Some of you have seen my quest to get my 240D to 40 MPG, highway, and I am wondering if I haven't found the reason why most of these cars are not getting the mileage (and power) that they should be getting.

I have seen another website strongly push Monark injectors. Let me show you the following diagrams, and you tell me what you think. When I saw the spray pattern of the Monark (being wider than the Bosch), it seemed logical that it could be better, until I found out that the injector didn't directly go into the cylinder. Please note first photo PRECOMBUSTION CHAMBER 2

The injection nozzle does not even come close to reaching the cylinder. It stops at the point where NOZZLE REED is pointing to. I want to describe this well, as some may not be familiar with these parts. You can see that the Precombustion Chamber (PC) extends well past the bottom of the injector so it just reaches a little into the cylinder. Note how the piston has a cut out so it does not hit the PC.

Now look at the picture called PRECOMBUSTION CHAMBER Note that the bottom of the PC is closed EXCEPT for the holes on the side.

Now, this last picture put it all together for me. Look at NOZZLE SPRAY PATTERN This is from the Mercedes manual. Note how concentrated Nozzle A is. This is the correct spray pattern for the 240D and 300D. Now, the Nozzle B look deformed, but that is not the point. Go look at the first photo again. It makes no sense to me to use a wide spray pattern with this PC. Much of the fuel will hit the sides of the PC well before the openings at the bottom. Now look at the Mercedes recommended spray pattern. It is concentrated so that most of the fuel directly reaches the bottom of the PC and the holes on its side. Now, this makes sense to me. Not a wide dispersal pattern. The pattern should not dribble or bounce of the sides of the lower PC.

So, what is at work here? I DOUBT THAT 5% OF THE 240Ds and 300Ds HAVE EVER HAD THEIR PRECOMBUSTION CHAMBERS REMOVED OR REPLACED.

Do you have good combustion? Do you only get 30 MPG on the highway or a little more? I bet this is the reason. Further consider that there are reamers being sold to "ream out the carbon" through the glow plug hole (glow plug is also in Photo PC 2. Consider that this PC is in little cut out between the piston and the top of the cylinder head. Think about 30 years of that kind of abuse. Could it be any wonder that the lower end of the PC could be in very poor condition? I look at these three little holes in the bottom of the PC and it leads me to the conclusion that the harder the spray hits the end of the PC, the better the dispersal pattern will be in the cylinder head. This is what MB designed, and this is what I want.

The only trouble, other than cost? I called Bosch technical services, and I was told that their rebuilds are set to pop at 1450 PSI. This is the minimum standard for Mercedes. I guess I have to rebuild my own using Bosch nozzles at 1650-1675 PSI.

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