do_ob

Hey all. I just bought a 2000 XJ which ran fine when I went to pick it up, but now is not getting fire to the coil (I think).

Long story, but here goes.

I went to look at this thing after a guy posted it for sale online - said he couldn’t get a good brake pedal. So I go check it out, and it starts and runs good. He has hard wired the starter to the battery with a switch inside because he couldn’t turn the ignition cylinder all the way over. It also has dual electric fans, one of which is broke and the other is also hardwired to the battery with a switch inside. And, like he said, the brake pedal was going all the way down to the floor.
He said when he bought this thing, he had driven it back to his house from where he bought it (about a 45 minute drive) and the brakes were pulling hard to the right. When he got home, he put new calipers and pads on the front but couldn’t get a pedal after bleeding them. He gave up and put it up for sale.
So I buy this thing and bring it home on a trailer after looking it over. There was a busted brake line on the rear end and he had put the calipers on the wrong sides. During the course of bleeding the brakes, I had this Jeep running several times throughout the afternoon (I always like to have a vehicle running when bleeding the brakes...don’t know if it’s necessary but yeah). My point is, it started up and ran decent. There were some vacuum lines unhooked. Someone in the past has also replaced the exhaust from the manifold back and did not install any 02 sensors or a catalytic converter (rednexxx). But it started and ran. Surprisingly well, considering.
After getting done with the brakes, I put the tires back on and dropper her back down on the ground. Now she won’t start. It cranks over fine, and I am getting fuel to the fuel rail. I dont have a gauge to check the pressure, but it squirts out when the needle is pressed so I assume it’s not a fuel issue.
Next I went through and checked all the fuses. Every one in the junction block (inside the passenger floor area) was good EXCEPT the 20 A fuse that’s connected to those 2 red wires. I’m not sure what this one is for (couldn’t find it on any diagram) but I went ahead and replaced it. Under the hood, fuse 10 (starter relay) was blown so I replaced it. All the other fuses were good. The relays are all clicking when the ignition is turned on, so I think they are good.
Note: when I replaced fuse 10, the ignition cylinder started working normally and will crank the engine over now. So now I can engage the starter with the regular ignition OR with the switch mentioned before.
My next thought was the crank position sensor. I went ahead and bought a new one and put it on, thinking surely that was the problem. Nope. No change at all. I watched BleepinJeep’s video on testing the CPS’s ohms/resistance and did so. My ohmmeter/voltmeter did not go to zero so that told me the new CPS wasn’t bad if I understood correctly.
Next, I attempted to check the spark to the coil using the old screwdriver-in-the-plug-boot method and got no spark when someone cranked it over. So ****, no spark, maybe the coil’s bad? Before spending more money, I tried to read some tutorials and threads on how to check the coil on these for resistance (this Jeep has the coil rail, no distributor/plug wires). I found a couple informative posts here and there, but my multimeter is a cheapie and I’m not an electrician. I also read one post where someone said you can’t check this type of coil one-boot-at-a-time...something about wiring different plugs together that fire from the same coil pack... I ended up just buying a new coil rail to see what happens, which I was told I could return if it didn’t help my problem. Put it on, and still nothing. It’s still on there.
Next I’m thinking maybe the pigtail to the coil isn’t supplying any juice. Again, I’m not an electrician. I pulled the pigtail off the new coil and checked the voltage (multimeter set on 20V) and got ~0.6V on each of the 4 female terminals when someone was cranking the engine. Someone later told me that that number should have been damn near 12, but I’m not sure.
After this, I figured I could check the resistance of the new coil and compare those numbers to the old one. They were different (old was ~6 and new was ~18 IIRC). I don’t know if that’s good or bad, or if those numbers matter in terms of the coil providing fire to the plugs..

• So at this point, I’ve changed and checked the crank position sensor, fuses (inside and outside), and changed the coil rail.

