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Unread 12-08-2012, 05:43 PM   #1
blackhelix1969
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4.0 help!!!!!

hey so i have an 89 cherokee and it starts fine then after about 10 mins it starts freaking out and dropping idle or the idle will jump all over the place drop go back up drop again then it will just die but turn right back on. i replaced the icm and i am going to replace the iac but i need other ideas of what it could be.

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Unread 12-08-2012, 06:06 PM   #2
blackhelix1969
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i also have a emissions light on but didnt think anything of it. could a bad o2 sensor be causing it??
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Unread 12-08-2012, 06:20 PM   #3
josh94xj
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Sounds kinda like a sensor problem, o2 sensor, maybe but I'd guess TPS just my .02cents maybe wrong but it wouldn't hurt to test it, there are rite ups on here how to do it.

Sent from my 2 door Cherokee!
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Unread 12-08-2012, 06:42 PM   #4
blackolive99
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X2 on the TPS
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Unread 12-08-2012, 06:53 PM   #5
cruiser54
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Emissions light is on a timer/mileage guestimate. Means it's time to replace your oxygen sensor.

Are your intake manifold bolts tight?
Got a multimeter and know how to use it?
All your vacuum lines intact, especially the one from the throttle body to the MAP?
When was the last tuneup with plugs, wires, cap, rotor, and fuel filter?

Want some things to check?
Read some of these:

http://www.cherokeeforum.com/f51/cru...x-tips-153657/
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If you own a Renix Jeep, you'll want to check this out. >

An index to over 25 write-ups can be found in Post #1.

Cruiser's Mostly Renix Tips
Refresh*Connections*Before*Replacing*Components
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Unread 12-08-2012, 07:30 PM   #6
87manche17
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Im having a somewhat similar issue, and Ive narrowed it down to my ECM. Hopefully in your case its just a bad sensor.
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Unread 12-08-2012, 08:00 PM   #7
blackhelix1969
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well i tried the tps. it isnt that. how did you find out it was your ecu?
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Unread 12-08-2012, 08:47 PM   #8
blackhelix1969
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so if i unplug the iac shout it make a difference in idle or change anything? because i just did and it didnt make a difference
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Unread 12-08-2012, 09:00 PM   #9
cruiser54
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Quote:
Originally Posted by blackhelix1969 View Post
so if i unplug the iac shout it make a difference in idle or change anything? because i just did and it didnt make a difference
Not necessarily.
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If you own a Renix Jeep, you'll want to check this out. >

An index to over 25 write-ups can be found in Post #1.

Cruiser's Mostly Renix Tips
Refresh*Connections*Before*Replacing*Components
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Unread 12-08-2012, 09:01 PM   #10
cruiser54
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Quote:
Originally Posted by blackhelix1969 View Post
well i tried the tps. it isnt that. how did you find out it was your ecu?
Did you adjust the new TPS?
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Originally Posted by chris87xj View Post
If you own a Renix Jeep, you'll want to check this out. >

An index to over 25 write-ups can be found in Post #1.

Cruiser's Mostly Renix Tips
Refresh*Connections*Before*Replacing*Components
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Unread 12-09-2012, 07:27 AM   #11
87manche17
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Quote:
Originally Posted by blackhelix1969 View Post
well i tried the tps. it isnt that. how did you find out it was your ecu?
I replaced every sensor on it
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Unread 12-09-2012, 12:14 PM   #12
GetLifted
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Sounds like a bad o2 after closed loop starts. Try unplugging the o2s and see if it still happens.
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Unread 12-09-2012, 01:35 PM   #13
cruiser54
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Quote:
Originally Posted by GetLifted View Post
Sounds like a bad o2 after closed loop starts. Try unplugging the o2s and see if it still happens.
Only has one O2, and yes that could be the cause. Still haven't found out yet if the OP adjusted his new TPS. Putting a new one on just willy-nilly can cause it to run as bad or worse.
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Originally Posted by chris87xj View Post
If you own a Renix Jeep, you'll want to check this out. >

An index to over 25 write-ups can be found in Post #1.

Cruiser's Mostly Renix Tips
Refresh*Connections*Before*Replacing*Components
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Unread 12-09-2012, 05:18 PM   #14
tjwalker
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1. Adjust your TPS per below procedure from Cruiser54. The TPS for 87-90 4.0 engines MUST be adjusted.

2. Replace your oxygen sensor. They aren't that expensive and they can be the best money you spend. They have a finite lifespan and that lifespan is a little less on the RENIX engines. Bosch or NTK will be fine here. Spend the money.
--------------------------------------------------------------------------------------

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.
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