A newbie that needs help

[opie]

Hi All, I just picked up a 91 base.  4WD, 5 speed, 4.0

 

My Temp gauge maxes out at start up then goes down to zero and stays there.  I changed the sensor at the rear of the manifold against/near the firewall but it still does the same thing.  All my other guages work.  Is there a seperate fuse?  Is there something I am missing?

 

Also, the previous owner passed away so I don't know the history of it.  Can you all tell me what fluids I need to put in the front and rear pumpkins?  I have read many different things.  As well as in the 5 speed tranny and in the 4wd transfer case?  I don't know what tranny is in it.  The back of the rear pumpkin says 35G.  Not sure it if is the original tranny or not.  I see new screws under the shift boot so it's hard to say.

 

Thanks so much.

[Siopposition]

It's almost positively an ax-15 trans, maybe a Dana 35 (turdy-five) rear diff.

 

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[Tex06]

Here's what I used:

 

Pumpkins: Walmart brand rear end dope (80w-140 I think....whatever was cheapest)

 

Transfer case: ATF

 

Ax-15: Valvoline Synpower 75w-90. I'm particular about this due to the yellow metal that make up the synchros.

 

More info on that here: https://www.bobistheoilguy.com/forums/ubbthreads.php?ubb=showflat&Number=2554764

 

Also, make sure your radiator is full for the temp gauge. Should be able to ground the connection to the block and see you gauge max out (tests the wiring from sensor to gauge that way).

 

 

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[HOrnbrod]

To test the gauge temp sensor, first clean the wire connector and the sensor stud (left rear of the cylinder head) and make sure it makes a good tight connection. If okay, with the key ON pull the wire connector off the temp sensor  and the gauge should deflect to LO (0*). Then short the wire to ground and the gauge should peg to HI. If it does, the wiring is temp gauge wiring should be good, and it's new temp sensor time.

[opie]

Ok i checked the volts from the cable with key on and it read 5 volts. Then checked the new sensor andgot reaistance. Now what? Bad gauge? But all other gauges work.

[Tex06]

Ground the cable to the engine block or the grounding strap from the firewall. What does the gauge read when you do this?

 

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[HOrnbrod]

Do what I said above with the ignition key ON:

 

Cable disconnected from the temp sensor =  What reading on the temp gauge?

Cable touched to ground = What reading on the temp gauge?

 

Also make sure you don't have a temperature switch for the idiot light, make sure it's a temp sensor for the gauge.

[opie]

Ok...disconnect wire to air charge sensor. Temp gauge does same on start up. Maxes out then falls to zero. However the cel does come on. Then with wire not connected to air temp sensor i grounded the wire and there was no difference. It did the same thing. Is the gauge itself bad?

[HOrnbrod]

"air charge sensor"? Are you using the temp sensor on the rear of the cylinder head near the firewall?

 

The sensor should look like this:

 

Try it again w/o starting the engine. Just turn the ignition key to ON, they pull the temp sensor wire and watch the gauge with it disconnected then grounded to the block.

[opie]

Yes sir. Drivers side near firewall. Its not in the coolant. Its got a dfferent tip. A black plastic cage that senses hot air passing through it. Am i chasing the wrong one? I know it is NOT THE ONE at the THERMOSTAT.

[opie]

Mine has 2 wires in the connector on the harness.

[Tex06]

The 4.0 has two coolant temperature sending units. One of them is in the front at the thermostat, pretty easy to see. This one sends the temp to the ECU. The second is on the driver's side in the very back, by the valve cover. Kinda in the same spot as the firewall ground. Looks like the one above in 91 I'm told, mine looked like the 93 cherokee version. Both are single wire sending units.

 

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92+ sending unit

 

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As it looks on the 92+. Same location as yours, different color.

 

 

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(Borrowed image from cherokee forum!)

[HOrnbrod]

^^ Disregard all that - it's for a 92, not 91.
 

Yes sir. Drivers side near firewall. Its not in the coolant. Its got a dfferent tip. A black plastic cage that senses hot air passing through it. Am i chasing the wrong one? I know it is NOT THE ONE at the THERMOSTAT.

You must be looking at the IAT sensor on the intake manifold. Here's a pic of the 91 coolant sensor - one wire - NOT mine but like my 91:
 

[opie]

ok ok ok...first let me say thank you for all of the help.  Secondly I am an IDIOT. I was looking at the wrong sensor.  The one in the manifold is the one I looked at and changed and was chasing wires on.  So much for trusting YOU TUBE.  I saw the new picture above, it was tucked in there pretty well and hidden.  Actually my neighbor was giving me an extra set of eyes and said..."Look, there is an extra wire with a boot on it sitting there not connected".  Snapped it on, checked the gauge and VIOLA!!!

 

Thanks again.

[87MJTIM]

We've all done that.   :oops: