AIR IN THE SYSTEM
Air can cause numerous problems with the diesel engine and is one of the hardest problems to solve. The best way to determine that air is the problem is to hook up a clear hose in the return system. If air is coming through the return system then it is probably getting into the system on the inlet side somewhere and causing problems with the fuel system.
Air can enter the system two ways. The first is a bleedback where air is evident after the engine sets inoperative for a period of time and the fuel drains back to the tank and the system has to be reprimed. The engine may or may not start but if it does start it may only run a few seconds, die and refuse to start immediately. The lift pump is one of the most common causes of this situation, however any opening in the fuel system can allow this situation.
Constant air out the return and constant rough running, missing and white smoke can also be an indication of air in the system. In this situation air is usually entering the system somewhere prior to the pump inlet. If a fuel leak is evident this should be checked and repaired first, however a fuel leak does not necessarily have to be evident where air is entering. Sometimes the fuel system can be pressured up by an external fuel pump. If a fuel leak then becomes evident this could be the source of the air leak. Visual inspection of rubber hoses, line fittings and steel lines where they have been rubbed should also be made to isolate the source of the air. BACK TO >> DIESEL PAGE
BLACK SMOKE
Black smoke can be caused when there is an improper air to fuel ratio. The fuel does not burn completely and the partially burned particles are expelled in the exhaust. One of the most common causes of black smoke is an air inlet restriction. This can be anything from a plugged air cleaner, an intake hose collapsing or anything else causing an air flow problem even plugged exhaust. On automotive applications the airflow through a paper filter is sometimes restricted enough to cause black smoke especially on acceleration. K & N has developed an air filter that allows for excellent filtration as well as plenty of air flow. The filter is also recleanable and can be used up to 50,000 miles without having to be cleaned.
Injector malfunction is also a common cause for black smoke as is incorrect engine timing. Overfueling can also cause black smoke and is one of the reasons setting a fuel system above factory specifications is strongly discouraged. Internal injection pump problems can also result in black smoke. BACK TO >> DIESEL PAGE
ENGINE STALLS
When the engine stalls on deceleration it is usually an indication of lubrication problems in the pump. The first thing that should be checked is the idle RPM. If it is too low it could put the pump governor in a position where it cannot recover from the deceleration quick enough to keep the engine from stalling.
If the idle is set to the proper RPM, a lubrication fuel additive might be used. In some cases a slight amount of water has passed through the system or an extra dry fuel has been used. This causes the metering valve or plungers & barrels to stick slightly. A lubrication additive in the fuel could solve this problem.
In severe cases where an additive does not work, the pump needs to be torn down and cleaned. In extremely severe cases the metering valve or plungers & barrels may need to be replaced to solve the problem. BACK TO >> DIESEL PAGE
GLOW PLUG PROBLEMS
One of the main reasons an automotive style engine can be hard to start is faulty glow plugs. Not all the glow plugs have to be bad before the engine gets hard to start. Glow plugs can be checked several ways. One of the easiest ways is with a continuity meter. If the meter does not read when connected the glow plug is bad. Weak glow plugs can also be detected by the actual meter reading, however each application has it's own specification that must be known before the test can be accurate. If no reading is achieved the glow plug must be replaced.
It has been our experience with a 7.3L Ford pickup that if two or more glow plugs are bad, the controller will cut off prematurely causing an extreme hard to start problem with a cold engine.
A faulty relay and controller can cause glow plug failure so it advisable to check out the entire system. If all glow plugs are burned on the end it could also indicate the timing is advanced too far. BACK TO >> DIESEL PAGE
HARD TO START / WILL NOT START
One of the most common diesel complaints is a hard to start or will not start situation. Every detail is important when trying to diagnose such a problem. One should determine if engine temperature has anything to do with the problem, ambient temperature should also be considered. Close attention should be paid to the cranking R.P.M. as well as the glow plug system. Starting problems are often electrical related since cranking R.P.M. and the glow plug system are very critical to getting the fuel to burn. Batteries and the starter should also be a consideration if cranking R.P.M. seems slow.
Once the electrical system is ruled out, air entering the system should be considered, especially if the engine cranks, dies and is then hard to restart. Air can enter the system through any break in the fuel line or through a bleedback condition. To determine if air is the problem, install a clear return hose on the return side of the injection pump. If air comes out it is getting in the inlet system someplace. The injection pump is very seldom the cause for air entering the system. In most cases the fuel lift pump or a faulty inlet line usually ends up being the problem.
Engine problems can also be the cause of starting problems. Low compression or timing problems can start out a hard to start condition. Checking these usually involves special tools but it can save a lot of troubleshooting time in the long run.
Fuel supply and quality should also be considered when searching out a hard to start problem. If the vehicle never starts a fuel restriction may exist. Fuel quality is an important part of getting a diesel engine started. Poor quality fuel may not burn properly leading to poor starting. If this appears to be the problem, adding a conditioner may be just the cure. In extreme cases the fuel may need to be changed out and the system reprimed.
The pump and injectors can occassionaly cause a hard starting condition. If a fuel mileage drop or increase in smoke has been experienced the injectors should be suspect, especially if they have ran 75,000 miles or more. If there is no fuel coming out of the injection pump then it becomes a major suspect. First determine if the solenoid is opening by listening for a "click" inside the pump when the ignition switch is turned on. If no click is heard then the pump needs servicing. If a "click" is heard but still no fuel is being pumped, fuel supply and air in the system need to be ruled out as potential problems. One might try using a fuel lubricant, in case the metering valve has stuck in the shutoff. This will sometimes help weak injectors also. If all of these checks are to no avail the injection pump should beBACK TO >> DIESEL PAGE
INJECTOR PROBLEMS
(Special note - this article will actually be referring to nozzle holder assemblies used in most direct and indirect engines other than the Cummins PT system and Detroit diesel)
Several symptoms relate to possible injector problems. These symptoms include but are not limited to: oil dilution, engine running rough, a dead miss, smoke (white or black), a drop in fuel economy and starting problems.
