How do you test for a PCM going bad?

tomtaylz

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So this morning, after having some issues to/from Utah some of my issues are back. I was getting a sort of bucking when accelerating up a hill and CEL pointing to cam sensor which has been replaced 2x. Previously I’ve had the speedo jumping all over the place e too.

How do I know if the pcm needs repair?


Edit: I replaced the OPDA with a new crown and did not see issues come back. I also about a month later had my battery tested as bad - something I think might have been contributing.
 
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I believe there are procedures outlined in the FSM. Have you looked out of curiosity? I genuinely don't know, that's why I brought it up.
 
An erratic speedo is either a bad sensor, or the output shaft is not torqued to spec.

FWIW--I had an issue where my speedo was disconnected completely, it threw a CEL and it would stall whenever I came to a stop.
 
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Is it still P0344 (Camshaft Position Sensor Circuit Intermittent) only, or are you popping other codes? I realize your issue seems to be load/heat related, but hear me out.

If your OPDA shaft wobbles (even if only under certain conditions and only for an instant or two), this will cause this code to pop since the camshaft sensor and OPDA shaft tone wheel air gap is not consistent during the wobble. It goes out of spec and the signal is lost as seen from the PCM. I've heard of folks having to replace their new Crown unit just after installing with another new Crown unit after experiencing the wobble. Crown isn't perfect either...

You can pull the OPDA cap (2 screws) and watch it spin with the engine running. See if you can detect any wobble at idle as the tone wheel spins.

Here is my story that is somewhat related, same code, different conditions:
  • About 6 months after the Crown OPDA replacement, I added a thin shim (foil washer I made) to pull the camshaft sensor back away from the OPDA tone wheel a tad bit (~0.001-.003").
  • In very cold weather (~0 degrees F), I was getting a P0344 (Camshaft Position Sensor Circuit Intermittent) on start. I could dupe every time on a 0 degree day. After warm, no issues. This is because the tolerances are so tight and the OPDA shaft (with tone wheel) likely wobbles ever so slightly on startup in this drastic condition.
  • No issues or codes since, but still keeping an eye on it.
Next, even if the OPDA is in good order (no shaft play), on higher mileage engines and sometimes without higher mileage, tolerances are off just a bit on a spinning camshaft and tiny adjustments like this become required (unless you want to rebuild the engine). I've seen a few manufacturers selling these shims for similar camshaft and/or crankshaft sensors due to the "old age" out of tolerance conditions. This is our only option since we can't adjust the cam sensor "air gap" on the 4.0L.

Here is an example of a crank sensor shim for a Chevy Vortec. Check out info about why they are prescribed:
https://www.eficonnection.com/home/product/sensor-shim-kit
Finally, the aftermarket camshaft sensors and even the newer Mopar sensors, have been reported to have problems operating in the cold without throwing a code. Not sure if they wold have the same issues under high heat conditions or not, but thought I would also throw that out there.
 
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@tomtaylz do you have a warranty on the OPDA? I think @mots is on to something considering the jeep wasn't having issues before the new OPDA. No harm in 1. installing the OEM back in or 2. Getting Crown to replace the current one.

Worst case we burn some time installing the sensor. Best case no 1k+ pcm rebuild, and all the hassle that seems to follow.
 
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@tomtaylz do you have a warranty on the OPDA? I think @mots is on to something considering the jeep wasn't having issues before the new OPDA. No harm in 1. installing the OEM back in or 2. Getting Crown to replace the current one.

Worst case we burn some time installing the sensor. Best case no 1k+ pcm rebuild, and all the hassle that seems to follow.

Not sure I’ll have to look. Maybe we put the mopar back in and see, just wish there was a way to test
 
An erratic speedo sensor is either a bad sensor, or the output shaft is not torqued to spec.

FWIW--I had an issue where my speedo was disconnected completely, it threw a CEL and it would stall whenever I came to a stop.
Could the Speedo Healer have any impact on this issue?
Not sure I’ll have to look. Maybe we put the mopar back in and see, just wish there was a way to test
I honestly think Mots theory of OPDA makes the most sense since it was running fine prior to the installation of the new part.

How long were you driving it this morning prior to the CEL?
 
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Could the Speedo Healer have any impact on this issue?

Unless he is using the hall sensor that came with the speedo healer. @Igoo65 had a bad sensor from Blue Monkey right out of the box. It should just be a regular hall sensor, its the same one the rubi comes stock with.

I cant comment to much on the OPDA as I dont have the experience with it as others do.

I think actual PCM failures are incredibly rare, people tend to replace them because their mechanic says so (though that is obviously not the case with you).
 
Could the Speedo Healer have any impact on this issue?

I honestly think Mots theory of OPDA makes the most sense since it was running fine prior to the installation of the new part.

How long were you driving it this morning prior to the CEL?

Not long it was at slow speed, maybe 5 mins which is a first.

Wondering if the speedo healer got overheated when things got hot, then maybe the bucking is the ODPA?
 
If you're around Monday we can take a look at it in the morning. Charlie will be at daycare so I'm free from around 8am-12:30pm
 
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Cool, keep us posted on what you find out. Us 2005-06 guys gotta stick together on figuring out all this damn OPDA stuff!
 
Plot twist, the CEL put itself out and was fine for the remainder of the day 50-75 miles

Only reason I’m not sure if the speedo jumping is the blue monkey related is the speedo does that only after the CEL for the cam sensor comes on. I’m not sure if those are related in some way?

P0344 is the only code I’ve seen so far, I’ll scan for more tonight see if I can see the one that dismissed itself today.
 
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The speedohealer, hall sender at the transfer case and opda all use the same 5V regulated power supply from the computer. If you suspect the speedohealer just disconnect it. Your problem still seems like it could be wiring related, I'd go over all those wires again and pay close attention to grounds.
 
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The speedohealer, hall sender at the transfer case and opda all use the same 5V regulated power supply from the computer. If you suspect the speedohealer just disconnect it. Your problem still seems like it could be wiring related, I'd go over all those wires again and pay close attention to grounds.
Any particular ground?
 
Another day another CEL. Bucking and speedo jumping. Was going about 65 when it happened.

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