General SU Testing Process to Confirm SU Fuel Pump is Functioning Properly by Car Model

Tech Tip: Testing Process to Confirm SU Fuel Pump Functioning Properly

The procedures in this technical sheet involve testing the fuel and electrical systems of a vehicle equipped with an SU fuel pump. Testing may require disconnecting fuel lines and handling gasoline. If you are unsure of any procedure, lack the proper tools, or are uncomfortable working with fuel or electrical systems, do not proceed.

Gasoline and fuel vapors are highly flammable. Work in a well-ventilated area away from sparks, flames, cigarettes, and hot surfaces. Wear appropriate eye protection and use a suitable fuel-safe container when performing flow tests.

Improper testing or repair may result in fuel leaks, fire, vehicle damage, component failure, personal injury, or unsafe operating conditions. Flow rates and pressure specifications may vary depending on the specific pump, vehicle, and modifications, so verify the correct specifications before diagnosing a pump as faulty.

When in doubt, stop testing and seek assistance from a qualified technician experienced with SU fuel pumps and classic British automobiles.

The person performing the work assumes all responsibility for the use of the information contained in this document.

Recommended Safety guidelines: 

Work in a well-ventilated area.

Relieve fuel system pressure before disconnecting lines

Keep sparks/flames away

Wear eye protection

To start, it is important you identify the model of pump on your car. Look at the body (casing/valve section).

On most SU Berlin pumps (non-brass), the part number is stamped directly onto the body.

This is usually on the main casing near the valves, not on removable parts like the cap or electrical end.

If it’s a brass-bodied pump, it’s an earlier or different variant and typically won’t follow the same identification method.

 Testing Techniques:

Symptom-based diagnostics process, which is to diagnose from symptoms like noises, vibrations, smells and flow rate.

To confirm whether a SU fuel pump is working properly, you can actually diagnose them by their clicking behavior as much as with tools.

Listen to the clicking (signature SU test)

• Turn the ignition ON.
• The pump should click rapidly at first, then slow down or stop once fuel pressure builds.

1. Rapid clicking that slows/stops is normal
2. Continuous fast clicking fuel not reaching carbs (air leak, empty tank, blockage)
3. No clicking is a bad pump not operating (electrical or internal failure)

Check fuel delivery at the carbs

Refer to the car and pump model specifications provided below to determine whether the pump is operating within acceptable parameters. The listed rates correspond to the vehicle’s original design requirements; vehicles that have been modified may require different operating parameters

The flow rates given are designed for 30 second run tests.

To Test Flow Rate

• Disconnect the fuel line at the carburetor.
• Place it into a Graduated container.
• Turn ignition ON (for 30 seconds).
• Measure volume of fuel delivered in container.
•  

MG Midget / Austin-Healey Sprite (1098cc–1275cc)

AUF214 (2.5–3.0 PSI)

• ~0.26–0.30 L in 30 sec = healthy, normal
• ~0.18–0.25 L in 30 sec = borderline (check filters, voltage, fuel lines, air leaks)
• <0.17 L in 30 sec = problem likely (pump wear, sticking valves, diaphragm or restriction)

Austin Healey 

100 / 100-6 BN1 - BN4 C.E.60412)

 AZX1331DP (2.-3.8 PSI)

•  ~0.26–0.28 L in 30 sec = healthy, normal
•  ~0.18–0.25 L in 30 sec = borderline (check filters, voltage, lines)
• <0.17 L  in 30 sec = problem likely (pump wear, restriction, or air leak)

100-6 / 3000 BN4 from C.E.60413  – BN6, BN7, BT7, BJ7; BJ8 to (c)28244) 

AUA 157 (2.-3.8 PSI)

• ~0.45 – 0.50 L in 30 sec = healthy, normal
• ~0.30 – 0.44 L in 30 sec = borderline (check filters, voltage, lines)
• <0.29 L in 30 sec = problem likely (pump wear, restriction, or air leak)

3000 BJ8 from (c )28225 

AZX 1307DP (2.5-3.5 PSI)

•  ~0.54 – 0.60 L in 30 sec = healthy, normal
•  ~0.40 – 0.53 L in 30 sec = borderline (check filters, voltage, lines)
•  <0.39 L in 30 sec = problem likely (pump wear, restriction, or air leak)

MG TC to approximately (c )4400

                AUA 25B (0.75 – 1.5 PSI)

• ~0.24 – 0.26 L in 30 sec = healthy, normal
•  ~0.17 – 0.23 Lin 30 sec = borderline (check filters, voltage, lines)
•  <0.24 L in 30 sec = problem likely

MG TC – TF

                AUA25 (0.75 – 1.5 PSI)

