Auto Service World
Feature   September 1, 2009   by Jim Anderton, Technical Editor

Last Dance

While EFI rules the roost, there are still opportunities for low pressure in-line fuel pumps...especially for obsolete applications

Back in the days B. E. (Before Electronics) fuel delivery in automotive applications was a simple affair: move fuel from the tank and get it to the top of the engine. Pumps were mechanical and engine-driven with a cam or push rod, or they were electric and almost always external to the fuel tank. The key difference to modern EFI was the operating pressure. Pressures over 10-15 psi in the carburetor were rare, and often a sign of trouble. Actual fuel metering was performed by gravity feed of fuel through a float controlled needle valve, reducing the pump to a float-bowl filling device. This made them simple and as a result pump diagnosis was usually reduced to check then replace.

Today, in-line electric pumps are seen in diesel applications, fuel transfer between dual tanks and, where most techs see them today, older vehicles. Common older cars still in the Canadian fleet are European models like Mercedes, Jaguar and Volvo, plus some Volkswagen and the many models of small British sports car, like the MGB. In each case, OE pumps are rare, expensive and not necessarily a good choice as a replacement.

SSGM tested a U. S.-made in-line replacement pump, Federal-Mogul’s Carter P74019. The test victim was a late model (1982) Triumph convertible, sporting an SU electric pump. SU pumps were common on English (and some Volvo) models for half a century before fuel injection and operated on a solenoid principle. A coil is progressively energized and de-energized through contact points like the points inside older distributors; a flexing diaphragm moves the fuel past check valves. Problem areas include leaky or split diaphragms and, in SUs, dirty or sticking points. Bad points give either a no-start, hard start or intermittent operation, which often clears temporarily by rapping the pump body. Replacement points and complete pumps are available, but are expensive and don’t completely solve the wear/sticking problem without going to electronic transistorized switching units. Can the American unit swap in without issues?

So how did it work? Perfectly, with one of the fastest install times of any pump I’ve seen. The small size, supplied clamp and self-tapping mounting bolt made the pump installation a 20-minute proposition; repairing the harness took another 30. Better yet, the Carter unit ticks very much like the SU pump it replaces, giving an authentic feel and a positive sound from the driver’s seat that lets the customer know it’s working. Inside the car, it feels just like the original SU, except as a sealed unit, it’s more reliable and less expensive. With an easy one-hour under-car time and plenty of pressure and volume, the Carter P74019 has a boring name, but excellent performance as a replacement for older or obsolete pumps.

Add your knowledge, expertise and experience.

Print this page


Have your say:

Your email address will not be published. Required fields are marked *