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Discussion Starter #1
Hey guys,

This is cross-posted at NissanMurano(.org) forums but I haven't gotten any responses there.

I'm new to the forum and I'm hoping I can get some help. I'm being plagued by the infamous P0420 code and I'm trying to avoid going to the mechanic if I can help it.

I have a 2010 Nissan Murano S AWD 6 Cylinders A 3.5L FI DOHC.

I'm not really seeing or feeling any loss of power but I feel like I can hear a hissing sound coming from the upper, rear, central region of the engine bay. I know that probably sounds confusing but here is a stock image I found to give a better idea of the location.

6225


I've taken that plastic cover off and spent many hours over the past two weeks trying to identify where the hiss is coming from using my eyes, ears and a cool little endoscope I got on eBay and I'm coming up empty. I am really thinking there is a vacuum leak somewhere but I'm drawing a blank. I could just be hearing normal engine noise but the optimist in me is hoping it is a vacuum leak because the P0420 code is just an absolute nightmare to diagnose.

So have any of you folks encountered something like this or have any suggestions. I am a novice when it comes to car repair but I do have basic experience.

Any help would be greatly appreciated :)
 

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The P0420 fault code could definitely be caused by an intake system vacuum leak. The best way to find a vacuum leak is to use a vacuum gauge. So 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 and other hose connections 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.

If you plan on removing the throttle valve because to inspect/replace the large hose, DO NOT DISCONNECT THE ELECTRICAL HARNESS CONNECTOR or else you'll be faced with several re-learning procedures; something I'm sure you don't want to do.
 

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Discussion Starter #3
Okay, I finally got some free time and hooked up a vacuum gauge. From what I can tell, everything seems normal.You might have to fast forward a little bit because I was by myself and had to make sure my phone was set up at the right angle. I couldn't figure out how to attach the video to the post so I uploaded it to YouTube.


Its a bit hard to read with the angle, sunlight, and shitty quality, but the engine is warm and idling and the needle is sitting right in the middle of the green. I then accelerated to 2,000-3,000 RPM a few times.

Everything looks issue-free right?
 
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