My other Jeep is a 98, so next I pulled the PCM/ICM/computer out of it and put in the ‘00. Took 2 minutes, so why not try it. This didn’t help anything either. After reinstalling the original computer, I did that test where you hold the odometer pin in and let the gauges cycle...all the gauges and lights did their thing like they should.
At this point, I’m starting to grasp at strings. I bought a new camshaft position sensor and ignition switch and installed both of those - old cam sensor’s internals were very dirty, so I cleaned it and reinstalled to no avail...and the key was hard to get out of the ignition cylinder so... - no change at all in the cranking. I ended up returning the new cam sensor and reinstalling the old one. Kept the ignition switch.

So now I’ve done this:

• checked and replaced fuses
• eyeballed over wiring
• replaced and tested new crank position sensor
• replaced coil...attempted to check, not sure what I’m doing
• checked voltage of coil pigtail...got numbers but not sure if they’re good or bad
• swapped ECM with good one, swapped back
• Replaced ignition switch
• Replaced camshaft position sensor, then put old one back on

At this point, I’m at a loss. I know my 02 sensors are gone, but this thing went from starting and running fine to not starting at all in a matter of an hour. I haven’t found any broken/burn wires, loose connections/grounds anywhere. I have a buddy who is supposed to bring his OBDII over Saturday, but I’d really like to get this thing drivable before the weekend. If anybody has any ideas, please let me know.

—————
TLDR: changed brakes now won’t start. Got fuel, no spark. Changed crank sensor, cam sensor, coil rail, computer, ignition switch, fuses...not in that order.

PatHenry

Have you checked your Auto-Shutdown Relay? That's what I'd do next.

Go to cruiser54.com -> technical manuals and grab the 2000 XJ FSM - there should be specifics regarding testing the relay there, or you can do a search and find the steps listed numerous times in previous forum threads.

jordan96xj

do_ob,

In your long story you said back-to-back that it was cranking over fine, but that the starter relay fuse was blown. Those two facts are mutually exclusive. They can't both be true. Check that fuse again, and see if it is blown again.

do_ob

i got it running. Turns out my ASD fuse under the hood was testing good but was actually bad...not sure how that happens, but I replaced the 30A fuse with a new one and it started.

For some reason, though, most of my fuses in the interior junction block are not lighting up my test light, although everything seems to be working...only fuses 1,2,13,15,20, and 21 test good...

I’m happy it’s running again, just a little confused.

dave1123

Just a little tutorial on that coil pack ignition system you may find interesting. The coil pack contains 3 coils that fire 2 plugs at the same time every revolution. One on compression and one on exhaust. They are constantly supplied with 12 volts when running and are grounded thru drivers in the PCM (ECU). When a coil is commanded to fire, the PCM ungrounds it allowing the magnetic field to collapse creating the spark. Firing order, 153624 so 1&6 fire together as do 5&2, 3&4. This was done to reduce the complexity of the electronics and reduce emissions. The injectors are likewise hot all the time and the PCM grounds them when commanded to inject fuel. Both systems are controlled thru the ASD relay. The PCM turns on the ASD relay and fuel pump relay when it gets a signal from the CPS. BTW, Mopar recommends NGK ZFR5N (3459) plugs with the coil pack ignition for some reason. I've been living with this system for 7 years on my 2000 WJ and know it well.

The contacts on that 30A fuse in the Power box must have been corroded and allowing voltage to leak thru for a while. I've found just removing and reinstalling fuses and relays (cleaning the contacts) can sometimes get it to run.

do_ob

thanks very much for the explanation. This is the first XJ I’ve owned that didn’t have a distributor so that aspect is a little foreign to me, and it’s nice to have some understanding of what’s going on. I took a screenshot of your post and saved it on my phone. Thanks again.

dave1123

If you begin to get random cylinder misfires, you might want to replace the coil pack. They tend to short internally, usually between #1 and #6 because of the long connector between those plugs.

I recently bought a 2000 XJ and actually enjoy driving it more than the WJ. I hope she doesn't hear that, LOL!