Mustang shuttering and misfiring under power - Mustang Evolution

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Old 04-23-2013, 09:35 PM   #1
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Mustang shuttering and misfiring under power

Its a 03 Mach 1, just put a new motor in the car. It'll run good for about 5 minutes till it gets up to temp, and then she starts shuttering underpower. It will go from shuttering for about 10 seconds and then runs great for a couple seconds and keeps jumping back and forth from the two. Put a Ob2 on the car, got the codes for

O2 sensor circuit high voltage bank 2 sensor 1.

Lack of H02s21 switch indicates rich

system too rich bank 2

So it seems like it might be a bad o2 sensor? Just wanted to see what you all thought before i went out and spent the money. Want this to run right after we spent the time dropping the new motor in it!
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Old 04-23-2013, 10:10 PM   #2
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Its a 03 Mach 1, just put a new motor in the car. It'll run good for about 5 minutes till it gets up to temp, and then she starts shuttering underpower. It will go from shuttering for about 10 seconds and then runs great for a couple seconds and keeps jumping back and forth from the two. Put a Ob2 on the car, got the codes for

O2 sensor circuit high voltage bank 2 sensor 1.

Lack of H02s21 switch indicates rich

system too rich bank 2

So it seems like it might be a bad o2 sensor? Just wanted to see what you all thought before i went out and spent the money. Want this to run right after we spent the time dropping the new motor in it!
I would say its your o2 since you have a circuit high code on it. I have the same issue on mine except on both banks however im just too lazy to buy 2 o2s lol. But to rule anything out when you swapped motor was it a straight foward drop and go or did you have to swap parts like manifold and such possible causes that can attribute to the code? Intake leaks would cause it just a thought but more than likely im leaning towards the o2

---------- Post added at 11:10 PM ---------- Previous post was at 11:10 PM ----------

And its the upstream o2 not the downstream so you only need one but may i suggest buying both upstream o2 sensors. Better off knowing both are new rather than it being a pita to go under and change the other side if it goes bad
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1996 Mustang GT, 17x9 front and 17x10.5 cobra r replica rims, 255/40/17 front 285/40/17 rear at the moment,
o/r x-pipe flow master 40 series dump downs, cai/ram intake, 75mm c&l throttle body and plenum, pi heads and intake swap, msd wires, stock gears, untuned at the moment, no dyno numbers for now.
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Old 04-23-2013, 10:59 PM   #3
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i might just go ahead and buy both while im at it. But we reused the intake manifold, upper and lower. Did the starter fluid thing where you spray the manifold to see if it raises the rpm. Didnt do anything on the upper, but i didnt check the lower. I also replaced the bottom o rings on the injectors, i think they were leaking a bit. Still having the problem so Ill go ahead and get the o2 sensors. Does yours run really bad with the sensors being out??
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Old 04-23-2013, 11:35 PM   #4
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Sounds and runs like its cammed and idle is weird along with you can see the alternator bounce along with the lobing it does.
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o/r x-pipe flow master 40 series dump downs, cai/ram intake, 75mm c&l throttle body and plenum, pi heads and intake swap, msd wires, stock gears, untuned at the moment, no dyno numbers for now.
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Old 04-24-2013, 06:37 AM   #5
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Could be bad injector... maybe
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Old 04-24-2013, 12:00 PM   #6
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Could be bad injector... maybe
Bad injector would cause running rough and cause cylinders to not fire throwing codes for misfire on certain cylinders i.e. p0305 cyl num 5 misfire and so on. Op doesn't to my knowledge have misfire codes so id rule out injectors. However one can always be wrong so its possible. If thats the case i would also see if the fuel regulator is leaking thru the vacuum.
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1996 Mustang GT, 17x9 front and 17x10.5 cobra r replica rims, 255/40/17 front 285/40/17 rear at the moment,
o/r x-pipe flow master 40 series dump downs, cai/ram intake, 75mm c&l throttle body and plenum, pi heads and intake swap, msd wires, stock gears, untuned at the moment, no dyno numbers for now.
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Old 04-24-2013, 01:37 PM   #7
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Yea true I was thinking more of partly clogged maybe if u sit at idle and your tach jumps up and down I thought that was a sign of injector problem. Ur probably right tho
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Old 04-24-2013, 01:40 PM   #8
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You sure the sensor is pluged in or it didn't get smashed while the engine was getting put in?
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