Guideline to troubleshoot various diesel engine

[SNIPER 3000]

DRIVER
ENERGY EFFICIENCY
TIPS


DIESEL ENGINE
DIAGNOSTICS

Most diesel engine problems are related to the injection system. As such diagnosing diesel engine problems requires knowledge of engine and injection system operation.



This brochure provides you with the guideline to troubleshoot various diesel engine and injection system problems.

DIESEL ENGINE DIAGNOSTICS
Diesel engine problems that are most frequently encountered may be identified as follows

1. Excessive Exhaust Smoke

2. Engine Knocking

3. Engine Missing

4. Hard Starting

5. Lack of Power

6. Poor Fuel Efficiency

7. Fuel Leaks

8. Clogged Fuel Filters

These potential problems are briefly discussed below.


1. EXCESSIVE EXHAUST SMOKE
Excessive diesel smoke is due to incomplete combustion, normally caused by faulty injection system or other engine troubles. A small amount of exhaust smoke is normal during initial start-up or rapid acceleration.


Type of Smoke
Abnormal Exhaust smoke may be black, white or blue. Each type of smoke indicates engine problems and these are discussed below:


Black Smoke


Excessive black smoke is caused by a rich air-fuel mixture. This may result form problems with the injection pump or infection timing, which may in turn be clue to a choked air cleaner, worn fuel injectors, adulterated diesel fuel or the engine itself.


White Smoke


White smoke occurs mainly during cold starts, when the fuel tends to condense into liquid and does not burn due to cold engine parts. The most common reason for white smoke are in-operative glow plugs low engine compression, a bad injector spray pattern, late injection timing or injection pump problems.


Blue Smoke


Excessive blue smoke indicates problems from low engine compression and/or worn piston rings, scored cylinder walls or leaking valve stem seals The blue smoke is caused by crankcase oil entering the combustion chamber and being emitted after partial combustion through the exhaust


2. ENGINE KNOCKING
All diesel engines produce a "knocking" sound when running. In a diesel engine fuel ignites when infected into the combustion chamber. This rapid combustion produces very high pressures generating a rumble or dull clattering sound Abnormally loud "knocking" may be due to diesel engine miss.


3. ENGINE MISSING
A diesel engine miss results from one or more cylinders not burning fuel properly. This is caused by injection system problems which include:

Faulty injectors
Clogged fuel filters
Incorrect injection timing
Low engine compression
Injection system leaks •
Air leaks
Faulty injection pump


4. HARD STARTING
If diesel engine does not start it may be due to:

In-operative glow plugs
Restricted air or fuel flow
Bad fuel flow solenoid
Contaminated fuel
Injection pump problem
Low battery power

A slow cranking speed is a common cause for starting problem. Being a compression ignition engine, a diesel engine must crank fast enough to produce sufficient heat for combustion


5. LACK OF POWER
·Lack of engine power may be caused by

Slack throttle cables

Incorrect governor settings

Clogged fuel filters

Dirty air fillers

Low engine compression

Other factors affecting combustion


6. POOR FUEL ECONOMY
Poor fuel economy may be due to:

Fuel leak ·

Dirty air filter

Corrected injection timing

Leaking injectors


7. FUEL LEAKS
Leaking fuel lines or loose connections can adversely affect the performance of a diesel engine Pinpointing exact locations of fuel leak become much more easier when the engine is on Since fuel is injected at high pressure extra care must be taken as the leaking fuel can cause serious injury



If signs of fuel leakage are detected use a piece of cardboard to find the leak, move the cardboard around each fitting If there is a serious leak, it will strike the cardboard and not your hand, thereby avoiding serious injury to your hand


8. CLOGGED FUEL FILTERS
Other than the main filter installed in the fuel line for draining water, diesels have sock filters fitted in the fuel tank and some times in the injector assembly as shown below For optimum performance these filters must be kept clean.



DIESEL TESTS
Diesel Compression Test
Diesel engine compression test is similar to compression test for petrol engine. In diesels compression pressures are in the range of 3,000/ 4,500 psi Readings in each cylinder should be in the range of 50 to 75 psi of each other


Cylinder-Not-Firing Test
The resistance of each glow plug increases as the cylinders fire A no change in the resistance of any particular cylinder's flow plug will show that the cylinder in NOT firing. Pyrometer, a temperature sensing device can be used to detect temperatures at exhaust of each cylinder to confirm the NOT firing cylinder.


