Renix I-6 high revs at startup

[jamespwsullivan]

I'm guessing that I'll get at least a couple of suggestions here. I have a 1987 Comanche with the original inline 6. I've only owned it for 6 months. It has about 245,000 miles on the odometer. Runs strong, compression is good across all cylinders.

When I start it up it revs pretty high for 1-2 seconds. a couple of times it has wanted to stay at high revs (well past 1000 rpm-I don't have a tach) and I had to shut it down and wait for a few minutes.

 

What should I be looking at?

 

Thanks in advance. I'm loving the MJ so much I'm going to replace the floor pan in my XJ and keep them both.

[cruiser54]

Throttle Position Sensor aka TPS is probably failing. But, I wouldn't do anything else until I had refreshed your grounds and cleaned the c101 connector as they can add resistance to the TPS circuit and cause exactly what you describe. Have a multi-meter? If so, post back and I'll post up some instructions to deal with the ground and c101 issues.

[Geonovast]

If the voltage readings at the TPS are fine, I would tackle a probably-sticking IAC.

 

On a side not - is your SN your real name, or are you just a huge fan of Monsters, Inc?

[MancheKid86]

IAC is sticking :thumbsup:

[jamespwsullivan]

@cruiser54 - Yes I have a multi-meter and actually know somewhat how to use it. Is the C101 the big ground at the fuse panel?

[jamespwsullivan]

@Geonovast-

Real name is James Sullivan but I go by Pat.

How is the MJ parts hunting over in Springfield?

[Geonovast]

Wouldn't know. Living in an apartment, making practically nothing, haven't touched the MJs in years. I'm actually trying to get rid of them, because where they're sitting needs them gone, and I'm sick of them... sitting.

[jgrabner]

I have this same problem. never happens when you first start it up but seems to stick once warmed up at least more often once warmed up. I vaguely know how to use a Multi Meter as well and it doesn't cause enough trouble for me to do anything about it yet. I'd be interested in what ends up solving it. I do have a spare tps i pulled a while back out of the JY if that is the colpurt.

[cruiser54]

I have this same problem. never happens when you first start it up but seems to stick once warmed up at least more often once warmed up. I vaguely know how to use a Multi Meter as well and it doesn't cause enough trouble for me to do anything about it yet. I'd be interested in what ends up solving it. I do have a spare tps i pulled a while back out of the JY if that is the colpurt.

 

It's not hard to test a TPS. For the issue you guys are having, use the flat 3 wire connector for diagnosis.

 

 

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 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.

FOR AUTOMATIC TRANSMISSION RELATED 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 05-28-2012

[jamespwsullivan]

Thanks. I'll try and at least get through the IMPORTANT NOTE this weekend so I'll know if I need to alter the harness.

[cruiser54]

Excellent idea.