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BMW 3-Series (E90 E92) Forum > E90 / E92 / E93 3-series Technical Forums > Mechanical Maintenance: Break-in / Oil & Fluids / Servicing / Warranty > Loud tapping/knocking from underneath the car.



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      12-06-2022, 04:06 AM   #1
nicholas.hudson
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Exclamation Loud tapping/knocking from underneath the car.

My car is making a loud tapping/knocking noise from underneath the car whenever the engine is running.
My car is a 2006 E92 with 157,000km in the clock, which I bought only 5ish months ago. It had the common case of lifter tick which I thought was fairly normal, but I later found that the previous owner had neglected to tell me that the car had been in a crash sometime in its life (I realized this when I found broken glass in the cowl, paint pen writing from the wreckers on the front subframe, and that the radiator wasn't sitting in its saddles and instead held by zip-ties). I have recently done some work on the car, replacing both oil filter housing gaskets after finding some oily other-worldly substance in the coolant res (shown below), and repairing the bent and cracked power steering brackets.

Below is the oily stuff I found in the cooling system.
https://photos.app.goo.gl/NRsTVkh1K9EgE5YE6

Since changing the oil and filter, the lifter tick has become less noticeable, and as such this other tapping sound has become more obvious. I used a scan tool to clear and recheck for codes and I currently have three codes on the DME:

29E1:Mixture Control 2
2E83:Electric Coolant pump, power-reduced operation (But I'm not getting any engine management warnings on the instrument cluster, and I know that the pump is working cos I bled the coolant system just the other day)
2D06:Air-Mass System

Not sure if these could contribute to or cause this knocking.
There was no forbidden glitter in the oil or filter when I changed it, so I don't think it's a bearing eating itself but I have no clue what this could be. The following video shows what the sound is like. It is more obvious from the side of the car and in the cab.

https://photos.app.goo.gl/ruuobrcncVjHVeqPA

I also have a leaking valve cover or eccentric shaft motor seal, and a leaking sump gasket. There is also a considerable amount of vacuum in the crank case.

I'm really hoping this isn't and expensive thing to fix.
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      12-06-2022, 09:24 AM   #2
Suvorovo
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Before spending anymore money on the car, verify the alignment to see if there's a bigger issue after the crash and have the car inspected by a mechanic. I guess they'd see things that we'd miss.

You need a waterpump/thermostat ASAP before it completely fails.
Oily stuff in the coolant probably came from the oil filter housing gasket/cooler. These cars don't have problems with head gaskets.

Are you running a manual transmission? The knocking noise underneath the car could be a worn dual mass flywheel or there's a metal heat shield cover somewhere underneath that is known to become loose. I forget exactly, but have seen the issue in other posts. I think you confirmed it's not the engine, which is great.

Vacuum is a bad PCV, have that replaced ASAP. It's why you blew out the valve cover gasket, oil pan, and oil filter housing.

Oil pump/thermostat kit less than $400 USD in parts.
PCV $375 USD

For your 2D06, try cleaning the MAF first. It's kind of expensive to replace $200 USD, but do fail overtime. Could also be caused by a failed PCV causing unmetered air to enter. Cracked hose?

Only buy the pierburg water pump and borg warner thermostat.
I'd also recommend getting the Genuine BMW PCV system. No idea how reliable OE replacements are and have seen fitment issues for the hose connections. They're not that much cheaper anyway.
VDO MAF, if needed is fine.

To comfort you about the cost, I spent around $4000 in parts/tires between 120-125k miles to make sure my n52b30 is 100% reliable for the next 100k miles.

Last edited by Suvorovo; 12-06-2022 at 09:48 AM..
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      12-06-2022, 10:05 PM   #3
nicholas.hudson
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Thanks for the reply.

Yeah, it's a manual trans. It was supposed to have a new clutch installed a few months before I bought it, but if was done by the same people who "fixed" it last time I wouldn't be surprised if there's something they missed or installed incorrectly.

The car also shudders a bit when revving down from around 2k rpm. Could this show a problem with the flywheel/clutch?

I just put the car on stands to see if I could find where this sound was coming from, and it sounds like it's inside the bell housing as it definitely sounds rotational.

I was logging some data just the other day and noticed that the coolant and oil temp was up to around 104 degrees Celcius while cruising at 100 km/h. And previously the oil temp never rose much above 80 Degrees Celsius.

I also saw that for some reason the RPM that the ECU is reading drops down to ~800 rpm while cruising down the highway. Could be linked with the mixture error codes?
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      12-06-2022, 10:09 PM   #4
nicholas.hudson
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Also any recommendations for flushing out the oily gunk from the cooling system? I've tried coolant flush but that didn't seem to work very well.
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      12-07-2022, 08:24 AM   #5
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Could be an issue with the install or they cheaped out and replaced with a single mass setup. Those will cause a chatter. You'd really have to take a look.

104C is within operating spec. These cars run pretty hot.
Here's a post: https://www.e90post.com/forums/showt...'re%20fine.

Go to a mechanic for a coolant flush. They have the tools to pressurize the system. Not terribly expensive.

Can't comment on the ECU stuff, sorry.
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      01-04-2023, 04:58 PM   #6
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Quote:
Originally Posted by Suvorovo View Post

----

Only buy the pierburg water pump and borg warner thermostat.

----

why specifically the borg warner and not the mahle?

i am just curious really

i already have the pierburg pump in my cart at fcp
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      01-09-2023, 07:31 PM   #7
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Quote:
Originally Posted by nicholas.hudson View Post
My car is making a loud tapping/knocking noise from underneath the car whenever the engine is running.
At idle? Cold or after some bit of driving?
Does it change if clutch is operated?
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      01-09-2023, 08:47 PM   #8
michaelalex17
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This was going to be my question. If you are are in neutral and you press in the clutch pedal does the knocking go away? If so Iím going with throw out bearing.
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