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Stalling - ECM or CPS?


NAXJA Forum User
I've read I don't know how many threads on the CPS and it being a possible culprit for no start/stalling issues. I spent about an hour today trying to get the damn thing off today, no luck. I can't get a ratchet on it.

Anyway, my Jeep was recently submerged in quite a bit of water and stalled when it hit the deep water. I've been tinkering with it today as it wouldn't start, just cranked. I took out the computer and water dripped out of it when I tipped it upside down. I've tried drying it out as best I could. When I plugged it back in, the Jeep will start up, but will only run for about 1-2 min. and then shut down and won't start back up for awhile. Also, a few minutes after it shuts down, the relays in the fuse block under the engine start clicking on/off very rapidly for a few minutes. If I unplug the ECM, it stops.

So, the question is: Is it a bad ECM or is this be the CPS??? I really don't want to spend another hour getting frustrated trying to take the CPS out only to find out it's not the problem.
It's really hard to say. Could be the CPS, or the ECM or something else. Water and electronics obviously don't mix. You can test the CPS (use the SEARCH function) so I'd do that first. Throwing parts at it is an expensive and not always successful strategy.
yeah, I'm going to test the CPS today.

Other info. that leads me to believe it's the ECM. When I turn the ignition to on, the fuel pump doesn't kick in until a few seconds later. While running, the Jeep is misfiring alot! After it stalls, the vacuum servo (I think that's what it is - the canister type thing on the passenger side engine bay with vacuum hoses connected) starts cycling on/off and you can hear it discharge air. The the fuel pump starts cycling on/off randomly. The electric fan starts turning on/off. It's obviously some electrical malfunction.

Why would Jeep put a ECM under the hood that has a hole in the top of it, just asking for water to get in!? The next one's going to be waterproofed for sure.
ttt...I just ordered a used ECM from a 2000 XJ from Ebay. Should be here by the end of the week. I'll know if that's it or not then, I guess. Any other ideas would be great, though!!!
If the Power Distribution Module (the black box with all the fuses and relays in it) gets flooded with water, it can cause all sorts of problems with relays and circuits.

My PDM on my mini-van was full of dirt, I foolishly washed it out with simple green and the hose. Sure enough, I had all sorts of electric trouble, although the motor ran fine. I used a compressed air and blew it all out and then removed each fuse and relay and blew them out, and their socket, with compressed air. All the problems went away.

The PCM (a.k.a. ECU) internal electronics are sealed in silicone. Most Chrysler Passenger Vehicles, the PCM is in a metal box totally filled with silicone, no voids to fill with water. Most of the Chrysler Truck PCM, have a plastic case with voids in it that could hold some water, but the circuitry is still encased in silicone. So water dripping out of the PCM shouldn't have fried it.

You bought a used PCM off eBay. We are assuming you've checked by Part Number and it is the proper one for your XJ, there are different PCM's for years/options within years for your XJ and that PCM may NOT be right.

What reader are you using? There is OBDI, OBDII, CAN, and many other protocols that other manufacturers use, if the reader can't read the protocol your XJ is using, it would probably show NO Link. Even if it is the right reader, it does NOT confirm the PCM is bad, it could be moisture in the circuit that is shorting something between the link, thus NO link.

I also could NOT fit a socket between the CPS and the Firewall either, that is why I used an old fashioned open/box end wrench to pull the bolts, its much smaller and flatter than a socket wrench.

Have you pulled the distributor cap and dried out the distributor? Have you left the hood open all day to let the engine compartment dry out?

Did you ingest water into the engine? The PCM is mounted up by the air box, if you submerged the PCM, you could have submerged the air box, and ingested enough water to cause hydro-lock in the motor and damage it. BUT, hydro-lock would NOT be a stall out of the motor, the motor would seize/stop instantly and would have been far more violent than just stalling out. Hydro-locked motor can bend connecting rods and mess up the valve train, if you have that damage, if the motor ran at all, it would run very poorly. Don't freak out, if the motor just stalled, then its very likely something just fried or is still shorted out with water still in it.
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Well, the Jeep's been sitting for over a week since it was submerged. I've sprayed all electrical connections/fuse boxes with brake cleaner and left unplugged for a week to dry out. The ECM has a 1/4" - 1/2" hole in the top of it and that's where it took on water and sat with that water in it for about a week before I was able to get it towed to my house. I've swapped all of the relays in the black fuse block under the hood and all the fuses are good and that's had plenty of time to dry out, so I don't think that's the issue.

I have a cowl snorkel, so water intake into the engine was minimal, mainly from just having the engine sit completely submerged for 15 min. waiting to be towed. I pulled the plugs and pumped water out of cylinder 1 at the trail. So, it wasn't hydrolocked.

The reader I'm using is an OBDII scanner. I've read the codes on the Jeep before fine, now it just says No Link. And yes I made sure the computer I bought was from the same engine, AT, OBDII, etc.

Thanks for the suggestions!
If I were a betting man I would say the ECU/Computer. Can you have someone crank the motor for you and then grab ahold of the wires that go into the ecu and move them up and down, see if that has any bearing on the way it runs, or if it starts for you. Be gentle with the wires.
If the ECU/PCM was burned out, it would stay burned out. So you would NOT have been able to get it started and run 2-4 minutes.

I have had "Drivers" in the PCM burn out from shorts, that would let the motor run, but it would very poorly. "Drivers" are the additional circuitry added to the PCM, that is NOT part of the computer. They are the high power circuits that drive the fuel injectors and coil/coils. So, in my case, I burned out one of the fuel injector drivers, the computer portion of the PCM was just fine, but the motor ran like crap because one fuel injector was non-functioning. It did set a code for a bad "fuel injector driver circuit".

Since you've gotten the motor running once, but only a few minutes, and you can't get the PCM to talk to the Reader, I suspect the PCM may be fine, you still have wiring or fuses that are still shorted, probably from water that still hasn't dried out.

If you already have a new PCM, it can't hurt to swap to confirm. BUT, I'm guessing your going to have to start unwrapping wire harness's looking for shorts/moisture/dirt and clean that all out and repair what you can find.

Since the PCM is Chrysler, it should give you the codes through the CEL or Odometer, by turning the ignition key on-off-on-off-on and counting the blinks or reading the odometer. The blinks give off a 2 digit code that you have to look up. Not all Chrysler equipped vehicles have this feature, but almost all do.
mines OBDII, so I can't do the turn the key to get the code trick. I have to use the scanner which isn't linking. I'm going to pull all of my fuses and relays again tonight, spray them out with WD-40 and see what happens.

Here's why I keep thinking it's the computer:
1. fuel pump, electrical fan, and vacuum servo cycle on/off randomly after the Jeep shuts itself down.
2. Fuel pump will not prime with the key in the on position until a few seconds later, if at all (usually primes right away for 2-4 sec.)
3. Jeep will only run for 1-2 min. then shut down, regardless of idling or revving.
4. Jeep will usually run normal, but sometimes will sputter and almost stall, then get back to idle, repeat, etc., still shutting down in 1-2 min.
5. Jeep will run slightly differently depending on the position of the computer (horizontal v. vertical, etc.)
6. Computer is not linking with the scanner.
7. Computer was sitting for a week with water in it.

This is what I'm basing my diagnosis on. Hopefully the computer I ordered will be here soon so I can finally either fix it or lay this to rest and start troubleshooting from square one again!