Hockett

2007 GT cammed out with shorty headers and no cats just started backfiring and loss of power after missing 2nd gear and rev limiter kicked in followed by loud POP and immediate CEL. Prior to this, never seen check engine light. Has 52K miles and I have changed the following since incident. All coils(Duralast) All plugs(Motorcraft) All O2's, Hitachi MAF. Ran smoke through it and it exited out of Ingen Air Filter and back of tailpipes. I backfire between every gear and it sounds as if its coming from under my feet. Considerable loss off power. Waiting on tune file email as previous owner kept tuner when he sold car to dealership. Also changed fuel filter but original fuel pump still on car. Running lean codes and Onboard Diagnostics System not ready code. Any input much appreciated as the car sounds like its about to blow. Also, what should spark 0-2000 2000-4000 4000-8000 be set at? This is all new to me but Im def fast learner. Thx

Dino Dino Bambino

Sounds to me like you might have overrevved the engine, floated the valves, and seen at least one piston make contact with them when you missed the shift. This is known in the trade as a money shift and the reason is pretty obvious.
I suggest you begin by doing a compression test on all cylinders. There'll be zero (or near zero) compression in any cylinder that has bent valves. Then if you perform a leak down test on the offending cylinders, you'll determine if they have bent intake or exhaust valves 'cause you'll hear hissing either from the intake manifold or from the exhaust tailpipe.
If you have access to a bore scope, you can look down on the crowns of each piston to see if there are any crescent shaped witness marks that would confirm contact with the valves.

Derf00

Agree with Dino Dino, you probably floated a valve and that "Pop" was a piston smacking a valve. If the car was running fine before the incident, it is not tune related. Do NOT ***** with the tuning, It's not going to fix anything and you could make it worse by burning a hole in one or more pistons. You're already running lean.

Also, Put the stock coils back in. aftermarket coils for these year cars are known sources of problems and it's Autozone (aka durajunk). Motorcraft or nothing.

Hockett

Thank you both! I had a Ford guy tell me the same months ago, but my mustang guru buddy said "Naw, it wouldnt be running if you bent a valve or floated one, it wouldnt be running" so I went and replaced everything ignition related. Now Im convinced after hearing it from you two so thanks again!
Do i have to have ford do the compression and leak down tests or is something I can fo with the right tools?

Dino Dino Bambino

With the right tools and after watching some How To YouTube videos, you can DIY.

Derf00

I would skip the compression test and go right to the leak-down test. Compression test will only confirm there is a problem with a cylinder (low compression), it will not tell you why it's leaking.

And yes, cars can run on bent valves, especially if it's only on one or two cylinders of a V6 or V8. Heck, i've seen four cylinder cars run with a bent valve, not very well and they may stall but, they still run.

For a leak down, you will need an air compressor and a gauge set that designed for a leak down test.