Words by Harry Lewellyn and Mark Allen Photography by Karl Dietrich
Here’s a fascinating way to look at fuel delivery. At 10L/100km, your 4WD will use 10L of fuel to travel 100km. Alternatively, if that 10L of fuel were in a pipe-like container (much like a fuel delivery line), it would need to be 100km long and approximately two-thirds the thickness of a bee’s whatsit in diameter. Now that’s thin and one good reason for needing good fuel filtration. Naturally, flakes of dirt, rust or other contaminants will easily block fuel lines. With the introduction of fuel injection in the 1950s came the need for cleaner fuel than that used in carburetted engines. By the 1990s, all 4WDs were running fuel injection of some sort. Fuel injection offers more power and better fuel economy and is therefore better for the environment, but by nature demands very clean fuel. The fuel-delivery holes in each injector are minute and very easily clogged.
How Contamination Enters
Contaminants may enter the fuel system in a number of ways. The fuel you put into the 4WD tank may be ‘wet’ or dirty. It’s not uncommon for water to accumulate in underground filling station tanks, or your spare jerry can may be contaminated with rust or dirt. Dirt may also enter the system via a bad filler spout cap or vent connections. If air can get in and out, then so can dust. Tank lines may create rust or aluminium oxide, which will find its way into the tank and then the supply lines. Metal filings or dirt may be left in the tank at the time of manufacture, which can happen for either original equipment or aftermarket tanks.
Filtering
Most vehicles have two fuel filters: one in the fuel tank and one in the delivery line.
The tank filter is almost never replaced or cleaned, as it is not easy to gain access to, which is usually done by removing the tank from the vehicle. It is designed to stop (filter) large particles that would damage the fuel pump and prevent water from entering the rest of the fuel delivery system.
The second fuel filter, the inline filter, is the engine's primary line of defence against dirty fuel. It sounds obvious, but manufacturers' guidelines should be followed for replacement times for this filter.
Contaminant Damage
Dirty fuel can damage engines in three ways. The least likely is direct pump or injector damage; more likely it’s injector clogging. Most likely to happen is ‘sanding’ of internal engine parts like valves, valve guides, pistons and cylinder walls. Aluminium and iron oxides can form in the vehicle's fuel tank and lines, and are powerful abrasives. Let's say your tank is half empty (or half full); the upper half of the tank is exposed to moist, oxygen-laden air. The sloshing action of the fuel in the tank, combined with whatever dirt or rust may be present to start with, acts as an abrasive mixture. The abrasive mixture scrubs the tank's wall, forming rust on the exposed walls, which then makes for a more abrasive mixture to start a vicious cycle that will see filters block very quickly.
One way of making outback touring that little bit safer is to fit a pre-filter inline before the main fuel filter. If that pre-filter should become blocked, it is an easy job to either replace it or remove it from the fuel line altogether. This second pre-filter can be a cheaper unit than the main filter and be of less filtering quality, helping to save a few dollars. However, if your filters are consistently blocking, a full cleanout of the tank may be on the cards. Treatment of newer tanks - OE or aftermarket - is significantly improved than tanks of yesteryear, however the constant abrasive action of fuel and dirt will eventually wear thin any internal coatings of a new tank. Vents are always a source of dirt ingress. They are designed to allow the movement of air, both into and out of the tank. Should the vent become dislodged from its normal position, dust can suck straight into the tubing and into the tank. No amount of tank cleaning and filtering will keep dirt out if your vents are not fitted correctly.
FILTER DESIGNS
Filters take on two general designs: depth filters and surface filters. Depth filters try to trap the contaminants within the filter. Old-fashioned oil bath filters are an example of a depth filter and are old technology that only prevents about 95 percent of harmful contaminants passing through the system. Surface filters, on the other hand, attempt to trap contaminants at the surface and manage to stop about 99.9 percent of harmful contaminants from passing through to the engine. A surface filter will trap particles as small as 10-20 microns. A human hair, by comparison, is approximately 60-70 microns in diameter; talcum powder is 10 microns; airborne dust can be 1-3 microns; and tobacco smoke as little as 0.5 microns. The human eye cannot distinguish particles finer than 40 microns. Most modern fuel filters are pleated, surface paper filters.
PLEATED PAPER FILTERS
A pleated paper filter is a surface-type filter and must maximise surface area without unduly increasing filter size. A simple flat surface filter would clog too fast, hence the pleating to increase the area. An improvement to the pleated filter is an arched pleated filter - basically a filter built into a canister.
Removal and Replacement
Fuel filter removal and replacement varies from vehicle to vehicle. Some require special tools, but others can be removed with pliers, screwdrivers or common tools in the toolbox. Before removing the filter, take note of the flow-direction arrow that is usually printed on the side of the filter. Remember the direction when installing the new filter.
Installation is generally a reversal of the removal procedure. Sometimes it’s easier to attach the inlet and outlet tubes to the filter and then reattach the filter to the vehicle. Otherwise, fit the filter then reattach the hoses. It is always a good idea to refit the outlet line first, as fitting the inlet first will allow fuel to run through and out of the filter.
Once fitted, start the engine and check for leaks from the whole system, starting from where you have been working.
Trackside Repair
Fuel filters are generally unable to be opened or fixed, although some washing of the element is possible. To do this, fill the filter from both inlet and outlet tubes, shake the filter in your hand and pour the contents out through both holes. Continue doing this until clean fuel can be poured out of the outlet hole freely. Since an engine will run on a less than perfectly clean filter, it is possible to keep your 4WD going by washing the filter of the majority of its contaminants. The best bet is to always carry replacement filters while out in the bush. Practice changing the filter in the comfort of your driveway at home, and you should only be held up for a short period if you get a gut full of dirty fuel while travelling the outback. Additionally, avoid filling your 4WD from old 44-gallon drums, jerry cans or any other suspect containers without first filtering the fuel through a funnel with an in-built filter. That way, you'll spend more time seeing the beautiful outback (than seeing the underbody of your fourby!).
Safety
When working with any type of fuel, always consider safety as the number-one priority. EFI fuel systems operate under high pressure. This ‘pressure charge’ is stored even after engine shutdown. Be prepared for fuel to forcefully squirt out, creating both a personal and fire hazard.You must either relieve the fuel pressure at the fuel rail test point or be prepared with a rag wrapped around the joints. Always refer to the user's manual when working with the fuel lines.
|
|
