Hey guys,

I'm new to the forum and Jeeps but have extensive background with automobiles. I bought a 96 cherokee 4.0 4x4 a couple of months ago as a winter beater and recently I have been having some peculiar problems..

I first noticed something was odd when the cherokee began to backfire during deceleration. Soon after that, I noticed that the temperature gauge was not reaching 210 like it usually did. I assumed it was running rich because of not getting up to temperature so I changed the thermostat 3 times with the same result.

I have bled the cooling system properly with a coolant funnel, replaced the thermostat with a stant superstat and placed cardboard in front of the half of the radiator where the e-fan is...It still runs cold and backfires... If I come into town and drive around in stop and go traffic for ~20 minutes the temperature will begin to rise slowly but as soon as the radiator gets any airflow through it, it cools right back down.

I am beginning to think fan clutch, but I do not want to throw unnecessary guess and check money at a 700$ vehicle.

I know it is a longwinded explanation but I am at my wits end !

Please HELP!!! Thanks in advance.

 

Possible bad circulation from water pump?

 

Bump!
Come on guys, help me out..
i've searched and searched
i'm beginning to think the two are unrelated...
would a vacuum leak past the MAP sensor cause the backfires?

 

Vacuum leak generally causes a lean actually. Based on your description it definitely sounds like you are running way too rich - so much fuel will make it run cold as well as backfire. Running cold will not make the computer dump in enough fuel to cause backfiring.

Prime list of suspects:

1. Manifold Absolute Pressure sensor: Check for good vacuum, not sure if '96 is on the firewall with a little vacuum hose or if it's bolted to the TB like 97+. The MAP used to set fuel mix based on how much air is supposedly flowing through the system (doesn't work the same, but similar purpose to a MAF). Can cause the computer to dump max fuel if it thinks there's a lot of air going into the engine.

2. Throttle Position Sensor: A potentiometer like a volume ****, used to set fuel mix based on how much the throttle is opened (how far you've pushed the pedal). Can cause the computer to dump max fuel when you've only gotten the throttle open a small amount.

3. Upstream Oxygen Sensor: Used to set fuel mix to the optimum A/F ratio based on the composition of exhaust gasses. Can send false readings indicating that the engine is running too lean, triggering the computer to spray more fuel. Only comes into play after the computer enters closed loop mode - I've read somewhere this is triggered when the coolant temperature sensor reads 125 degrees Fahrenheit or higher, not sure if this is accurate though.

4. Coolant Temperature Sensor: See note above


There are diagnostic and repair/cleanup procedures for these things all over the forum, hopefully this gives you a starting point.

 

update....
I replaced the fan clutch, made no difference. When first started, the temp will initially spike to ~210 then when the thermostat opens it drops all the way down to the first tick mark and then settles halfway between 210 and the first tick.

I have a check engine light for a misfire in cylinder 1 and I am loosing a little bit of coolant. Possibly headgasket? Showing no other symptoms besides from misfire and loss of coolant.

 

Spike? What do you mean? It doesn't warm up?

As for coolant where is it going? If it's burning off in a significant quantity you should be able to smell it. Have you checked the entire cooling system for leaks?