Fuel pumps have evolved from the days when a few psi were enough to keep even the most powerful engine well fed. Today, fuel pumps need to provide fuel at 35, 40 or up to 100 psi to keep fuel injection systems functioning properly.
This job has largely fallen to in-tank units, which spend their lives immersed in fuel. While they generally work well, their replacement is often difficult, making the right procedure and performance even more critical then ever. In any discussion of fuel pumps, it is important to mention that fuel pressure must be maintained in a system even when the engine is shut off.
Also, fuel strainers must be replaced any time a pump is replaced. Sometimes, especially if a bare pump assembly is being installed, an installer may be tempted to reuse the old strainer. This is a recipe for a comeback. The strainer is the only protection for contamination that an electric pump has. Once it has become plugged or contaminated, it is virtually impossible to clean. A contaminated strainer is frequently the cause for low pressure of flow in a fuel system.
This last point brings to the fore the subject of proper diagnostics. An important aspect of diagnosing fuel pump problems is determining whether the pump supplies the correct fuel volume and pressure. It can be difficult for installers to find these specifications, but troubleshooting without them is sure to lead to problems. A fuel pump must be able to provide sufficient pressure and flow (or volume) to the fuel injection system. If either specification is not met, the engine will not perform properly. Testing for only pressure, for example, won’t reveal a volume problem and this could lead the technician down the wrong path in determining the origin of a driveability problem or no-start condition. It has also been known for a pump to work well when cold, then suffer from problems after a period of continuous running for some time.
In both cases, only a proper diagnostic procedure will reveal problems.
Some vehicles suffer from specific problems that seem designed to throw technicians for a loop. One of the classic problems is a seemingly non-functioning fuel pump with no power in the circuit. Generally, this is revealed as a no-start condition that has no apparent cause and has appeared without warning. Before ordering and installing a variety of components and going through numerous system checks, technicians faced with such a problem would be well advised to check for a safety switch. Designed to shut off the fuel pressure in case of a collision, these can sometimes be triggered by the slightest of bumps, from parking by “feel” or even tossing a bag of golf clubs in the trunk. It’s an easy check and worth the trouble.
A worn out pump may also be the victim of restricted fuel flow in the lines. Failure to replace clogged or kinked lines will not only result in an ineffective repair; it will also lead to early failure of the replacement pump.
Keeping yourself and your installers reminded of these points will not only help you sell pumps and additional parts, it will result in a more complete repair and reduced comebacks.
Special thanks to Master Parts Division, Blue Streak-Hygrade Motor Products, and Hella Inc. (Pierburg) for information used in this article.
AVOIDING THE COMEBACK TRAIL
After having sold a fuel pump, you want to keep it sold. Here are some reasons they can end up back on your counter.
1. Contamination in the fuel is the main reason for pump failures and returns.
2. Improper pump mounting or installing the strainer incorrectly can lead to noise or pump failure.
3. Incomplete fuel system diagnostics can lead to a pump replacement that is not required, then sent back because it was not needed and the expense was more than a customer would pay.
4. Pumps can also be damaged during installation. Some fit very tightly when placing them into the tank and if force is used, the hanger assembly can be damaged, causing improper function of the pump or the fuel sender.
5. Application errors are also popular. Some vehicles may have multiple pumps listed and the wrong pump will be returned. Be meticulous when checking catalogs.
There are many reasons why a customer will return a fuel pump. The main thing is to make sure that the application is correct, that complete diagnostics are performed, and that the pump is installed into a clean environment.