98 2500

I am brand new to diesels. had no idea how they work, so i went to howstuffworks.com and got a general idea of diesel operation. But i still have a ton of questions.

1. The lift pump supplies fuel to the injectors?Why not use a cheaper electric fuel pump, in-tank?

2. I assume a cam operates the valves, seems as noone does cam upgrades. BAsically i need more info on the valvetrain operation.

3.Ok on the intake side it takes in air, compresses it, then fuel is injected (on the website it also shows compressed air being injected with the fuel, i guess this is my question) and then exhaust stroke.

4. How is timing set/adjusted/measured.

5. Glow plugs, i understand they help aid in heating to ease startup, but where are they located, is all they do is heat.

6. what turbo do i have, and operation of the entire turbo system, wastegate etc.

7. i know my engine does not use a fuel plate, but i would like to understand them, and understand the difference between what i have and a fuel plate

8. why do you guys call mods bombs

9. why does more power seem to equal more smoke

10. where can i find diagrams/pictures etc. on engine component operation. meaning heads, bore placement, crank rods pistons and specs on all of them

11. the engine is so loud as is, how do i know if something is not operating correctly.

Thanks guys, I have more but will get the basics covered first.

magnum

98,

I'll take a stab at a few of the questions, but I'm limited in my diesel knowledge.

1. The lift pump supplies fuel to the injector pump. (vp-44)


4. I don't believe that we can manually adjust timing on the 24 valve, I believe that it's all electronic.

5. We DO NOT have glow plugs, we have grid heaters which heat intake air.

8. bomb=better off modified baby (I think)


9. I'm probably way off on this one, but with a diesel, the introduction of massive quantities of fuel gives us all kinds of power and hence lots of smoke.

I've probably misled you enough already, I'm certain some of the more intelligent folks will steer you in the right direction, otherwise, you could go and do a "search" on any of the above topics. It will keep you reading for weeks.

98 2500

yeah so i wonder why not use a regular fuel pump, providing the needed psi at a much cheaper price to drive the injector pump or is it pumps. why have two pumps anyhow? so is it only the 12v that have manual timing? where are the grid heaters located, in the cylinder head or in the actual combustion chamber?

thanks for tryin to answer at least searching on forums is generally so hard i just avoid it, cause people spell wrong, you get a hundred respsonses that don't really get you what you want. ya know

billg

Here is a place to get a lot of answers. http://www.dodgeram.org/tech/dsl/maint/3rd_Gen-24v.htm
http://www.dodgeram.org/tech/dsl/Facts/98ISBspecs.html
http://www.dodgeram.org/tech/dsl/ECM/index.html
http://www.dodgeram.org/support_pgs/diesel_ix.htm
This will answer a lot of questions and might give you some more?
Hope this helps

drafalske

I'll take a stab at some of those.

1: The lift pump is a low pressure pump that supplies the fuel to the injection pump. The VP44 is a rotary pump, and there is one line going to each injector, a feed line, and a return line. Think of it as a distributor for a gasser… that about as good an analogy as I can come up with.
2: Most diesel engines are turbocharged, and there is no throttle like a gasser has. The engine is free to intake as much as needed. You cannot lean-burn a diesel. Therefore, a cam upgrade is not needed unless you’re drag racing or sled pulling, and need absolute maximum possible horsepower and torque.
3: The air is compressed by the turbo, is taken into the cylinder, compressed, and then the fuel charge is injected directly into the combustion chamber (which, I believe, is actually in the piston, not the head). The amount of fuel is directly proportional to how hard you are pressing the accelerator pedal. Then the exhaust stroke.
4: Timing on the 24 valve is controlled electronically by the VP44 injection pump. The 12 valve is mechanically controlled, and timing is manually adjusted.
5: Our engines use a grid heater, it is located where the intake horn joins the engine on the drivers side. You will see two thick wires attached there… that’s it. It heats the intake air in cold weather to help cold starts. There are no glow plugs.
6: I’ll let someone else chime in here.
7: I’ll let someone else chime in here too. I know more about the properly valved engines.
8: BOMB means Better Off Modified Baby!!! And they are.
9: More fuel = more power = more smoke. Smoke is cool. Kind of a status symbol.
10: Have you tried Cummins.com? Maybe they can point you in the right direction.
11. Over time, you’ll realize what your engine is supposed to sound like… you’ll get used to it in other words. Anything out of the ordinary is exactly that.

