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  #1  
Old September 5th, 2017, 16:27
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1988 (Renix) Xj: TPS Signals; TPS Output/Terminal "C" only mV Range

I have been in arrears in performing diagnostic work on my Xj. A new IAC has helped reduce my engine start rpm flare and I found the TPS output signal (i.e., terminal C in the connector) to only provide a millivolt level signal yet, this is supposed to be a volts level signal.

Renix vintage Xj control systems desire the TPS output to be 83% of the input/supply voltage. Note I converted my '88 Xy from the auto to an AX15 years ago and installed the correct PCM for a manual transmission. I also learned here at that I could still use the auto TPS. Hopefully, this remains correct. I should also add that I have tested (2) used auto TPS sensors and (1) used manual TPS sensor in addition to the new auto TPS sensor I just purchased today.

Here is a (potentially) useful summary and recall the TPS is a simple potentiometer:

Measurements A-B: TPS input; A = B+/Start signal, B=Ground, shared with coolant Temp., Air Temp and MAP. If MAP was messed up I think this would result in a no start. In turn, I suspect my TPS ground is okay. When I measure A - to engine ground I still obtain a good supply voltage signal yet, it is slightly higher than that measured at "A."

B-C: TPS output and the "C" measurement is the obvious problem.



Lastly, note I have used the manual TPS to check voltage at "A" and "C" while exercising the wiper arm of the sensor and the voltage output did vary with wiper motion.

Going out now to repeat some measurements on the new auto TPS.

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  #2  
Old September 5th, 2017, 16:40
lawagoneer lawagoneer is offline
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Re: 1988 (Renix) Xj: TPS Signals; TPS Output/Terminal "C" only mV Range

Have you checked your ground on the TPS. When you changed to the manual transmission did you upgrade the TPS ground. I got all sorts of funky readings until I ran a ground direct to battery from the TPS.
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  #3  
Old September 5th, 2017, 16:53
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Re: 1988 (Renix) Xj: TPS Signals; TPS Output/Terminal "C" only mV Range

On an automatic, you probe a different connector to set things up and instead of 87% it is 13% (850mV) IIRC. It seems like there was a TSB that may have recommended a slightly different set point.
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  #4  
Old September 5th, 2017, 17:28
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Re: 1988 (Renix) Xj: TPS Signals; TPS Output/Terminal "C" only mV Range

I should have stated that I am using the flat 3-terminal connector dedicated to the ECM rather than the square 3-terminal connector dedicated for the TCU. My FSM shows different procedures for the auto/manual TPS calibration yet, I thought I should be using the manual procedure because, it is a manual ans was converted by knowledge I gained here on . The engine does not start (and possibly no starter crank) if you do not follow the threads posted here.

I suspect I verified my TPS ground to be good by performing a continuity test between terminal "B" and the valve cover. The power steering pump mounting bracket was good for the terminal "A" (5.000 V) measurement but, not the ground. When I connected my DMM leads to the valve cover and TPS-B I hear "beep"! Shortly after converting to the AX15, I refreshed all my grounds (sensor grounds on passenger side of engine block and installed a section of an old negative Xj battery cable between the engine block and the fire wall as instructed here...my power windows work much better!

old_man - It is good to see you are still here offering useful advice to us all. I cannot speak to the existence of a TSB as I only had my initial 1989 Xj and the second 1997 Xj in Jeep dealers for service. I have never had my 1988 in for service and have no one at the dealer I know to be able to contact to discuss my current issues with in a non-formal manner because, we live in a new area. The dealer local to me now did perform some service work on my 1997.

I need to read the auto TPS procedure in my manual and check all the other Renix sensors to get a better handle on this. In fact, I may need to read the posts I archived (printed threads as pdf's) when performing this work in the past. The controls are back together and the engine started fine so, at least I can go to work tomorrow.
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  #5  
Old September 6th, 2017, 04:49
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Re: 1988 (Renix) Xj: TPS Signals; TPS Output/Terminal "C" only mV Range

Have you ever visited my website?

www.cruiser54.com

Do Tips 1 through 5, and then clean your throttle body and set your TPS according to the site's instructions.
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  #6  
Old September 6th, 2017, 04:50
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Re: 1988 (Renix) Xj: TPS Signals; TPS Output/Terminal "C" only mV Range

Quote:
Originally Posted by old_man View Post
On an automatic, you probe a different connector to set things up and instead of 87% it is 13% (850mV) IIRC. It seems like there was a TSB that may have recommended a slightly different set point.
You should always use the engine side connector to set the TPS unless you're diagnosing a trans issue.

http://cruiser54.com/?p=54
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  #7  
Old September 6th, 2017, 07:58
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Re: 1988 (Renix) Xj: TPS Signals; TPS Output/Terminal "C" only mV Range

I never thought that a manual trans would has much use for a TPS...but, my MJ was a manual, and it had one and a TCU. Did you swap in a newer AX15? Does it have the old AW4 TCU?

The internal wiring and pin outs on the TCUs' are different if the TCU connectors are different colors/eras. E.g. cream color can't go to green and vise versa

I tried to use the 94 AW4 TCU (green) that came with the trans to replace my 88 5 speed TCU (cream). Didn't work. So I had to go to the yard and get a 90 engine side harness, including the AW4 TCU. Cream to cream.