Injectors can suffer from a drop in opening pressure. This usually occurs after several thousand miles or hours in use. A drop of 200- 300 psi is normal and usually does not have a noticeable affect on the performance of the engine. If a pressure drop is more than 300 psi the injector should be reset to manufacturers spec. in order to assure peak engine performance.
A second problem injectors develop is poor fuel atomization. The main purpose of a nozzle holder assembly is to break the diesel fuel into small enough particles that it will burn properly. An injection nozzle is lubricated by the diesel fuel and any lubrication problems such as water or poor lubricating fuel quality can cause the nozzle to stick. This will hamper it's ability to atomize the fuel properly. Another problem causing poor atomization is an improper valve seat. Sometimes due to contamination or wear the valve seat will become damaged. This also stops the injector from atomizing properly. In some cases a diesel injector cleaner in the fuel will help in these situations. In more severe cases the nozzle will need to be removed from the assembly, cleaned and reset to the manufacturers spec. In most cases the nozzle tolerances are so close that once the nozzle is damaged it is not repairable and the nozzle must be replaced in the nozzle holder assembly. New nozzles must then be checked and set to manufacturers specs on a pop tester.
All injectors rebuilt by DIS come with new nozzles for premium performance along with a one year unlimited miles/hours warranty. BACK TO >> DIESEL PAGE
LOW POWER
In most cases low power accompanies other systems such as smoke or a miss. In these cases the other symptoms should be researched first and when fixed the low power is usually fixed also.
If low power is the only complaint then quantity of the fuel supply should be checked. On engines that have primary supply pumps the supply pump has been found to put out the propper pressure without pumping the proper quantity of fuel. A fuel restriction should also be researched, partially plugged fuel filters, blocked fuel lines and filters in the tank on some applications. If the tank is not vented properly it could build a vacuum which could act like a fuel restriction. Poor fuel quality can also result in low power.
If the fuel system is getting air mixed with the fuel, low power is often the result. Air intake restrictions, exhaust restrictions, transmission problems and internal engine problems have also been known to cause power problems. BACK TO >> DIESEL PAGE
TURBO PROBLEMS
Turbo problems: Inspection - A faulty turbo can cause low power, black smoke, excessive oil consumption, oil in the intake, oil in the exhaust as well as other problems. To determine if the turbo is the problem an inspection of the shaft assembly can be made. Remove the intake and/or exhaust plumbing to the turbo. Look for any evidence that the wheel has toughed or rubbed the housing. If no signs are evident physically push the wheel to one side and see if the wheel can be made to contact the housing. If either of these conditions exist the turbo should be repaired or replaced. If the shaft is tight and wheels have not rubbed other checks should be made before replacing the turbo.
Turbo problems: Oil leaks - Before replacing a leaking turbo several checks should be made. The oil drain out of the turbo should be checked for any restriction. A buildup of crankcase pressure caused by a bad PCV valve or excessive blow-by can also cause the turbo to leak oil. Oil leaking on the intake side of the turbo is strong evidence of an air restriction. If the air cleaners are working properly, inspect the intake hoses for soft spots, they may be collapsing. This could also cause occasional black smoke and low power.
If an engine is idled for an extended period of time it is not unusual for the turbo to leak a little oil. This leak should go away once the engine is loaded up and boost is generated.
Turbo problems: Lack of lubrication / Hot shutdown - A common cause of a turbo having excessive end-play is hot shut-down. This results from the oil supply to the turbo being shut off while the turbo is still spinning at a high rate of speed. Turbos sometime operate with shaft speeds of over 100,000 rpm. If an engine is shut down while the turbo is still spinning at a high rate of speed, the insides of the turbo will cook the little oil remaining and continue to destroy itself from a lack of lubrication. To prevent this damage be sure and allow a cool down period before shutting the engine off.
Turbo problems: Lack of lubrication / No oil at startup - A common mistake when changing a turbo is to crank the engine and even accelerate it prior to the turbo receiving oil. This causes extreme wear on internal turbo parts and could cause the turbo to go bad before it's even had a chance to run.
One way to prevent this problem is leave the oil drain line on the turbo loose. Prevent the engine from cranking by unhooking the coil wire (gasoline), pulling the kill cable or unhooking the pump solenoid. Spin the engine over until oil pressure is achieved and oil is evident out the drain line. Tighten the drain line and reconnect the coil wire or pump solenoid. BACK TO >> DIESEL PAGE
WHITE SMOKE
White smoke usually occurs when there is not enough temperature to burn the fuel. The unburned fuel particles are then exhausted usually by a rich fuel smell. In cold weather it is not uncommon to get white smoke until engine temperature builds up. One cause of white smoke on engine start up could be faulty glow plugs or glow plug system. Low engine cranking speed can also create an excessive amount of white smoke.
If the problem persists after the engine is up to operating temperature several other things should be checked. A faulty injector can cause white smoke. Timing is often a factor when white smoke is excessive. Low engine compression can cause the problem and the injection pump can also have problems that result in white smoke. Air in the fuel system can also result in white smoke. BACK TO >> DIESEL PAGE
