering column, to the upper right side nearly behind the A/C dash controls. It is difficult to remove by itself. Renix ECU failures are nearly unknown, but a bad wire that is nearly broken or another ground in the dash / ECU area might be worth looking for. It is possible to drop the ECU to a point where you can test the TPS input directly at the ECU to help isolate a wiring problem.

Have you tried letting it idle from a cold start to fully warmed up with the TPS disconnected to see what the idle does. Then very slowly give it some gas to 2000 rpm then slowly return it to idle? (do it slowly or it will probably backfire, hesitate and die with out the TPS connected). The idea being to see if the idle changes with out the TPS attached.

Also probably time to get an electrical physical layout and electrical diagram from an FSM.

Send me a PM with your email address if you need one.


as i said earlier i had a bad ECU(thanks for clarifying) and it did fix the bucking and hesitating.
keep us informed on progress
 
What one of these is the ECU?

Ecu1.jpg


Ecu2.jpg

(Btw that black box says "Bendix").
 
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