Tech Stuff

It may not be the pump: Problems can be caused by a variety of fuel system issues

The fuel pump electrical system can be diagnosed with a DVOM and amp clamp and oscilloscope, but this special circuit verifier can save time. It tests the condition of both the fuel pump and its circuit.
<p>The fuel pump electrical system can be diagnosed with a DVOM and amp clamp and oscilloscope, but this special circuit verifier can save time. It tests the condition of both the fuel pump and its circuit.</p>

Weber is president of Virginia-based Write Stuff. He is an award-winning freelance automotive and technical writer and photographer with over two decades of journalism experience. He is an ASE-certified Master Automobile Technician, and has worked on automobiles, trucks and small engines. He is a member of the Society of Automotive Engineers (SAE) and numerous other automotive trade associations. He has worked as an auto service technician, a shop manager and a regional manager for an automotive service franchise operation.

Unless you are into racing or collectable cars, you have probably not seen a mechanical fuel pump in many years. The same could be said for most external electric fuel pumps. With the death of the carburetor and the advent of fuel injection, electric, in-tank fuel pumps have become the norm.

In general, these fuel pumps are designed to last the life of the vehicle, or at least 200,000 miles. And they probably would if it were not for outside issues. And, quite often a problem that appears to be a fuel pump problem at first glance may be something entirely different.

No professional technician wants to have a comeback due to a blown diagnosis. A rough running, poor performing and even a non-running engine can be the result of a variety of fuel system issues.

Common contaminants

Before condemning a fuel pump, check for lack of fuel. Yes, it actually happens and techs have actually overlooked it. Check the fuel gauge, but don’t trust it 100%.

There may be contaminated fuel in the tank. Contamination is, in fact, the number one cause of fuel pump failure. Although the filter sock on the fuel pickup in the tank does a pretty good job, it cannot stop everything. If it filtered too well, fuel pressure and volume would be inadequate for the engine. If the debris is small enough, it will pass the sock and enter the pump where it will eventually cause internal wear and failure.

Replacing a complete fuel pump module is quick, easy and ensures against a comeback.
<p>Replacing a complete fuel pump module is quick, easy and ensures against a comeback.</p>

Dirt and other foreign matter can enter the tank during refueling. The gas station may not be changing its filters often enough or the tanker has just made a drop and stirred up the stuff in the underground storage tank.

Remind your customers to avoid buying gas when they see the tank truck on site. On fuel systems that feature a return loop, debris that is caught by the fuel injector screens may get washed back into the tank.

One of the most common contaminants is water. Not only will water cause a rough- running engine, it can wreak havoc inside the fuel tank.

Tags: Bob Weber  Fuel pump 
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