P0308 - Misfire in Cylinder 8

[PROJECTeleven]

Oddly enough, I got this code the day after putting a FF tune on, and about 7 gallons e85.

Cold start at lunch, code came on.

cleared the code, did a kam reset, let it idle. Drove around normally, jumped on the highway and let it rip.

several pulls and the light has not returned, yet.

I believe my ECU was still learning the flex fuel tune.

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[Stlsinger]

Mine was from a broken imrc shaft. Dealer could not find the problem. Everything operates normally on the outside. But the flaps inside are not in the correct position. I had to pull the intake myself to find it

 

[XDsm]

Update:

My original dealer basically did nothing to actually diagnose the problem and flat out refused to accept the intake manifold could be the problem. The service manager end stand was that he doesn't know tunes very well and thinks it's the tune.

Sooo, I take it to a completely different dealer. Night and day difference with customer service. They take it in and get to work doing full diagnostics. Checked compression, checked the PCV system, and finally pulled the intake manifold. They found bank #2 of the intake runner control system had failed. The shaft was broken. They put me in a rental car while they waited for a new intake manifold. Replaced it and now everything is fixed. The service advisor said they added a note to the internal Ford message board system in case another dealer got a Mustang with the same problem other techs would have something to reference.

 

[Stlsinger]

I knew it!! Lol. Glad they found it!

 

[FordTechOne]

Update:

My original dealer basically did nothing to actually diagnose the problem and flat out refused to accept the intake manifold could be the problem. The service manager end stand was that he doesn't know tunes very well and thinks it's the tune.

Sooo, I take it to a completely different dealer. Night and day difference with customer service. They take it in and get to work doing full diagnostics. Checked compression, checked the PCV system, and finally pulled the intake manifold. They found bank #2 of the intake runner control system had failed. The shaft was broken. They put me in a rental car while they waited for a new intake manifold. Replaced it and now everything is fixed. The service advisor said they added a note to the internal Ford message board system in case another dealer got a Mustang with the same problem other techs would have something to reference.

Glad to hear they took care of you. The IMRC (Intake Manifold Runner Control) has been a well documented issue; in fact, Ford issues a Special Service Message (SSM) to dealers to inspect for said issue when diagnosing misfires on 5.0 S550s.

 

[socalx]

I know this is an older thread but I just wanted to say that the 2 dealers that I went to did not want to address this issue. They wanted to change plugs and coils but did not want to look at the intake. I changed my own plugs just for the sake of the argument after Ford quoted me almost $600 to do it.

After that, the misfires came back so I bought a new takeoff intake and installed it. You can see how the old one was faulty. It was so obvious.

Having said that, what intake manifolds do not have this design flaw? I see this coming back in another 50k miles.

 

[Chappers]

If you're misfiring below 3k revs with that error code it is definitely the intake manifold I had this issue in the end after a couple of weeks the engine management light came on, you notice the engine performing rough prior to total fail

 

[CEHollier]

If you're misfiring below 3k revs with that error code it is definitely the intake manifold I had this issue in the end after a couple of weeks the engine management light came on, you notice the engine performing rough prior to total fail

Out of curiosity is it just the factory manifold or the GT 350 too? I did a swap. No problems. Just curious.

 

[Chappers]

Out of curiosity is it just the factory manifold or the GT 350 too? I did a swap. No problems. Just curious.

Mines stock I'm not sure about GT350.

 

[Cobra Jet]

Glad to hear they took care of you. The IMRC (Intake Manifold Runner Control) has been a well documented issue; in fact, Ford issues a Special Service Message (SSM) to dealers to inspect for said issue when diagnosing misfires on 5.0 S550s.

Yea, and I’m surprised Ford is still using that POS IMRC system; it’s been a problem since the 1996 4.6 DOHC Cobra engines... and even once repaired, the owner can or should I say will experience a future IMRC failure...

Most DOHC owners back then opted for aftermarket IMRC delete plates which eliminated the troubling IMRC BS all together.

Doesn’t the aftermarket have IMRC deletes for the S550 5.0 yet?

 

[JackBauer]

MMR makes IMRC lockouts. i believe you would need a tune to remove the CEL that would come from it.

 

[aero84]

Glad to hear they took care of you. The IMRC (Intake Manifold Runner Control) has been a well documented issue; in fact, Ford issues a Special Service Message (SSM) to dealers to inspect for said issue when diagnosing misfires on 5.0 S550s.

Do you have a reference to the SSM?

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