Critical Component Testing - Fuel Pumps

Critical Component Testing – Fuel Pumps

Our biggest single selling items, after Scan Tools, include the Bosch & Goss range of EFI Fuel Pumps. Not to dwell on the quality, but let’s start at the end – the Warranty Claim. this is where we see most failed attempts at fuel pump testing. All but the most extreme examples are normally corrupted with contaminants.

Consider this, the clearance in a roller cell fuel pump, I.E High volume Bosch, is 6-7 microns. But good quality prescreens cannot be any finer than 20-40 microns, or starvation will occur. Therefore it is essential that you clean & test the fuel/tank upon fuel pump replacement.
Pump testing should then begin with supply current. Most 12v pumps increase there output proportional to voltage. i. e, a good power supply will ensure maximum fuel volume. (Pressure remains constant as determined by the Pressure Regulator).

A current clamp is a better indicator of fuel pump operation as it tells a bigger story than the available supply voltage. Here are some common current draws;

  1. Bosch Roller Cell   10-13 amps
  2. Gerotor                      5-7 amps
  3. Rotary Vane              5-7 amps

Things that will increase current draw include  blocked fuel lines / filter, low voltage supply, bad pump earthing. A decreased current draw could be poor electric motor brushes – not allowing complete conductivity.

Nissan & Subaru style JECS pumps, (manufactured by Bosch) are voltage controlled pumps. Read this, it is very important…
These pumps receive a varied voltage (via duty cycle) as engine demand calls for it. These pumps are traditionally twice the price of similar output 12-14v pumps, because of the complex nature of the driving electronics. Quite simply put, a standard pump will not last very long with a 70% duty cycle supply voltage.
Test these JECS style pumps with a scope such as the PDC 150 or FSA 450 to ensure duty cycle(%) switching is occuring.

A cavitating pump may be able to acheive the pressure to fool the technician, but it essential that there is also sufficient volume available to the injectors. Our rule of thumb is 1/2 litre in 30 seconds. Alternatively, using the Fuel Monitor tester, you would expect to see between 1.5-3.0 l/min flowing at idle. Any less may starve the engine under medium to light loads.