WANT TO save money on a diesel-engined vehicle? Then one
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way is to look after the fuel injection system by keeping it clean, and leaving well alone.
With the little extra care, both the engine and its owner can benefit by having a more efficient system, which means optimum economy, and the prevention of that foul black smoke.
I spoke to two experts in the field of fuel injection, Tony Brooks, senior field service investigation engineer for CAV Ltd, and his colleague, John Harper, service product engineer.
One of the main points they raised was that the operator must assess the fuel consumption of each vehicle, and decide if the figure is what it should be. That way he will know if his truck is thirsty before it goes over the warranty period.
It has been the surprising experience of the CAV fleet engineers that many operators do not keep a careful enough check on fuel consumption of individual trucks during the first year, and by the time any discrepancy is followed up, the offending machine is well out of it s warranty.
The only way dirt can get into the fuel system in everyday use is through the fuel tank itself. It is virtually impossible for it to become contaminated anywhere else along the line.
CAV as a company, is so conscious of the problems caused by dirt and water that it recommends a number of precautions which the operator can take Fuel storage tanks must be covered so that rust and water cannot get in and scale will not form. The tank material should definitely not be galvanised.
If a new storage tank is .installed, the recommended layout is shown in the accompanying diagram.
The tank should be inclined slightly with the sludge cock positioned at the lower end, and the draw-off cock at the opposite end. This enables water and sediment which collect at the lower end to be drawn off periodically.
CAV recommends that, after a delivery of fuel to the storage tank, the fuel should be allowed to settle for as long a time as practicable before drawing any off.
If any fuel is spilt during refuelling, especially around the neck of the truck's tank, it should be wiped up immediately. This is not just for cosmetic reasons.
Dery does not evaporate as petrol does, so if it is left it gathers dirt and this is just what we are trying to avoid. Cotton waste is not recommended as the fluff nearly always ends up in the tank.
On the subject of cotton waste and rags, how many times have you seen a handful of rags stuffed into the neck because the filler cap\has been lost?
Keeping fuel clean from storage to tank is half the battle but it is physically impossible to exclude every partical of dirt getting into the fuel. To prevent it from entering the injection pump, a filter is installed in the system.
Most filters today are made of a replaceable paper element, In the CAV range of filters, the element consists of impregnated paper which is wound around a central core, the whole then being enclosed in a thin metal canister.
CAV claims this method of construction provides a filter area many times the size of that provided by other filters of similar dimensions.
Both Tony Brooks and John Harper were very firm in stressing that the mileage figure given in the operator's handbook for changing the fuel filter is a maximum figure.
In their opinion, it is false economy to take it up to this limit. Clogging filters can cause the engine to lose power and make starting difficult.
Fuel flow
Mileage figures quoted in manuals for changing filters are convenience figures to draw the operators attention to the need for a filter change.
To check on the need for a change of element, the rate of fuel flow through the filter should be measured. When the rate declines, a new filter is required. This is obviously impractical, so a recommended mileage figure is the only viable alternative.
When changing the element (it cannot be cleaned) it must not be forgotten that the same rules of cleanliness still apply. Making sure any cloths are well out of sight, the other components of the filter assembly should be washed in clean fuel oil. Apart from contamination, the area which causes CAV the most headaches is injection pump timing. Mr Brooks said that in the past, a number of operators had complained about the performance of their trucks after they had supposedly been serviced.
In cases like this, the first question the CAV field service engineer is trained to ask is -Have youhad the pump off recently?' If the answer is yes, then the next question asks whether the injection was retimed when the pump was replaced.
Mr Brooks recalled -It's amazing how often the answer is ''well . erl
in this case the moral is clear. If the pump has been off the engine for whatever reason, always have the injection timing checked. It can often become retarded due to stretch in the timing chain or the back lash not being taken up correctly.
It's all very well having the pump calibrated correctly, but the whole object of the exercise is lost by incorrect fitting.
'Leave it alone`
When it comes to tne internal workings of the injection pump, CAV advice is to leave it alone. As the equipment becomes more and more sophisticated it becomes more and more advisable not to fiddle with it.
If tne operator has no servicing facilities himself, tnen a quick 100k through the Yellow Pages will find him an injection specialist with the correct equipment.
As engine manufacturers are constantly trying to improve their product by getting more power with less smoke, a constant process of updating is going on. and this aiso applies in tne field of injection pumps.
Quite often tnere will be a complete replacement available for earlier models which the operator can obtain to get modern performance.
At tne end or tne line, we come to me injectors themselves, if a driver complains that his engine is smoking, the first thing to try is a 'wash and brush up' of the nozzles with a wire brush.
If this fails, the injectors can be overhauled, but, as with the pumps, unit exchange schemes can be very competitive with repairing the old ones. It pays to ask around. Although it is an obvious point to make, it is worth mentioning that fuel leaks cost money, and just because a drip can be seen at one point in the system is does not automatically follow that the source is also at this point.
On in-line injection pumps the lowest point is usually the advance box, so if there is a leak anywhere around the pump body, it always leaks down to this area.
To check on the source of the leak, a useful tip is to clean the area with a degreasing agent like carbon tetrachloride, or keep the engines clean in the first place!