2001 QX4 Has bad engine knock at all speeds under load -check light comes on then goes away after a few days This problem is at it's worst when engine is hot I use 94 octane 112,000 KM ....Mech. told me it is the mass air sensor...any help would be great.

just a guess, maybe you're using too high of an octane. I know my pathfinder manual says to use between 87 and 91. I personally use 91 no problems

It can't be the octane....unless it was below 87. I've used 90-94...same thing. pinging.

I'm sorry i have only one reply.......Is this something un-usual, or is this post too complex?I tried to state my problem clearly.......Any help would be welcome.

Is the ECU giving you any codes? If the maf was not functioning properly, and was reading alot less air than is actually going into the engine, it would cause it to run lean which could lead to detonation. Are you engine temps up or are they normal? Have you done anything that could have messed with the timing?

Pinging could be caused by having too hot of a spark plug installed.

Carbon build up on a piston can sometimes cause this, but is very rare. Carbon deposits are normal but sometimes a small peak can form and this peak can retain heat causing pre-ignition or ping.

The knock snesor is supposed to supress pinging by slightly retarding the timing electronically. Check your thermostat. When was it last changed?

This image is from my Xterra manual but the location is similar your your ride.

1) Obtain a spray can of electrical contact cleaner.2) Locate the Mass Air Flow Sensor (MAFS) usually close to the airbox.3) Leave the ignition off, disconnect and remove the sensor.4) Look at the image I enclosed and notice the RED cirlce on the sensor. This it the resistor wire that can sometimes get dirty and cause problems with fuel economy.5)Spray the contact cleaner on that resistor to clean it. Don't touch it with anything or you could damage the wire and that sensor isn't cheap!6) Allow the sensor to dry ( 15-20 minutes ) and reinstall.

This may not fix your problem because if the MAFS is worn out it needs to be replaced. The dealer can scan it with a more detailed system than an OBD scanner and their system can tell you how far out of the resistance range your MAFS is. ANd if it needs to be replaced. Expect to pay 50-60.00 for this test. (I just had my Xterra tested last week for this same issue)

my engine lifgt has been on about a year ago. I recently have autzone check the code. It was knock sensor p0325. I did not do anything but swicht octane from 87 to 91. I drove my car to work with full tank of 91 octane about 75miles back and forth to work. Next day the check enginelight is gone. I think the 91 octane has taken care the engine knock. Mine is 1998 pathfinder.