Strange noise from engine - driver side

[DTM_Theory]

Since yesterday I've been getting this weird sound that seems to come from the driver side of the engine. It doesn't sound like rod knock as it only happens while the engine is warm after several minutes of driving. The source sounds more like plastic knock or rattle if you will. On a cold start the noise is not even there at all.

One thing I should mentioned as I did rebuild my DISA with the rebuild kit from GermanAutoSolutions. While assembling things back together there a a bit of a drag in the flap retracting when testing the diaphragm. Could this be a DISA valve issue? Any Ideas? I'm kind of freaking out right now.

Here's a video for reference - hopefully the noise is clear.

https://streamable.com/ak5ioh

Thanks

[andrewwynn]

Disa usually sounds like rattling plastics in a jar. I hear a tiny flutter that could be disa. Mine was very loud when it failed (both mine and wife's).

I hear a pretty pronounced knock though are you saying that's absent at cold start?

Oil is much thicker when cold. I would definitely explore that with a stethoscope or even a rod down the plug holes and tap on each piston to listen for a loose rod bearing before I'd drive it.

You have to catch a rod bearing very quick to not damage a crank. Replaced two motors last year rebuilding one more this year due to spun rods.


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[DTM_Theory]

Originally Posted by andrewwynn

Disa usually sounds like rattling plastics in a jar. I hear a tiny flutter that could be disa. Mine was very loud when it failed (both mine and wife's).

I hear a pretty pronounced knock though are you saying that's absent at cold start?

Oil is much thicker when cold. I would definitely explore that with a stethoscope or even a rod down the plug holes and tap on each piston to listen for a loose rod bearing before I'd drive it.

You have to catch a rod bearing very quick to not damage a crank. Replaced two motors last year rebuilding one more this year due to spun rods.


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Yeah on a cold start this morning I didn't hear the noise at all. Although it was just a brief check for a maybe 2 minutes.

When you say the plug holes do you mean the spark plug holes? What would I use for that sort of test. I'll try unplugging the DISA and see if the noise goes away.

I also want to mention I'm long overdue for an oil change I intend to do later tonight. Due to a busy life i've been topping off oil every so often. Which is bad of course on old oil.

[DTM_Theory]

ok quick update.

Just ran out there again to test. Fired it up, no noise at all. Turned on the temp gauge menu - currently reading at 82c. Not too long ago when the noise was present it was fully warmed up at around 94c the moment I parked.

This is strange. I'm thinking my DISA is malfunctioning or the diaphragm failed. I'll see about getting a stethoscope.

[andrewwynn]

Disa only held on by two bolts; easy enough to see if the repair failed and you can suck on the vacuum inlet to determine if the diaphragm is intact.


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[andrewwynn]

So interesting you mention about top off oil. I used to get lifter noise when i was low on oil but just on cold starts.

You can put a rod down a plug hole to tap on the piston head. If the bearing shell is worn there'll be slop and you can hear the motion as a tap. Look for a YouTube video demonstrating. Also: find a YouTube video with m54 with confirmed rod knock and then one more thing: a friend that was absolutely convinced he had rod knock for months discovered the sound was from a loose spark plug! It sounded exactly like your video so i would check that prob first. Maybe when cold the block shrinks tight on the plug loosens when hot. Would be a little crazy if that's what it was.


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[DTM_Theory]

I am experiencing a bit of lifter tick. I've got fresh oil and lifter additive ready to go in later tonight.

I just recently replaced all 6 plugs and ignition coils too while doing a valve cover gasket job not too long ago - that's funny you mentioned that side story. I was pretty picky with the entire process and ensured correct torque specs. But who knows, weird things can happen with these engines. There's a possibility one could be loose.

I'll definitely check for slop on the bearing shells. I really hope that isn't the case.

Thanks for the information.

[andrewwynn]

If you use stethoscope you can listen for bottom side or top side source. Then also maybe trace to a potential cylinder before pulling plugs. A crumb of rust can absolutely be more torque than the spec. I wish i had video of my buddy's car it sounded near identical to your video.


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[andrewwynn]

https://chatgpt.com/share/6a739f2c-2...c-e91ba17e970f
here's what GPT has to say... def. pull the DiSA and start there... mine made a very different sound much faster rattle when it failed but especially since that was a recent repair, it's good to check. when doing the repair, you did track down the little pin from the OE disa correct ?

[X5chemist]

Pull the vacuum hose off the intake runner diverter. See if it stops. Check the intake rear vacuum plugs.