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Fuel pumps: Rolling the dice

September 17, 2014
By Larry DeHays , Fort Myers Beach Bulletin, Fort Myers Beach Observer

So here he was, driving over a high bridge in the Florida Keys, admiring the view of the turquoise water below, when his engine died. His forward momentum carried him over the top of the bridge, and then the 30-foot boat on the trailer behind him wanted to get to the bottom of the hill. He could coast down, he thought, but he would have to stop at the bottom to pull off the road.

A problem appeared. Practically all vehicles now come with power brakes. That means that power is provided by the engine to help your foot apply pressure to your brakes. That means: no engine power, no power assist. Foot power alone is woefully inadequate to stop a heavy truck and trailer going downhill. That's not all. You also have no power assist to the steering. It takes two hands and muscle to turn the wheel. Usually your butt's off the seat because you're standing on the brake pedal with all your weight while hanging onto one side of the steering wheel.

Should something like this happen to you, try to remember to downshift the transmission. That will use the engine as a brake and the spinning of the engine will generate some power assist for the brake and steering. In this case, he made it, with possibly a few new gray hairs and, after a very expensive tow, we found that his fuel pump had failed.

How can a fuel pump fail so suddenly? (You may ask). For the same reason a light bulb blows out suddenly. (I may answer). They're electric. All fuel pumps are now electric, and located inside the gas tank. The reason they are there is because everything is now fuel injected rather than carbureted, and that requires a much higher fuel pressure. If the pump was located outside of the tank, is would result in a low pressure from the tank to the pump, (the suction side), which would result in vapor-lock. If you remember your high school science, lower pressure requires a lower temperature for the boiling point. Vapor lock is simply gasoline boiling in the lines. Having the pump in the tank pressurizes the entire fuel line, making vapor lock a thing of the past, except for the breath caught in the lungs of the driver when that little electric gadget goes pop. That's real vapor lock.

How can you tell if a pump is about to fail? In most cases, you can't. They often fail without warning. There are, however, a few symptoms that might appear that give warning. Sometimes you can hear the electric pump whining from the inside of the car. That's an indication that the bearings are bad in the pump, and it will soon fail. Or sometimes the vehicle will be hard to start, requiring a long cranking time before starting. That is an indication that the check valve in the pump has failed, letting the pressure drop when the engine is off and/or the pressure from the pump is low, requiring a long time to reach enough pressure to run the engine. That pump also is destined to fail. Having the pump pressure checked with a pressure gauge might be helpful. If the maximum pressure is on the low side of the allowed range of pressure, it would indicate a weak pump, however, some pumps fail while they are putting out plenty of pressure, so high enough pressure is not a guarantee that the pump will not fail.

Simply changing the pump pro-actively is a tough pill to swallow, because it is often a very expensive job. Pumps run from $100 to $500, and the gas tank must be drained and removed in most cases, requiring $200 or more in labor charges. A few cars and trucks (usually foreign) have removable panels in the floor giving access to the top of the fuel tanks where the pumps are located. These are less labor, but usually have the higher priced pumps. (It's probably a conspiracy, but I don't know how you'd get Volvo to conspire with Chevrolet.)

Some vehicles run on their original pumps for hundreds of thousands of miles, and some (like the above mentioned truck) will need another one after only three years. It's a crap-shoot, like many things in life. If yours' doesn't show any symptoms, "don't worry, be happy." Worrying about fuel pumps will give you gas.



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