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Diesel FAQ's From the Mailing Lists

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General Questions and Terms

Q: What is a dowel pin?    Note: 24 Valve engines are not vulnerable to pin damage.

Q: What is a CPL number?

Q: What is a TSB?

Q: What is an ISB engine?

Q: Can a 24 Valve ISB head be installed on my 12 Valve engine?

Q: What is a TST kit?

Q: Is there a TST kit for the 24 Valve ISB?

Q: What is a turbocharger and how does it work?
      Includes intercooler, boost, wastegate, and silencer ring

Q: What is the TDR?

Q: What is the difference between direct injection, and indirect injection?
Note: The Ram Turbodiesel and the Ford Powerstroke both use direct injection.

• Direct injection (DI) uses a fuel injector mounted in the top of the combustion chamber to inject the fuel directly into the combustion chamber.
• Indirect injection (IDI) has the injector mounted in a small pre-chamber where the fuel first ignites and the remaining fuel then sprays into the combustion chamber and burns.
• DI engines usually are easier to start in very cold weather than IDI engines are.
• DI engines usually get better fuel economy that IDI engines do.
• DI engines produce more particulate emissions than IDI engines do.
• DI engines are usually noisier than IDI engines are.

Q: What Are Delivery Valves ?

• Inside the P7100 injection pump are six delivery valves, one for each cylinder. Their main function is kind of like a check valve to prevent fuel flowing from the injection line back into the pump after injection ceases. They are located on top the injection pump where each fuel injector line leaves the pump.

Q: What is the difference between a "wet sleeve" engine and a "parent bore" engine?
Note: The Ram Turbodiesel and the Ford Powerstroke both use parent bore engines.

• A wet sleeve engine uses removable sleeves for the cylinder walls. The sleeves form the cylinder bore on the inside of the sleeve, and the coolant cavity on the outside of the sleeve. O-rings at the top and bottom of the sleeve seal the coolant passages at the top and bottom of the block. A scored or worn sleeve can be replaced, creating an entirely new cylinder. Sleeves are prone to cavitation pitting on the coolant surface which can result in complete failure of the sleeve and coolant loss into the cylinder or oil pan. Special wetting agents are needed in the antifreeze mixture to reduce cavitation.
• A parent bore engine has the cylinders cast as an integral unit with the block. If the cylinder wall is damaged or worn, the cylinder must be bored oversize, and an oversized piston must be used. Parent bore engines are not usually susceptible to cavitation erosion. Some Navistar 7.3L engines used in Ford pickups before 1997 have porous cylinder castings that can be damaged by cavitation.

Q: What is the difference between the 1998 Encore and Eclipse engines?

• Encore = 24 valve, Eclipse = 12 valve

Q: Is there a difference, other than the PTO port, between the NV241D and the NV241DHD transfer case?

• The NV241DHD has a PTO drive gear and an extra bearing in the input shaft.
• The NV241DHD has a wider drive chain and sprocket set.
• The NV241DHD has a torque rating of 1400 lb-ft vs. a rating of  1028 ft-lb for the NV241D

Q: The 97+ rams use the power steering pump and a hydraulic (instead of a vacuum) brake booster. Where does the truck get vacuum for AC, Cruise Control, etc?

• There is a small vacuum pump mounted in front of the power steering pump.
• The ISB uses the engine computer to electronically control the injector pump for cruise control.

Q: Is it safe to take the truck to the car wash, and spray the engine down?

• From:  Josh Berman <j.e.berman@metc.cummins.com>   - As long as you don't direct the high-pressure wash directly at the electrical connectors at really close range, the engine should be fine. You might also be careful of pulling into the car wash right after a long, hard pull and spraying the exhaust manifold & turbo... the rapid cooling might cause problems. However, if you've just been driving around town, the manifold & turbo shouldn't be hot enough to cause a problem.
• Personal note:  I have washed the area under the hood several times without a problem. Once, water worked it's way into the Water In Fuel Sensor and lit the warning lamp a few miles down the road.  I quickly stopped, hit the water drain, and noticed that the WIF sensor plug was wet.  The warning lamp went out when I unplugged the connector and dried the contacts.

Q: Which engines have a catalytic converter?

• All 12 valve engines in trucks built AFTER Jan 1, 1994 have a catalytic converter.
• 12 Valve engines built before Jan 1, 1994 do not have a cat.
• ISB equipped trucks do not have a cat.  Note: They have a resonator that look like a cat.

Q: The shift light doesn't work on my truck. Are they only for gas engines???

• There is no shift light feature on the diesel equipped trucks.

Q: What causes the chirp sound from under the hood when I shut down the engine?

• The best explanation is that the engine suddenly lurches to a stop due to the high compression, and the accessories such as alternator, water pump, fan, etc keep turning and produce the belt chirp. This is normal and will not cause any trouble.
• There was a report in TDR #20 that a Goodyear Gatrorback belt #4080810 stopped the chirp in a 97 model.

Q: How often should I drain the water separator, and how do I do this?

