Hey everyone...

So I consider myself as a sort of amateur DIY kind of guy, but I ran into something which I thought many of you may be able to chime in to steer me in the right direction.

I bought a 2010 E350 with approx 68k miles on it a few months back. Currently it has about 74k miles on it, and not knowing if the spark plugs were previously changed or not, I decided to go ahead and change them out anyway.

I replaced the plugs with the ones listed in the owner's manual (Bosch Y7MPP33). Even though they came pre-gapped, I checked the gap on them and they were all to spec (0.031). I also torqued them to the specified torque (17 ft lb). I kept the same coils and did not change them.

The job seemed to be straight forward. Then when I turned the car on, I heard an odd noise at idle. Seems to be a tapping noise? (My friend said the car now sounds like the older MB diesels.) The car didn't have this noise before.

I tried to capture it in the video which I have posted here:


The noise is a steady noise. It's not really loud, but clearly audible. There are no check engine lights. Car runs fine with no loss of power. The noise doesn't increase with increases in RPM either. It's only audible when the car is in idle (even when in Park, Drive, Reverse, and Neutral).

I thought maybe the new plugs were bad and swapped the new ones out for the old ones and I am still having the same problem.

Wondering if anyone may have some idea what I should look into? Should I have also swapped out the coils when I changed the plugs?

Thanks in advance!

 

well, obviously it is not the plugs.

In my car the engine cover/air box is held in place with four big clamps that go over "*****" mounted on the engine. It is easy to install the cover not getting one of the clamps on fire wall side in place correctly. This could cause the box to vibrate and make noise at clamp when the engine is on idle and engine shake normally is the worst. Should be easy just to put weight on the box at each corner while on idle to see if it helps. Also make sure the metal wire holder is in place correctly behind the box by the fire wall.

 

Thanks for your reply!

I checked it out and everything was in secure and tight. Put weight in it too and no luck either. This issue is really busting my head...hahaha

 

Sounds like a top fuel dragster. LOL I have no clue what that may be if it isn't running up or down with RPM. I hope you figure it out without a lot of extra effort.

 

If the noise doesn’t increase/decrease with RPM’s I’d look into whatever under the hood has a constant speed. Radiator cooling fan? You may have bumped it just enough while changing the plugs so it’s hitting the shroud or something’s hitting it. You only hear it at idle because any higher RPM drowns out the sound. Total WAG though. Good luck.

 

So the sound magically disappeared the other day...I'm guessing the car just wanted some attention? Haha....anyway, been driving around for a while and haven't heard it again. Still no clue where it came from, but I'm not complaining since it's gone (for now....).

Thanks for chiming in folks!

 

Hi mate, I recently changed my spark plugs and I also ran into the same problem! But few miles of driving later, the engine must’ve just wanted to wear into the new part lol

 

@PaulFM @Mistah Hassan have you folks figured out what was the cause? I just changed my spark plugs and coils and it's making a sound very similar to what's in the video and it's driving me insane!

 

When I changed my S550 plugs I had to index them as it is a DI engine. The washers had to be set for correct thickness for this and while doing this all I accidentally mounted one spark plug without the washer. It made sound like that. Luckily found it on the first plug as I went to check them all.

 

Another @kennyd video to the rescue.
Watch his video and do as he does. This is what @Arrie was talking about when he said he had to index his spark plugs. basically mercedes spark plugs all need to be pointing in the same direction (and in a certain direction). Just torquing the spark plugs to spec doesn't always achieve this result, so some extra work is needed.

 

It just is that this guy on the video erroneously claims that the plugs from dealer with MB logo are exactly the same as the Bosch plugs you can buy from elsewhere. THEY ARE NOT THE SAME.

In the picture below I have marked the end of the thread in the MB and regular plugs. Threads end in 90 degrees different location that makes the regular plugs stop 90 degrees short from the correct position just like it happens in the video.

And that is exactly the same what happened with my plugs. I had to sand the washers to 1.25-1.30 mm thickness to have plugs index correctly.

Also, the plugs ID is different. The MB plug starts “Z6S…” while the regular plug has “ZR6S…” with rest of it the same.

Other than this a great video to show how plug indexing is done.

 

Thank you for your answers. I will definitely have to get the car checked at another shop monday morning and check if the spark plugs have been installed correctly, which doesn't seem so. The guy who installed them works at Mercedes and has a small shop in his spare time so I thought he knew what he did. He did the procedure next to me. He didn't blow air/do any vacuuming in the spark plug sockets, and simply mounted them. As far as things go nothing mentioned about the gap or the index.

