Trelos

Can someone post a walk-through on how to replace the high-pressure fuel pump on the M276
I know how to remove the intake manifold that’s not a problem I’ve done it before I just need to know if there’s anything special about the high pressure fuel pump I should know about. Or is it just unbolt and replace?
i’ve been getting an intermittent code and rough idle about the High pressure fuel sensor short-circuiting to ground.
it’s a cheap part and if I’m going to take that apart I might as well throw in a new Bosch high-pressure fuel pump because it’s about $350 on FCP Euro

chassis

User @S-Prihadi has a detailed M276 3.0 TT refurbishment thread. I think in the W212 section. It doesn't specifically say how to remove the fuel pump but you will get a feel for this engine. You have the 3.5L NA engine, which in principal is similar but there are differences. I haven't seen anyone on this site remove or replace an M276 fuel pump. Torque specs, single-use fasteners and finely machined close-tolerance parts are something to be careful of with this project.

CERNICALO1

See this video for reference of how to get to, and remove the pump:

You Tube

I have just performed the PCV Valve parts replacement, which is a major pain in the neck requiring the partial removal of the High Pressure Fuel Pump. Unfortunately, my GLK350 (M276 NA) will not start immediately after "finishing" work. The engine turns over, and even seems to spark for a second, but never idles. I have a feeling I am missing a step for either resetting a fuel cut-off switch, or purging air from the fuel line. Please help with any suggestions of how to move forward.

Fuel Rail Pressure while cranking: 202 psi
Picture from Carly App Screen (Do not get Carly, it sucks for most of the things needed)
https://photos.app.*******/mdFCMaHNiSenTKDT8

Fuel Rail Pressure while idling: 2164 psi (Taken prior to start of work)
https://photos.app.*******/hZB7VneNWuBpsFry9

Trelos

Think I’ll just do the sensor that’s causing the issue then. Thanks for the replies

CERNICALO1

Thank you all for the replies. I found the issue that caused my earlier question, but I now have another issue and still need your help.

Unfortunately (for me), at some point while I had the HP Fuel Pump housing slightly off the camshaft, so I could install the new PCV valve, the follower which pushes the pump fell off. Let's just say it took me a couple of hours to find it in a nook behind the engine, and then retrieve it. I mounted it the way it can (roller towards the camshaft, alignment pin in the housing groove). However, although the engine started, and has ran fine for a couple of hundred miles, it has a noticeable knocking sound which I have confirmed coming from the HP Fuel Pump area (via Mechanic's Stethoscope)

If anyone could help with an exploded view of the M276 HP Fuel Pump and its housing, hopefully including the follower and any possible cushioning part I may still be missing, it would be very appreciated. I would also take any additional input which may help me understand what is going on.

Thanks again

CERNICALO1

Adding diagrams I have been able to find, in case it helps the case.

Does anyone have any experience with the HPFP and its Housing knocking after reassembly? Roller shown with Up/Down arrows is what pushes the HPFP. Thank you,

https://photos.app.*******/9a3wQFM2APV5s5EW7

https://photos.app.*******/G5zGzcHRQUJCjpk29

CERNICALO1

Just an update in case it helps anyone else.

I purchased a new High Pressure Fuel Pump , the roller which actuates it as it follows the camshaft cam, and the housing at the end of the camshaft, + a new PCV valve. Reassembled the whole thing with all the care in the world.....and I still have almost exactly the same knocking of the engine. A mechanics stethoscope confirm the issue is in the area of the HPFP.

Did not see any signs of issues in the parts removed. Will wait 6K miles until my next oil change, and will analyze the oil as I usually do, but will take a close look at wear metals.
Could there be a required assembly sequence?..I do not see why for these small pieces, which are clearly hub centric, and tolerance for their intrinsic slop.


If anyone has any insight into what may be happening, please enlighten me. Thank you

chassis

How many miles are on the GLK350?

