I have just taken possession of my first Mercedes, a 2005 E320 CDI with 29k miles. I don’t beleive I have to tell any of you what a wonderful car it is. I am a little concerned, however, about the amount of noise it makes. I didn’t notice this in another CDI I drove. At idle and under moderate to heavy load it seems normal, but under light acceleration at low engine speed (when just starting out) it produces clatter reminiscent of a Dodge/Cummins pickup truck. It goes away as soon as the engine load or speed is increased or the engine returns to idle. The engine is at normal operating temperature. Is this normal?
Simple answer: Low cetane (Cn). Low cetane contributes to the noise levels of the CDI. The CDI is designed to run on 50 Cn or greater, most fuel in the US is around 40-45.
Prescription: Add some Power Service, The effective ingredient is 2-ethylhexyl nitrate (2EHN), 2 options:
Either product will result in improved Lubricity when used with even the worst US ULSD spec fuel (520 HFFR), using as little as 1.5 oz per tank will drop the HFFR rating to 400 thus complying with the optimum specification that Bosch requires for maximum diesel fuel system component life.
The regular Power service is great for winter if gelling is a concern where you live. Add 4-6 oz initially, tapering down to 2 oz per tank there after. Any more than 6 oz will not have any further impact on the Cn rating of your fuel with a 20 gallon tank.
Higher noise from your engine occurs as the ECU cycles in and out of a mode that introduces 2 injection events per combustions stroke. The first injection is called "Pilot Injection" the second "Primary injection".
Pilot injection is used to dampen the pressure rise of the expanding gasses in the cylinder, by breaking up the combustion into two phases the noise is reduced by virtue of the smoother rise in cylinder pressure resulting in greatly reduced diesel knock.
I would start with your fuel source. Fuel that has a low cetane rating causes the fuel to have a greater "Ignition Delay" tranlated it takes longer for the fuel to ignite this causes the time between ignition of the fuel to be reduced causing significantly higher noise output, yes like an old non common rail Cummins.
Another aspect that may be affecting your situation is cold weather. In colder weather due to emissions, timing is advanced causing autoignition to occur at a point where the highest cylinder pressures are generated during light to moderate loads on the motor, The amount of advance takes into account ignition delay with 50Cn fuel so lower Cn ratings will greatly increase the noise levels. High cylinder pressure and low cetane combined increase the noise level from the motor.
With only 29K on the car I suspect you are simply hearing the result of the colder weather.
FYI, I have no affiliation with Power Service...
DB
Last edited by drivbiwire : 12-11-2006 at 01:55 AM.
I'm a recent owner of a 2006 E320 CDI. I think, I've heard heavier clatter noice as well, probably like what you described. I think it happens occationally during the gear shifting at light throttle.
I'm still trying to adjust to what's normal and what's not in this car, specially the way the transmission shifts - at times, it was almost feels like free wheeling for a fraction of a second (slow in between gear shifting). Let me know if yours drive like that.
[quote=drivbiwire]Simple answer: Low cetane (Cn). Low cetane contributes to the noise levels of the CDI. The CDI is designed to run on 50 Cn or greater, most fuel in the US is around 40-45.
Many thanks for the complete and informative answer – what you wrote makes perfect sense. We live in California , SF Bay area; the air temperature was about 45-50 degrees when I first noticed it and it was the same today at around 60. The fuel in the tank is what was in the car when I bought it (from out of state). Maybe the local fuel will be better. I'm trying to find a local source for the Diesel Kleen +Cetane Boost – haven't found it yet. What do you think of the other diesel fuel additives, such as Red Line 85 Plus, Schaeffers Diesel Treat, FPPF Cetane Improver, Berryman Diesel Cetane Booster or Gunk Diesel Milemax, all of which claim to do the same thing?
The sound doesn't bother me - I rather like it - I just want to make sure there isn't a problem, after hearing so much about how much quieter the CDI is than the older cars (which indeed it is).
Good answer except for introduction of "lubricity" which has nothing to do with it and is a nonissue in any event.
Lubricity is an issue with ULSD. The current specification calls for a maximum of 520mµ HFFR rating. Bosch specifies a maximum of 400mµ HFFR. Given the higher pressures of modern diesel systems (23,500 for the CDI soon to be 37,500) lubricity along with proper filtration will ultimately determine component life.
As the fuel system ages, the nozzles and needles will wear. The amount of wear will be determined again by filtration and lubricity of the fuel.
Loud combustion can be associated with nozzles in poor condition which is why the mileage of the car is of significance here.
The addition of some Power Service during filling covers the owner(s) on multiple levels that all lead to greater component life and significantly lower costs of ownership later on down the line.
Our work with high pressure line feeds (35,000 psi) supports what DBW reports. Filtration was a key factor in component life, and additives (Power Service) helped substantially.
Our work was centered on the Cummings engine fond in Dodge products, wth a much higher pump pressure and cylinder head design, increasing horsepower to +600 HP. The principle is the same, different engines yet same school of thought.
On a side note, wear to injectors at these pressures can have severe wear related problems with the pistons as well. Early examples actually blew holes in the pistons.
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I tried using different brands of fuel, and it seems to be a little different with each one, but not dramatically different. I have used Power Service in various concentrations, and while it seems to quiet combustion noise in general, the noise is still very much present. Maybe I can do a better job of describing it.
When the engine is cold, all seems to be normal. As the engines warms, the abnormal (what I think is abnormal) noise gradually begins to appear, getting more pronounced as the temperature increases, and worst at normal operating temperature (halfway up the gauge). At idle up to light throttle, normal. At medium-heavy throttle, normal. Just past light throttle, the rattling begins, and occurs in a narrow throttle range, but this the range where most of usual driving occurs.
I just can’t believe that the noise my car makes is normal. In the three months since my first post I have been to the dealership three times. The first time, they found a rattle in the catalytic converter, and replaced it. The second time, they changed all the fuel injectors. The mechanic said he heard nailing, and after the injectors were replaced, they said it was fixed. Well, one of the cylinders *was* a little louder than the others, and now they are all pretty much the same, but it didn’t change the basic nature of the abnormal noise.
The third time the dealership they identified a loose baffle in the left muffler, which they had to order. When it arrived and they put it on, they discovered that the design of the mounting bracket on the back was changed, so now they have to change the right muffler to match. I never heard the rattle from the muffler, and since it has been replaced, the rattle from the engine has not changed.
I’m thinking about the EGR valve. Three times the engine has gotten into a oscillating “surge mode” at low speed/light throttle, but I cannot duplicate it at will. It also misses a little at light throttle, and this goes away after a few rounds of heavy acceleration, as though the EGR passageways are being cleared of soot. I also have considered the MAF sensor. There is smoke from the exhaust at full throttle, but I can only see it at night in the headlights of cars following me. It must smell pretty bad because they slow down to increase their following distance.
I made an mp3 file of how it sounds with the microphones in the engine compartment, with brake on, transmission in drive. I can’t post attachments yet but you can download it here: FilePlace Free File Hosting. Sorry for the long post, but this is really driving me nuts – and I can’t find another CDI to compare mine with. There are very few in California. Anybody in the San Jose area with an E320 CDI? Any advice and opinion will be greatly appreciated.
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