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Bad output voltage from TPS?

smithmiester

NAXJA Forum User
Location
US
I just got done putting a 96 H.O. in my 89, and after working out some issues, i got it to start. But when it is running, if i take my foot off the gas, it immediately dies. So i got out my multi-meter, and ran a check on the TPS. Im getting a solid 4.7 input, so if i times that by .83, my output should be 3.9...... but its not. Im barely getting an output reading at all. Its giving me an output reading of about .15..... Does that mean i have a bad TPS? (the TPS was new a few months ago)
 
Have you gone for a short drive to re-reestablish the OBD-I idle and driving parameters in the ECM memory ?
 
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First off, im about 99% certain the 89 renix is PRE-obd1, and second, i cant move the thing two feet without it dying. Im not getting any output voltage from the TPS< so thats fairly conclusive, yeah?
 
we would need more info on the engine swap. if you used a complete 96HO engine and fuel system and all, you will also need to use the OBD1 computer to control it. now if you are talking about useing the renix fuel system on a 96HO engine, then i believe you have a missmatched intake and will probably give you poor performance. what exactly did you use, and which TPS are you useing, renix, or HO?
 
Since you say the TPS was new a while back, I'll assume it is the Renix TPS and you installed a later long block. If so, use these instructions to test/adjust your TPS. Be sure to do the sensor ground test at the beginning under IMPORTANT NOTE.

Also, did you get all the ground wires back at the engine dipstick stud? Is the stud shiny clean or coveredin paint or grease?
RENIX TPS ADJUSTMENT
Before attempting to adjust your TPS be sure the throttle body has been recently cleaned.
It's especially important that the edges of the throttle butterfly are free of any carbon build-up.
IMPORTANT NOTE: Using the positive (red) lead of your ohmmeter, probe the B terminal of the flat 3 wire connector
of the TPS . The letters are embossed on the connector itself.
Touch the black lead of your meter to the negative battery post.
If you see more than 1 ohm of resistance some modifications to the sensor ground harness will be
necessary. The harness repair must be performed before proceeding.
I can provide an instruction sheet for that if needed.
MANUAL TRANSMISSION:
RENIX manual transmission equipped XJs have a three-wire TPS mounted on the throttle body.
This manual transmission vehicle TPS provides data input to the ECU. The manual transmission
TPS has three wires in the connector and they're clearly embossed with the letters A,B, and C.
Wire "A" is positive.
Wire "B" is ground.
Key ON, measure voltage from "A" positive to "B" ground by back-probing the connectors..
Note the voltage reading--this is your REFERENCE voltage.
Key ON, back-probe the connector at wires "B" and "C". Measure the voltage. This is your
OUTPUT voltage.
Your OUTPUT voltage needs to be seventeen percent of your REFERENCE voltage. For
example: 4.82 volts X .17=.82 volts. Adjust the TPS until you have achieved this percentage. If
you can't achieve the correct output voltage replace the TPS and start over.
AUTOMATIC TRANSMISSION:
RENIX automatic transmission equipped XJs have a TPS with two connectors. There is a flat three-
wire connector, same as the manual transmission vehicles have, and it is tested the same as the
manual transmission equipped vehicles--FOR ENGINE MANAGEMENT RELATED ISSUES.
However, the automatic TPS also has a square four-wire connector clearly embossed with the letters
A,B,C, and D. It only uses three wires and provides information to the Transmission Control Module.
Key ON, measure voltage between "A" positive and "D" ground. Note the voltage. This is your
REFERENCE voltage.
Back-probe the connector at wires "B" and "D". Measure the voltage. This is your OUTPUT
voltage. Your OUTPUT voltage needs to be eighty-three percent of your REFERENCE voltage.
For example 4.8 volts X .83=3.98 volts. Adjust the TPS until you have achieved this percentage.
If you can't, replace the TPS and start over.
So, if you have an automatic equipped XJ your TPS has two sides--one side feeds the ECU, and
the other side feeds the TCU. If you have TRANSMISSION issues check the four-wire
connector side of the TPS. If you have ENGINE issues check the three-wire connector side of
the TPS.
For those with a MANUAL TRANSMISSION--the TPS for the manual transmission XJs is
stupid expensive. You can substitute the automatic transmission TPS which is reasonably priced.
Revised 11-28-2011
 
Thanks cruiser. I did test the four-way connector that goes to the TCU, as i have done this test several times before. Im getting 4.7 input, and virtually no output. My first thought was that i have a faulty TPS, but then i read a few other forums on here where guys had low output voltage, and replacing the sensor did nothing to alleviate the issue.... So i would like to be more conclusive before i proceed. I will do the ground test on the three wire connector that you mentioned, and i will also go make sure my grounds are f$#^ing perfect. I appreciate your help.
 
