axim

Hello there

I'm posting on behalf of my mum, who bought a new 2011 Mustang V6 Automatic Convertible a couple years back. About three months after buying it, she and my dad went on a holiday to Italy, and while there, at one point the engine started stuttering and shaking for a bit and the warning light came on. Then it was fine again. They took it to the garage when they were back home, they read out the error memory, which said that cylinder #6 had a misfire, which they assumed was probably due to cheap foreign gas. They replaced the spark plug and thought it was fixed, but it wasn't.

The problem would occur again sporadically, but no one ever figured out why or how to fix it. We had the car at different garages a couple times, no one figured it out.

Fast forward to two months ago, I finally got my license, and my dad asked if I wanted to go for a drive in the mustang. I said yes of course, and when we were just leaving our town on a country road with little traffic, he said I should floor it, so I did. It pulled nicely for like half a second, then at just over 4.5k rpm it misfired again and started shaking violently. I was honestly scared to **** and thought something was gonna come apart, but after about 10 seconds it was fine. So we took it to the mechanic, who read out the error memory again, apparently this time two cylinders, 4 and 6 had a misfire. We left the car there overnight, they replaced two ignition coils and all spark plugs, which once again did nothing to fix the issue.

In the meantime we figured out how to reliably reproduce the issue. Whenever the engine revs to 4.5-5k, one or two cylinders would misfire and take 10-15 seconds to come back. It doesn't matter how warm the engine is, it doesn't matter what quality gas you put in, the engine just can't go above 5k revs.

Because very few people drive mustangs around here (we live in Switzerland) mechanics have little to no experience working on them, even those at official Ford garages, and seem just unable to fix it. For now the temporary solution is to be careful with the gas pedal and back off a bit once the engine revs to about 4k, but that doesn't mean the problem is fixed.

So I guess my question is, has anyone around here seen or heard of something similar to this, and have any idea what could be done to fix it. Maybe some pointers we can give to our mechanics what to look for and what to do, because they are unable to figure it out on their own.

tl;dr: Cylinder 4 and/or 6 consistently misfire at 4.5-5k rpm, what'd up with that?

Greetings,
Axim

WindyMustang

Welcome to the forum Axim!

There was an issue with something similar a while ago...see http://v6mustangperformance.com/repairs/misfire-codes-certian-mods-repairs/ for more information. It's possible something hasn't been updated in the ECU, and a simple reflash should fix it up. If the dealers are not so well trained or equipped, you could get a performance tune and a hand-held tuner from someone like American Muscle, which would also let you diagnose your own error codes. (I use a iTSX tuner and their turning service, and it's working out very well!)

Although a misfire CAN scare the **** out of you, in most instances they are more bark than bite. Generally the "Cyclone" engine has been working out pretty well, but still it's better to get that software checked out to be sure.

Good luck!

yourmom6990

^^ Exactly what I was thinking.