• The owners manual says to drain the water separator at each fuel stop
• On 1st Gen 12V engines, rotate the drain valve on the bottom of the fuel filter.
• On 2nd Gen 12V engines, pull up on the drain valve on the bottom of the fuel filter.
• On 3rd Gen 24 ISB's, lift the drain valve lever on the side of the fuel canister - you may have to rails and lower the lever several time to get the drain flowing.
• It is better to drain the fuel filter/water separator while the engine is off. Any water that gets separated by the filter will migrate to the bottom of the filter where the drain is, because water is heavier than fuel. However, if you've got flow through the filter (as you do when the engine is running), it may disturb the water and move it from the lowest point in the filter. Draining the filter at that time may give you a false "negative," meaning that it may look like you don't have water, but you do. That's why we (Cummins) recommend draining the filter in the morning before you start the truck.   Josh Berman

Q: What are all of those radiators behind the grill?

• closest to the engine is the engine cooling radiator
• in front of that is the intake air aftercooler
• in front of that is the AC condenser
• there is also an automatic transmission oil cooler on trucks with the auto
• under the driver's side radiator support is a power steering fluid cooler.

Q: Where is the Cummins ISB computer, or the  computer that tells the engine what to do.  Where is the Dodge computer that monitors the Cummins computer, and if there are any other computers, where are they?

• The Cummins ECM is located on the "driver's" side of the engine block, just below and a little behind the fuel filter can. The fuel pump actually does have a computer built into it, and it's mounted on top of the pump. Basically, the computer on the pump translates the requests for fueling and timing that the Cummins computer sends it into "on" times for the timing and fueling solenoid. That way, our ECM can say, "I'd like 8 degrees BTDC timing, and 33 mm^3 of fuel" and the computer on the pump says, "ok, to get that, I need 28% duty cycle on the timing solenoid, and 1.2 msec open time on the fueling solenoid..." (those numbers, by the way, are totally made up ;-)   -Josh Berman
• There are also separate computers for the ABS and Airbag operation.

• It varies somewhat, but averages around 7.1 lb per US gallon.

Q: What should the fuel pressure after the filter on a 24 valve be?

• The maximum pressure during cranking is 6psi, and the  minimum  pressure during operation is 10psi. The electric lift pump runs at half-speed during startup, and at full speed at all other times.

Q: Doesn't Ford own Cummins?   If the Cummins engine is so fantastic, why doesn't Ford use the Cummins engine?

Back in the early 90's, Ford bought less than 15% of outstanding Cummins stock. Many companies buy into other products to add diversity, corner a market, or form an alliance. In 1997, Cummins repurchased all stock previously owned by Ford, and no Ford management is now on the Cummins board of directors. Since 1998 in the pickup market, Cummins B engines are exclusively contracted to Chrysler, an arrangement that both companies are eager to continue. Ford medium duty (class 6 and 7) and heavy duty (class 8) trucks are available with Cummins B engines. Hey, if it's good enough for a Ford 10 ton truck, I think the Cummins B is adequate for my Ram pickup! You can keep your Power Stroke. :-)

From the Cummins website: Ford does not own Cummins stock
No, at one point Ford owned less than 10% of Cummins stock, but now Ford doesn't own any Cummins stock.

Again, from a Cummins press release: http://www.cummins.com/news/benefit.html
     CUMMINS ENGINE TO ISSUE 3.75 MILLION COMMON SHARES TO ESTABLISH EMPLOYEE BENEFITS TRUST. REPURCHASE OF 3 MILLION SHARES ALSO AUTHORIZED BY COMPANY - SHARES REPURCHASED FROM FORD MOTOR COMPANY - KENNETH DABROWSKI RESIGNS FROM BOARD. COLUMBUS, Ind.
       (Jan. 3, 1997) - Cummins Engine Co. Inc. today announced that it will issue 3.75 million shares of its common stock to an employee benefits trust for use in meeting the company's future obligations under employee benefit and compensation plans. While the trust shares may be used to fund a number of these plans, the principal use will be in funding contributions to employee retirement savings programs the company revised on January 1, 1997.
    Formation of the trust and issuance of the shares to the trust will have no effect on the company's earnings per share calculation. Shares of common stock held by the trust will not be used in calculating the company's reported earnings per share until the shares are distributed from the trust and allocated to a benefit plan.
     The company also announced that it has repurchased 1.3 million shares of its common stock from Ford Motor Company and has authorized the repurchase of an additional 1.7 million shares in the open market. In accordance with the terms of the company's 1990 investment agreement with Ford, Kenneth R. Dabrowski, a Ford vice president who has recently served on the Cummins Board of Directors under the terms of the investment agreement has resigned, effective with the repurchase. Following the repurchase from Ford, the company has approximately 38.2 million shares outstanding.
      Cummins, headquartered in Columbus, Ind., is a leading worldwide designer and manufacturer of diesel engines and related products. These engines provide power for its key markets: automotive, power generation, industrial and filtration.

Fuel Economy

Q: What is the typical fuel economy of a Ram with the Cummins diesel?

• No such thing as typical!  Loads,  right foot "operation",  frontal area,  terrain,  temperatures,  and winds vary widely!

