Occasional misfire cause by PCM?
I have been dealing with an intermittent misfire over the past month or so. It only happens on hot days in Vegas (so over 100 degrees F) and after driving for a bit either in stop and go traffic going up a long hill.
Before the misfire started I had the following done at the dealer:
PS flush, Trans fluid and filter replacement (no flush), transfer case fluid replaced.
I noticed a slight misfire within a week of that service. It took a week and lots of driving before it finally threw a CEL. Went to autozone and the following codes were active:
P0202, P0203, P0206, P0207, P0208 which are the codes for the fuel injector circuits, stating the was a short or disconnected plug.
I had them clear the codes and continued to drive it around. It started getting worse and worse over the course of another week and I brought it to my mechanic who found a vacuum leak. Fixed the vacuum leak but still had an intermittent misfire. (obviously less frequently)
A week later it through P0300 (random misfire) so I brought it back to the mechanic. He ran through a bunch of testing and didn't find anything and couldn't reproduce the misfire. So he cleared the codes, and I went on my way. I also replaced the TPS since it was easy and could have been the issue.
It threw P0300 again a few days later and I brought it to the dealer. The dealer hooked up the scan tool and I remember seeing stored codes for the ICM and FCM but didn't get a printout of the codes. The dealer looked only into the P0300 code and said they couldn't find anything wrong and told me the spark plugs are a little worn. So I changed the spark plugs and replaced all the ignition coils with champion plugs and mopar coils. That didn't make a difference.
Drove it around for a few more days and brought it back to the dealer after the CEL went on and back off on its own. The stored codes were:
From PCM: P0206, From WCM: B1A25, From FDCM: U0431, U0141
I had the dealer look into the problem again and again they didn't find anything. They said they specifically checked the fuel injector circuits and O2 sensor circuits (after I specifically told them too) Still didn't find anything wrong. Had them clear all the codes and went home. This was yesterday. Of course CEL comes back on on way home, its missing constantly. Went to autozone and got the active codes:
P0300, P0202, P0206, P0205
After autozone i started heading home. missing got really bad and suddenly the missing stopped. CEL on the entire time. I assume it must have went into a "limp" mode.
This morning I brought it to the dealer near my house to get all the stored codes from last night:
From PCM: P0300, P0202, P0205, P0206, Frm WCM: B1A25, From FDCM: U0431, U0141
I also stopped by the private mechanic I know this morning and he said it sounds like the PCM is going bad.
While driving it around the misfire seems to only be related to the outside temp and the engine temp. I have tried driving in different gears when the misfire starts, tried it in reverse, park, tried different rpm ranges. I tried jiggling the harnesses at the PCM and the fuel injectors when it wasn't missing. From what I can tell the only causing factors are engine temp a tick mark on the gauge above where it used to be at normal operating temp when it was in the 80's outside, and it being over 100 degrees F outside. Doesn't do it when its under 100 or when the engine temp is under a certain temperature. It has never stalled.
Its a 2007 Commander 4.7 4x4.
Descriptions of the DTCs:
P0300: Random misfire
P020X: Injector circuit has detected a short circuit, open circuit, or overload. for injector on cylinder X
U0431: From FDCM: The FDCM is receiving no message or implausible data for Ambient Temperature from the FCM
U0141: From FDCM: Buss messages not received for 2-5 seconds
B1A25: The SKREEM does not receive a transponder response after 8 consecutive transponder read attempts
Now the questions:
1) Limp mode for the engine on the commander, if this happened yesterday how could I tell?
2) The dealer mentioned there were four software flashes available for my vehicle:
Software flash for PDM, Software flash for FCMCGW, Software flash for CCN, Software flash for PCM.
They had no idea if they would help. Does anyone think any of these would help, they are $30 each to try?
3) Is there a way to verify if the PCM is the issue?
4) If the FDCM is complaining about not receiving information from the FCM and the FCM was the source wouldn't another module such as the TCM or PCM complain about that as well?
5) Could issues from the FDCM indirectly cause a random misfire? Where is the FDCM so I can check the connection?
6) This all started after dealer service to trans and x-fer case. The transmission sucking in air from a crack in the filter or an old seal can cause the engine to stall. Could the occasional bubble cause a miss without throwing any DTCs?
7) anything else I should look into?