Injection Pressure Test
An injection pressure test uses special valves and high pressure gauge to test the following

Injector opening pressure

Injector nozzle leakage

Injection line pressure balance

Injection pump condition



Due to the versatility of this tester it helps in quickly locating bad nozzle, clogged injector filter or faulting pump.



DIESEL INJECTOR SERVICE
Most diesel engine problems are associated with the injection system Major injector system components have been discussed in driver energy tips No. 4 titled "Understanding and Maintaining Diesel Vehicles" In the following section information is provided on the proper functional characteristics of the diesel injector


Injector Opening Pressure
Typical diesel injector opening pressure is approximately 1,700 to 2,000 psi (pound per square inch) of opening pressure is not within service manual specifications, rebuild or replace the injector.


Injector Spray Pattern
Some diesel injectors make chattering sound during operation while others do not. However, all nozzles should make a swishing or pinging sound when spraying fuel.



As shown above there should be a narrow, cone shaped mist of fluid. A solid stream of fuel, uneven spray, excessively wide spray or spray filled with solid droplets indicates that the injector needs service and or replacement

DIESEL INJECTION SERVICE TIPS
1. Wear safety glasses when working on a diesel injection system.

When in doubt, refer to a service manual for the make of vehicle being serviced. The slightest mistake could upset engine performance or cause engine damage.

Always cap lines or plug fuel end fittings to prevent entry of foreign matter.

Never drop a diesel injector or injection pump. They can be damaged.

Remember that high pressure inside a diesel injection system can cause serious injury.

Some diesel injection systems must be bled (air removed) after repairs.

Clean around fittings before they are disconnected.

Adhere to all torque specifications. This is extremely all the more important on a diesel engine.

. Never use a bent, frayed, or kinked injection

[SNIPER 3000]

I posted in the diesel boy trend some where in the first 100 page.
It is a good guide.

[Greypatch]

I am going to borrow this ...

[Mr. Ralliart]

exceleent post

[SNIPER 3000]

........

[joe cool]

SNIPER 3000,this is really useful info, thanx

[SNIPER 3000]

How much does a gallon of diesel fuel weigh?

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

Taken from here
http://dodgeram.org/tech/dsl/FAQ/diesel_fuel.htm

[SNIPER 3000]

In a diesel engine, only the air is compressed during the compression stroke. The higher compression ratio means that the temperature increase gets it well above diesel fuel's vapor point. The fuel is injected AS A LIQUID and thus must be vaporized almost instantaneously at the top. The fuel begins to burn as soon as it vaporizes, but the phase change must be occurring at the same time, thus resulting in a combustion dynamic that produces a much longer power stroke duration: A controlled "long-duration" burn versus a controlled "explosion;" both terms are mis-nomers to an extent, since the time interval we're talking about is on the order of about 30 milliseconds.

(also why a diesel motor produces soot: the soot is the un-burned, carbonized liquid fuel.)

Now, the Cetane rating will determine the ability of the diesel fuel to undergo that vaporization in a smooth manner. A higher cetane rating will vaporize LESS readily, but has more BTU's per gallon than a lower cetane rating. Thus it's ability to give you more bang for the buck, pun intended. BUT, high-cetane fuel's low vaporization qualities make it a terrible fuel, combustion wise, for cold temperatures, especially starting environments. During starting, a diesel engine can't generate enough compression heat to heat the air AND the cylinder walls, AND the piston crown, AND the head assembly. The cranking rate is too slow to keep the process in the "adiabatic" range; that is, the heat also heats the environment, not just the system. Thus some of your heat of vaporization is sucked out of the air by the motor itself. The fuel doesn't vaporize, and the liquid fuel doesn't burn. Note that during a normal running stroke, the process happens so fast that there's no time for the heat to transfer to the walls; the process remains in the adiabatic range, and will easily vaporize the fuel, even when running cold.

Also taken from the same site.