Nissan Repair: Converters, mass air flow sensors, air flow sensors

Question
QUESTION: Hi, I recently got my exhaust system repaired with a new flextube, catalyic converter, and muffler.  The mechanic did not inform me that this car had two converters and now I suspect that the front converter is stopped up and not letting the car breath.  I had a mechanic to look at this problem and so far this is what I have done to my car which is a 2000 Nissan Sentra 1.8 engine, change all 4 o2 sensor, fuel pump, replace two coils in the engine, change the spark plugs, put on a new Mass Air flow sensors, and changed the alternator and the battery. I am still having this same problem of losing gas pressure and choking.  The car has put me 1,000 in the hole already but I am not in a position to buy another. Do you think this problem could be from a clogged front converter or is it just an old car?

ANSWER: Hi Courtney -

Can you please elaborate on your car performance?

Losing gas pressure - are you speaking of the fuel pump or regulator?

Choking - car dying, hesitating, during acceleration, at a stop, no power?

Thanks, it helps. The more information I can get, the better I can diagnose. It is difficult with the car not physically in front of me, so I appreciate it.

let me know -
aloha
calvin

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QUESTION: Calvin,
Hesitating is the word that most describes the way the car is running.  It will start off slow and then give itself a HUGE boost. It stays idle up if that such a word. But I have already put a fuel pump in the this car, can you also get me some more information on the front converter because I afriad that's where the problem is coming from???!!!! Also if you have one motor coils that goes bad will all four coils go bad also, thanks Calvin for whatever information you may have.

Courtney

ANSWER: Hi Courtney -

While the car is hesitating under acceleration, does it have a miss? Like the car is puttering, and then it goes? OR, does it just have a flat spot where there is no activity, and then it accelerates, OR, does it take a few seconds to build up speed with no roughness.

Coils are independent, so one will not affect the other.

I have a hard time being convinced it is the converter, you have no Check Engine Light on, correct?

mahalo
calvin

---------- FOLLOW-UP ----------

QUESTION: The car has a miss and I feel better already about the converter!!!!  The check engine light is on and the code keeps refering to the CO2 sensor. I have two that are direct and two that are universal, would that affect anything? Thanks for being patient with me, I am tired of being miseducated and cheated because of ignorance.

Thanks,
Courtney

Answer
Hi Courtney -

That's why I volunteer. Ta assist people from getting steered into unnecessary work and cash outlay. There are a lot of mechanics out there who get paid on commission, and all they care about is the bottom dollar amount. BUT there are a lot of good ones too. Just got to filter them out.

Anyway, if the car is missing, then I would check the other 2 coils. I am assuming you replaced the spark plugs, distributor cap and rotor, ignition wires? If not, it might be a good decision to check that first. Maybe take it to an Autozone and have them place the engine on a tune up machine to tell you what is causing the miss. It sounds electrical to me.

As for the 02 code, it is probably on because of the miss. Engine runs rich when a cylinder is not firing, thus turning on the light. So, find and fix the miss, and I think you should be good to go.

Let me know your progress

calvin