Here are some 12V rules of thumb:   YMMV!        Due to EPA emissions regulations, ISB engines get 2 mpg less than the 12 valve engines.

• 3/4 ton 2WD with manual, street tires and
• 3.54 axle:   23 enpty, 20 loaded, 12 -17 mpg towing
• 4.10 axle:   21 empty, 19 loaded, 12 -16 mpg towing
• 3/4 ton 2WD with automatic, street tires and
• 3.07 axle and 3 speed auto: 20 empty, 18 loaded, 12 -16 mpg towing
• 3.54 axle:   21 enpty, 19 loaded, 12 -16 mpg towing
• 4.10 axle:   20 empty, 18 loaded, 12 - 16 mpg towing
• 3/4 ton 4WD with manual, trail tires and
• 3.54 axle:   22 enpty, 19 loaded, 12 -16 mpg towing
• 4.10 axle:   20 empty, 18 loaded, 12-16 mpg towing
• 3/4 ton 4WD with automatic, trail tires and
• 3.54 axle:   21 empty, 18 loaded, 12 -16 mpg towing
• 4.10 axle:   20 empty, 18 loaded, 12-15 mpg towing
• ALL 4WD trucks:
• Larger tires do not hurt mileage and may actually help by 1/2 mpg.
• Lift will cost about 1 mpg for each 2"
• brush guards and winch bumpers will cost 1 mpg
• 1 ton 2WD, 4WD - look at comparable 3/4 ton and:
•  take 1 mpg from empty and loaded mileage, towing mileage is about the same as 3/4 ton
• All models: expect 1 - 2 mpg less in winter

Diesel Engine Noise

Q: Why is the diesel engine so much noisier than a gasoline engine?

Note: the P7100 fuel injector pump is quite noisy in operation, and a fair percentage of the noise produced under the hood of 94+ 12 valve engines is from the injector pump.   (source: TDR)

Subject:     RE: What makes all that noise anyway?
From:        "Paul H. Mason" <74160.642@CompuServe.COM>

> I was wondering, the non-uniform combustion, would that cause piston
> rattle/slap as others have described?
> Or, maybe worded better, is that noise the combustion itself, or metal
> hitting metal?

While it's true piston slap causes a light rattle modern piston engineering has produced cam-ground pistons. Design forms the piston skirts tightly to the piston walls when the engine is cold and as the engine/piston warms up the clearance stays the same. Of course any high performance engine using drop forged pistons will rattle slightly cold or hot as the skirt to piston wall clearance doesn't change much and is usually fit loose in the bore. The aluminum alloy pistons used in modern diesel engines usually have a fairly close skirt clearance with some industrial Cat and other engines being the exception.

Rather than "metal hitting metal" it's the flame hitting the metal. Check out at: University of Wisconsin-Madison
"www.engr.wisc.edu/centers/erc/project.html".  If you have a web browser there's a bunch of good diesel combustion research at the ERC (Engine Research Center) University of Wisconsin-Madison like:

> SAE 950162 "Single-Surface Flame Quenching Distance Dependence on Wall
> Temperature, Quenching Geometry, and Turbulence," by DJ. Cleary and P.V.
> Farrell. <

Another reason we have to treat diesel CI (Compression Ignition) engine coolant differently than SI (spark ignited) engine coolant is the high flame pressures cause "pitting" or "cavitation erosion." Cylinder wall "vibration" characteristics are also being studied by the ERC.

--Paul         Reference: www.engr.wisc.edu/centers/erc/project.html

Q: After driving for a while on the highway, my 2001 diesel engine sound changes noticeably when the throttle is moved slightly. Is this normal?

When you are traveling at a nearly constant highway speed, any change in the throttle causes the engine computer to adjust both the fuel rate and the injection timing. The timing change produces a noticeable change in the sound produced by the engine. Note: The change is more noticeable if larger injectors have been installed to increase engine power,

FAQ/Comments Frequently heard in parking lots and fuel stops:

Does the 5.9L have enough power in a 2500?

Mertens, Darren  (darren.mertens@lmco.com) 
"there is no such thing as enough power in a truck, you must seek more"

"How do you like that diesel truck?"

Bruce W. Wells   (bwells@ntr.net)
Usually, somewhere in the ensuing conversation, I use my analogy of this truck to sex for the first time.

How do you explain sex to the uninitiated person? Despite your best efforts at using the English language, you cannot command enough adjectives to describe the activity. So it is with the Dodge/Cummins combination. Most people (yes, even pickup owners who drag trailers around regularly) have no concept of what this truck/engine is about.

And finally, I end the page with this DiRT posting from Joe Donnelly:

Subject:   Re: DiRT: diesel aroma and music
In a message dated 98-07-19 13:42:23 EDT, someone with a V10 wrote:
<< You might be a redneck if.....the sound of a diesel sounds like Mozart.  Ha Ha. >>

naaah,    Mozart has too many violins.
More like Bach fugues at idle, or under full power - Wagner.

Joe, no one could have said it better !!

Last update November 1, 2002