Brand new to the forum! I recently purchased a 2012 Base Mustang with the 3.7L V6 and the manual 6 speed. Great car so far and love driving it with one annoying issue I can't seem to make sense of. I have a misfire in 3 and 4. This misfire happens around 3k RPM. The CEL will flash and the car loses power. This only lasts a few seconds and the CEL quits flashing and power is restored. Longest lasting issue so far has been about 15 seconds. The CEL stays on solid. If I clear the CEL I seem to have no issues for a while. Sometimes it may last a day and others it may last 3 or 4 days before the CEL comes back on and I start having the misfire again. Misfire is always in 3 and 4. Car had an engine failure about 30k miles ago according to previous owner and paperwork. Engine was swapped from a F150 with around 60k miles on it. Engine currently has around 90k. Engine swap paperwork confirmed. Previous owner was trying to chase it and stated he changed plugs and coil packs with no change. Car has BBK long tube headers and Roush exhaust. Any help tracking this down would be incredible!

 

When I had that same thing happen on my 2013 after an engine replacement it was because the installer forgot to do the crank relearn process. If you have an SCT tuner you can run it yourself (with long tube headers you probably should have a tune). If you don't have one, the dealer can do the crank relearn for you.

Whenever the engine and transmission are separated you have to run that crank relearn process to teach the computer where everything is on the engine. If you don't do that then you get all the symptoms that you describe because the computer is not responding properly to what is really happening with the engine.

 

This is awesome news man. I’ve got a good bi directional scan tool. I will check this out as soon as I get back to the shop this evening. I should be able to run this procedure at home. If not, I’ll call the local dealer in the morning. I’ll update what I find out. Thanks!

 

So I have somewhat of an update. I definitely believe the crank sensor to be the issue. With my scan tool I can see that it needs the relearn process completed. However, when I attempt the relearn, it fails for communication issues. I am planning to try with a different scan tool but I fear this may be either a sensor, wiring or pcm issue. Any thoughts on this?