The latest issue in the summer of problems...

Goodness what a year...

I bought my 98 Cherokee in January to replace a 2001 GC that blew an engine last year. It has almost 250k miles, but a previous owner had a new inline-6 motor put in around 225k.

February brought single-digit temps in the mountains, plenty of chances to test out my 4wd, an engine code and eventually a no-start condition that required replacing the NSS and a few new fuses to correct. Then I spent a week or so in March tracking down a short in the back hatch wiring harness that was burning through 10amp fuses and knocking out my tail lights. I also got a chance to take apart some of the front end to replace the sway bar links, mounts, and put in new performance brakes. Sidenote; when you forget to spray the discs down with cleaner, they smoke like a chimney. The jeep ran great for the rest of the spring, including several trips to the coast and lots of mountain driving.

Back in May a leaking fuel injector caused an engine fire that required replacing a bunch of my top end. New injectors, new fuel rail, new wiring harness, etc. I spent most of the summer on a construction project in Ohio, so I had the local shop do the work. After the heep came out of the shop last month I was driving down the highway and all of the electronics went out on me. No gauges, no lights, nothing. I made it to the side of the road and the engine idled for a few seconds before dying. Turns out an unused amp power line coming straight off the battery fell behind the PDC and grounded to the frame. Managed to get it jumped and it ran fine for the rest of the weekend.

The next week, I went to start the Jeep and I could tell the engine was running strangely. Excessive vibration, definitely misfiring. The misfire seemed to straighten out and the engine ran just fine after I accelerated through 2nd gear and hit around 2500rpm. The computer showed a p0303, misfire in cylinder #3 (same cylinder as the leaky injector). The misfire shows up pretty randomly, and consistently straightens out after the engine comes under load (merely revving the engine doesn't make it go away).

I've also gotten the following codes randomly over the last couple of weeks: p0700, p0705, p1694, p1698. These codes have shown up and disappeared with no action on my part. No transmission symptoms have been noted by me or by the mechanic. I have an OEM NSS, the Jeep only starts in P and N, I have reverse lights... basically no transmission issues that I can figure out.

Which brings us to this past weekend, and the problem I'm seeking help with. I was driving around on Saturday and started smelling burning plastic. I popped the hood and there were flames coming from the back of the electric cooling fan. I put the fire out and removed the fan assembly. Turns out the fan supports snapped, which I assume caused the blades to jam and the motor to burn up. The Jeep ran fine without the fan, so I drove it back to the house. No overheating, no codes, no problem.

I picked up a stock replacement fan from Advance yesterday and got it all hooked up, but when I cranked the engine the fan would not turn on. I let the engine run until it was up to temp, no action from the fan. I pulled the fan relay from the PDC and tried replacing it with the starter relay which is definitely good. The fan cut on for a second then stopped. After a bit of tinkering, I figured out that the fan would run if I just barely pressed the relay prongs into the slots. In that position, I could hear the relay clicking and the fan would run. If I seated the relay or moved it out of that exact position, no fan running. Then, once I went back over to the driver's side, I noticed the CEL was lit. Code p1491, which from my brief searching online seems to be some sort of cooling fan trouble code.

I'm not really sure where to go from here. Do I need to figure out how to replace my PDC? Is this some leftover issue from the fire and associated repairs? Could it be related to my intermittent misfire?

I am looking for help with the fan issue now, but I'd welcome any and all thoughts you all have about the misfire, the trans codes, or the general state of affairs.

I have a FSM for a 99 sitting right here. According to this, straight from the manual, "the P1491 is for an open or shorted condition detected in the radiator fan control relay control circuit. This includes PWM solid state relays."

Did you check wires from the computer to the PDC? Temp sender wires?

Can you get a pick down to the pins for the fan relay and bend them a little bit to see if the better contact with the relay will fix the issue?

I can scan the FSM and put them on here as photos for the diagnostic procedure if you'd like..

From the description you give, you simply have a contact problem in the PDC. Clean up the corrosion and use some dielectric grease there and that should fix it.

I would also check the condition of the connector for the electric fan. If it got hot enough for the fan to catch fire, it could have melted the insulation or even the connector. Although if I recall correctly the connector was on a relatively long lead. But the wiring going into the fan could have been compromised. Personally, if it was me I would just replace the fan.

Just to be sure since some don't know. The fan is only suppose to come on once the engine hits 220*~ or the air compressor is on (a/c or defrost).

Just making sure. Didn't want you to have to go through a bunch of work in case you didn't know.

Sent via messenger pigeon - i talk, he types.