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11K views 15 replies 5 participants last post by  DanHas3 
#1 · (Edited)
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#2 ·
I'd remove the serp belt, start it up, and do the same test. If the noise does not happen with the belt off, then it's likely to be a pulley or bearing from one of the parts being driven by the belt. But if the noise is still there with the belt off, then use a mechanic's stethoscope (or a piece of wood) to locate exactly where the noise is coming from.
 
#4 ·
......I should also add that I got this car for scrap because it had suspected engine damage. It was possible that it was run for a while (few weeks) with low oil......
I had previously missed this part of your post, but I'd still recommend first doing the things I posted above. But now I'll also add some additional steps as well.

Since it sounds like you want to keep this engine if at all possible, IMO it's important to find out (as best you can) how healthy it is. First do an oil change, emptying it into a clean container, in order to see if there is any sludge or metal in the oil. Then do a compression and a leak down test, or have them done at a shop if you can't DIY.

Those 3 things would give a good picture of the condition of the engine. If the compression and leak down test results are good, but the oil is black, you can try to clean it up by doing multiple oil changes, until it comes out looking clean. But if the compression and/or leak down tests are not good, or there's lots of metal in the oil, then you should begin to plan for either an engine repair or replacement (better choice if you can't DIY the repair).
 
#6 ·
... The only thing I am struggling to understand is why does the noise go away if I unplug the MAF sensor?....
I don't know what's going on with that either. However, with an engine run low on oil and with an unknown maintenance history, IMO it's much more important to try and determine the condition of the engine (to whatever extent that can be done). Then if the testing turns out well, you can proceed to figure out what that noise is all about.
 
#11 ·
Do you have a video of the vehicle idling? I have a 2006 Mazda 3 s and I'm having a weird noise as well just trying to see if its the same noise? I can hear mine from inside the vehicle I haven't lifted the hood and listened to the sound yet. Or do you have a video of the noise from the inside of your vehicle?
 
#13 ·
Hi,

It doesn't make any unusual noise at idle, it only does it when the throttle opens on deceleration.

As I am only recording it on my phone the noise wouldn't be noticeable from inside the car, although I can hear it in person.

Cheers
 
#14 ·
I have "Open Loop Control due to System Fault" on Fuel System 1.
The code may be from running the engine with the MAF disconnected. Connect MAF, clear codes, and see if it returns.

The Short term fuel trim (bank 1 sensor 2) is at 99.22%
I think that's a bogus parameter. I'd ignore it for now. Otherwise, your fuel trims look very good to me as do your O2 sensor voltages.

Engine sounds the same to me in both videos to be honest.

You seem convinced that the MAF is the key. Use the chart I've attached and work you way through the list till you find the interaction that might cause the problem.
 

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#15 ·
The code may be from running the engine with the MAF disconnected. Connect MAF, clear codes, and see if it returns.
The MAF is connected

I think that's a bogus parameter. I'd ignore it for now. Otherwise, your fuel trims look very good to me as do your O2 sensor voltages.

Engine sounds the same to me in both videos to be honest.

You seem convinced that the MAF is the key. Use the chart I've attached and work you way through the list till you find the interaction that might cause the problem.
Thanks for looking at the fuel trims and o2 voltages. Does anything look amiss to you?

The noise is hard to hear in the poor quality videos but I assure you it's there! :)

I'm not convinced that the MAF is the key but people are suggesting all kinds of mechanical problems without considering that the noise goes away when the MAF is unplugged. In my eyes this says it is a sensor and if it was mechanical, it would do it regardless of the MAF being plugged in.

Thank you for your reply and for the chart.

Joe.
 
#16 ·
I'm not convinced that the MAF is the key but people are suggesting all kinds of mechanical problems without considering that the noise goes away when the MAF is unplugged. In my eyes this says it is a sensor and if it was mechanical, it would do it regardless of the MAF being plugged in.
Yes, I get that. It's hard even for me to equate what interaction the MAF sensor might have with something that would contribute to a noise like you describe. If it were me, I would use the chart to try and find what relationship the MAF has to other things on the car that might make noise and slowly work through it to try and locate the noise. Having said all that, don't rule out a mechanical problem and the possibility that the MAF changing things may just be some weird coincidence. You've got yourself a good challenge!
 
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