p0308 Cylinder 8 Misfire

Hi All,

Just wanted to document and share the issue I had with my car recently.

The Stang was running great until last week while cruising on the highway I got a CEL with codes:

P0300 - Random/ Multiple cylinder Misfire Detected
P0308 - Cylinder 8 Misfire Detected

The only Engine Mod I have is Steeda CAI w/o restrictor and Steeda Tune - which I got about 6 months and 15k miles ago.

I drove the car for a little while and the CEL went away by iteslf. It was good for a week until last night. I got a CEL with the same codes again. This time the CEL went away on the next startup within a couple of hours..

I am wondering if anyone faced a similar issue. The car is only at 30K miles.

I am guessing it could be one of these:

Spark plugs
Coil Packs
MAF sensor
Vaccum Leak
Low Compression in Cylinder 8

I did email Steeda regarding this issue to see if they can look at some datalogs. They advised it can't be the tune since it has been running fine for 6 months or so. So I ordered a Steeda CAI restrictor. I hope it comes in today or tomorrow, then I will put that on, flash the car back to stock and take it to a Mod friendly dealer and have them test out the issue.

I am hoping it is something as trivial as a spark plug gap or coils but I will keep everyone updated.

( I do feel like the CEL came on when I did a WOT in 5/6th gear if I remember Vaguely :shrug: )

2015 Mustang GT - (Nov-17-2015 -> present)
Mods:
STEEDA CAI without Restrictor
STEEDA Tune
Eibach Prokit lowering Springs
MRT catback exhaust

Updates:

July 12th: I re tuned my car with Lund Tune and so far I haven't got any misfires yet..Although i would doubt it would have anything do to with the tune, I am still testing it...

July 12th 8 PM: The CEL came back on - p0308. This time it was after I put fresh Gas (shell 93 octane) and was driving normally.

July 13th: I changed the coil and spark plug on cylinder 8. Did a compression test Cyl 8 was at 210 compared to CYL 7 @220 ish so it looks Ok..
This was done at a mechanics shop

Also, another thing I noticed is higher than average IAT's since this issue started happening. It could be 100 degree plus weather here in Texas. But it constantly stays 15-20 above ambient even on Highway going 75 MPH..

July 14: Drove from Austin to Dallas. Car drove pretty strong, no issues. No CEL

July 15: Driving my fiancé to work my CEL came back on again! So it might not be a bad coil and plug. Could be something different.
Also I feel like my Cylinder head temps and IAT's are a little higher than normal (205-208 CHT and IAT 15-20 over ambient even on the highway). Made an appointment with a dealer and they won't get to look at it before August...

August 2: Still having the same issue. Random misfires with the same codes. I have an appointment with the dealer next week so I'll let ya'll know how everything goes.

Ali I have just started to have the same issue. I scheduled an appt with the dealership but the code went away. They could not give me any direction. Now it is back again. Please update this when you can. If it does not go away then I will schedule another appt and let you know the results. Thx in advance!!

KENS550TX said:

Ali I have just started to have the same issue. I scheduled an appt with the dealership but the code went away. They could not give me any direction. Now it is back again. Please update this when you can. If it does not go away then I will schedule another appt and let you know the results. Thx in advance!!

Click to expand...

Sorry to hear that. I know it can be frustrating. Did you tell them about the error codes? If they say "Oh I don't see anything - then you tell them I saw p0308, can you check if the plug and the coil are still good on cyl 8. Ask them if they did a compression test just to be on the safe site. I hope it gets resolved for you!

(Check my new update)

Thread Updated

crank relearn?

cop on my back said:

crank relearn?

Click to expand...

What does that do?

@alimustafa23 What ended up happening with your misfire issue?


I recently changed plugs in my GT and on the first drive I got a CEL and the car went into limp mode and had to be power cycled off and on in the middle of the road...


Plug job:
1. Removed NGK 6510's gaped to .030 and replaced with NGK 6510 gaped to .030

2. Ensured the coil packs were left in a clean area when removed (top of the intake manifold away from dirt and debris)

3. Snugged down the coil packs and clipped on the wire harness and pressed the locking tab to ensure proper connection.....

4. I am befuddled as I have done numerous of plug swaps over the 15 years I have been driving and never have I had an issue.