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Discussion Starter #1
This is going to a long detailed story of what's going on with my wife's focus. It's a 2006 zx4 with a 2.0l and an automatic. Car just tripped 200k miles.

Car will run perfect when cold and once you drive it for about 15 minutes or more it acts like it's running out of fuel. You will hear no noise, no popping or missing, it will just die down and stall out. You can press the pedal to the floor and it will still just die right out. Then all of a sudden it will pick right back up like normal and you can drive maybe a mile or 100 miles before it does it again.

So far I pulled codes with my scanner and replaced the following:
Bank 1 oxygen sensor
EGR valve
Plugs
Fuel filter
Fuel pump and both strainers

After that I unhooked the fuel line from the fuel rail and cycled the pump to make sure good clean gas came out of the line and it did. NONE of that helped alleviate this issue. Please guys what is causing this? The only code it is showing is the oxygen sensor/catalyst below threshold code. Can a bad catalytic converter cause this issue? I'm getting tired of throwing money at a car and not getting it right. It's a nice clean car and the motor has great compression and runs awesome and trans shifts good so I'd like to keep it and let the wife have a reliable car again. Never had a single issue out of the car until a month ago when this problem arised.

Thanks for any and all help guys!!!!!!
 

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Wow, lots of ideas and thoughts... You think your story is long? How about a longer and semi-worthless reply?

No, the Cat will likely not cause the problem because your symptom is so intermittent. The O2 sensors or bad wiring could be triggering and toggling your car into Open verses Closed loop fuel/spark delivery strategies. Even if so, it should not cause your symptoms.

You mention replacing one, but which O2 sensor was it? B1S1 (upstream) or B1S2 (down-stream)

If fuel pressure was intermittently dropping to near zero psi and causing your symptom; I would expect that a DTC would set. So I will briefly assume your fuel pressure is not the problem.

With most scan tools, you can monitor the voltage output of both O2 sensors. This would help you. I use a ELM237 OBDII adapter and phone Torque App = a $20 solution. This App allows me to easily see when in Open or Closed loop. Also makes for a great way to monitor your fuel pressure while driving.

Comments below based on my car, my testing, and a tiny bit of guesstimation:

If one O2 sensor becomes unreliable/unbelievable/dead, as sensed by the PCM, it sets a rich or lean code; will likely go into Open Loop mode; but does not set the Cat inefficient DTC. Once in Open Loop, both O2 sensor voltage outputs go to Zero and/or are no longer displayed on my graphed chart in Torque. The voltage outputs go from "bouncing" to a flat line! Kind of like an EKG of a person whose' heart rate has just stopped. -beeeeeeeeeep, ur dead.

If one O2 sensor becomes a poor performer, as sensed by the PCM, it might set a rich/lean code; might go into Open Loop mode; and might set the Cat inefficient DTC. If getting a Cat inefficient DTC the B1S2 O2 sensor might be bad -or- your Cat might truly be bad. If your Cat is bad, that STILL should not be causing the symptoms you have described.

Exactly what DTC's do you have?

After all that babble, I do not know what your engine issue is.
 

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Discussion Starter #3
I replaced the upstream o2 sensor that is closest to the engine manifold. I just drove the car for almost and hour and it messed up about 7 or 8 times total. It's so weird how the car will run perfect 99% of the time and then act like it's getting the fuel cut off. When it does it you can floor it and it is at idle almost and then all of a sudden it will take off WOT like it should. I'm so confused!
Can the fuel pump driver module under the back seat cause this?
Or could a faulty crank sensor cause this?
 
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