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Unread 01-11-2010, 04:23 PM   #1
H_Swank
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Temp gauge issues

I have a 91 YJ, with a 97 TJ 4.0L motor. I am having a problem with the temp gauge. It hasnt came up past 120 but the heater is blowing nice and hot. I am thinking its actually over 120. I tied the gauge wire into the PCM where it would originally have went to the TJ gauge. Is this right? Should I have put it directly to the brn/blk wire on the sensor? And last are the sensors the same between the 91 4.0 and the 97 4.0??

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Unread 01-11-2010, 04:27 PM   #2
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No one here knows what they are talking about. You should try Pirate 4x4 they will be happy to help you.

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Unread 01-11-2010, 04:28 PM   #3
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The YJ gauge ran off of a sender that is at the top of the head, driver's side near the firewall. It has a single wire which is purple with a yellow strip. Does the TJ head have a provision in the head for such a sender? I assume you are still running with the OBDI set up?
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Unread 01-11-2010, 05:16 PM   #4
H_Swank
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Yes OBDI set up, and the 97 has no sending unit. It comes right from the sensor to the PCM to the gauge. So... what do I do now?
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Unread 01-11-2010, 05:42 PM   #5
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If there is no hole in the head (as depicted in the pic provided by Max), then I have seen where others in your situation have done one of the following...
: Tee in a fitting to the heater hose to install the gauge sender.
: Install the sender in one of the block coolant drain plugs.
: Drill and tap the head to accept the sender.
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Unread 01-11-2010, 06:52 PM   #6
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So coming off the 97 PCM wont work for the 91 gauge?
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Unread 01-11-2010, 06:55 PM   #7
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So coming off the 97 PCM wont work for the 91 gauge?
Huh? You said you were running an OBDI set up. If you are running the '97 PCM/ECM, then you are running OBDII.
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Unread 01-11-2010, 06:56 PM   #8
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So coming off the 97 PCM wont work for the 91 gauge?
I wouldn't think so. The PCM sensor value is a different type of signal.

The YJ temp gauge uses a single wire "TURD" sender ground input.

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Unread 01-11-2010, 07:25 PM   #9
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Ok, thanks Max. Luckily my buddy has his 91 YJ parked in the other driveway, so I will take a look at how his is setup and go from there. Thanks alot.
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Unread 01-12-2010, 07:33 PM   #10
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Ok, I am still having so issues. I am just not seeing how this is supposed to work. Correct me if I am wrong.

I am supposed to add a sending unit to the 97 motor. It screws into the head on rear driver side of the motor, and the single wire plugs right in? And the 97 head will have a place this goes into?
If that dont work...
I am supposed to T off from on of the hoses going to the heater core? (dont understand how that is supposed to happen)
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Unread 01-12-2010, 08:22 PM   #11
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If there is no provision for a sensor to thread into the head on the '97 block, then what you can do is get a metal Tee that will splice into a heater core line. At the top(middle) of this Tee, drill and tap a hole that will accept the OEM sender for the temp gauge. Clear as mud? (I assume you miss-spoke and are indeed running the '91 ecm?)
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Unread 01-12-2010, 08:52 PM   #12
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I understand a little better now, but thats a pretty big t fitting, and my only worry is that will show the temp in that line, and not the temp in the motor itself. I understand its not far off, but just a little OCD I guess. Also I am running the 97 PCM, but gauges are 91.
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Unread 01-13-2010, 05:08 AM   #13
idaholtby
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There are two other options that were provided earlier that will get you a reading from the block, they just aren't quite as easy. Interesting that you are running a '97 ECM. I guess there may be other issues you are fighting as well unless you did the full blown OBDII install.
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Unread 01-13-2010, 09:32 AM   #14
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There should be a provision to thread into the head.

On my cherokee 4.0 head it was near the front of the head on the drivers side.
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Unread 01-13-2010, 05:21 PM   #15
H_Swank
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Douglas- can you post a pic of where you placed it?
I didnt get a chance to look at it today. I talked to my Dad today, which is an awesome mechanic and he said there should be a place near the alt to put it in, and putting a t in the heater core hose isnt a good ideal cause its not accurate, and the purpose is to monitor the motor not the heater core.

idaholtby- The swap wasnt actually to bad. Basically it was only 4 wires from the 91 fuse block to the 97 PCM to get it started. I just kept the motor harness separate from everything else, and the wiring for the gauges are the only issue.
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