I've got a 2011 Mustang GT that got a reman sourced from Ford.com. Swap went fine but there was a misfire that's driving my mechanic crazy. He's checked all connections and grounds multiple times and can't find issue there. The car has a bare noticeable miss at idle. It also will trigger blinking engine light at part throttle occasionally if I'm holding RPM's up somewhat while accelerating up a longish hill near my house. It seems to be a bit down on power but I'm not sure since about 6 months passed between motors(took over 3months for Ford to deliver new motor). I don't believe it's bad gas since I've run about 10 tanks through it since the swap. It has new plugs and coil packs which actually helped quite a bit but didn't totally solve issue. No stored codes. Any suggestions? Ford dealership has a 3 month backlog and it could get expensive if they start throwing parts at it...I can do that.

I'm not sure where to explore next.

 

Have the ECU scanned for fault codes and hopefully they'll guide you to find the problem.

 

Ford's not going to throw parts at it. (at least my dealer never has).

Your mechanic did a throttle relearn?

What happened to the previous engine and did it have any mods on it that required a tune? Using what's now a stock motor with what could be a modified tune for an engine that is no longer in place will cause issues.

 

This car is totally stock. I ordered it directly from Ford and received in June 30, 2010. Everything from intake up is from original motor so I don't think the throttle relearn is necessary. The car has a little over 77k miles on it because I only live about 4 miles from work. I'm told that the lack of a complete heat cycle is a cause of abnormal engine wear and oil usage.