CERNICALO1

Only 89K. The initial plan was to change the PCV Valve, because I saw oil in the Air Filter cavity.

chassis

You’re sure the sound is not timing chain, tensioner or check valve related?

CERNICALO1

Many thanks for your reply, Chassis.

I have not detected any related noises in the Timing Chains (3), or the belt tensioner, but I will check once again with my Stethoscope. However, I am not sure what you mean by "Check Valve"; would you please help me with a bit more information.

I did not mention it earlier, but the first time I opened the area, I also changed the "Drip Pan", which is what I think of as an oil slinger. It is mouted at the rear end of the outboard passenger side camshaft, and it is the part the PCV valve actually mates to at its center. I verified is was still properly fastened during my last foray into the area.

Looking forward to info about the Check Valve. Thanks again

chassis

Timing chain tensioner check valve. https://mbworld.org/forums/w212-amg/...ck-valves.html

I don't recall seeing any M276 HPFP failures posted on this site, besides this thread. There are other, less expensive and time consuming potential issues to check for.

CERNICALO1

Once again, thank you very much for the information.

Today I spent some time searching around the engine with the stethoscope. I tried at 1000, 1500, and 2000 RPM, and never noticed anything strange in any other part of the engine away from the HPFP, where I can hear ("feel") the knocking. Given my recent learning about the oil check valve near the timing chain tensioner, I am possibly not able to envision how the knocking in question is coming from this area, but I actually "feel" more inclined to believe one of these two following actions is what caused my issue (although I still do not know what it is):

1- I royally screwed up, and reassembled the whole engine the first time, without realizing that the roller which actually pusher the HPFP from the camshaft had fallen out on me, and I attempted to crank the engine over 6 or 7 times. What could have been damaged because the roller was missing?
I have confirmed that the HPFP spring could not make contact with the camshaft cam, but perhaps oil flowed where it wasn't supposed to. I see oil passages in the HPFP roller housing.

2 - When I replaced the "Cylindrical Part" at the rear end of the PCV camshaft (MB: Drip Pan), I loosened, and at the end tightened the bolt which fastens this part to the camshaft, relying on the timing chain to keep the camshaft in place....There was no movement of the camshaft as far as I could tell, but could something have gotten damaged in the head assembly because of this "Back, then Forward" torque?

Again, the noise seems to come from the HPFP area, but I am completely open to other suggestions from anyone well familiar with the M276 or 278 engines. In the meantime, I will keep my hear to the ground (engine), and will provide update here if I can diagnose, or solve the issue.

Any other info or help perhaps pointing me in the correct direction would be much appreciated.

Msnrasool

Do you have any uodate on the issue. My GL with M278 make same noise with warm engine. Local Mercedes dealer confirm its HPFP piston noise. Another local german shop pointed to the same issue. I am planning to replace both pump myself.

Jamal

CERNICALO1

In part, I have been expecting others to have the same issue shortly after they attempt to replace their PCV systems, but I am sorry you are now another statistic too.

Unfortunately, I have not been able to completely diagnose the issue, which is still present. I did reach the next oil change interval (6K after issue start), and performed the oil analysis as usual; the results do not show a major issue (Crank/Rod bearing wear), but may be indicative of a steel part wearing, see picture at link below. I have considered adding oil additives to hopefully address a stuck hydraulic lifter, but have not found any convincing options. Next step will be to visit local non-dealer MB expert, if he is agreeable to let me be part of the diagnostic.

https://photos.app.*******/Uip4VmN7pw8xNHmB7

Please let us know how you approach your case, and if you find any culprits. I have a feeling the HPFP requires specific steps in the installation, which are not disclosed to the general public.

chassis

If you are willing to go to the next level of diagnosis, photograph the intake valves by removing the intake manifold. This could be done at the same time as spark plug replacement. Use an endoscope to take well lit and clearly focused photos of the intake valves to see if there are heavy deposits, especially in the area of the HPFP.

