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While under load, the engine sounds like there is a bunch of marbles bouncing around in the engine. Revving the engine in neutral does not create the noise. Filling the gas tank with 93 octane instead of 87 "solves" the issue with the noise.

Filling up with 93 octane seems silly and expensive for such an old car. Some Notes:

  • Prior to the issue occurring the spark plugs were replaced while troubleshooting a misfire, that has been resolved. I double checked and the plugs are correct for the engine.

  • The car has the 1.8L engine and ~200k miles

Is it possible that this is an issue with spark plugs or something else?

  • Is that 93Octane measured by the American method? Or is that 93RON? – Captain Kenpachi May 18 '15 at 7:47
  • @JuannStrauss I assume by the American method, I am in the US and I selected 93 octane at the pump instead of the 87 octane I usually use. – stoj May 18 '15 at 12:39
  • From a quick google search, you should be using 91 at minimum. that would be about 95RON (if anyone else is interested). Though why it was working previously and now it isn't, I don't know. Was it particularly hot, or were you in slow traffic? – Captain Kenpachi May 18 '15 at 13:11
  • I seriously doubt the 1.8L needs 91. That's the economy engine. There is probably something wrong causing the pinging, but the higher octane is preventing it for now. Beyond that, my 325i recommends 91, but if I run 87 it doesn't knock, I just get a little less throttle response, because the knock sensor protects the engine. The knock sensor may have failed in this case. – Lathejockey81 May 19 '15 at 2:13
  • @stoj Paulster2 is spot on with the answer. Did you try the solution, it WILL resolve the issue and you can go back to normal fuel octane saving tons of $$'s. Could you be so kind as to award Paulster2 with the answer? Thanks and I hope you tried the solution. as Paulster2 said, you'll be golden. Take care. – DucatiKiller Jan 4 '16 at 23:22
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Pinging is caused by one of several different reasons. It is usually a hot spot in the combustion chamber which is causing the issue. A hot spot is usually made of carbon buildup, the edges of which get hot very easily, will glow red as such, and will ignite the air/fuel mixture. If a hot spot is present, it will pre-ignite the air/fuel mixture during compression.

What you have to do is clean out the combustion chambers. The easiest and most effective way to achieve clean combustion chambers is to give your engine a SeaFoam treatment. Once the hot spot(s) in your engine are cleaned out, you should be golden.

  • I get the same symptoms (the engine sounds like there is a bunch of marbles bouncing around in the engine) and my intake manifold valves are covered in carbon blowby (as I just took it off for service). I'm curious how it got there, do you think from PCV ? Should I install a catch can between the PCV and intake to filter out oil from the recycled fuel ? Also, do you think this can cause engine overheating ? – amphibient Jun 19 '15 at 20:40
  • @amphibient - Haha, you should ask your own question and refer back to this one if needed, lol! – Pᴀᴜʟsᴛᴇʀ2 Jun 20 '15 at 0:31
  • Man, i need an answer more than following formalities at this point – amphibient Jun 20 '15 at 0:33

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