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DIAGNOSING A FAULTY FUEL PUMP

We had a vehicle towed in to our work shop, it was a No Start.

When we tried to start the engine, the starter motor was turning the engine over well. So the first question; Is it a fuel issue or and electrical issue?

While feeding fuel manually into the engine fuel intake, the engine ran. This indicated a fuel supply problem. The 15 amp fuel pump was blown. We replaced the fuse, amp clamped the line and fed the graph onto our very large VDU screen where every minute detail can be seen.

Interpreting the graph we see that the left hand trace is showing that the fuel pump is drawing 19 amps and rotating at 29 rpm. The graph trace on the right is what we should be seeing drawing only 4 amps and spinning at 6500 rpm.

Diagnosis is a faulty pump!

After fitting a new fuel pump, the car ran like a dream… another very happy Gil Auto customer.

Lets take a closer look at why the Fuel Pump was faulty: We cut the metal covering of the pump to show the cause of the issue.

In the photo below you can see the fuel pump cut in half, showing the commutator and carbon brushes. Both are in good condition and show hardly any sign of wear.

The commutator should spin easily on it’s bottom bearing and the impeller blade. As you can see it was jammed tight and could hardly me moved even with a pair of pliers.

Viewing the impeller through the port the impeller looks like it could be in good condition. However something was jamming the commutator

Cutting open the rear end of the pump one can see the fault. The plastic impeller had expanded and was jammed against the metal housing.

We hope you enjoyed this explanation

For more information for the technically minded follow this link:
https://static.nhtsa.gov/odi/rcl/2020/RCLRPT-20E085-9538.PDF