DippinBob

I'm starting this new thread on this to share my experiences with this P0308 Check Engine code. The reason why is because I'm at 56K miles and other posts seem to indicate this was happening while their Mustang was fairly new.
This all started in June 2018:

1. First noticed check engine light on Monday June 4th. Codes showed P0300 & P0308, cleared codes.
2. Check engine light came on while driving home Tuesday June 5th after approximately 70 miles since codes cleared. Codes showed P0300 & P0308, cleared codes.
3. Check engine light came on while driving home Wednesday June 6th after approximately 70 miles since codes cleared. Codes showed P0300, P0308, P0308 P. Cleared codes.
4. Check engine light came on while driving home Thursday June 7th after approximately 70 miles since codes cleared.
5. Pulled MAF sensor, inspected and cleaned Saturday June 9th. Cleared codes.
6. Check engine light came on while driving home Monday June 1th after approximately 70 miles since codes cleared. Did not clear. Made diagnostic appointment for Thursday June 21st.
7. While driving on Friday June 15th using Max A/C and 100 degrees outside, noticed first performance degradation, A/C started blowing warm air and Check Engine light started flashing. Turned A/C off, check engine light stopped flashing, A/C blew cold air. This occurred several times until I got back home to check codes. Codes showed P0300, P0308, P0306 and P0308 P. Cleared codes.
8. Check engine light came on while driving home Tuesday June 19th after approximately 70 miles since codes cleared.
9. Turned MAX A/C on to see if that problem would re-appear and it did after approximately 150 Miles. Same symptoms with check engine light flashing, A/C blowing warm air and performance degradation.

DippinBob

While at the dealership, the technician showed me the diagnostics results at it clearly showed that cylinder 8 was having misfire issues to the tune of 1200+. He also showed that cylinder 6 was also having misfire issues but only around the 250+ and both of these were within the "last 10 Key-on" cycles.
By the way I drive almost 100 miles each day to/from work.


The tech. said they needed to replace the spark plugs and coil packs for both 6 & 8 and reset the ignition program. He said that whenever they put new plugs in they need to do that so the engine will re-learn the sequence. Within 5 miles of leaving the dealership I did notice better power but the check engine light came on and there were spots where it ran rough but smoothed out. I drove into work the next day and it was smooth for the 48 mile trip. However, on the way home it started running rough again so I called. I was told I need to bring it back in and leave it because it obviously has a bigger problem and that driving it with the misfiring could damage the converter. I was on the phone so I'm assuming catalytic converter. I take it back on Monday (6/25) and they are giving me a F150 loaner. At least I get to do some off-roading while I wait...

DippinBob

Thursday 6/28:
First thing to report is I've got my Mustang back. (Ahhhhhhhh!) The dealer gave me a F250 loaner which was nice but I'm glad to be back in my convertible.

The dealer techs found the problem and fixed it, all covered by my warranty. The second diagnostics showed that the entire right side bank of cylinders was misfiring with number 8 still taking the lead. The following are the misfire counts read during the last 10 drive cycles:
Cylinder 5: 43 misfires
Cylinder 6: 108 misfires
Cylinder 7: 156 misfires
Cylinder 8: 1,126 misfires

The left bank with cylinders 1 - 4 were all at "0".

This lead them to remove the intake manifold and this is where they found the Intake Manifold Runner Control or IMRC had failed on the right side. The Dealer Rep. showed me how he could pry open the left side and when he let go it would snap back into place whereas the right side would remain open in the position that it was moved to. The fix was to replace the entire intake manifold and the GT Convertible is back on the road. It took them about 4 hours to perform the repair.




I had to enhance this shot so you could see the IMRC stuck open. It should have sprung back against the right side.



Had to cut this photo in two so I could show the data.



This shows just cylinders 5 - 8. Cylinders 6 & 8 are circled.

DB

DippinBob

Sorry for the HUGE pictures, I didn't think it would show that big.

smoke_wagon

DippinBob

Hi Smoke_Wagon,
I took the picture because the dealer couldn't give me the failed intake. That was because it was covered under my warranty and they needed to send that failed unit back as proof of the issue. He said if they don't then they don't get paid. The diagnostic is something I specifically asked for so he was able to grab it before the tech. shredded it. I'm thinking this should all be automated and associated with my account. That way they have a good history of the vehicle. Even though it was covered by the warranty I happened to see the bill which was roughly $550.00.

I do admit that this dealer has been by far the best I've ever dealt with. When I brought it back last Monday I noticed the passenger side rear window wasn't rolling up completely. I mentioned that and the fact that my Sync 3 upgrade kept failing so they handled both of those items as well as part of the over all trouble call. To fix the window they just had to lubricate the window track. I asked if this is something I should be doing and he quickly told me no. He said that when I bring it in for the standard oil changes, just mention the window track lube every so often and they would get it done. I felt that I had exceeded my question limit so I didn't ask why the Sync 3 upgrade kept failing. I suspect it was due to my terrible internet at home anyway.

Sean G

Thanks Dippin Bob. I am having the same exact issue. Gonna make a appt this week with my local dealer.
Sean