Misfire codes (P0308, P0306, P0300) on a stock gen2 coyote with 60k miles

[BluePonyGT]

Update:

went for a drive today. On the freeway I saw the check engine light flash a bunch then stop. A minute or so later it did it again. Then again: 3 times total. Then it stayed off.

rather than use my obd2 reader I’m going to check engineering mode and see what it tells me:

Sponsored

 

[Fat_Joe]

I have been following this thread and wanted to share my experience too. I also have a gen 2 coyote. Specifically a 2016 Mustang Gt Premium with only 27k miles. I have been battling multiple misfires every since I bought the car back in April of this year. The car misfires mostly on cylinder 4. Although when I use FORScan, I can see counts on all cylinders. And it has thrown codes for the other cylinders from time to time. I have tried the following with no luck:

• New spark plugs, torqued down
• Swapped coil packs, still misfires mainly on cylinder 4
• New injectors
• New o2 upstream sensors
• New intake manifold (2018+)
• Cleaned MAF and throttle body
• Went with a new tuner (VMP)
• Retorqued everything under the hood and checked vacuum lines
• Crank Relearn and KAM reset
• A different shop did a compression test and vacuum leak test. Everything looked good

I will be taking my car to a Ford Performance dealership next week to see what they can find. But I don't have high hopes

 

[Torinate]

I have been following this thread and wanted to share my experience too. I also have a gen 2 coyote. Specifically a 2016 Mustang Gt Premium with only 27k miles. I have been battling multiple misfires every since I bought the car back in April of this year. The car misfires mostly on cylinder 4. Although when I use FORScan, I can see counts on all cylinders. And it has thrown codes for the other cylinders from time to time. I have tried the following with no luck:

• New spark plugs, torqued down
• Swapped coil packs, still misfires mainly on cylinder 4
• New injectors
• New o2 upstream sensors
• New intake manifold (2018+)
• Cleaned MAF and throttle body
• Went with a new tuner (VMP)
• Retorqued everything under the hood and checked vacuum lines
• Crank Relearn and KAM reset
• A different shop did a compression test and vacuum leak test. Everything looked good

I will be taking my car to a Ford Performance dealership next week to see what they can find. But I don't have high hopes

Do you feel the misfires or just know they're there?

Auto or stick?

How is it coming off idle as soon as you press the gas - do you have a hesitation? I'm battling something similar with misfires but also an off-idle stumble hesitation.

 

[Fat_Joe]

Do you feel the misfires or just know they're there?

Auto or stick?

How is it coming off idle as soon as you press the gas - do you have a hesitation? I'm battling something similar with misfires but also an off-idle stumble hesitation.

It's a manual. And sometimes I do get jerky acceleration when letting go of the gas and pressing the gas again. The car is overall jerky but it could be because I am still learning how to be smooth with the clutch. It does sounds like it backfires (pops) when up shifting gears sometimes or letting off the gas. The car mostly misfires around the 1800 - 2200 rpm range on the highway when cruising in top gears. I don't feel the misfires but I do get the check engine light flashing.

 

[Torinate]

It's a manual. And sometimes I do get jerky acceleration when letting go of the gas and pressing the gas again. The car is overall jerky but it could be because I am still learning how to be smooth with the clutch. It does sounds like it backfires (pops) when up shifting gears sometimes or letting off the gas. The car mostly misfires around the 1800 - 2200 rpm range on the highway when cruising in top gears. I don't feel the misfires but I do get the check engine light flashing.

Gotcha.

Good luck with finding the issue. Hopefully the new tuner can pinpoint something and it can get corrected. Sounds different than mine - mine are mostly at idle and so far no flashing or check engine light...

 

[BluePonyGT]

I’ve been driving mine since new. I’ve noticed when it’s cold in the morning I have to give it time to warm up before I drive off which for V8’s I’m used to. Clutch is a bit jerky when cold too, but one it’s warmed up it runs and shifts great. I may have gotten used to some off idle issues with the throttle snd leaving in first but I don’t kill the car and have to restart, but every once in a while I have to give it more throttle than normal.

I still wonder if voltage is an issue. Every once in a while the voltmeter will read 12.5 volts or so. Normal should be 13.5-14.5. That would be the charging system.

I also wonder about injectors, but nothing other than 92 octane has gone into this car.

so pp 3 upgrade is on the way: intake, throttle body, cold air box, coils, plugs and a gt350 tune with the tool plus I’ll get the shifting optimization.

 

[Fat_Joe]

Gotcha.

Good luck with finding the issue. Hopefully the new tuner can pinpoint something and it can get corrected. Sounds different than mine - mine are mostly at idle and so far no flashing or check engine light...

Thing is my tuner said everything looks good. So I don't know what it could be. I did buy some F-150 o2 sensors as I heard they are longer. My car has long tube headers and has the extensions on them for the upstream o2 sensors. I heard they can cause issues sometimes. They will get delivered when the car is in the shop next week so I will have to wait afterwards to get those installed if the shop doesn't find the cause of the misfire. It's more of a backup plan and nice to have a spare of o2s as I will be running e85.

 

[Fat_Joe]

I’ve been driving mine since new. I’ve noticed when it’s cold in the morning I have to give it time to warm up before I drive off which for V8’s I’m used to. Clutch is a bit jerky when cold too, but one it’s warmed up it runs and shifts great. I may have gotten used to some off idle issues with the throttle snd leaving in first but I don’t kill the car and have to restart, but every once in a while I have to give it more throttle than normal.

I still wonder if voltage is an issue. Every once in a while the voltmeter will read 12.5 volts or so. Normal should be 13.5-14.5. That would be the charging system.

