Dear All,

I would like to solve a starting issue with injectors in my E350 CDI. I'm interested in the details of the problem and I'd like to understand the reasons behind them.

Vehicle details:

• Mercedes-Benz E350CDI 4MATIC BlueEfficiency (S212 Estate)
• 2011 model year
• OM642.858 engine
• 270'000km (~168'000miles)

Symptoms:

• Clearly audible diesel knocking sound when engine is cold
• Barely audible diesel knocking sound when engine is warm between 1500-2000rpm
• No misfire/judder, performance or consumption issue (Avg: 6.5L/100km)

Performed tests:

• Compression test: TBD (I understand it's required to give corrections any sense, so I'll post the updates)
• Quantity correction values of smooth running control
  • 
    
• Visual inspection
  • No sign of residue/leak around injectors
• Mechanical inspection
  • Oil and filters has been changed recently and no metal chips were visible

Hypothesis:

• My general understanding on diesel injector issues
  • Misfire/judder: caused by lack of fuel --> stuck/dirty injector --> injector is under-fueling
    • If there are no mechanical issues with the pistons, valves
  • Knocking: caused by bad injection timing --> worn/leaky injector --> injector is over-fueling
    • If there are no mechanical issues with the bearings, rods
• My general understanding on quantity correction (Xentry)
  • The calculated quantity of additional fuel required to maintain smooth running (to get a proportionally equal torque delivery from the cylinders)
  • As we are talking about injectors in the same system, one injector might be balancing out torque delivery issues caused by other ones
    • Positive values: more fuel (torque) is required --> injector is under-fueling
    • Negative values: less fuel (torque) is required --> injector is over-fueling
• Based on my understandings and measurements
  • High positive values --> more fuel required --> under-fueling injector --> stuck/dirty injector --> misfire/judder
    • Cylinder 6, but there is no misfire/judder
  • High negative values --> less fuel required --> over-fueling injector --> worn/leaky injector --> knocking sound
    • Cylinder 3

Actions I would make:

• Change injector on Cylinder 3

Questions:

• Can someone suggest whether my hypothesis is valid or not?
• Can someone suggest whether changing injector on Cylinder 3 is an appropriate action to solve the issue?

Thank you very much in advance!

 

Do a compression test before final conclusions.
I never had to go that far, but injector leak test seems to be pretty popular.
270k km is not high mileage for injectors, but since you are having trouble, I would consider replacing all of them.
Having roots in Poland, I can get rebuild, certified injector for $110, so it would not be a big deal for me.

 

I appreciate the time and effort you took to collect data and deduce a hypothesis-------I would suggest that spend an equal amount of time researching "injector quantity correction and ohms tests" then you may want to revise your data and hypothesis

 

Thank you for your suggestions!

• Regarding changing all injectors
  • If I cannot figure out what's the issue, I will change them all. But currently I'm interested in finding out the cause.
• Regarding resistance measurement
  • I'll definitely do that. I remember on VAG vehicles VCDS can even display capacitance which is useful for piezzo injector fault finding.
• Unfortunately I did not have the time to do the compression test so that's still among the todos.
• Meanwhile I checked after a cold start where the knocking is coming and it seems to be on the left side (facing front) which includes cylinder number 1-2-3 so it's a usefuly info
• I also checked rolling out the car from 2000rpm to 1000rpm and the knocking is not audible so the sound seems to be audible during injection

 

Hi
I got same issue!
Can you please let as know ,what was the problem?

Regards
K Dimitrov

 

Hello,
After my last post I've done the following:

• Did a compression test with Xentry where everything was OK
• Tested HPFP pressure regulating valves
• Started to replace injectors one-by-one
  • Ordered a refurbished one, replaced one, brought to the local bosch mechanic for measuerement (replaced if bad, installed if good)
• Meanhwile I had to replace the crankshaft sensor and cleaned the camsaft sensor because the ECU did not update the learned correction values
• Currently there is no audible knocking

Lessons learned:

• Compressions test will likely to tell you if there is an issue with your pistons or injector sealings
• Quantity correction can only tell you the bad injector if it's extremely bad
  • One injector had to be cleaned and new IMA was generated by the bosch test-bench
    • There was no sign in the corrections
  • One injector had to be replaced because the resistance under load was out of specs (starting piezzo failure)
    • There was no sign in the corrections
  • The ECU is quite smart and it will balance out the incorrectness of the bad injectors
• If doing the job for yourself, I would suggest replacing the injectors one-by-one
  • When replacing all at a time, it is horrible to bleed to complete system
  • Replacing only one at a time: car will start within 5-6s
• The ECU will only learn adaptations under certain conditions
  • Rpm is in range 1300-3000rpm
  • Decelerating
  • Oil temperature is over 80C
  • Fuel temperature is between 30C and 50C
• Make sure about your engine variant because there are updated ones
  • For example mine is 642.858 which is the updated LS DE30 LA
  • It needs different injectors, washers

When I will have time I can provide a guide on how I've done the replacement.

 

Thank you very much for all information!
Can you check please the attached file to check if the knocking was the same!

 

Can't you shut off individual injectors with Xentry to see if one of them is the problem?

 

I will try this weekend .The sound appears and disappears. It is not constant. There are no traces of metal in the oil filter.

Thanks

 

Whats your VIN

 

4JG1668241A507649

 

Thanks for the VIN.
Within WIS I could not find any injector or ECU corrective actions requiring and update to your VIN
After listening to your sound attachment, It is my opinion that the sound is not injector related and that can be corroborated by you taking a sound probe on the pump and injectors or wherever you believe the sound is coming from to locate the source

 

That is the vacuum pump. It is located right in front of the oil cap and has a plastic line running over to the brake booster. Your seal inside the crappy plastic push-on connector is leaking air.

 

Just changed my oil so I thought I’d show you where the sound is coming from. If you want to exchange contact info I can send a much longer video. Engine has about 250k miles on it. If the oil cap was on it would have sounded just like yours. It’s a spring diaphragm vac pump so if it is holding vacuum the lobe that drives the lever just bumps it a touch and makes that knocking sound. Same as the old 616, 617, 606’s that I have had. First run in with that noise scared the mess out of me too.