TPS adjustment questions.

I'm working on getting my heep to pass smog and thought I would check out my Throttle Position Sensor. I measured for Ref voltage + on term A and - on term D and got 4.64.
If I understand correctly, that means I need output voltage to be around 3.85. I measured + on B and - on D and got 4.45. I adjusted the sensor to get that value to 3.83. Started it up and now it idles at 2500rpm. Idled at around 600rpm before. What am I doing wrong?

The TPS in the Renix is actually two TPS in one. Half is for the tranny and half is for the ECU (engine management). You usually set the tranny side, the voltage starts high and lowers as the throttle is opened. The ECU side of the TPS starts out at the low voltage and goes up as the throttle is opened.

Too high initial voltage on the ECU side of the TPS will typically raise your idle. I'd volt test the ECU side of the TPS and see what the low voltage is, typically between 0.6 volts and 0.8 volts with the 0.8 volts being ideal.

The TCU side of the TPS and the ECU side of the TPS have different voltage in sources (typically 4.6-4.8 volts, book says 5 volts), so the formula for setting them up is seldom exact. You are likely getting two different voltages into the two sides of the TPS, so an exact ratio isn't likely possible.

You always have to ohm your grounds for both sides of the TPS, nothing screws up the system quicker than bad grounds. Water or even solvent in the TPS can also cause erroneous readings. The TPS is no way water resistant, a typical engine wash can screw it up. I've gotten a 2500 RPM idle after getting water in my TPS.

A quick setup for me is 3.8-4.0 volts on the tranny side of the TPS and 0.6-0.8 volts on the ECU side. Messing up the setting on the TCU side will affect shift points, but other than that, it isn't as critical as the ECU side for a good running engine. Sometimes you have to cheat a little and split the difference.

You might also want to clean the connectors to the TPS with a good contact cleaner, a little bit of oil, coolant or even water in the connector can screw up your readings.

You also need to set the TPS with the connector connected! Trying to back pin the connector is a pain, I usually cut a tiny slit in the wire with an exacto knife and test straight to the wire core, then either tape or a dab of silicon to seal the slit up again. If you run the TPS wires over the top of the rubber TB inlet tube, they are a lot easier to test.

Went back out and started it up and it idled fine at around 600. Not sure what is going on. Can't find any vacuum leaks.

Your IAC may have stuck open, you may have loosened the IAC connector a little while you were fiddling with the TPS, it can be tight in there..

I tested the ground and it measured .01.

I've gotten the 2500 rpm 2 more times, but have not been able to get it to do it again. It starts and idles normally.

I have been testing the TCU side. I test the ECU side and it was a bit off. I split the difference.

Took it for a test drive and didn't notice a difference. Not sure if this will affect my smog numbers or not, but at least I know that the TPS is working.

clean your grounds to see if you can get your reference voltage up and readjust. if you are getting the hi revs at start up thats mostly the TPS. Consider a new TPS if that continues.

jrowell said:

I tested the ground and it measured .01.

I've gotten the 2500 rpm 2 more times, but have not been able to get it to do it again. It starts and idles normally.

I have been testing the TCU side. I test the ECU side and it was a bit off. I split the difference.

Took it for a test drive and didn't notice a difference. Not sure if this will affect my smog numbers or not, but at least I know that the TPS is working.

Click to expand...

ALWAYS set the engine side to spec and let the trans side fall where it may, unless you're troubleshooting a trans issue.



RENIX TPS ADJUSTMENT

Before attempting to adjust your TPS, there are two things that need to be done.

1) 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.

2) With the Key OFF, and using the positive (red) lead of your ohmmeter, set on the lowest scale, 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.

TPS ADJUSTMENT FOR ENGINE ISSUES

Both RENIX manual and automatic transmission equipped XJs and MJs have a flat three-wire connector to the TPS which provides data input to the ECU. The three wires in the connector are clearly embossed with the letters A, B, and C. Wire "A" is positive. Wire "B" is ground. DO NOT UNPLUG THE CONNECTORS !! 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.

TPS ADJUSTMENT FOR AUTOMATIC TRANSMISSION ISSUES

RENIX automatic transmission equipped XJs and MJs 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 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. First off, DO NOT UNPLUG THE CONNECTORS !! Key ON, measure voltage between "A" positive and "D" ground by back-probing the connector. 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 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. The square 4 wire connector is just not used.
Revised 12-15-2013

Thank you, i referred to that write up when doing it. Somehow i missed the part about high idle. I'll go through and re-adjust it next weekend.

Nvm

jrowell said:

Thank you, i referred to that write up when doing it. Somehow i missed the part about high idle. I'll go through and re-adjust it next weekend.

Click to expand...

I revised the write-up in December to make it more user friendly.

Am I correct in assuming you did the ground refreshing and sensor ground test?

cruiser54 said:

Am I correct in assuming you did the ground refreshing and sensor ground test?

Click to expand...

Yes, Ground tests at .01 ohm

Cruiser54, can you point me to a write-up to test the Mass Airflow sensor? and does anyone know a source for new ones? Can't find them on Rockauto.

XJ has no MAF. It is a "speed/density" setup. AIT and MAP are what our heeps use.

Johnnie Walker said:

XJ has no MAF. It is a "speed/density" setup. AIT and MAP are what our heeps use.

Click to expand...

Ya that... Seems to come up different on every parts site I visit, although none have them.

IAT= Intake Air temperature sensor
MAT= Manifold Air Temperature sensor
IAT=Intake Air Temp sensor