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As many Ford Focus MK3 owners did, I noticed disturbing “grinding” noise from the car transmission. For me it happens almost all the time when car slows down on an incline. Engine RPM increases at the same time to cope with the increased load, and engine output feels a bit rough.

This behavior made me to come up with an explanation theory – I want to share it with you and show a way to mitigate those transmission behavior issues. I speculate that inhalation of the engine bay hot air can lead to sudden incoming air temperature increase. As car control algorithm expect this parameter to be relatively stable, this parameter fast change throws the algorithm out of whack – so it is desperately looking for a proper gear selection while its change is not really needed. Again, it is just a speculation, although it is somewhat supported by the fact that transmission grinding noise surfaces more often during hotter weather and after prolonged driving.

Now for the remedy. MK3 Focus air intake (pre-filter connections) is known for its leaking. It has been discussed for a long time that there is a gap in the rubber gasket where 2 air filter box pipes meet. Plugging this gap increased engine stability at the car take off – observation reported by many. Please note that I keep the original intake snorkel intact – replacing it with Focus ST intake scoop did not do anything positive in my experience, and the engine “diesel-like” sound became even more pronounced.

I decided to examine the air intake path in more details for extra leakage. In addition to the place mentioned above (I used silicone to make the gap air tight), I found 3 more places – all of them are inside the air filter box – the box cover and the air filter have to be removed for this modification.

First place is the air resonator at the bottom of the air box – it has a foam gasket that is relatively leaky – I covered the gasket with a bit of construction silicone.
The second one is where rectangular pipe meets the air box –it has some gaps around its perimeter. Again, I used a bit of silicone to plug the gaps in, trying not to overdo it.
The third place is the drain hole at the bottom of the filter box (in the corner). I added about 1ft rubber tube to the drain hole (dangling lose near and inside the bumper area) in attempt to minimize the engine bay hot air inhalation (but keeping it capable of draining water (!)).
After silicon polymerized, I moved air filter in place and re-attached the cover.

Modification results:

1. Car has no noticeable engine stumbling on the acceleration; Overall engine revving is quite smooth at all speeds;
2. Engine “diesel-like” sound muffled quite a bit; I know some people like louder engine sound, but not me, I prefer quiet engines;
3. Transmission grinding diminished a lot. It no longer surfaces while car driving on an incline at low speed. I still need more time assessing this aspect of modification.
4. Overall transmission shift is more “crisp” and “smooth” at all speeds.

Some history behind my 2012 Ford Focus SEL (manufactured May 2012) transmission repairs to establish a baseline:

1. Transmission clutch pack (Rev. D) and seal were replaced in July 2013 (16,000 Miles); Firmware is updated as well;
2. Update of transmission firmware – May 2014 (28,000 miles)
 

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Sounds like the TSB in May corrected you concerns. However, internal damage might have occurred. You have an extended warranty 7 years, 100,000 mile so sleep well.
 

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Sounds like the TSB in May corrected you concerns. However, internal damage might have occurred. You have an extended warranty 7 years, 100,000 mile so sleep well.
Transmission firmware re-flash did not solve "grinding" issues - they were always there until I did this air intake modification. It is a very well known fact that Ford does not have software solution for the issue at the moment.
 

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I truly do not know what “diesel-like” sound you are referring to. The only noise I have heard like that comes from the manual transmission equipped MTX-75 which exhibits gear lash rattle when the transmission is in neutral and the clutch is not depressed. But you have the DPS6 automatic. The only other noise I can think of is the fuel injectors which can make a clicking sound. The air sealing techniques you performed might improve drivability and reduce hesitation but would not have any effect on injector noise.

You have already reinstalled your factory snorkel. That should help with NVH.
You could try installing a factory engine cover if you don't have one. It has sound dampening material on the bottom and it might might shave off a couple of db.

I had a 2012 SE with the DPS6 and it had the "marbles in a blender" sound when driving along sometimes but never sounded like a diesel at idle.
 

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supernova1, I too have a 2012 with a revision "C" clutch installed at 14,000 August of 2013. I will look at those areas and do what you suggested. My car has been great since that revision and I'm quite happy with how it behaves. I use to drive it too conservatively but now tend to give it a bit of extra pedal and she responds fine. Thanks for your observations and tips.
 
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