•  ~0.24 – 0.26 L in 30 sec = healthy, normal
•  ~0.17 – 0.23 Lin 30 sec = borderline (check filters, voltage, lines)
•  <0.24 L in 30 sec = problem likely (pump wear, restriction, or air leak)

MGA 

AZX1331DP (2.-3.8 PSI)

•  ~0.26–0.28 L in 30 sec = healthy, normal
•  ~0.18–0.25 L in 30 sec = borderline (check filters, voltage, lines)
•  <0.17 L in 30 sec = problem likely (pump wear, restriction, or air leak)

MGB RD to (c )44438 (Aug 64)

AZX1331DP (2.-3.8 PSI)

• ~0.26–0.28 L in 30 sec = healthy, normal
•  ~0.18–0.25 L in 30 sec = borderline (check filters, voltage, lines)
•  <0.17 L in 30 sec = problem likely (pump wear, restriction, or air leak)

MGB RD from (c )44439, all GT

AZX 1307DP (2.5-3.5 PSI)

• ~0.54 – 0.60 L in 30 sec = healthy, normal
•  ~0.40 – 0.53 Lin 30 sec = borderline (check filters, voltage, lines)
•  <0.39 L in 30 sec = problem likely (pump wear, restriction, or air leak)

MGC

AZX 1307DP (2.5-3.5 PSI)

• ~0.54 – 0.60 L in 30 sec = healthy, normal
•  ~0.40 – 0.53 Lin 30 sec = borderline (check filters, voltage, lines)
•  <0.39 L in 30 sec = problem likely (pump wear, restriction, or air leak)

JAG XKE-6CYL 

AZX 1318EP (2.5-3.5 PSI)

•  ~0.47 – 0.57 L in 30 sec = healthy, normal
•  ~0.30 – 0.46 L in 30 sec = borderline (check filters, voltage, lines, air leaks)
•  <0.29 L in 30 sec = problem likely (pump wear, restriction, or air leak)

XKE-V-12

AZX1405 (2-3.8 PSI)

• ~1.20 – 1.45 L in 30 sec = healthy, normal
• ~0.90 – 1.19 L in 30 sec = borderline (check filters, voltage, lines, air leaks)
• <0.90 L in 30 sec = problem likely (pump wear, restriction, or air leak)

 XK120 / XK140 / XK150 / Early Sedan Mk I, II, & 340

AUA152 (2-3.8 PSI)

•  ~0.50 – 0.65 L in 30 sec = healthy, normal
•  ~0.35 – 0.49 L in 30 sec = borderline (check filters, voltage, lines, air leaks)
•  <0.34 L in 30 sec = problem likely (pump wear, restriction, or air leak)

XJ6 1969-75

AZX1307EN ( PSI )

•  ~0.55 – 0.70 L in 30 sec = healthy, normal
• ~0.40 – 0.54 L in 30 sec = borderline (check filters, voltage, lines, air leaks)
• <0.39 L in 30 sec = problem likely (pump wear, restriction, or air leak)

XJ12     

AZX1405 (2-3.8 PSI)

• ~1.20 – 1.45 L in 30 sec = healthy, normal
•  ~0.90 – 1.19 L in 30 sec = borderline (check filters, voltage, lines, air leaks)
•  <0.90 L in 30 sec = problem likely (pump wear, restriction, or air leak

If The Results Are:

Good flow with 30 sec test will fall in your model car average normal deliver rate.

Weak flow 30 sec test resulting in less than normal delivery rate for your model car.

• Weak or no flow → pump issue or blockage
  1. To determine if there is a blockage in the line. Re-test the SU fuel pump using a fuel delivery line that has been verified to be free of any obstructions.

Measure pressure (if you want precision)

SU pumps typically produce: Around 1.5 to 3 PSI (depending on model)

Use a low-pressure gauge to determine if the failure is caused by:

• Too low → worn diaphragm or valves
• Too high (rare) → incorrect pump or internal fault

Tap test (classic SU trick)

If the pump stops clicking: Lightly tap it with a screwdriver handle.

If it starts working again: Points are worn or sticking (very common on SU pumps).

Check electrical supply:

• Use a test light or multimeter at the pump terminal.

Results:

• Power present but no clicking → bad points, coil, or internal failure
• No power → wiring, ignition circuit, or fuse issue

Inspect common SU failure points

SU pumps are mechanical-electrical hybrids, so typical issues include:

• Worn contact points (most common)
• Sticking diaphragm
• Dirty or stuck check valves
• Air leaks in fuel line (causes constant clicking)

7. Observe behavior while with engine running

Pump should click occasionally, not constantly

If it keeps clicking rapidly: fuel demand isn’t being satisfied → blockage, leak, or weak pump

Quick summary

• Clicking that slows/stops = good
• Strong pulsed fuel flow = working
• Constant clicking = supply problem
• No clicking = electrical/mechanical failure