Mazda 3 engine noise - 2.0L Duratec

[anonymous-user]

The initial message was deleted from this topic on 18 December 2021 at 16:41

[PaulKemp]

It's better if you hold the revs at the point it makes the noise, revving it does not give people the chance to hear the problem
If the problem goes away with the maf disconected it could be the maf that's the problem
Have you connected an OBD reader to check fault codes?
There is a lot to check before changing anything

[AER]

Sounds very much like knock, as in combustion knock.

Likely a fuel quality issue or something's not right with the ECU and sensors. Start with checking the TPS is healthy and that the fuel system is running near 100% short and long term adaption values.

Transient knock like this is sometimes a characteristic of some cars and won't be gotten rid of easily. Does it affect your day-to-day use of the car?

[Team 17]

Do you know what the compression ratio is for this engine?

maybe run a few tankfuls of shell vpower and see if it helps, certainly did when I had a similar issue.

edit: just checked and it has a high ratio, definitely try the vpower as it may just be 'pinking' (pre-detonation of fuel) caused by the compression ratio.

Edited by Team 17 on Thursday 1st September 06:51

[PaulKemp]

If it's knock and showing under no load or transient on closed throttle that's a first for me (stand to be corrected) I'd start putting a strobe on it to check advance at different revs
From what I heard it's just noise as pulleys and belts, possibly tensioners rattling

[Ian_UK1]

Joef said:

If so why would it stop when the maf sensor is unplugged?

This is only conjecture, but the ECU may be going into a safe, or limp-home, mode when the MAF is unplugged. In this state, it may well run a lot less ignition advance to protect the engine. You can check this with a strobe or a proper ODB reader (most will display the ignition timing in real-time).