An SU fuel pump rarely fails without warning. In most cases there are clear signs that something is wrong before the car lets you down — if you know what to listen and look for. Here is a straightforward guide to diagnosing a failing SU electric fuel pump.
The Symptoms
Continuous Rapid Clicking
A healthy SU pump clicks steadily when starting and slows to an occasional tick once the float chambers are full. If your pump clicks rapidly and continuously while the engine is running, it is working harder than it should. This usually points to a fuel leak (check the carburettors and fuel lines), a failing diaphragm that cannot hold pressure, or a worn valve that is letting fuel bleed back.
Slow or Laboured Clicking
A slow, irregular click — or a pump that seems to struggle to complete each cycle — usually indicates worn contact points, a weak armature spring, or a diaphragm that has lost its flexibility. The pump may still deliver fuel but will not keep up under load, leading to fuel starvation at higher engine speeds.
No Clicking at All
Silence is the most dramatic symptom. With ignition on and the engine off, a working SU pump should click. No sound at all with power confirmed at the pump terminal points to either seized contact points, a stuck or corroded armature, or a blown filter. On older pumps, gently tapping the pump body with a screwdriver handle will sometimes free a stuck armature temporarily — if this gets it going, a rebuild is overdue.
Fuel Smell or Leaks
Fuel weeping from the pump body or diaphragm cover is a clear sign the diaphragm has failed. Modern ethanol-blend fuels attack the original rubber compounds and can cause cracking even on pumps that appear outwardly fine. Do not ignore fuel smells — a leaking pump is a fire risk.
Hard Starting or Fuel Starvation
If the engine starts readily when cold but cuts out under hard acceleration, or requires excessive cranking before the engine catches, suspect a pump that is not building adequate pressure. This is often an early sign of diaphragm or valve wear.
Quick Checks You Can Do
- Listen to the click rate. Start the car from cold and count the clicks. A healthy pump will click several times per second at start-up, slowing progressively as pressure builds.
- Check the inline filter. A blocked filter starves the pump and mimics many of the symptoms above. Replace it before condemning the pump.
- Check fuel delivery. With the fuel line disconnected at the carburettor, turn on the ignition and check that the pump delivers a steady pulse of fuel into a container. Weak or intermittent delivery confirms the pump needs attention.
Rebuild vs Replace
Original SU pumps are robust and well worth rebuilding. The body castings last indefinitely and a proper rebuild with new diaphragm, valves, rocker mechanism and seals will restore the pump to as-new performance — often better, because modern diaphragm materials are far more resistant to ethanol than the originals.
Pattern replacement pumps vary enormously in quality. For a car you intend to keep and use, a rebuilt original is nearly always the better investment.
Our SU fuel pump rebuild service covers single and dual pumps, includes full strip, bead blast and repaint of the body, and carries a 2-year guarantee on all fitted parts. Send us your pump and we will do the rest.