The engine in my scenario is a m274, the car is an e250 coupe facelift. I don't know if for the m274 you need to get the index right for the spark plugs, I found some mixed things on google, but I will keep looking into it. Unfortunately for me, when I changed the plugs I had no idea of all these things, or I wouldve mentioned them.

My problem is that after the sparks where mounted and we turned the car, the mechanic told me about that sound - the sound described by the OP as well - and that it doesn't sound ok, it sounds like a piston and I have to change the engine.

 

That's very odd for an M274 engine to do that after replacing spark plugs (and being torqued to the proper torque specs). On my M274 I've never actually had to index my spark plugs, and never wanted to for that matter. I just buy the plugs at Mercedes and torque them to 18 ft lbs. I just did this service like 3 weeks ago and no indexing was required (at least not on the M274 engine).

 

The m274 should be a direct injection engine and spark plugs correctly indexed but if you get plugs from the dealer you don’t need to do anything but just screw them in. They will index correctly.

If you use Bosch plugs from other sources you need to make sure they index correctly and they probably do not without washer adjustment.

It seems MB does not allow Bosch to make plugs correctly for people to be able to buy them much lower cost from other sources.

NGK does not have a problem with this so they may have correctly indexing plugs out the box. While searching about this issue for my plugs I read that NGK has plugs for the m278 engine that are made right so that is my next spark plugs make I will buy if I need to (hopefully) change plugs again.

 

I can tell you that spark plugs directly from MB do not index properly without adjustments. (atleast on my car they don't).

On my M274 E300, I have a specific thin walled socket used specifically for spark plugs only. I drew a line on the socket and start all of the plugs facing the same way, and the socket line pointing up towards North. when they bottom out and are torqued to the proper spec, none of the spark plugs, nor the socket ever point in the right direction (meaning the spark plugs aren't all pointing the right direction and all facing the same way). I've had to sand down the copper washers on my E300 before, but the last 2 times @ 90 & 120K miles I did spark plugs I didn't bother doing that because it honestly doesn't make any difference in my opinion. just wastes time doing the job. My E300 currently has 163,000 miles and I've done the spark plugs a total of 5 times already (every 30,000 miles).

The first 2 times I just hand tightened them down and torqued. @ 90K and 120K miles I indexed them properly, and @150,000 I just only torqued, no indexing. I am waiting for 180,000 miles to do my next spark plug service and will just be hand tightening them down and torquing to spec. No need for indexing.

As for AMG specific engines, i would highly suggest indexing them. MB or OE aftermarket, I would still double check.

 

Do the plugs you buy from the dealer have the MB logo on them?

 

If you're asking if OEM plugs that come in Mercedes branded boxes/packaging + the Mercedes price of OEM spark plugs, then yes, they are the MB original ones. I just did my spark plugs about 3 weeks ago and they have the blue star on the white part. They come pregapped but I always check that anyways, as they've come in the wrong measurement before.

 

This is a video of the sound that my car is making, the sounds starts around half (0:06). The plugs had the Mercedes sign, my only other concern beside being installed poorly is that I received these plugs when I bought the car from the previous owner and didn't check if they were precisely for c207 M274.

 

Honestly that sounds like every M274 engine i've ever heard. Maybe the video doesn't pick up what you're hearing, but that sounds fine to me. For a peace of mind, just buy four new MB spark plugs and torque them to 28Nm and call it a day. You're ignition coils are probably fine. You could buy new Bosch units (not MB ones) from FCP euro for really cheap. They are the exact same units that MB will sell you, but without an MB logo.

If you really want to be technical and sure, buy a leak down tester, do a compression test, and look at your cylinder walls with a borescope. Those three things will tell you everything you will need to know about your engines health.

 

Ok, quick update for whomever may find this useful in the future. I bought a "car stethoscope" and listened to the engine, around the spark plugs, coils, injection etc. The problem in my case was the High Pressure Fuel Pump (HPFC). When I put the stethoscope on the case of the pump the continuous tap tap tap noise was in my brains. Not entirely sure if that's normal, as I heard some folks saying it's normal for Mercedes, but I will change it just to be safe.

 

HPFP + Roller is a good maintenance candidate around 90 to 120 kMi. with the nearby PCV breather system.

 

car just hit 100k so I suppose it’s about time. What’s the roller you mentioned?

 

Is your pump keyed into the rear of intake camshaft instead over on top with a roller ??

 

it looks like in this image. It has that metal case on top.

 

here is the answer:
your HPFP is driven by camshaft lobes + ROLLER/follower.

red circle is pump lobes


4x 90° lobes here

The roller can develop a flat and stop rolling when needle bearings get contaminated - That is an incentive to keep clean fresh oil on 5kMi schedule.