Thread: E320 Cdi
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Old 01-10-2004, 06:02 PM
73MB280SEL 73MB280SEL is offline
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Join Date: Nov 2000
Location: Mustang, OK
Posts: 509

I have heard this before but I don't understand the advantage that TDI would have over CDI. The one main advantage that CDI has over other forms of Diesel injection is that the injection pressure (and thus atomization) is not a function of engine RPM. In the old style with a pump driven off of the timing chain/belt, at low engine RPM, you do not have enough injection pressure to completely atomize the fuel. At idle, older mechanical injection systems atomize fuel very poorly and thus the familiar Diesel knock.

Having the injection pressure more precisely controlled is the same advantage that electronic ignition has over the points system. The spark plug voltage varies with RPM on a breaker points ignition system whereas electronic ignition always applies the same voltage of spark.

Another CDI advantage over mechanical fuel injection is the ability to perform a pilot injection, though most electronically controlled injection systems (CDI or not) now do this.

What is it about the TDI injection system that you think is better? My understanding is that rotary pumps are the cheapest, MB inline style pumps are the best of the mechanical injection systems, and CDI (electronic) injection systems are the best. Most Domestic manufacturers of non CDI engines are the rotary types, for instance, and they are not know for being very durable.

What else, '73 MB 280 SEL (Lt Blue)
Daily driver: '84 190D 2.2 5 spd.
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