Engine light on... 2012 Mustang GT (5.0 Coyote - automatic)

praga37

New member
I'm stuck... Along with a "cylinder 6 misfire" issue, I also have a "Bank 2 Air/Fuel Ratio Imbalance message" as well as a "Misfire Detected on Startup First 1000 Revolutions" - My guess is these messages are all related. I replaced the spark plugs and it seemed to fix the problem for a while. I also switched the coil #6 with coil #5 and, to my chagrin, I have the same issue... I have a Flowmaster Outlaw catback exhaust and a Borla cold air intake. I'm not aware if other mods have been done to the vehicle since I purchased the car used from a dealer in Halifax in May 2020. This issue started later in the fall of last year. Anyone else encountered the same issue? and what could be possible fixes?
 

2001BlackGTvert

Administrator
Staff member
I'm stuck... Along with a "cylinder 6 misfire" issue, I also have a "Bank 2 Air/Fuel Ratio Imbalance message" as well as a "Misfire Detected on Startup First 1000 Revolutions" - My guess is these messages are all related. I replaced the spark plugs and it seemed to fix the problem for a while. I also switched the coil #6 with coil #5 and, to my chagrin, I have the same issue... I have a Flowmaster Outlaw catback exhaust and a Borla cold air intake. I'm not aware if other mods have been done to the vehicle since I purchased the car used from a dealer in Halifax in May 2020. This issue started later in the fall of last year. Anyone else encountered the same issue? and what could be possible fixes?
That sucks. I don't have a 5.0 but we have a few members on here that do. Hopefully someone has encountered the same issue or heard about it and can offer up some assistance
Fingers crossed it's a simple fix for ya.
 

67 AGAIN

Enthusiast
A couple of thoughts for you.

Along with plugs and coils, injectors can cause misfires.
You’ve gone along way toward addressing the first two.
I would suggest you visit a dealership and let them run a diagnostic.
They can run tests on the injectors.
They do a bunch of key cycles with specified accelerator positions in a certain order with their laptop plugged in.
This pinpoints misfires and measures injector pressures for each injector.

An injector issue could also possibly be the cause of the air-fuel issue.

I don’t know where you got your information but if it’s from a handheld tuner, that’s not nearly as precise as a dealer diagnostic.

I doubt your cat back is the issue.
I would look at the intake end rather than exhaust.
For example, that cold air intake you have, does it have an oiled air filter or was it cleaned with one of those clean and oil kits like a K&N?

Too much oil on the filter can migrate to your mass air sensor and corrupt its ability to read air flow.

Several tuners and CAI manufacturers don’t use or recommend oiled filters.
Roush, Airaid, C&L, Ford Performance and JLT all use dry filters.
You just wash them in a detergent and water solution, rinse and put back in dry.

Make sure you have your tuner with you when you visit the dealer.
If they need to do any updates, you need to revert the car to stock, let them run the update and then dump your modified tune back in.

If I was you I would visit the dealer you bought the car from and seriously investigate if you can somehow contact the previous owner to find out exactly what was done to the car before.

PS, I had an injector caused misfire before and changed the one injector that diagnostics were telling me to change.
Did not have anymore codes.
Problem solved right? Wrong!

I took the car to get tuned shortly after.
The tuner (the person, not the electronics) was having problems getting it just right.
I told him about my injector issue.
He proceeded to change all 8 injectors with Ford Racing units.
The car tuned right up like a champion and laid down great numbers.
That was 8-9 years ago and no issues at all since.

Like your situation, my car was bought used.
My theory is that the previous owner neglected gas maintenance during winter storage, and although only one injector caused codes, all 8 were gummed up or affected by the bad gas.

Good luck.
 

praga37

New member
A couple of thoughts for you.

Along with plugs and coils, injectors can cause misfires.
You’ve gone along way toward addressing the first two.
I would suggest you visit a dealership and let them run a diagnostic.
They can run tests on the injectors.
They do a bunch of key cycles with specified accelerator positions in a certain order with their laptop plugged in.
This pinpoints misfires and measures injector pressures for each injector.

An injector issue could also possibly be the cause of the air-fuel issue.

I don’t know where you got your information but if it’s from a handheld tuner, that’s not nearly as precise as a dealer diagnostic.

I doubt your cat back is the issue.
I would look at the intake end rather than exhaust.
For example, that cold air intake you have, does it have an oiled air filter or was it cleaned with one of those clean and oil kits like a K&N?

Too much oil on the filter can migrate to your mass air sensor and corrupt its ability to read air flow.

Several tuners and CAI manufacturers don’t use or recommend oiled filters.
Roush, Airaid, C&L, Ford Performance and JLT all use dry filters.
You just wash them in a detergent and water solution, rinse and put back in dry.

Make sure you have your tuner with you when you visit the dealer.
If they need to do any updates, you need to revert the car to stock, let them run the update and then dump your modified tune back in.

If I was you I would visit the dealer you bought the car from and seriously investigate if you can somehow contact the previous owner to find out exactly what was done to the car before.

PS, I had an injector caused misfire before and changed the one injector that diagnostics were telling me to change.
Did not have anymore codes.
Problem solved right? Wrong!

I took the car to get tuned shortly after.
The tuner (the person, not the electronics) was having problems getting it just right.
I told him about my injector issue.
He proceeded to change all 8 injectors with Ford Racing units.
The car tuned right up like a champion and laid down great numbers.
That was 8-9 years ago and no issues at all since.

Like your situation, my car was bought used.
My theory is that the previous owner neglected gas maintenance during winter storage, and although only one injector caused codes, all 8 were gummed up or affected by the bad gas.

Good luck.
Thanks a million for your ideas and advice Sir. Injectors seem to be the common denominator in responses I collected over various sources from the web. However, as you suggested, I'll start by taking the car to the dealership for a thorough diagnostic and see where this leads. Thank you :)
 
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