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Recently my 2014 E350 developed a weird knocking sound coming from the rear of the engine, close to the firewall, on the passenger side with no codes or check engine light. There was alway this weird noise coming from that area of the engine for years that I understood was the high pressure fuel pump, but the noise has gotten louder and louder in the past 30 days to the point where it sounded like a Diesel Semi Truck. Could it be a failing pump or piston slap?
Recently my 2014 E350 developed a weird knocking sound coming from the rear of the engine, close to the firewall, on the passenger side with no codes or check engine light. There was alway this weird noise coming from that area of the engine for years that I understood was the high pressure fuel pump, but the noise has gotten louder and louder in the past 30 days to the point where it sounded like a Diesel Semi Truck. Could it be a failing pump or piston slap?
Any ideas what it could be? No check engine lights has been illuminated on the dash yet.
I very possibly is the fuel pump and it does not necessarily mean the pump itself. There is a roller lifter that runs on the cam shaft that could have failed but this most likely would cause engine run issues.
I very possibly is the fuel pump and it does not necessarily mean the pump itself. There is a roller lifter that runs on the cam shaft that could have failed but this most likely would cause engine run issues.
Seems like it, but I haven't noticed any issues while driving, just this knocking noise that keeps getting louder. I always had a low knocking noise issue years ago when the car was still under warranty, and the techs told me it was how the direct injection fuel pump was supposed to sound. Now it's just getting louder and louder.
If you have a video editor which can show the audio channel, that knock sound would be very visible audio signal spikes.
You need to know your engine RPM first, and then you do a minimum 20 seconds video record.
At the video editor , take 10 seconds of the video timeline and count the audio signal spike numbers.
If the suspect is HP fuel pump, your M276 3.5 NA engine uses 3 lobes camshaft for fuel pump.
So, at 600 idling RPM let say, the signal noise spike would be [ (3 lobes x 600 rpm) / 2 ] / 60 seconds = 15 times per second.
Camshaft speed is 1/2 of crankshaft speed.
If your camera can do 60FPS, its better to catch the signal spike.
However, the way I hear the knock-knock sound from your video simply by ear, it is not fast enough to be a HP fuel pump.
The car is direct injection so you certainly have a high pressure fuel pump. Early VW/Audi 2.0t’s (05-10) had a lobe that ran on the cam for the fuel pump (also direct injection). The lobe would wear out, the cam would wear through it, and send metal shavings into the engine. Lead up symptom was engine power cutting out under load. My thinking is if you’re not experiencing abrupt power drops under moderate acceleration, then it’s probably not a bad fuel pump. These cars are extremely fuel efficient, any reduction in the slightest bit of fuel supply into the engine, and you would notice it clearly.
how many miles do you have on the car? Have you ever had the PCV replaced? It’s back there too and does get clogged up after a while. Costs about $800 via indi mechanic to replace (pain in the a$$ to get to). I did mine around 65k miles, and it made a noticeable difference in the smoothness and noise factor of my engine. I didn’t quite have the knocking thst you do, but I was forming a rhythmic ticking, and did have oil leaks in the cam solenoid seals at around 40k miles.
the engine cover comes off with an upward tug. If you can remove it, it should make it easier to isolate location.
hey, at least it’s not at the front of the engine where the timing chain lives!
Seems like it, but I haven't noticed any issues while driving, just this knocking noise that keeps getting louder. I always had a low knocking noise issue years ago when the car was still under warranty, and the techs told me it was how the direct injection fuel pump was supposed to sound. Now it's just getting louder and louder.
It gets louder when the clearance in the "gap" gets bigger with failing part. It can also be the spring in the pump that weakens and does not keep the cam follower against the cam and lets it be "jumping" against the cam.
When it gets bad enough it will take out your cam shaft. Pump is driven by the lobes in the cam shaft.
If you have a video editor which can show the audio channel, that knock sound would be very visible audio signal spikes.
You need to know your engine RPM first, and then you do a minimum 20 seconds video record.
At the video editor , take 10 seconds of the video timeline and count the audio signal spike numbers.
If the suspect is HP fuel pump, your M276 3.5 NA engine uses 3 lobes camshaft for fuel pump.
So, at 600 idling RPM let say, the signal noise spike would be [ (3 lobes x 600 rpm) / 2 ] / 60 seconds = 15 times per second.
Camshaft speed is 1/2 of crankshaft speed.
If your camera can do 60FPS, its better to catch the signal spike.
However, the way I hear the knock-knock sound from your video simply by ear, it is not fast enough to be a HP fuel pump.
Because a single roller does 3x more work than the 3 lobes. The lobes will usually be equally worn on 3 lobes.
The Audi-s old model dumb-azz roller tappet usually worn out VERY fast.
This kind of design :
Because a single roller does 3x more work than the 3 lobes. The lobes will usually be equally worn on 3 lobes.
The Audi-s old model dumb-azz roller tappet usually worn out VERY fast.
This kind of design : https://www.amazon.ca/Suuonee-Follow.../dp/B083TT4FF8
I would still check the pumps/lifters out as this kind of noise is very "mechanical" and other than something interacting with the cam shaft is difficult to understand if the noise is coming from the passenger side back end of the engine where the fuel pumps are located.
Thank you for such an in depth diagnostic S-Prihadi! I will get the oil serviced with liqui moly engine flush then add some liqui moly hydraulic lifter additive and will report back! I'm thinking it might be the lifter. My trusted Mercedes shop did an A service last year with Liqui Moly Ceratec, but they are not open until the 12th due to holidays. Fingers crossed!