Thanks cruiser. I did test the four-way connector that goes to the TCU, as i have done this test several times before. Im getting 4.7 input, and virtually no output. My first thought was that i have a faulty TPS, but then i read a few other forums on here where guys had low output voltage, and replacing the sensor did nothing to alleviate the issue.... So i would like to be more conclusive before i proceed. I will do the ground test on the three wire connector that you mentioned, and i will also go make sure my grounds are f$#^ing perfect. I appreciate your help.

For driveability issues don't use the trans side of the TPS for diagnostics. Use the 3 wire engine side as described in the write-up. They are totally separate circuits.

And, it sounds like your TPS MAY be bad. Retest it using the instructions.
 
In the TPS write-up, it describes how to test the three-wire connector for auto and manual. But one thing it doesnt say is what lead of my multi-meter goes in B or C, etc. Do you have that info?
 
I wonder(not really. I think you should) if you should do this.

Cruiser’s Renix Jeep Sensor Ground Test
Using the positive (red) lead of your ohmmeter, probe the B terminal of the flat 3 wire connector
of the TPS . The letters are embossed on the connector itself.
Touch the black lead of your meter to the negative battery post.

Wiggle the wiring harness near the injectors and near the MAP sensor while observing the meter.
If you see more than 1 ohm of resistance a modification/upgrade to the sensor ground harness will be
necessary.
This project will require soldering skills.
 
Please tell me that if i have to reground the TPS, it just goes around the back of the head to the dipstick ground. Wiring harness repair scares the crap out of me.
 
BTW, i tought myself how to solder, just like i tought myself everything else i know about mechanical work. When i got my first XJ 4 years ago, i didnt even know how to change the oil on a car. But out of shear necessity, and a little help from google and NAXJA, you can see where im at today
 
Please tell me that if i have to reground the TPS, it just goes around the back of the head to the dipstick ground. Wiring harness repair scares the crap out of me.

Super easy and I have a write-up.

Check it first. I have confidence in you. I didn't know how to solder at one time and electrical problems scared me. It's called stretching. Reaching out of your comfort zone. You've got a handle on it.

Anyway, get us the ohms reading on the sensor ground.
 
DUDE! I did the resistance test on the TPS ground, and i did it several times to verify, and im getting over 10 ohms of resistance in my TPS. I even when to the friendly jeep specialist shop down the road and verified that i had my multi-meter on the correct ohms setting (200). Also, this guy who has been a jeep specialist for 20 years said that the alternator that came with the 96 is not compatible with the renix system, so he said i should put the alternator off my 89 on. Cruiser54, can you still send me the re-grounding procedure? I want to do it ASAP, so i can get back to work. Hit me up.
 
Here it is and some people have a hard time understanding it while others grasp it just fine. Feel free to ask questions.


Find your Intake Air Temp sensor. It's the sensor just to the rear of the throttle body, has 2 wires, and screws into the intake manifold.
Where it's connector plugs into the harness you will see that one of the wires on the harness side is brown with a white stripe. Follow the brown with white strip wire back into the harness. You'll have to open up the split-loom plastic sheathing to follow it. It will come to a splice with 2 other brown with white wires. They're from the TPS and the CTS. The 3 wires will be  spliced to a single wire headed toward the C101 connector if you have an 87 or 88. If you have an 89 or 90, you do not have the C101 bulkhead connector.
 
Now go to the MAP sensor. Follow the brown with white wire into the harness from there. You will find a splice with 2 more brown with white wires. At the splice you will find the 3 wires connected to a single brown with white wire going toward the C101, or just along the firewall towards the engine if you have an 89 or 90. Along with the MAP sensor that you traced, they are the ECU sensor ground port and the diagnostic connector on the passenger inner fender.
 
You now have 2 sets of 3 brown with white wires, one near the firewall and one near the engine.
 
Cut the splices out of each set of wires eliminating not only the crappy factory splices, but also the single wire between them. Bring both sets of 3 wires together. Solder the 2 sets of wires together and insulate them properly with tape or shrink tubing.
 
Zip-tie up your new sensor loom to allow for engine movement. I prefer to cover it with some new split-loom or wrap it neatly with electrical tape when done.
 
 
Revised 12-02-2011


 
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