Msnrasool

Just for a record, I have 2014 GL450, M278 engine with 114K miles. I have own this car about 7 months and drove little over 7k since purchase. For me this ticking noise started/noticed about a month ago and my first reaction was camshaft adjuster, tentioner or an issue within valve area. I have taken the car to a local Mercedes dealer and they came back with nothing wrong with the adjuster, tentioner or valve area but a piston noise of HPFP. They told me I don't need to change or do anything as this is a known issue to MBUSA. This told me they have compare thiis noise with one of their loaner vehicleI and that car has same ticking/noise. I have asked if replacing the pump will help and was told that noise may still.be there after replacing pump but may toned down little.

For 2nd opnion, I Have taken the car to a reputable german car works, that been in business for 50+ year. They pointed the noise to HPFP area too and ruled out adjuster tentioner valve etc as opening the oil cap when running didn't change the noise intencity. Since M278 has 2 pumps, they weren't sure which one is bad as they need to take it apart.

I have put stethoscope on both banks around adjuster area, valve cover and don't notice anything different between both side. However when I put it on one of the fuel line from driver side HPFP, there is mental hitting noise. Intensity of that noise is less on passenger side HPFP fuel line.

i have no misfore at idle or during drive, HPFP pressure is within the specified range at idle and in drive and goes all they way up to 176 bar. No other code for any sort in any module.

I have ordered both Bosch pumps, tappet rollers, and new fastners. I.am thinking this noise came for a reason as it wasn't there before. So let's see.....

Jamal

CERNICALO1

Remember changing the tappet roller housing is recommended. I did, along with all the parts you have in mind, noise still persisted.

CERNICALO1

Thanks for replying. I did not take any decent pictures of the top of the valves when I have had the manifold off, but do remember them looking dirty for a 89K mile vehicle; I assumed that was the price of direct injection and not having the intake mixed air cleaning them. Anyhow, my noise started exactly when I took the system apart to replace the PCV Cover

I am not sure the picture was visible for all on my previous post. So I have attached here via site album.

Msnrasool

You mean where roller sit and pumps are bolted onto? i belive that is the housing part that go on the cam lobes. We are not alone, there is another fella who rebuild the entire engine and hearing the same noise. I am rethinking if replacing pump will.solve noise issue

Mercedes dealer gave me the attatched doc at diagnostic appointment.

Msnrasool

I have pumps and tappet rollers at hand but no housing. i haven't started the job primarily because you are the 2nd person that say it didn't work and noise is still there. Yesterday I have received a exhaust valve warrenty extention letter from MBUSA that says warranty has been extended to 12 years or 120,000 miles. I am going to check with dealer and see what they have to say..

CERNICALO1

As much as I would like to find data regarding a solution to this issue, which would require others to perform work in the area in question, I would suggest you to hold still until a more definitive diagnosis is revealed. Also, the MB document you posted earlier may be referencing the NORMAL pinging and clapping these engines make (like a low diesel engine rumble), due to their HPFP in normal operation - you can confirm by comparing to lower mileage vehicle without any work done to HPFP (OR PCV Valve components).
-Note, the sound in my vehicle is a (light) knock, knock, knock sound which is heard more from the cabin than outside the vehicle - although the noise definitely comes from the engine and follows "engine speed" (Valve?/Crank?/Spark? - cannot tell), and I have traced it with a stethoscope same as you.
--I have deduced there is a spring element involved, because even after 6K miles, it has not diminished - If there had been a definite interference (e.g., Spark-Plug/Piston, or Valve/Piston), one of the parts would deform, and the knocking would subside --- and major misfire would ensue, which has not happened at all in my vehicle.--- HOWEVER, I did notice engine lost about 80% of a quart of oil in 7K Miles, which was never the case before I worked on the PCV-HPFP area.

