Nothing Special

Hi. I'm new here, with what seems to be a semi-common problem. But as I've searched other threads I haven't found the solution for my vehicle.

I have a 2001 Cherokee Sport. Last spring it developed a horrible lower end knock, resulting in it getting a new engine (at only 81K miles). Immediately after getting the new engine it had a check engine light, the engine started running rough, lost power, and then died. Key off, restart and it ran fine. Turned out to be a crank position sensor code. I had the CPS replaced, but about a month later the same thing happened. I brought it to a different shop who replaced the CPS with a genuine Mopar part. Problem solved... for a while.

Now about 4 months later I'm getting the same symptoms, almost always under hard acceleration, and sometimes when slowing down for a stop. But now I'm getting a variety of codes rather than just one. P0351 was the first (coil #1 not reaching peak current in time). So I replaced the coil. Still the same symptoms, but now I'm getting P0351, P0352, P0353 (coils 1, 2, 3) and P1391 (cam position sensor?). I'm not getting all of them every time, it varies between those. Some searching indicated that getting this particular potpourri of codes was likely due to a bad ECM, or at least bad connections in the ECM. So I got a new ECM, but still the same thing.

I've thrown too much money at this already to just throw more. Can anyone help me get a better idea what this might be?

CCKen

I would suspect the Camshaft Position Sensor. Everything seems to point at it.

You don't want to shotgun a PCM at this time.

Edit: Went back and looked...I see you already changed the PCM...tsk tsk

CCKen

Here's the list of possible causes for 1391:

CMP SENSOR OUT OF SYNC
DAMAGED TONE WHEEL/FLEX PLATE (CRANKSHAFT)
DAMAGED TONE WHEEL/PULSE RING (CAMSHAFT)
IRREGULAR LAB SCOPE PATTERN OF CMP SIGNAL
INTERMITTENT CKP SIGNAL LOSS WHEN WIRING IS WIGGLED
IRREGULAR LAB SCOPE PATTERN OF CKP SIGNAL
WIRING HARNESS INTERMITTENT
INTERMITTENT CMP SIGNAL LOSS WHEN WIRING IS WIGGLED
SENSOR CONNECTOR/WIRING
SENSOR CONNECTOR/WIRING
CAMSHAFT POSITION SENSOR
CKP SENSOR CONNECTOR/WIRING
CRANKSHAFT POSITION SENSOR

TEST ACTION

Nothing Special

How do I get to that? Even ignoring the crank position sensor issues from a few months ago (since I'm not sure they are related), I've had codes for all three coils. Do those point to a cam sensor?

Turbo X_J

Hope that wasn't just a couple of loose bolts.

Nothing Special

Nope. There were pieces of piston in the oil pan.

Back to the question at hand. What's likely to cause all of those codes? The best suggestion I've found so far (at least that had any experience behind it) was bad connections between the header pins and the PCM board. I found numerous posts saying the pins for the coil, crank sensor and cam sensor all came in around the same place and that place was troublesome (for some reason) on the board, so replacing the PCM was likely needed with that particular mix of codes. But a new PCM later it's doing exactly the same thing.

I suppose the next thing down the line is the connector where the wiring harness connects to those header pins. I've unplugged and replugged all three PCM connectors, and none of them seem to be making a poor connection from what I can see or feel. One of the retainer clips is broken on the white connector, but it still seems to attach solidly with the other clip working.

Does anyone know which pins on which connector are for the coil, crank and cam sensor? And is there a better way to check or improve the connection that unplugging it and plugging it back in?

CCKen

Again, I would suspect the Cam Sensor. And since this problem started immediately after installing the replacement engine, I would further suspect the cam sensor is out of sync (see list) due to not being properly installed.

I'll dig up the CMP sensor installation instructions and post them so you can see what "sync" is about.

