Auto Service Professional

OCT 2017

Magazine for the auto service professional

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Page 23 of 77

22 | ASP October 2017 Technical connector that is used to replace the car's original connector. Pump replacement A typical fuel pump will last for years if the gas is always clean, but contaminated fuel can kill a pump in just a few weeks. Before installing a new fuel pump, find out if the old one was ruined by something in the fuel. If possible, start by getting some informa- tion from the customer. Do they usually buy the cheapest fuel they can find? Do they frequently drive with less than a quarter tank of fuel? Do they ever pour additives into the tank? How many times has the car been run out of gas? Did the car stop running soon after they bought gas? When removing the old pump, check the condition of the tank seal. Does it look like dirt or water might be getting past it? Now drain the fuel tank. If you use a fuel caddy with a filter, you can return the gasoline to the tank later. Otherwise plan on putting in a few gallons of fresh gas (always a safer choice). Inspect the tank for rust, corrosion and other solids. ese can accumulate even in plastic tanks because metal in the pump unit cor- rodes, especially in humid climates. Also, it's inevitable that some dirt will fall in while the tank is being filled, especially in dry, dusty climates. Finally, examine the fuel itself. Is it cloudy or discolored? Pour at least a cup of it onto a clean white rag or paper towel and see what it looks like after it dries out. Is there an even tan stain or is it a rainbow of colors? Are there solid particles? How long did it take to dry out? Did it dry out completely or is it still wet or oily? If there's any question at all about what's in the fuel, clean or replace the tank and have a conversation with the customer about fuel contamination and your warranty. If a replacement pump fails soon after installation, it's almost always due to fuel contamination. Sometimes it's because dirt fell into the tank when replacing the pump, but more often it's a result of sediment being stirred up when the pump is replaced. at sediment often contains corrosion from metal parts of the pump assembly that react Current draw One quick and easy way to test a fuel pump is to measure the current flowing through the circuit with a digital volt/ohm meter (DVOM). This test will only show if current draw is too low, indicating high resistance somewhere in the circuit; it will not pinpoint the problem. However, it only takes a few minutes, and if the current is not too low, the fuel pump circuit is probably OK. There's no specification, but a rule-of-thumb says the current flow should be about half the fuse rating with the pump under load. For example, the fuel pump fuse here is rated for 20 amps, and the circuit flows about 10 amps with the DVOM set to capture min/max read- ings and the throttle snapped wide open.

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