See Pics Below:

Saddest of all for me, after all the work to replace the PCV system components, which is what got me in the jam of removing HPFP, I still found traces of oil in the Air Filter box only 6K miles later:

Oil in Engine Air Filter Box


Just in case it makes any difference to anyone working on this issue, please also note, my engine (276) seems to have had the oil check valves in stalled (blue head bolts indicators [Factory?, 2015 model year]), and when the oil filter is removed, it takes about 20 minutes for the oil in its basin to drain to the oil pan - I drain oil by the bottom at every oil change (please do not start debate about this practice).


Lastly, I have always used the exact same filter MB sells for the vehicle, although I purchased it directly from manufacturer and before MB stamp is placed on it.

chassis

Blue paint on the cylinder head front cover screws is factory.

MoMoney-MoMods

@CERNICALO1 Has this been figured out yet? I have to replace my PCV (crankcase vent) and oil centrifuge on my M276 engine that has 10 years and 120k miles and was planning to just also replace the HPFP and Tapit while I was in there, but your story about a newly created knocking noise has me concerned. Could it be the new pump has a firmer spring still compared to the worn spring of the existing pump and will soften/quite with time? I was going to buy the same Bosch pump from FCP Euro as I'm sure you did.

Out of curiosity did you follow the extra steps from WIS where they warn can cause issues if you don't?
Did you make sure your engine was on cylinder 1 at 40 degrees after top dead center so the cam lobe was flat to the fuel pump before working on it?
Did you remove and install the fuel pump by alternating the bolts 1/2 turns each so it comes out flat?
Did you prime the fuel pump for 5 sec before trying to start engine?
Did you follow the tightening sequence and torque spec of the pump and housing?

Attached are some docs on the install and there seems to be lots of opportunity to miss something and potentially cause an issue. Maybe these can help pinpoint what went wrong.

CERNICALO1

First of all, thank you for the documents included in your post. Although I did not have such information available either time I removed the HP Pump/Tappet/Housing assembly, I did follow a sequence of removal/reassembly somewhat similar - but I did not align the camshaft, because I deduced that an installation of the Pump bolts in minor alternating steps would cause the spring to compress with proper alignment.

Unfortunately, the short answer is that I have not been able to absolutely diagnose, and then correct my knocking sound. However........, I do have more data that has given me a clue.
1-I have reached the next oil change interval (9K Miles), and confirmed oil analysis shows no extraordinary metal wear.
2-I have compared another vehicle with less miles has the same sound (actually feel) in the pump area, felt with a Mechanics Stethoscope.
3-Upon taking my vehicle to a local recommended Mercedes specialist, his take was that the only issues he saw with the car where "completely worn out engine mounts, and perhaps a related exhaust leak due to exhaust system related misalignment". * This latter comment caught my attention, because I have heard engines emit a similar "knock" to mine, because of exhaust manifold/pipe connection minor leaks. So I replaced both engine mounts, and transmission mount, and released any stress in exhaust piping (except at the exhaust manifold/pipe connection); exhaust tone did return to factory quietness (it has been a bit on the throaty end of the spectrum). Then I used a Medical Stethoscope (with the diaphragm removed), and searched for the knocking sound (not feel) while the engine was loaded at 1500RPM - I could not find the actual knocking sound in the area of the HP Pump...but did find it in the area of the driver's side exhaust manifold. Dealer confirmed there is no Lead Doughnut at this location, and I have not had the time to loosen, then retighten the bolts in an attempt to relief stress at this joint. I also have not had the time to search for a possible crack of either the manifold, or the exhaust pipe in this area. It is relevant to me that the vehicle works fine in all other regards (i.e., no codes, misfires, loss of fuel efficiency, etc.).

So, my two cents about the M276 PCV system maintenance for all other owners: Unless you have an actual issue of direct intake manifold (negative) pressure affecting the crankcase cavity of the engine, do not mess with replacing the elements of this system, because Mercedes royally screwed up the 272->276 design update, and left the PCV system in a location that requires removal of the HP fuel pump so service it, which is a pain in the rear. I have resigned myself to cleaning the little bit of oil deposited in the Air Filter cavity (see above), at each oil change interval. Best of luck!