Odd misfire, cylinder 4 & 7

[TXGTPig]

So I've been chasing this misfire for a bit now. Cars a '21 GT A10. It's only a blinking CEL/pending code, and other then the blinking CEL, you'd never know it misfired. It only does if I hang the RPM above 3500 for more than 7-10 seconds. So if I'm manually shifting and hold a steady throttle position/RPM, say 4200rpm, for more then 7-10 seconds, it'll "misfire". It's always cylinder 4 & 7. It will not do it if I continue to apply throttle/increase RPM. It's only when I hold it steady at any RPM above 3500. It does not do it any other time, and the car dives absolutely great. I know its not the plugs or injectors, as those were replaced. I also know its not the coil pack, as I've swapped them to other cylinders and it does not follow. It started doing this after I had a new short block installed. When they did the short block I also had LT headers installed and the IMRC lockouts installed. I'm thinking of pulling the manifold and seeing if possibly the cylinder 4 & 7 o-ring have a slight clip and also check to make sure the IMRC butterflies aren't broke/lose. Any suggestions and advice is greatly appreciated.

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[nibjones]

Did you have it tuned for the IMRC lockouts? That alone could make it throw the misfire codes

 

[NightmareMoon]

Of course you did a crank relearn with the new short block, right?

 

[TXGTPig]

Did you have it tuned for the IMRC lockouts? That alone could make it throw the misfire codes

Yes sir.

 

[TXGTPig]

Of course you did a crank relearn with the new short block, right?

Great question. I have no clue if the shop did it or not. Off to google to school myself up. I'm assuming its not to late to do it?

 

[NightmareMoon]

Great question. I have no clue if the shop did it or not. Off to google to school myself up. I'm assuming its not to late to do it?

No its not too late and pretty easy. They probably did it but its easy to do and no harm.

 

[Craig Brown]

I have been chasing misfire code too, Thought I might have a vacuum leak but did a smoke test today and I had no leaks, it held 5 lb. pressure. I made a purge valve mount so that it wasn't just floating around and that did nothing, so I have a new PCV valve, but I haven't tried it yet. Like yours I don't have a misfire I just have codes. Manual transmission and I am not sure when the codes are triggered. I have catted LTH MBRP race exhaust, 2018 intake on a 2015 pp GT Calimer stage 2 transmission, Mcleod RXT twin disc ceramic clutch with aluminum fly wheel, Dorman one piece aluminum drive shaft, UPR catch can, UPR expansion tank. Auto Mafia performance tune, JLT CAI, soon to have a Reische 170 Ford D thermostat, So I am at a loss for reason. I have done every test I know about. Oh, and I replaced the purge valve.

 

[Cobra Jet]

Great question. I have no clue if the shop did it or not. Off to google to school myself up. I'm assuming its not to late to do it?

Here’s a thread I had with details of the crank relearn and KAM resets if needed:
https://www.mustang6g.com/forums/threads/engine-misfire-problems.203556/#post-4075889

 

[nibjones]

Great question. I have no clue if the shop did it or not. Off to google to school myself up. I'm assuming its not to late to do it?

It’s not too late and relatively easy to do, if you know anyone with a scanner or Forscan. I would just take that step anyway

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