2000 Nissan Maxima SE Trouble starting, runs rough...

[sycordr]

First off, I'd like to say that I would love to go through more of the posts already on here to figure this out on my own. However, I am currently deployed to Afghanistan, and we only get 30 minutes at a time online. So thanks to everyone who replies! Ok, sometimes the car has trouble starting, then when it does start it idles really low. It rarely goes dead, but it has. It almost seems like one cylinder isn't firing. It has a really hard shift when going slow 10-15 mph. As long as I am accelerating hard though, it shifts much more smoothly. I've taken it to a Nissan dealer before. They told me that the scanner was showing my catalytic converter was bad. I have no idea if that would cause all of these problems or not. I am quite tempted to just replace my entire exhaust system. However, I have no clue what I would need to buy. I have read a couple of posts on here, and some of the same problems seem to be related to the MAF sensor. I should also note that I know very little about cars, I've had a motorcycle for 13 years, and only had a car for about six. I really need to buy the repair manual for my car... Well, my time is up, hope I get some help with this soon.

[MinisterofDOOM]

A catalytic converter code can indicate a bad O2 sensor. That's where I'd start, since a bad O2 sensor can cause the car to run rough.

Welcome to NICO, and thanks for serving.

[sycordr]

How many O2 sensors does my car even have? Would you recommend replacing them all at the same time? Also, would that affect the car's ability to start properly too? Thanks for the reply, and thanks for your gratitude!

I forgot to mention, you can smell exhaust in the car. It can be pretty bad sometimes too, causes eyes to burn and water...
Modified by sycordr at 9:39 AM 2/3/2010

[loystock]

Based on the symptoms provided, your catalytic converter is shot. The cat oxidizes HC and CO and reduces NOx into CO2, N2, O2 and H20. Low power and buckling during acceleration plus smell of raw gas points to a clogged cat and burned internal honeycomb (platinum, palladium and rhodium).

The car may have been running 'rich' for an extended period of time causing fuel to accumulate in the cat and ignite. The 'rich' condition most likely was due to failing O2 sensors which was not addressed. A failed O2 sensor makes the ECM run the engine 'rich.'

It's possible that you have to replace the cats and several O2 sensors. Your best best is to get a free OBD II scan from Autozone and the likes. Make sure you get a printout of the fault codes as they will point to defective components.

There are 3 catalytic converters in your car - Pre-Cat for Bank 1 (close to the firewall, cylinder 1-3-5); Pre-Cat for Bank 2 (close to the radiator, cylinders 2-4-6) and Main Cat. There are 4 Heated O2 sensors - Front and Rear sensors for Bank 1 and Bank 2 Pre-Cats. There are no O2 sensors for the Main Cat. Three of the connectors are mounted close to the radiator while the 4th one (Bank 1 Rear O2 sensor) is mounted on top of the engine.

You can refer to the threads in the links below for additional info:

zerothread?id=120838

zerothread?id=471537

OEM cats are expensive but last for a long time. Aftermarket ones are cheaper but less amount of precious metals and last a couple of years. For O2 sensors, best pricing is from NGK.com a.k.a. "sparkplugs.com."