Nothing Special

Maybe I'm just missing something, but I'm seeing very little point to the cam sensor. Help me understand please. Would an out of sync cam sensor give the P0351, P0352 and P0353 codes as well? And does it make sense that the P1391 code wouldn't show up until 5 months after the engine was installed if the cam sensor wasn't installed correctly at that time?

sv41878

I know it's not the same as a Ford but we just had a Ford ranger throw cam codes a year after the sensor was changed. Same symptoms, only on hard acceleration or hard braking. Turned out the cam sensor had moved ever so slightly and when we got on it hard it was enough to their a code. I would start there since that tells the PCM when to fire the coils and the three coil codes may just be following the cam sensor (the PCM sees the coils not working correctly cuz the cam sensor isn't giving the correct position)

CCKen

^ Spot on.

Here's the FSM procedures. Note that if the CMP was installed correctly you will still need to go to the dealer and have them hook up their DRB III tool for final adjustment.

At least you could do is check the installation.....

Nothing Special

I'll take a look at the cam sensor when I get a chance (no time this weekend). But I'm still not sure how that affects the coils. The instructions CCKen posted specifically say that the cam sensor is not used to set ignition timing, so it doesn't seem like it can be what sv41878 said.

CCKen

It sounds like you just don't think the CMP can cause your problem, even though it popped a CMP code.

The CMP does detemine location of a cylinder, in terms of TDC compression, and its need for fuel injection and ignition. It informs the PCM of this info and the PCM will trigger the proper ignition coil, as well as the fuel injector. On your engne, the ignition coil fires two cylinder spark plugs together, one on a cylinder's compression stroke and the other on a cylinder's exhaust stroke. It's called a Waste Spark system.

The CMP's signal is used in conjunction with the crankshaft position sensor to differentiate between fuel injection and spark events. It is also used to synchronize the fuel injectors with their respective cylinders.

So, the CMP must be synchronized with the Crankshaft Position Sensor.

sv41878

To break it down in its simplest terms your crank sensor tells the PCM where the crank is (ie #1 tdc) your cam sensor tells the PCM when to fire the injector and then fire the the coil based on cam position (and where the crank should be in correlation to cam position), if they don't match you will have misfire codes. Since you have a cam code, your cam sensor isn't reading correctly causing your misfire. Before chasing misfire codes fix the cam code and see what happens. You could have a bad coil pack bad connection at one of the connectors but it could also just be a bad cam sensor. BTW alldata and Mitchell online (shop tech databases) say fix the cam code before diagnosing the misfire so I'm not alone

Nothing Special

I'm not saying that I think the CMP can't cause my problems. I'm saying that if the PCM doesn't use the CMP for setting timing (the instructions you posted on adjusting the CMP said that, I'm not making it up), it doesn't seem likely that a CMP would cause all of my problems. And since they all showed up at once it seems likely that they are all caused by the same thing.

That said, I don't think I'm infallible, I certainly don't understand this all completely, and as I said in my last post, I am going to look into the CMP, even though it doesn't seem like the most likely culprit to me.


That is not necessarily true. What it means is that the PCM isn't getting the signal it expect from the cam sensor. That could be because the cam sensor isn't reading correctly, but it could also be because of a bad connection in any of the wiring, or any of the other things in the list CCKen posted in one of the first posts above. But that said...


it is sounding more reasonable that the cam sensor could be causing this, and as I said, I will be looking into it when I have a chance to work on the Cherokee again.

By the way, I'm afraid I've sounded ungrateful in some of my replies. I do appreciate all of the input. I'm questioning it because I'm trying to understand it better. So thank you all who are helping me here.

Nothing Special

Found the problem. It was the crank sensor... again.

Based on CCKen's instructions and comment that I'd need a diagnostic tool I don't have to sync the cam sensor (and since my wife was getting annoyed with me) I decided to bail and take it in (to the same garage that replaced the crank sensor in April, not the garage that replaced the engine in March, for what that's worth). Cam sensor was their first guess too, but that didn't prove to be it. They checked all of the wiring as best they could, checking voltage readings at the pins and wiggling and jiggling the harness. Eventually they decided to throw a new crank sensor at it, even though it wasn't throwing the crank sensor code this time. And voila! It's fixed!

Which of course begs the next question: Why have we needed to replace the crank sensor three times since the engine was replaced in March? The garage said there was no indication that the crank sensor was getting hit by anything. Is there anything else that could be done wrong in an engine installation that would wipe out crank sensors this fast?