Please forgive my ignorance. Are the CDIs mechanically injected with an injection pump or do they rely on electronic fuel injectors?
Why do they make so much more power than the old diesels and even some of the new gas engines?

These are "Common Rail" injection engines. This means that there is a rail that supplies fuel at the same pressure to the top of all injectors. The bottom of the injectors are exposed to the combustion chambers. The injector is actuated electrically to act as a valve between the pressurized fuel in the rail and the nozzle into the combustion chamber.

This is much like a modern EFI system except that the fuel is injected directly into the combustion chamber rather than the intake air stream.

Most all modern diesels operate this way. The old mechanical injection pumps are pretty much a thing of the past.

There are numerous reasons for more power. It's just due to the advancing technology that allows the engines to draw more air which allows more fuel to be injected without causing excessive combustion chamber heat.

Some of the reasons for more air are; four valves/cylinder, turbo chargers, resonant intake systems etc.

Also these engines are direct inject. This means that there is no precombustion chamber. I don't know the exact advantage that is derived from this, but I expect that it has to do with more even flame propogation which prevents hot spots, thus allowing more combustion within the chamber.

Hope this helps,

I'm no expert, but part of it is the ultra high pressure injectors, 30,000 psi on some new diesels!

240dnewbie,

Aren't you off by a factor of 10 on the fuel pressure?

P E H

hotskillet, CDI means compression engine direct injection. LarryBible hit most of the high points for the computerized version. They seem to make more power because the computer is in control. The computer changes the air rate, fuel rate, and timing to meet the changing loads on the engine, and this results in your perception of more power. All this happens on the old engines too (except timing), but the computer can change things faster. No prechamber helps response time too - some of the American manufacturers went to computer control before changing to direct injection, with mixed results. 240dnewbie is talking about the solution to the early common rail problems of the rail not pushing enough fuel fast enough to get past the injector electric solenoid before it closes. Today the challenge is an absolutely flat torque curve and a straight hp curve from idle to redline and simultaneously controlling emissions. They're almost there on that one, too. The only drawbacks to CDI are cold starting (need glow plugs to stay on a while) and the fact that you're dead if the electronics fail in any way.

Here's a dirty little secret I learned while testing emissions on modern gassers: the computer shuts off the emission control scheme for a heavy acceleration event, then turns it back on when the engine catches up to the load demand. The people who paid for the testing have enough clout to make a stink about it, but not as much as the big automakers and the oil companies.
Sorry about the puns.

__________________
daBenz - 1970 220D

Fuel pressure in the common rail is NOT off by a factor of ten. I believe the 05 Sprinters are pushing 25,000psi. (At least the info on the Yahoo Sprinter list confirms these pressures)

__________________
1977 300d 70k--sold 08
1985 300TD 185k+
1984 307d 126k--sold 8/03
1985 409d 65k--sold 06
1984 300SD 315k--daughter's car
1979 300SD 122k--sold 2/11
1999 Fuso FG Expedition Camper
1993 GMC Sierra 6.5 TD 4x4
1982 Bluebird Wanderlodge CAT 3208--Sold 2/13

Kerry,

25,000 seems awful high. Must be a rugged fuel pump to make that type of pressure. Are you sure its in PSi and not pascals?

P E H

I've heard that 25,000 PSI is correct. This kinda of pressure allows the fuel to fully atomize the fuel, this means lower emissions.

I'm really excited about the CDI engines, I just can't understand why MB did not bring them in years ago. Most of the people on this list are going to have to wait 10-15 years to get their hands on one.

Here's a link to an article about the new US E320CDI. Says the fuel pressure is 23,000psi.

http://www.kfvs12.com/Global/story.asp?S=1721153

__________________
1977 300d 70k--sold 08
1985 300TD 185k+
1984 307d 126k--sold 8/03
1985 409d 65k--sold 06
1984 300SD 315k--daughter's car
1979 300SD 122k--sold 2/11
1999 Fuso FG Expedition Camper
1993 GMC Sierra 6.5 TD 4x4
1982 Bluebird Wanderlodge CAT 3208--Sold 2/13

Tim,

10 to 15 years: or never. I don't like anything I can't repair myself.

One little electrical problem and the CDI is dead and its tow truck time. What if the nearest dealer is hundreds of miles away? Or a thousand like when I was in Alaska?

What I hear of the newer MB, they are not too reliable now. What will they be like in 10-15 years?

P E H

PEH:
The Sprinter list at Yahoo has a lot of happy owners and they are all CDI engines. One person had over 300k on his motor before the van was totalled. There have been problems with the EGR on Sprinters. I think the new EGR on the 05's is water cooled.
Yes, there are electronic issues but surely the wily frugality of PEH will result in alternative fixes like carrying a spare computer from a junkyard vehicle??

Although your point about Alaska is well taken. Last week there was a post from a Sprinter owner deep in Mexico with electronic problems, looking for a quick fix to get home. Someone came up with an EGR bypass process. I don't know if it worked or not.

__________________
1977 300d 70k--sold 08
1985 300TD 185k+
1984 307d 126k--sold 8/03
1985 409d 65k--sold 06
1984 300SD 315k--daughter's car
1979 300SD 122k--sold 2/11
1999 Fuso FG Expedition Camper
1993 GMC Sierra 6.5 TD 4x4
1982 Bluebird Wanderlodge CAT 3208--Sold 2/13

Kerry,

OK I concede on the 25,000PSI.

Possibly its needed because of the double injection where a small amount of fuel is injected and the full charge injected slightly later.

P E H

That answers my question. It seems almost like these new diesels are like gassers without the spark plug. My feeling is that what they make up for in performance, efficiency and sophistication they lose the "character" of the old diesels that initially sparked our interest. Then again, this technology makes a strong case for diesels. I see that some of the CDIs actually outperform their gas counterparts with the same displacement.

Isn't the VW toureg going to be introduced with an immensely powerful TDI in the US market? I love my Golf TDI which has only 1/4 of the power of the Touregs'.

The '04 TDIs use pumpe deuse injection, with a individual cam-actuated injection pumps at each cylinder, which put out 30,000 psi.

__________________
'91 300D 2.5 Turbo 330K
'00 VW TDI Golf, 190K
'67 BMW R50/2
'73 Norton Commando Interstate

The technology that International ( and Ford ) is working on, uses the high pressures already present in the injection system to allow the computer to also control individual valve timing event. No camshaft to have to spin. They already ran such an engine up Pikes Peak a couple of years ago.