Hope this helps. Guys, correct me if I’m wrong. Enjoy your new truck.

-Dave

DieselDaze

7) I'll do what I can to answer this one. I'll keep it simple because I dont know all the details myself.

The fuel plate is also known as the cam plate. By what ever name, the plate has a notch cut in it that a lever slides against. How far the lever travels is determined by how the notch was ground in the plate.
There are different numbered plates that simply denote how that plate was ground.
The more travel the lever has, the more fuel is delivered to the injectors.
(Remember, Im not an expert here and Im trying to keep it simple because I dont know all the details).

Now, on your pump, the fuel delivery is controlled by a computer. There are a couple aftermarket company's that sell computer boxes that over ride/replace the factory settings and increase the fuel delivery to the injectors.

Hope this helps at least a little.

Rich.

98 2500

thanks for the replies guys, i think i'm gettin the hang of it. So what actually happens when i push the accelerator. In my 24v it is connected to a computer that gives a signal to the injector pumps telling them how much fuel to inject? i'm a little confused about how the intake of air is regulated, or is it not. the intake comes right into the manifold from the turbo. And the harder you step on the pedal the more fuel and in turn faster moving piston intakes more air. am i on the right track here. Wow diesels are cool haha

drafalske

Thats pretty much exactly right. The airflow into the engine is not regulated. Combustions does not occur until the fuel charge is injected. See, with a gasser, if you wanna add more fuel, you gotta add more air, if not detonation occurs. Thats not the case with a diesel. A diesel runs on compression, relying on the heat generated by compression to ignite the fuel, instead of using a spark plug like gasser. The more fuel you give a diesel, the more power it creates, and the faster it turns the turbo generating the required boost.
Please correct me if I'm wrong, but I believe the Standard Output Cummins uses something silly like 17.5:1 compression, and the turbo can reach upwards of 100,000 RPM.
Diesels are pretty frickin cool!!!

billg

Diesels are not as sensitive to air fuel mixture as gas. Where gas has to always be at or very near 14:1 diesel will work from 100:1 to25:1.
Here is how Cummins answered this. This is taken from the Cummins site See link below.
The Gasoline Engine. A gasoline engine is stochiometric. Stochiometric: the quantitative relationship between two or more substances, especially in processes involving physical or chemical change. With a gasoline engine there is a stochiometric equation of 14 parts of air to one part of fuel. Remember, always 14:1; whether at idle or full throttle, the fuel and air are mixed outside the cylinders in a carburetor or injection manifold and the mixture is introduced via the intake valve. 14:1 always.
The Diesel Engine. Fuel and air in the diesel design are not premixed outside the cylinder. Air is taken into the cylinder through the intake valve and compressed to make heat. Diesel fuel is injected near the top of the piston's stroke in an amount or ratio corresponding to the load on the engine. At idle, the air-to-fuel ratio can be as high as 85:1 or 100:1. At full load the diesel still boasts a miserly 25:1 or 30:1 ratio! It is in the injection system.
Fuel BTUs. "The btu value of diesel is greater." Quite true, the btu, or British thermal unit, for diesel fuel is 130,000 btu's per gallon and a weight of 7.4 lb/gal. The value for gasoline is 117,000 btu's and a weight of 6.0 lb/gal. If we go back to our basic physics rules for energy, you'll note the fuel in the tank has potential for work if it is injected into the cylinders and, combined with the compressed heated air, ignited. The piston is forced downward, the crankshaft rotates, the wheels turn. The diesel design (the "heat engine"), compression ratios (the "heat engine"), the fuel injection system (allowing 85:1 down to 25:1 air-to-fuel versus gasoline at 14:1) and fuel btu's (diesel fuel has more power), all these diesel attributes add up to more miles per gallon of fuel!
http://www.cummins.com/na/pages/en/p...530004AC33EA57

