How To Test An Electric Fuel Pump On A Classic Car

How To Test An Electric Fuel Pump On A Classic Car

This guide captures ‘bygone’ advice on how to Test An Electric Fuel Pump On A Classic Car. 

To see all my ‘bygone’ advice guides please visit Classic Car Maintenance DIY Guides.

Remember folks these are ‘bygone guides’ … useful but the safety and personal protective equipment measures are reflective of bygone awareness. Stay safe.


Electric fuel pumps (except those which operate on a rotary principle) work on similar lines to mechanical ones, in that they too use diaphragm assemblies.

But electric pumps use a solenoid to operate the diaphragm. They are usually very reliable and any faults which do occur are usually of an electrical nature.

If after the fuel pipes have been checked for blockages or leaks and the filter has been cleaned the pump is still inoperative the wiring and contact breakers should be checked.

How To Test An Electric Fuel Pump

Before testing the pump’s wiring it will be necessary to remove and plug the fuel lines. This is because the ignition will need to be switched on during testing and if the fault were discovered the pump might rattle into life and spew fuel everywhere.

In normal operation most electric pumps make a clicking noise particularly noticeable when they are first started up. So do not mistake this sound for a malfunction of some kind.

With the ignition off disconnect the lead attached to the rear of the pump. Touch this to one end of a circuit tester with the other end of the tester against a good earth (See Below).

Switch on the ignition. If the bulb in the tester fails to light up the wiring is at fault and should be overhauled. If it does light power is at least reaching the pump and further dismantling may be necessary to discover the fault.

After each use of the circuit tester turn the ignition off.

How To Test An Electric Fuel Pump
To test that power is reaching the pump place a circuit tester between the live wire to the pump and a good earth.

Next use the circuit tester between the pump wire and terminal. Failure of the bulb to light this time may simply be because the pump is not earthing properly. The pump will earth either through a wire a ached to the car body or directly through its mounting bolts.

How To Test An Electric Fuel Pump
If power is reaching the pump then test the pump by placing the circuit tester between the live wire and the pump terminal.

Check that this earth connection is free from dirt or rust. But if cleaning the earth connection fails to have any effect then another cause of the malfunction will have to be sought. So the next step is to dismantle and overhaul the pump.

How To Overhaul An Electric Fuel Pump

Burnt and dirty contacts are the most frequent fault in electric pumps. The contacts can be reached by first unscrewing the pump terminal (See Below) and removing the wire.

How To Overhaul An Electric Fuel Pump
The first step in dismantling this SU electric pump is to remove the pump terminal which is held in place by a nut.

Next undo the hexagonal nut and washer and pull the plastic end cover away. If the cover is sealed with tape peel it off gently so that it can possibly be used again.

How To Overhaul An Electric Fuel Pump
After having carefully peeled off the sealing tape and slid back the rubber band. The cover can be removed.

The contacts are now accessible. While the pump is not working the contacts should be closed. Test that they are free to open by sliding a card between them.

If they are in the open position already or are reluctant to open they will need to be replaced.

How To Test An Electric Fuel Pump
With a fingernail check that the contacts are free to open and close and that they are not dirty or pined.

Dirty or pitted contacts may be cleaned with a light abrasive such as 400 grade wet-and-dry paper. However this is only a temporary measure and sooner or later a new set will have to be fitted.

Slide out the top contact. If it feels very pitted it will need replacing. If it is only dirty clean it with a points file
How To Remove The Contacts On An Electric Fuel Pump.
To remove the lower piece of the contacts the first step is to remove the two retaining screws.

How To Clean The Contacts On An Electric Fuel Pump
Next the brass hinge pin needs to be pushed out with a fine point and then withdrawn with pliers
How To Clean The Contacts On An Electric Fuel Pump
The final step is to lever the contact away from the central pin with a small screwdriver. Just enough to free it.
How To Clean The Contacts On An Electric Fuel Pump.
The lower part of the contacts can now either be replaced (if badly pitted) or cleaned with a points file (if only dirty.

Further work on the pump is possible but replacement parts are often hard to come by. More to the point the price of a new pump compared with the difficult and fiddly nature of further repair makes the decision a little undesirable.

The rarer rotary electric pumps have a motor-driven impeller. These pumps are generally very reliable being of simple design.

If after all the preliminary checks described above have been made a rotary pump still fails to work it will probably be best to consult a specialist before going any further.

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