# CATALYTIC CONVERTER



## Brenda112167 (Nov 17, 2013)

I'm a newb here so apologies if this question is redundant. I'm in a bit of a pickle here with my 98 Altima GXE. I have searched the forum to an answer to my question and have not had any luck.

My 98 Altima failed emissions for the first time. It failed in the NOX reading. I took it to Midas and they said with 99% certainty that its my catalytic converter. The check engine light is not on and there are no codes.

I'm somewhat handy but if its the cat, I think I might be out of my element. It has about 226,000 miles on it.

There seems to be a WHOLE lot involved in getting this front cat out. Looks like we need to take out the alternator, disconnect the bottom flex tube thing, disconnect and empty the radiator, remove the radiator fans, and lets not even mention the timing chain etc.

Is there a video anywhere on how to do this job? I looked all over YouTube and nothing.

I hope the answer to this one isn't "trash the car" because I do love this car.

THANK YOU!


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## rogoman (Dec 16, 2004)

Before condemning the CAT, check the following:
- Check the EGR system for any broken lines. Make sure the EGR valve itself is working correctly.
- Check for any vacuum leaks in the intake system.


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## Brenda112167 (Nov 17, 2013)

Thank you so much for getting back to me rogoman. 

We checked the diaphram on the bottom of the EGR and its moving up and down normally. When we push it up, it acts like its going to die. I don't know how to check an EGR system or how to check for vacuum leaks in the intake system. I could probably search this forum and find it huh? Ay yay yay!

bre


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## rogoman (Dec 16, 2004)

To check the intake system for a vacuum leak, attach a vacuum gauge to a full vacuum source. With the engine fully warmed up, the reading at idle should be 18 - 20 InHg. At 3,000 RPM, it should be around 21 InHg.

If readings are under 18 InHg, check the intake manifold nuts to make sure they are tight. The gasket may have failed; spray a water mist at the gasket to see if the gauge reading changes. Also check the intake plenum bellows at the throttle valve and at the MAF for cracks or loose clamps.

Here's another EGR test:
1) Start engine and warm it up to normal operating temperature.
2) Observe the EGR valve lifting when revving from 2,000
rpm up to 4,000 rpm under no load.


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## Brenda112167 (Nov 17, 2013)

Hey Rogoman,

I looked at the emissions sheet and it coded an "0325 knock sensor 1 circuit malfunction", yet I don't have any check engine lights on. My nox reading is 2.3383. I think that the knock sensor is something I can do but I don't know how reliable these emissions sheets are or if I should just go ahead and change it out and hope for the best. 

What do you think?


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## rogoman (Dec 16, 2004)

A P0325 fault code apparently does not turn on the check engine light; however a scan tool will display the code. A “dead” sensor circuit would not be able to detect actual knock, timing would be overly advanced, and NOX exhaust emissions would increase. Before replacing the knock sensor, inspect the harness connector for being loose or any oxidation. Use a scan tool to reset the code, then drive the car for a while and check with the scan tool again to see if the fault code comes back; if it does, then you most likely have a dead sensor.


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## smj999smj (Jan 1, 2006)

With that many miles, you may need a top end cleaning. High NOX emissions are caused by heat and pressure. Carbon buildup on the tops of the pistons increases compression slightly, which can cause high NOX numbers. It would also cause pre-ignition detonation, which would also trigger the knock sensor code.


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