HTH
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  #8  
Old September 6th, 2017, 08:51
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Re: 1988 (Renix) Xj: TPS Signals; TPS Output/Terminal "C" only mV Range

If you are getting less than 1v on the output of the TPS, all is fine. Adjust for 850 mV and call it good. If it wasn't at least close, the engine wouldn't run worth a damn, so you have it all connected correctly. The ECU uses the O2, MAP and TPS to adjust the injector pulse width to add more fuel as the throttle is opened.

On the automatic, they adjust off the signal going to the tranny since it is more critical to have the tranny shifting good than having the mixture control signal perfect since the ECU uses the O2 signal to fine tune things anyway.
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  #9  
Old September 6th, 2017, 09:08
lawsoncl lawsoncl is offline
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Re: 1988 (Renix) Xj: TPS Signals; TPS Output/Terminal "C" only mV Range

Quote:
Originally Posted by ParadiseXJ View Post
I tried to use the 94 AW4 TCU (green) that came with the trans to replace my 88 5 speed TCU (cream). Didn't work. So I had to go to the yard and get a 90 engine side harness, including the AW4 TCU. Cream to cream.

HTH
Yup. The 94 TCU uses the 0-> 5 volt signal, same as the engine computer uses. The Renix AW4 tcu needed the reverse 5->0 volt signal, which is why Jeep had the dual output TPS sensor. If you had filed the key off the connector so it plugged in and hooked the TPS signal to the signal going to the ECU, it would have worked. The other minor differences between those years were the data lines would have been odb versus serial lines that land on the yellow diagnostic connector under the renix hood, and the power/comfort switch. I don't recall when the NSS switch changed, 98?

Anyway, the only thing different about the dual output TPS was the extra output for the trans computer. I used the dual output TPS on my manual because it was $15 cheaper than the single output sensor at the time. There was also no difference in the Renix ECUs between auto/manual.
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  #10  
Old September 7th, 2017, 04:59
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Re: 1988 (Renix) Xj: TPS Signals; TPS Output/Terminal "C" only mV Range

Quote:
Originally Posted by old_man View Post
If you are getting less than 1v on the output of the TPS, all is fine. Adjust for 850 mV and call it good. If it wasn't at least close, the engine wouldn't run worth a damn, so you have it all connected correctly. The ECU uses the O2, MAP and TPS to adjust the injector pulse width to add more fuel as the throttle is opened.

On the automatic, they adjust off the signal going to the tranny since it is more critical to have the tranny shifting good than having the mixture control signal perfect since the ECU uses the O2 signal to fine tune things anyway.
I have to disagree.

The Trans side is very forgiving. The Engine side is not.
It was a total mistake using the trans connector to set the TPS for driveability/diagnostic issues other than auto trans stuff.

They are totally different units inside the TPS and are connected in no way shape or form.

Using the factory method on the trans side, you can adjust the TPS, thinking you're doing the right thing, while the engine side of that same TPS is toast.

It's all explained in the link below.
http://cruiser54.com/?p=54
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  #11  
Old September 8th, 2017, 17:46
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Re: 1988 (Renix) Xj: TPS Signals; TPS Output/Terminal "C" only mV Range

old_man & crusier54,

Yes, I agree with your recent posts. In re-reading the FSM procedure it was clear something is wrong for a simple potentiometer. My searching identified the TSB in question. This should be TSB 8336 but, it looks like I do not have the ability to attach documents to my posts. The TSB states TPS output should be .8 VDC...which is the value both of you are referring to.

Thank you again for the support.
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  #12  
Old September 9th, 2017, 05:57
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Re: 1988 (Renix) Xj: TPS Signals; TPS Output/Terminal "C" only mV Range

The FSM was not good at explaining the test/adjustment procedure.

That's why I wrote mine to simplify things.

I was Service Manager and Shop Foreman at a Jeep dealership from 1980 through 1992.
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  #13  
Old September 11th, 2017, 17:32
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Re: 1988 (Renix) Xj: TPS Signals; TPS Output/Terminal "C" only mV Range

Are you able to provide me with a specification for how much the throttle plate should be open? I have not been able to locate this information in the FSM.
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Old September 11th, 2017, 17:59
lawsoncl lawsoncl is offline
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Re: 1988 (Renix) Xj: TPS Signals; TPS Output/Terminal "C" only mV Range

Not sure how authoritative this is, but this guy says 0.005" gap. That kinda jives with my memory from when I swapped throttle bodies and had to tweak the stop to bring the idle down - the old one was around 5 mil and the one I swapped in was 20-mil before I adjusted it to match. I also spotted his analyzer showing the TPS at .84 volts / 17% at idle which agrees with the 1988 FSM saying nominally 0.8 volts (and 4.2 volts on the AT side of the sensor).
https://www.youtube.com/watch?v=yspy-fhvpMM

Last edited by lawsoncl; September 11th, 2017 at 18:02.
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  #15  
Old September 11th, 2017, 21:33
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Re: 1988 (Renix) Xj: TPS Signals; TPS Output/Terminal "C" only mV Range

Quote:
Originally Posted by RAVC1 View Post
Are you able to provide me with a specification for how much the throttle plate should be open? I have not been able to locate this information in the FSM.
http://cruiser54.com/?p=94
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