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Bad TPS?

tjmotter

tjmotter

NAXJA Forum User
NAXJA Member
Location
Texas
How do you tell if a TPS is bad? I put a new one from a local parts place on the '90 XJ (auto trans) and it seems to works properly but after driving for a little while, the idle will start to creep up. If I shut it off and restart it is fine again so I am wondering if the TPS I bought is crap.

thoughts?

Thx
Todd
 
I went threw a couple before I just bought a OEM part. I wont ever buy another senor from anywhere but a dealer or MOPAR store. Are you throwing codes?
 
SBpunk said:
I went threw a couple before I just bought a OEM part. I wont ever buy another senor from anywhere but a dealer or MOPAR store. Are you throwing codes?
Click to expand...
Unfortunately the old renix systems aren't odbii compatible
 
Here's how to test it. Use the flat 3 wire connector for engine issues.


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: With the Key OFF, and 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 where it parallels the valve cover and also over near the MAP sensor on the firewall. If you see more than 1 ohm of resistance, or fluctuation in your ohms reading, 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 only a flat three-wire TPS mounted on the throttle body and it provides data input to the ECU. It 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. Loosen both T-20 Torx screws attaching the TPS to the throttle body and rotate the TPS until you
have achieved your desired output voltage. Tighten the screws carefully while watching to see that your output voltage remains where it is supposed to be. If you can't achieve the correct output voltage, replace the TPS and start over.
Sometimes, after adjusting your TPS the way outlined above, you may experience a high idle upon starting. If that happens, shut the engine off and reconnect your probes to B and C. Start the engine and while watching your meter, turn the TPS clockwise until the idle drops to normal and then rotate it back counterclockwise to your desired output voltage.
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, as outlined above—FOR ALL 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. THIS SQUARE FOUR WIRE CONNECTOR IS USED FOR TRANSMISSION/SHIFTING RELATED ISSUES ONLY. 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.
FOR AUTOMATIC TRANSMISSION RELATED ISSUES: Check the square four-wire connector side of the TPS.
If you have ENGINE ISSUES check the flat 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 09-22-2012
 
Sorry didnt notice it was a renix. I ordered mine from WeRMopar for much cheaper. Buuuut like I said not sure how the renix works
 
Check out the RenX files thread and Cruse54s Renix tips on grounds refreshing and TPS calibration.

The 87-90 Renix jeeps are notorious for weak grounds, that cause idle speed problems. Other sensors need to be tested after you verify and fix any bad sensor grounds. Also vacuum leaks can cause problems.

I doubt the new TPS is your problem. Did you calibrate it?

http://www.naxja.org/forum/showthread.php?t=905849

http://www.naxja.org/forum/showthread.php?t=1080172

http://67.228.170.170/forum/showthread.php?p=245653803
 
SBpunk said:
I went threw a couple before I just bought a OEM part. I wont ever buy another senor from anywhere but a dealer or MOPAR store. Are you throwing codes?
Click to expand...

I don't think I have a dealer part left on any of my jeeps.
 
SBpunk said:
Sorry didnt notice it was a renix. I ordered mine from WeRMopar for much cheaper. Buuuut like I said not sure how the renix works
Click to expand...

Not a whole lot of significant difference, just need to know how use a volt-ohm meter, and think through the cause effect method that is mapped out in the FSM guides. I think OBD-II is often overrated.
 
All grounds were refreshed 300 miles ago. In fact, just to be safe, I added an additional ground wire from the TPS ground lines to the ground point on the body (I also left the existing ones installed). TPS was calibrated at that time as well.

Throttle body was dissassembled and cleaned at the same time. Idle control servo was also removed and cleaned at the same time.

any other ideas?

thx
Todd

Ecomike said:
Check out the RenX files thread and Cruse54s Renix tips on grounds refreshing and TPS calibration.

The 87-90 Renix jeeps are notorious for weak grounds, that cause idle speed problems. Other sensors need to be tested after you verify and fix any bad sensor grounds. Also vacuum leaks can cause problems.

I doubt the new TPS is your problem. Did you calibrate it?

http://www.naxja.org/forum/showthread.php?t=905849

http://www.naxja.org/forum/showthread.php?t=1080172

http://67.228.170.170/forum/showthread.php?p=245653803
Click to expand...
 
Vacuum leak that changes with temperature, vacuum hose anywhere on the jeep, there are a bunch of them all over the place, one goes to the MAP sensor, throttle body gasket leak, or intake manifold gasket leak. Or a bad CTS, Coolant temp sensor or Intake manifold temp sensor, or loose contacts on one of the connectors.

When the idle rises, back probe the TPS and see if the output voltage is still at factory spec, .82 volts or if it went up, check the back voltage on the TPS ground wire to thhe battery negative post, it should be less that .02 Volts. In other words, verify the ground is not changing while the engine is running and idle is wandering.

Lastly, a fuel leak can raise the idle, like into the vacuum line from the fuel pressure regulator, or a sticking, leaking injector.
 
Thanks for the ideas. I recently refreshed all the vacuum connections and am confident they are good. I had the entire top end apart when I refreshed it so I am confident that I don't have any leaks in the throttle body/intake manifold areas. I measured the output on the temp sensors and they seem to be working correctly. At that time I was chasing down a low fuel pressure issue that was caused by a loose hose in the tank but used the opportunity to double check all the lines, upgraded the injectors and replaced the fuel regulator so I believe everything in this area is good.

In reading the post you sent earlier I think I will try the "disconnect idle servo" trick and will try your advice on remeasuring the TPS voltages. Since the idle issue goes away immediately if I shut down and restart, I will have to test the TPS voltage while the engine is running. Not too excited about this but I don't see any other way.

thx
Todd

Ecomike said:
Vacuum leak that changes with temperature, vacuum hose anywhere on the jeep, there are a bunch of them all over the place, one goes to the MAP sensor, throttle body gasket leak, or intake manifold gasket leak. Or a bad CTS, Coolant temp sensor or Intake manifold temp sensor, or loose contacts on one of the connectors.

When the idle rises, back probe the TPS and see if the output voltage is still at factory spec, .82 volts or if it went up, check the back voltage on the TPS ground wire to thhe battery negative post, it should be less that .02 Volts. In other words, verify the ground is not changing while the engine is running and idle is wandering.

Lastly, a fuel leak can raise the idle, like into the vacuum line from the fuel pressure regulator, or a sticking, leaking injector.
Click to expand...
 
Sounds like a good plan. Be sure to reinspect your work, it is easy to knock some lines loose, or forget to reconnect them.

You might also make sure you have 12-14 volts at the O2 sensor heater wires, and a good ground on it, as it needs that power/heat only at idle!!! Otherwise the O2 sensor gets too cold at idle and gives off bad data.

Is the cap and rotor pretty new, or at least pretty clean inside the cap?
 
Ecomike said:
Sounds like a good plan. Be sure to reinspect your work, it is easy to knock some lines loose, or forget to reconnect them.

You might also make sure you have 12-14 volts at the O2 sensor heater wires, and a good ground on it, as it needs that power/heat only at idle!!! Otherwise the O2 sensor gets too cold at idle and gives off bad data.

Is the cap and rotor pretty new, or at least pretty clean inside the cap?
Click to expand...


Good call on the loose lines, I will double check. Also, cap is new and O2 sensor is new but I will double check the connections.

thx
Todd
 
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