I also wonder about injectors, but nothing other than 92 octane has gone into this car.

so pp 3 upgrade is on the way: intake, throttle body, cold air box, coils, plugs and a gt350 tune with the tool plus I’ll get the shifting optimization.

My shifting get better as my car warms up too. When it's cold, I have to be really gentle with the clutch otherwise it would be very jerky.

It's weird that you mention your battery voltage at 12.5. Mine does the same exact thing. My car doesn't struggle to start though. But I wonder if that may contribute to the car misfiring. I do recall when I took my car in to get a spare key made. The guy that was working on it, said he was having trouble communicating with the computer because the battery voltage was low. He had to hook up a charger to get the new key programmed. But thing is, I never have an issue starting the car

 

[BluePonyGT]

My shifting get better as my car warms up too. When it's cold, I have to be really gentle with the clutch otherwise it would be very jerky.

It's weird that you mention your battery voltage at 12.5. Mine does the same exact thing. My car doesn't struggle to start though. But I wonder if that may contribute to the car misfiring. I do recall when I took my car in to get a spare key made. The guy that was working on it, said he was having trouble communicating with the computer because the battery voltage was low. He had to hook up a charger to get the new key programmed. But thing is, I never have an issue starting the car

Interesting. This car does have a charging system set of fault codes that are supposed to be separate from the CEL. I did get a battery indicator on my original factory battery, and already changed that about a year ago so I only have 12 months on the battery. I do have a dash camera, and the lithium battery that powers that independent from the fuse panel when the car is off is now being powered by the cigarette lighter, so it may be drawing too many volts too often, and could be causing an issue, but I would think the car would tell me if the alternator isn't behaving. I would suspect that if there's a fault in voltage regulation it would say so, but remembering way back struggling with single point distributors, bad coils, franken-wiring, and other problems diagnosing ignition systems the charging system was often to blame.

I've decided to go ahead and install my new plugs and coils for this weekend's trip to a car show across the water in Port Orchard, WA - it's a long enough drive where I can see if there's a difference. If not I know the intake is going to come off next and I'll inspect that.

 

[BluePonyGT]

ok so I installed my coveted ford performance coils I've had stashed away along with my new spark plugs - gapped and installed with the coils. I have to say it's way snappier and responds quicker. So I'll see what happens here this weekend.

Ironically my new intake showed up too (thanks FedEx) today. It feels like I'm about to kill this fly with a sledge hammer, but I'll take better performance and no DTC codes over what I had any day.

 

[Torinate]

ok so I installed my coveted ford performance coils I've had stashed away along with my new spark plugs - gapped and installed with the coils. I have to say it's way snappier and responds quicker. So I'll see what happens here this weekend.

Ironically my new intake showed up too (thanks FedEx) today. It feels like I'm about to kill this fly with a sledge hammer, but I'll take better performance and no DTC codes over what I had any day.

Nice!

Did the coils fix the cels?

Got a part number for the coils? Thanks!

 

[Fat_Joe]

ok so I installed my coveted ford performance coils I've had stashed away along with my new spark plugs - gapped and installed with the coils. I have to say it's way snappier and responds quicker. So I'll see what happens here this weekend.

Ironically my new intake showed up too (thanks FedEx) today. It feels like I'm about to kill this fly with a sledge hammer, but I'll take better performance and no DTC codes over what I had any day.

After doing a little bit of research on the battery voltage, it's seems like the mustang's have a smart charging system that only charges the battery under the right conditions. And how did the new parts go? Is it still misfiring? A little update from me, is I took my mustang to the Ford Performance service shop today so I am waiting to hear from them on what could possibly be causing the Mustang to misfire

 

[Fat_Joe]

Over the weekend I found an o2 extension that was burned on my car. I heard bad things about o2 extensions but they are needed when you have long tube headers. The passenger side was the only side that had an extension. I ended up replacing it with a f-150 o2 sensor as they are longer. Thought I had found the problem but after driving it, still misfires for me. Which in the end wouldn't explain why the driver's side misfires too

 

[Call_Me_Bruce]

PO308 and P308 misfires are are on the same bank. I would visually inspect the harness for any rodent damage. I would also get that sorted before putting any other parts.

 

[BluePonyGT]

Ok, here's a big update:

After installing the ford performance coils and plugs, and during the show last weekend yielded zero codes - until the trip home. It's been nothing but P0306 and P0308 codes since. Probably one every other day just like before.

I did inspect my wiring harness. That was actually a really good idea to check for rodent damage. Since the pandemic the Seattle area has had its share of rat outbreaks. They got into my garage over the winter and made a hell of a mess. They also got up into my engine compartment (probably for warmth) and made a mess there too which I spent several angry hours cleaning up and declaring scorched earth against any rats since then. After putting out some traps, and putting a sound/light emitter under the hood all of that nonsense stopped back in early February. This misfire thing started in July, but it could still be related. I looked over all of the coil connectors, the harness back to the loom, the injector connectors, and back, and in the back of the motor and I don't see any damage at all.

So all that being said I decide to go ahead and pull the trigger on the PP3 GT350 intake, throttle body and cold air box swap starting yesterday. I got the original intake off the engine and after pulling the fuel rail off and flipping it over I have the exact same problem as you see all over the web:

https://www.mustang6g.com/forums/threads/broken-imrc-shaft-p0308-p0300.100363/

The valve actuates just fine on the passenger side, but on the driver's side it sticks about half way closed and hardly actuates at all. I took a video of it:

I finished the swap and reprogrammed the PCU. It performs way better and I love the improved shifting. I can tell it responds a hell of a lot better. I’ll see if I get any codes.

Sponsored