Fuel System Diagnostics

As SSGM Magazine’s Editor, I enjoy seeing how engineering and technological progress changes people’s perceptions. This is especially true with automotive technology. Think about fuel systems for a moment. My wife and I own and still drive a 1991 Honda Civic. One thing I have to do every couple of years is change the fuel filter. In this Honda Civic, the fuel filter is on the passenger side of the engine compartment and can be easily replaced. Whenever I mention this to people, there is a look of astonishment that the fuel filter is even accessible; or that it has to be changed regularly.
There was a good reason for the fuel filter to be so accessible. It was to be changed regularly in order to keep contamination in fuel to a minimum and thereby keeping the engine running smoothly. As every technician knows, fuel filters today are built into the fuel pump module which sits snuggly inside the gasoline tank. Fuel blenders today operate at very high standards so there is very little risk of someone buying contaminated fuel from major supplier; and even smaller independent gasoline sellers buy from the major blenders.
That does not mean there is no chance of contamination from happening and the fuel system being compromised. What a technician has to keep at the top of mind is contamination is more likely not coming from bad fuel.
“Keep in mind, fuel contamination can come from several sources and can be caused by a variety of reasons, including dirt, excessive alcohol, water among others,” said Rocco Fini, product manager, powertrain with General Motors of Canada, customer care and aftersales. Contamination can be caused by incorrectly putting E-85 fuel into a vehicle which is not designed for such fuel, for example, Fini added.
The problem with high ethanol-based fuels such as E-85, is they require fuel systems to be specially designed to prevent corrosion from happening when fuel system parts come into contact with the ethanol. Materials with high concentrations of zinc, brass or aluminum can corrode and contaminate the fuel. Non-metal parts such as rubber or polyurethane and certain kinds of plastics can be damage causing contamination problems.
Older vehicles with rusting metal fuel tanks can also be a potential source of contamination. The problem with rust is the particles can sometime make their way past the fuel strainer system and possibly even the filter. Those particles then get into the pump and begin to damage the mechanism; or worse, get passed by the pump into the fuel system and begin to damage the fuel injectors. If a pump is damaged by such contamination and has to be replaced, it is crucial to properly flush out the tank to remove any possible future contamination; or to replace the tank entirely. Even plastic tanks can produce contamination as the inner lining can flake and the particles can begin to gum-up the system. Something else to keep in mind is to avoid too often using fuel and engine cleaning additives. These have to be used periodically to help remove buildups of contaminates in the engine system and improve fuel efficiency and performance. These work, however, by using corrosive agents that can, over too frequent use, damage the fuel system and create the kinds of contamination that one is trying to prevent.
Careful probing the electrical system
All this is pretty basic. The more troublesome issue about fuel system maintenance is around electrical issues which, in some cases, can cause premature failure of a fuel pump.
Frank Tonon, director of product training with Spectra Premium pointed out that early pump failure is “caused by heat and heat is caused by high amperage.” If such a problem begins to happen the terminal and connectors will begin to overheat and that overheating will cause a loss of connectivity.
“The fuel pump relay is a good example. It is a little set of points that are designed to work anywhere from four to 10 amps,” Tonon added. “But with time, those points will begin to burn and create a lack of contact.”
“Electrical issues come down to what we call high-resistance connection,” said Dave Ehle, chief engineer of vehicle electronics and thermal products with Delphi Corp. “If you are trying to make a connection from the fuel module to the harness, you want those to be good electrical connections with low resistance or no resistance at the connection points. If you have a lose terminal or a terminal that has sprung a bit through corrosion, then you will have resistance which reduces the amount of current to the fuel pump which can look as if you have a poor pump, one that is delivering lower pressure and flow.”
But checking the electrical can be tricky. If one unplugs a connector and puts it back in, it can clear up the connection interface and then the circuit will work fine. The technician then sends the customer back on the road having replaced the fuel pump – mistaking the electrical problem for a faulty fuel pump – only to have that same customer come back complaining about the same problem. The real problem of the contamination or wear causing the electrical fault in the first place is still there and interferes with the new pump’s performance. Something else to remember: one has to be careful when probing the connections. Jamming in a probe tip can bend the spring leaf of the terminal and create an electrical problem one is trying to avoid.
“The first thing I would always do is look at the connectors and examine the terminals and see if you see something like corrosion or soot,” added Ehle. “There is a thing called ‘terminal fretting’ where if you have vibration going on, microscopic wiggling in the two halves of the connector will create dust from that movement and that dust can act as an insulator and you give an intermittent connection which is hard to find.”
That is why technicians are encouraged to exercise patience with dealing with fuel system electrical problems. It may take a while to finally pin-down the problem; however, the result will be a satisfied customer and not having to replace a perfectly good fuel pump.