INSPECTING A MALFUNCTIONING VEHICLE
Once you have learned all that you can, look over the "symptoms" reported on this vehicle. See if they point to any part that may be defective or may be causing the trouble. Let's say that the truck has lost power. Another symptom, learned from the driver, is that it was using more fuel than normal. These two symptoms point out that the engine is either getting too much fuel or not enough air. One of the more probable causes in this case is a partially plugged air cleaner.
However, don't start removing parts! Don't be hasty and replace parts until all symptoms have been considered.
Symptoms that show up in engine power, fuel consumption, and the exhaust system can all be caused by a faulty air intake component. A poor troubleshooter may try to stop the engine from using too much fuel by repairing or replacing parts in the fuel system.
The main thing is to try to find out what is actually causing the trouble. This is called "diagnosing the symptoms" and "isolating the fault."
Another trouble that you might find is that the engine stops because of no fuel being injected into the cylinders. This could be caused by many different conditions. Let's see how to proceed to locate the cause of this trouble.
Remember, don't start removing parts. Make a good visual inspection of the fuel system first, to include checking that there is fuel in the fuel tank. Make sure the fuel lines are not cracked or broken.
Examine the linkage to the fuel injector pump. The accelerator linkage could be disconnected and, with the idle speed adjustment set wrong, the cylinders would be out of fuel. Another linkage item that could cause this trouble is the fuel shutoff control. Make sure it is not improperly adjusted. Check to see if the shutoff control cable housing has slipped rearward out of the clip on the fuel injector pump. This condition can cause the trouble, as it has the same effect as pulling out the control in the cab.
If you cannot see anything wrong, check to see if the fuel lines are open from the tank to the fuel injector pump. This can be done by first disconnecting the fuel line at the inlet side of the injector pump hydraulic head. Then, turn on the accessory switch and see if fuel is pumped from the tank through the line. Make sure you catch the fuel in a suitable container.
In the above inspection, you are finding out if the lines are not plugged and if the in-tank pump is operating. If the fuel does not flow out of the disconnected line, the trouble has to be back toward the tank. If the fuel does flow, the trouble must be in the fuel injector pump high-pressure lines or injector nozzles.
If no fuel flows, there could be many reasons. The lines and filters could be plugged, or the in-tank pump might not be operating. If you listen, close to the tank, you can hear the in-tank pump humming when it is operating. If the in-tank pump is operating, you can check its pressure. If the in-tank pump does not operate, check out the electrical circuit to the pump.
If the in-tank pump is operating as it should, but no fuel reaches the injector pump, the trouble can easily be located. With the in-tank pump running, loosen the fittings on the fuel lines or open the bleed valves, one at a time, to see if fuel will flow out. Start at the final stage (engine secondary filter) and work toward the tank. Let's say that fuel leaked when you loosened the fitting on the tank side of the vehicle primary filter. However, no fuel leaked from the fitting on the engine side of the filter. This indicates the trouble is in the filter. It's probably stopped up and needs cleaning.
If fuel reaches the injector pump and the linkage is all right, the problem must be in the injector pump or the injector nozzles and lines. You are authorized to replace the high-pressure lines; however, it is unlikely that they are all plugged. The next step would be to notify your support unit of the condition.
Another problem you may find in the fuel and air intake systems is an improper fuel-air mixture. A clogged air cleaner can cause smoky exhaust and low engine power. It can also cause the truck to use too much fuel-air mixture in the combustion chamber. The mixture is too rich (does not have enough air). Let's see what else can cause an improper mixture of air and fuel.
On some 2 1/2-ton, multifuel engines, a turbosupercharger helps supply air to the engine cylinders. If the turbosupercharger is defective, the fuel-air mixture becomes too rich, especially at higher engine speeds. A defective turbosupercharger will generally show the same symptoms as a clogged air cleaner. This includes smoky exhaust, low power, and use of too much fuel. You should check the air cleaner first when these symptoms appear.
If the air cleaner element is not clogged, check the manifold heater gaskets for leakage. The gaskets could be blown, or the manifold heater elbow could be loose. Any leak in this area will decrease the turbosupercharger output and cause the fuel-air mixture to be too rich.
If the manifold heater gaskets are not leaking and the air cleaner is not clogged, the fault is in the turbosupercharger. You should notify your support maintenance unit because you are not authorized to test, remove, or replace the turbosupercharger.
High fuel consumption is a problem that you should look into as soon as possible. This problem may not seem important; however, the driver and other personnel aboard may be riding a very unsafe vehicle!
When a vehicle uses too much fuel, the first thing to look for are LEAKS! If the driver says that the engine develops full power but uses too much fuel, it's a good possibility that this is what is wrong. Much of the fuel system is on the right side of the vehicle, and the hot exhaust system is there also. So, you can see the danger.
While you are looking for leaks, make sure all fuel line fittings are tight. If no leaks are found, turn on the in-tank pump and recheck for leaks. Start the engine and check for leaks.
Check the air intake system for a blockage, such as a clogged air cleaner. (Remember, a restricted air intake system generally causes black exhaust and low power.)
The engine will also use too much fuel if the injector pump is out of time or is improperly adjusted. Generally, when the engine is out of adjustment, it will also be low on power. If this seems to be the trouble, notify your support maintenance unit.
The manifold flame heater aids in starting the multifuel engine when it is cold. If you have trouble starting the engine even with the manifold heater, it is possible the heater is not working properly. You can troubleshoot the heater in the following manner:
Inspect the entire intake manifold flame heater assembly. Make sure it is all there and is connected properly. If the fuel lines, wiring, and ignition unit look all right, find out which system is at fault. It might be the fuel system or the ignition system.
First, make sure there are no leaks when the intake manifold flame heater switch is closed. Next, disconnect the high-tension lead at the spark plug. Hold the wire about 1/4 inch from the metal part of the spark plug and have someone turn on the intake manifold heater switch. If electrical sparks continue to jump the gap between the wire and the plug metal, the electrical system is all right. If no spark jumps, check out the rest of the electrical circuit.
If the electrical system is all right, check out the fuel system up to the fuel pump. Make sure the lines are not clogged. If the trouble lies in the fuel pump or nozzle, notify your support maintenance unit.
You should now be able to see what makes a good troubleshooting procedure. Make sure you make an inspection before you remove any parts. Question the vehicle operator, if possible, to learn all the symptoms he may be able to give you. You may have to make an operational check to find the trouble, such as starting the engine to find a fuel leak.
Always make a functional check after you have corrected the trouble to make sure that the vehicle is in operating condition. |