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Discussion Starter #1
Yesterday I bought a new to me 2003 Pathfinder. I thought it was a good deal as he gave me a huge discount because the check engine light was on and spitting a catalytic converter code. As we drove the 120 miles home, my wife was following me in our Nissan Altima. 10 miles from our house a tractor trailer hit my wife and totaled the little Altima. This car was in perfect mechanical condition and we had planned to keep it but... My wife is really sore and bruised but will be OK.

Now my problem, I also have a Toyota 4x4 that I am having issues with the alternator right now so it is out of commission. I plan to fix it today so I can park the Pathfinder until I can fix it.

On our grandson's 2004 Altima, the engine was toast because of the pre-cat situation. I replaced the engine and punched out the pre-cat, added two spacers for the 02 censer and his car is still running fine and passes inspection. My question: Can I punch out the two converters and use the spacers with our 2003 Pathfinder. Is there a reason it has 4 catalytic converters?

One more question, will the rear stabilizer bars being worn out cause the truck to act funny as in the rear end wobbling when it upshifts coming out of passing gear? I appreciate all of your help you guys flat out know Nissans.
 

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not sure about the cats, but your rear end issue is a common thing. i think its discussed in a sticky post here. if not, google 'R50 death wobble'
 

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Discussion Starter #3 (Edited)
not sure about the cats, but your rear end issue is a common thing. i think its discussed in a sticky post here. if not, google 'R50 death wobble'
dfrhodes, I have never heard of this problem but I told my wife it had to be worn bushings in the rear arms causing that. You confirmed that and I really do appreciate it. I just ordered new arms with the bushings installed. Thank you so much.

Hopefully I will tackle the catalytic converters today and hopefully by spacing the 02 sensor it won't kick a check engine light. If it does I will just have to replace the converters.

The reason I am hesitant to replace the front converters right now is I need to solve the problem of why they were fouled in the first place. I suspect the truck was running rich and the unburned gas fouled them, just a guess though. Once I solve that problem I will buy new converters. But to put new ones in there now-- with the same problem-- would only be throwing money, we don't have, away.

I just saw online a product that they say works cleaning the converters, anyone have any experience using a cleaner put in gas tank?
 

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Discussion Starter #4
I went ahead and ordered the new catalytic converters and 02 sensors, hopefully they will be here tomorrow. I also found a vacuum leak in one of the hoses on top of the engine, it goes to the VAP valve or something like that. I fixed it for now and will replace it soon.
 

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Catalytic converter "cleaners" usually don't work. On VQ-series engines, if you gut the upstream converters, you can sometimes run into a "lean" running condition that can only be corrected by having a custom tune installed on the ECM. The four catalytic converters are simply there for cleaner emissions. The upstream converters are three-way converters and their efficiency is monitored by the ECM using input from the upstream and downstream oxygen sensors on each bank. The rear converters are two-way and are not monitored. A number of things can cause converters to fail. Sometimes they just become inefficient at breaking down the exhaust gases; this can just happen on its own or sometimes caused by a misfire, typically a bad cam sensor or coil that caused incomplete combustion, sending unburned fuel to the upstream converter. Sometimes they can become clogged. This can happen due to coolant or oil contamination. One of the problems of the VQ35DE used in the R50 Pathfinders is that sometimes the oil control rings get stuck in the landings and create an oil burning engine, which can clog the upstream converter. The only way to repair this is to teardown the engine and re-ring the engine/hone the cylinders....or, replace the engine. Hopefully, this is not your case. With the upstream converters removed, look for burnt oil build-up on the front side of the converter substrate (the "honeycomb"). If you have it, that's likely the cause of the demise of the upstream converters and you will now have another big decision to make, unfortunately.
 

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Discussion Starter #6
Catalytic converter "cleaners" usually don't work. On VQ-series engines, if you gut the upstream converters, you can sometimes run into a "lean" running condition that can only be corrected by having a custom tune installed on the ECM. The four catalytic converters are simply there for cleaner emissions. The upstream converters are three-way converters and their efficiency is monitored by the ECM using input from the upstream and downstream oxygen sensors on each bank. The rear converters are two-way and are not monitored. A number of things can cause converters to fail. Sometimes they just become inefficient at breaking down the exhaust gases; this can just happen on its own or sometimes caused by a misfire, typically a bad cam sensor or coil that caused incomplete combustion, sending unburned fuel to the upstream converter. Sometimes they can become clogged. This can happen due to coolant or oil contamination. One of the problems of the VQ35DE used in the R50 Pathfinders is that sometimes the oil control rings get stuck in the landings and create an oil burning engine, which can clog the upstream converter. The only way to repair this is to teardown the engine and re-ring the engine/hone the cylinders....or, replace the engine. Hopefully, this is not your case. With the upstream converters removed, look for burnt oil build-up on the front side of the converter substrate (the "honeycomb"). If you have it, that's likely the cause of the demise of the upstream converters and you will now have another big decision to make, unfortunately.

Thanks again smj999smj, you are a wreath of information. I looked at the cats and the right hand side was really gray, no burned oil signs, it did show some signs of deterioration, I could easily see through the converter.

The one on the drivers side was worse, while no oil burned visible, that cat had quite a bit of the ceramic missing. Also part of the 02 sensor had broken off and was lodged in the ceramic. I decided to go ahead and buy new converters and now have them installed. As I stated in another thread, my main problem has been replacing the heat shield on the drivers side, that sucker is unreal hard to get on. Hopefully Monday I will have the truck back on the road and just the brakes to go and a couple of oil leaks to fix. I already have replaced all the trailing arms and the truck drives much much better.

While under there I did notice the bushings on the A frame might need replacing so I will check that a little further. Thanks again for all your help, it is very much appreciated.
 

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I understood the upstream O2 sensors adjust the mixture, so you cant run O2 eliminators or spacers on them.
 

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Discussion Starter #8
IanH, I chickened out, when I found out how hard it was getting the converters and 02 sensors off, I decided to go ahead and get new ones so I wouldn't have to go through that again if it didn't work. I appreciate your information and time.

Jim
 
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