Idle And D30 Front Disconnect Issue

[JFAComanche6]

First off, I have a Dana 30 front axle on my 89 MJ 4.0 from a 90 cherokee that doesnt wanna disconnect. The blue vacuum hose isnt hooked up because I don't know where it goes, but my 4wd works fine. it just bothers me enough now that I wanna know whats wrong.

 

Second, my MJ wants to idle at 2100 rpm's if its parked on uneven or pointed up an incline. if I turn it off and let it sit for a minute it stops, but sometimes the idle speed increases as I drive. I've replaced my idle air control, so I'm lost.

 

Thanks.

[Bounty Hunter]

The blue line is a vent, it terminates in a valve to keep water out.

 

If it doesn't want to disconnect, pull both vacuum lines from the front axle and feel for equal switching vacuum in the lines as somebody engages 4wd and 2wd. If the vacuum is equal and strong, the problem is in the disconnect at the front axle. If not equal strong vacuum, likely a bad vacuum line or bad vacuum switch on the transfer case.

[mvusse]

There are 3 lines going to the axle, one is to engage it that comes from the transfer case, one is to disengage it that also comes from the transfer case, and one that runs to a vacuum switch under the engine coolant reservoir that operated the dash "4wd" light. The transfer case has a third one that terminates at a vent on or near the firewall and a 4th one that supplies vacuum from the intake manifold.

 

Some YJ axles do not have the third line for the switch, but instead have an electric switch mounted directly on the axle.

 

Don't know the specific colors on any of these because I got rid of my vacuum disconnect crap years ago.

[cruiser54]

MJ- Check your TPS after cleaning the throttle body.

 

 

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 bodyand 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