dieselcrazy

98 2500 .... you are going about this in the right way. keep asking questions, there are lots of guys on here with lots of good info. i was on this site something like 4 months before i bought my ( properly valved ) rig. good luck, scott

infidel

9. why does more power seem to equal more smoke

It doesn't have to be that way. Smoke is just unburnt fuel coming out the tailpipe and doesn't add to increased hp at all. A properly balanced air to fuel mix and sensible driving habits can produce the hp without smoke.

98 2500

so where do you start to get limited by stock components. Do things like aftermarket heads, pistons, rods, cranks, and valvetrain have as much an impact in diesel as in gas. Do people bore and stroke the diesel. Seems like fuel delivery and turbo is where everyone spends their time. I'm still a little confused here. What your saying is that the stock valve timing and lift is adequate for just about all applications. So at any given time, there is more intake available than the engine can actually use, and the exhaust is always getting the maximum scavenge possible. What about porting heads, is this also not as useful, different intake manifolds, headers, etc...

jrs_dodge_diesel

I don't think there is much limit in a stock engine. The main bearings, crankshaft, valvetrain, and pushrods are quite adequate. All of those parts are built to be very strong. Heck the crankshaft alone wieghs 175 pounds ! These engines are built so strong that they can crank out over 1,000 ft lbs of torque with no mods to bearings, crank, valves, etc. Never heard of anybody porting and polishing the heads, or doing a bore and stroke job. Cummins designed this engine very well.

Most mods include larger injectors, bigger turbo chargers, and better fuel delivery systems. These diesels are very tough. I love my Cummins.

wannadiesel

Porting is very important, but not to actually make power. A diesel can make ridiculous amounts of power for a short time when overfueled, but the EGT goes sky high and the pistons come out through the turbo. Porting on both the intake and exhaust side is very helpful in keeping the EGT down under a sustained load. The added airflow doesn't help much with power, it just lets you use the power you're making for extended periods of time. Porting doesn't seem to be necessary until 400 HP or so. Headers are not helpful because we want the exhaust to stay hot until it hits the turbo. We are actually using the turbo to recover wasted heat from the exhaust, any heat that doesn't make it to the turbo is lost to us. Therefore we want the manifold runners as short as possible, and we want them to retain heat. Some guys actually put header wrap on their manifold and turbine housing to retain more heat. The pressure drop in the exhaust system is the turbo, so the stubby little cast iron manifold is not the restriction it seems at first glance. There are aftermarket cams and they are helpful in controlling EGT as well. The stock cam is certainly fine for most people. There isn't much room in the Cummins for extra stroke, the rod caps are on an angle so the rod bolts will clear the cam. The very high cylinder pressures make boring a risky way to make power. Guys making over 50 psi of boost find they need to o-ring the head and use studs instead of bolts, but the bottom end seems capable of handling anything as long as you keep the RPM sane.

welder27

The computer has sensors that tell it the position of the throttle and cam. If you want to accelerate the puter will tell the injectors exactly when to inject according to the position of the cam. That's why the air/fuel mixture can vary so much and the engine still runs great.

The exhaust is what turns the turbo. You have the exhaust side of the turbo and the intake side. The boost pressure (air intake pressure off of the turbo) on your engine is around 25-30 psi. That doesn't mean you have that much pressure going into your engine at an idle though. You only get that much pressure when you're at full throttle. So, in a sense, the air going into your engine is regulated by the engine's exhaust through the turbo via how hard you push on the throttle. You may have noticed how your engine lags a little bit when you stomp on the throttle but then it'll take off like a rocket. That's because the turbo needs that extra second or two for the engine to produce lots more exhaust gas to spin the turbo to develop the 30 psi the engine is asking for. So, long story short, the amount of air depends on the amount of fuel.