2000 Ford Mustang.  3.8 v6 and auto trans.

I have had an intermittent stutter from the car on and off for a while,  Never tossed a light until about a week ago.  

I was always under the impression it was an OD problem as it is supposed to be fairly common on these cars.

I bought a pretty nice little scanner and checked and reset the CEL.  About 3 days later same thing.  And again today.  

First code is Cyl 4 missfire,  which I am assuming is a weak coil pack since it is really pronounced under load at about 12 to 1400 rpm and then clears up for the most part after 1800.  There are new plugs gapped properly and new wires in the car.  

Then the codes that confuse me a bit.
On a DTC self test for the ECU/TCU.

P0703 B00 switch circuit fault......On demand DTC.

P1780.  Transmission control switch  O/D.  Cancel circuit out of self test range......On demand DTC


All live stream data seems in order.  Except for the O/D circuit,  Open on the live stream says fault and closed says normal.  
All solenoids are working properly,  All lights are working properly,  and shift range reads properly.


Any advise?  

Thanks.

ETA:  To further add to the WTF,  0703 is a brake light switch code.  The brake switch is functional and tests good.
1780 is the O/D cancel circuit (O/D cancel switch)  It also tests good.  

I'm leaning toward a crap ecu/tcu.  If that is the case,  it will stay bad.  Once the 4.6 cobra motor is installed the stock ecu will only control body control functions and the digital gauge cluster.

If you do the key on engine running test,it requires you to push the brake pedal,hit the O/D off switch and turn the steering wheel. If it doesn't see the inputs from those switches it flags a code.

******This is ONLY if it ran a KOER test.********
If it is a history code then you may still have problems.

Before you condemn the coil............disconnect the vacuum line from the egr valve and take it for a ride. If misfire disappears,you may have several clogged egr ports causing the egr gas to dump into one or a couple cylinders.

Both the KOER and KOEO fail with the same result.  

Everything checks good in the monitor screen and the stream.  

I have not done an egr test however.  That is a good possibility I didn't think of.  

Thanks!

I would ignore the other codes until you get the P0304 dealt with.

Remove & inspect the coil pack. They are good for developing cracks and allowing water into them.

I'm guessing that your scanner is not capable of running a power balance readout.

I will have to do that.  I do think if I look enough at the shop I do have a coil pack off of a parted 3.8.  But I don't know where at the moment.  lol
No it isnt.

missfire is corrected.  

The number four spark plug was bad with 6500 miles on it.  Electrode had a slight browning on one side and the rest was still white like brand new.  Put in a new plug and the missfire is gone.  I reset it with the scanner and so far so good.  

Still not having luck with the other issues.  Ill have to put it on the Genysys scanner and see if I have the same issue.  This little Creader works on every other vehicle I have used it on,  so I am leaning toward the PCM being screwey.

I was just about to tell you to pull the plug. It was probably fouled, if the tip was white looking you might have a small head cylinder leak. Replace gasket to if so.

It's throwing codes because it's missing some cylinders and a couple camshafts.

After about 25 miles the missfire is back.

I'm guessing it is a bad coil pack.  I wont replace it.  The motor is coming out soon.  There will be a DOHC Cobra motor going in its place.

Your advise worked.  Thank you!  

Removed the vacuum line from the egr and the misfire went away.