Any luck with the oil change & lifter additive? I have the same exact ‘tap tap’ (thought I was only one on the planet) - 2015 e350 wagon M276 with 59,000 miles. I’m beyond concerned and hoping to identify the root cause and proactively make the repair before conditions worsen. Thank you
Any luck with the oil change & lifter additive? I have the same exact ‘tap tap’ (thought I was only one on the planet) - 2015 e350 wagon M276 with 59,000 miles. I’m beyond concerned and hoping to identify the root cause and proactively make the repair before conditions worsen. Thank you
My mechanic finally figured it out after tearing it apart. It turned out for me it was a freak malfunction where the spark plug on cylinder #3 was cracked around the metal ring from the ceramic body of the spark plug, and was still sending spark into the engine, but the crack caused the spark plug electrode to vibrate with occasional misfire. Mechanic finally figured it out after revving the engine and detecting a misfire on cylinder #3. I had it in the shop for over 2 weeks now.
You may not believe this but I hope you do. My mechanic found the same exact root cause but on cylinder 4. The porcelain was cracked thus allowing combustion vapor to escape. Could see brown gasses on the connection boot and base of plug. Wild! $1,200 later (diagnosis and spark plug replacement) were fixed. Crisis adverted - for now…..
How old/mileage are the spark plugs to be that bad ?
They are genuine or aftermarket ?
I never ever in my life owning a car with spark plugs problem, let alone the ceramic cracking, as I replaced them usually ahead of time because I worry more
of steel based s-plugs seizing in an aluminum cylinder head more than anything else.
How old/mileage are the spark plugs to be that bad ?
They are genuine or aftermarket ?
I never ever in my life owning a car with spark plugs problem, let alone the ceramic cracking, as I replaced them usually ahead of time because I worry more
of steel based s-plugs seizing in an aluminum cylinder head more than anything else.
The mileage on the car is 112000, the spark plugs were replaced at 80,000 miles along with all OEM Beru ignition coils. They were Bosch ZR6II3320 double iridium plugs which got pulled out, and it got replaced by the same part number. I asked my mechanic, and the ceramic part did not crack, it just got separated from the metal ring and caused the ceramic cylinder to slide up and down inside the metal threaded ring of the plug which caused it to sometimes be able to deliver spark, and sometimes misfiring due to the sliding causing the electrode gap to open and close. He was only able to get the car to throw a code P0303 after putting the car on sport mode and driving it with high revs. Thankfully the plug did not shatter inside the engine and throw very hard ceramic inside the cylinder. I was surprised as well, this was the first time I heard of a spark plug suddenly fail physically! My mechanic said the ZR6II3320 plugs were the same as the OEM mercedes plugs, since the OEM plugs are just rebranded Bosch plugs.
Last edited by Geep 250GD; Feb 16, 2024 at 01:53 AM.
In my case. Car had 59k miles. Plug were changed at 41k back in 2022. Here’s a pic of the affected plug and boot next to one without issue. Genuine Mercedes plugs.
Wow! I can't believe you had the same failure. I owned many cars in the past and had never even though the spark plug could break like this! My mechanic was out of town for a while and I was just driving my older 250GD. My car had the spark plug fail at exactly the same place on cylinder #3. The ignition coil was still good but filled with the brown soot as in your case as well.
My mechanic was out of town for a while and I took it to the dealership first, they said there was nothing wrong with it and just how direct injection was supposed to sound. Thankfully it was sorted out before real damage occurred.
Wow, my ignition coil looked like that and the spark plug failed at exactly the same point but on cylinder #3! luckily my mechanic was also able to figure it out! Thankfully none of the ceramic shattered for me and went inside the engine. I know the Bosch plugs and Mercedes Branded plugs are all the same, never expected this failure to happen so commonly from them.
Last edited by Geep 250GD; Feb 16, 2024 at 05:13 PM.
Wow, my ignition coil looked like that and the spark plug failed at exactly the same point but on cylinder #3! luckily my mechanic was also able to figure it out! Thankfully none of the ceramic shattered for me and went inside the engine. I know the Bosch plugs and Mercedes Branded plugs are all the same, never expected this failure to happen so commonly from them.
This engine cracking plugs is strange, perhaps this is caused by repeated thermal shocks.
Could better engine cooling decrease heat failures ?
A better oil selection wouldn't hurt. Increased coolant circulation either.
Last edited by CaliBenzDriver; Feb 17, 2024 at 04:35 AM.
2015 SL400 (M276 Turbo), 2014 C350 Sport (M276 NA), 2004 SL500 (M113), 2004 Audi TT225 (BEA)
Originally Posted by 2015-E350-Wagon
And my dealer told me that the bearings were bad and gave me a $53,000 engine replacement estimate. Clearly I took it for second opinion?
LOL! I have an engine for you already installed in my car for that price. Sounds like they don't want you as a customer. What'd you do? Eat all the cookies and donuts in the waiting area?
This engine cracking plugs is strange, perhaps this is caused by repeated thermal shocks.
Could better engine cooling decrease heat failures ?
A better oil selection wouldn't hurt. Increased coolant circulation either.
My mechanic ran mobil 1 5w 40 with liqui moly ceratec for my last oil change. This time he ran liqui moly engine flush with liqui moly molygen with ceratec, and hydraulic lifter additive for the service. I live in South Florida, so thermal shock is probably not it. The ceramic did not crack, it separated from the metal ring/threads. The ceramic was still in 1 piece. It is not due to bad oil or cooling.
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, as I replaced them usually ahead of time because I worry more
