Smokin' Fuel Pump relay

Formula Renault single seater, running mappable

ECU was getting hot under the collar.
To carry on racing the relay had been by-passed.
However this isn't safe practice and the cause had to be found.
The rating of the relay was checked to ensure it was up to the job. Then the current draw of another car was measured. (left).
A peak of 12 amps and a running current of aroun 10 amps.

With this in mind I was expecting to find a fault either in the wiring or the pump resulting in a much higher current draw. This was measured at the pump wiring with the by pass fitted. This would exclude the ECU and associated wiring. the result is shown. (right).

A peak of 14 amps and a running current of 12 amps, however it is running much slower than the previously tested pump.

When tested at the relay (with the by-pass wiring removed) no current draw was observed.

The car would not start, and the fuel pump refused to prime.

Closer inspection found a broken terminal going into the relay block. Not on the relay that was getting hot but on another that shared '+' feeds.

Once repaired and re tested none of the relays were smoking and the car barked into life.

I quick check of the 'fuel pump relay' showed little more than 0.2 A draw, it wasn't the fuel pump relay, but the ECU supply. The broken wiring resulted in back feeding and this in turn over heated the relay circuit. Re routing and not securing the relay block to the chassis should prevent it happening again.