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I have this issue.. I already asked on FordOwnersClub, but I feel like here I might have a better chance to sort it out.

I bought a Ford Focus mk3 2011 with 1.6 ecoboost 134kW engine with 90k km. My issue is, that under heavy load (heavy acceleration or acceleration on a steep hill,) I can hear a knocking sound. It does only on first gear and only under acceleration. First I thought that it could be comming from a driveshaft, because I also felt vibrations on highways and I had that issue with my mk2 earlier, but it turned out to be a different problem (wheels not balanced.) Suspension seems to be okay, but I had a coil spring broken, which I had to replace.

So I started digging and observing and I thought that it might be LSPI, but I already had 100 octane petrol in it (europe). Basically best you can get here on gas stations. Anyways, I tried a different brand with similliar petrol quality and it stopped doing. Well, it had to be the petrol I put in. Turns out it wasn't. On the same tank 500km later, it started doing again.

I also recorded the sound and inspected it with spectrogram. Here is the audio https://sndup.net/3zt2. It starts at 4s.

ff3-2011

Things that I noticed:

  • It happens only on first gear under load with good petrol quality and even additional additives
  • It happens around 2500-3000RPM
  • It does not "knock" immediately after I press gas pedal. and even in the recording or the spectrogram above it is apparent, that the revs first built up to around 2500RPM and then it started knocking - it does not start knocking after I press gas pedal immediately
  • You can hear multiple "bangs" in one "knock". It is most apparent in the second knock. The first "bang" is quiet and not much noticeable. You can also see it in the spectrogram.
  • I only tried it with warm engine
  • When it starts knocking, I don't feel any power loss or any output in the steering wheel
  • You can also hear that the revs are building up more rapidly when (after??) it starts knocking. It might be a coincidence or it might be the turbo kicking in. Although, I don't think it is a turbo problem, because otherwise it would be noticeable in other gears as well. Especially on highway.
  • The intensity of knocking varies. It can be loud (just like in the recording) or I can't hear anything. Even on the same tank.

After I thought long about it, It does not sound like a premature detonation. It is a metallic noise and even the frequency does not indicate the LSPI. It would have to be much more frequent. The weird part of it is the stable frequency of the knocks.

The problem is, that it only does it on the first gear. I would say, that it is a transmission problem, but it can also be caused by the bigger stress on the drivetrain on lower gear.

I will be very glad for any kind of advice. I don't want to spend thousands on changing parts randomly hoping it would solve the problem. I would rather at least pin down the problem to engine/turbo/suspension/diff/trans/clutch or anything else it might be. One guy said that it might be bad suspension and that the sound might come from the wheel "bouncing". I certainly think it is a possibility. I only recently changed the coil spring, because the last one broke so that might be a clue, because coils don't usually break at 80k km.

Any help will be much appreciated.

I used these tools to inspect the recording

Spectrum Analyzer | Academo.org - Free, interactive, education. - spectrogram Free Online Time Stretcher | OnlineToneGenerator.com - to slow the recording

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  • Tough problem, but can you please clarify what about the spectrogram is different in the marked area? I see what looks like a bang about every quarter of a second, even outside the marked area.
    – lericson
    Jan 7 at 15:36
  • Thanks for comment. The marked area is the engine under load. You can see 3 knocks before I let the gas off. What happens in the recording before is sound of me turning and the blinkers I used. And also some other noise. Please listen to it. The image is going to make sense afterwards.
    – h00ki
    Jan 7 at 15:42
  • I have a clue maybe? I focused on the frequency of the knocks and I think that it is not coming from an engine. I calculated that my wheels turn around 4 times at the speed of 25-30km/h, which is what the frequency according to the spectrogram is. Well, that would mean, that the problem is between transmission and wheels. I also think that I found a test to test transmission. I could try to start at second or reverse and listen. I am thinking right now, that it might be a diff. Does anyone know how to test it?
    – h00ki
    Jan 7 at 17:30
  • yes is not the engine knock, do you have small recorder/ mp3 recorder / old phone? you can try to record the audio near your suspected spring or under the hood. Or you can try to jack the car, and try to engage in 1st gear and try to rev it carefully. the jack should be good enough to hold the weight and tall enough the drive tire not touching the ground. Jan 8 at 14:11
  • Let's narrow this down some ... is the noise engine speed related or highway speed related. This may be hard to tell if it is only happening in 1st gear. Have you tried putting it under load at higher vehicle speed at the same engine speed (2500-3000)? If it is only occurring at the lower vehicle speeds, it most likely is NOT diff related. Jan 8 at 14:13
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NOTE: The following applies to automatic transmission, not manual.

Sounds like clutch packs in the transmission, which slip under heavy load. There's no way it's engine detonation. Differentials don't fail in that manner.

Beginning in model year 2011, the Ford Focus had notorious transmission issues, particularly with the clutch packs. There were a number of lemon law complaints. There have been six revisions of clutch packs and transmission control modules since the design's inception. Check the ATF on the dipstick for a dark color and strong burning smell.

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  • Hi, thanks. Does it also include 6 speed manual transmissions? That's what I have. Sorry for not mentioning earlier. If it does not include manual transmissions, do you think that dual mass flywheel could be the problem? I looked up how it works and there doesn't seem to be anything that could knock multiple times like this. I mean.. there are springs, but I cannot imagine what would need to happen for this sound to occur.
    – h00ki
    Jan 8 at 11:07
  • No, my answer does not apply to manual transmissions. Add 150 ml of Bar's Leaks 1816 Differential Gear Repair to the gearbox (available on Amazon UK & Europe). If it helps, change the fluid entirely and repeat the Bar's Leaks additive, 150-300 ml.
    – Carguy
    Jan 8 at 13:02
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Just to throw another possibility in there, it could be a failing CV axle. If so, it should make a clunking sound as the failing U-joint revolves, especially under load.

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  • Hi, thanks. I looked up how bad CV axle sounds like and it sounds IMHO similiar. I could not test it any further, because it's freezing here and I cannot get enough traction to reproduce it. BTW: I was at the shop today and mechanic said that the clutch feels "too heavy". I don't know what that means, what could be causing it, but it might have something to do with my problem I guess.
    – h00ki
    Jan 12 at 9:49
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Since it's only happening in 1st gear it could be something to do with engine mounts or the rotating of the engine is hitting something. 1st gear puts the most stress on the engine mounts and drive axles.

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