I've talked to several mechanics and they say the coil pack is ALWAYS suspect when multiple misfires happen randomly. IDK myself, but I'd start with the TPS.

 

I also had a multiple misfire before I replaced the cam position sensor, now no problems.

 

I replaced the coolant temp sensor. Still acts up. Could it be a bad signal wire to computer. It starts fine when cold. it runs fine and temp rises normally until themostat opens. Then temp gauge drops way down, and it starts running rough, will stall at low rpm's, and hard to start, Needs to be floored to start.

 

Have you checked the fuel pressure?

 

fuel pressure holds steady at 55psi. I did check feed voltage to the ects and it was a little over 5volts. When cold, with connector unhooked, I jumpered off the feed to one side of sensor and the other side read slightly less than the feed, which I would expect. When the connector was hooked back up, and I backpinned and measured the voltage going back to the pcm, it was 12 milliVolts. Shouldn't it be higher than that?

 

I also checked my tps. It shows a voltage variation thru the travel range. In the middle, there seems to be one spot that's dead, but a very small spot. Also checked mas, and that seemed ok. Definitely temp related, and I don't see why the gauge would change so quickly especially with a new sensor. I'm going to look at the pcm, and jumper right from there back to the temp sensor and see if I get the same low voltage readings.

 

Just for giggles, change the thermostat. It sounds to me like it's not functioning properly. I sounds like it's opening all the way and not holding a normal operating temperature. This would cause the PCM to stay in open loop mode thinking the engine is still cold. 'Cause it is.

 

Yes, I thought that too, so I just changed the thermostat. What puzzles me is that the temp gauge changes from 100 up to 200 or the other way in a second. I was testing more last night, and I found the pcm pin for the coolant temp sensor. I put a back pin on that, and ran the jeep till it got hot. I also pinned the same wire right where it feeds the sensor. I'm not sure how the pcm tells what the resistance is, maybe current flow. I was thinking the other side of the sensor goes to a common sensor ground. Anyway while testing, I had 5.14v at the pcm, but only 2.45v at the sensor on the same wire. At that time, the temp gauge was reading 100. Sometimes the voltage right at the sensor was 5.14, and those times the temp gauge showed a seemingly accurate reading of 210 or so.

 

More testing. Feed voltage does fluctuate, but is consistent along the wire. When feed voltage is 5.14, temp gauge shows 100, and engine speed picks up. When engine speed drops, feed voltage drops to 1.9 or so and gauge shows 200. It goes back and forth like that every minute or so. Other side of sensor shows 13.4mVolts cold and 17.3mVolts hot. That stays fairly constant even though feed voltage changes. Could it be a bad pcm or bad ground somewhere. It doesn't make sense.

 

Here is what happened. Hope it helps someone in the future. Both pins on the connector of the engine coolant temp sensor weren't makng good contact. As things heated up, I saw voltage variations. I finally got the pins out, munched them down a little, and after a little time and persuasion, got the connector connected again. No more temp fluctuations, and hopefully no more stalling. I went for a 20 mile ride no problem. After the fix, the voltage on the ground side of the sensor was reading about 3.4 volts cold and would drop to .93 or so when hot when the gauge showed 210. Voltage trended smoothly down as it heated, and up a smidgeon briefly when the tstat opened and cooled slightly, but no big swing in voltage.
Here's what else I learned. I bought a new cam position sensor and crank position sensor and a new temp sensor. Probably $130 of parts I didn't really need. I saw the big temp swing, should have put that together with the poor run/stall at idle as the computer reacted to the seemingly low temp. Anyway I'm a happy man now, and hope someone may benefit from my experience.

 

Cool! (pun intended) The temp sensor is just a variable resistor so poor connections are a no-no. The IAT, trans fluid thermistor, and outside temp sensors are also just variable resistors. This stuff works on 5 volts, so good clean connections are vital. I'm glad you found it!

 

Buy a scan tool and throw a new set of plugs in it, make sure the right ones exactly per the sticker under the hood. Cam position sensor from a JY, not from parts store. (weak magnets) Replace distributor and cam sensor, replace crank sensor with OEM. Some ideas.