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:
Diesel Kleen (Silver Bottle / 4 Cn increase)
http://www.powerservice.com/dieselkleen_cetane.asp
or
Power Service (White Bottle / 2 Cn increase + Anti Gel)
http://www.powerservice.com/dieselfu...etaneboost.asp
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
