Re: Motor suddenly dying

Posted by DavidPackard On 2023/4/28 23:11:00

Packard51; my ’48 had the same symptom of running for many miles without incident, and then after a sharp turn the carburetor ran out of gas . . . but I’m getting ahead of the story. I know now it was running out of gas, but at the time all I knew was the engine would stop running. The car was equipped with an electrical fuel pump intended for ‘priming’. The instructions I was provided indicated that the e-pump was not necessary after priming. Ultimately there was sufficient evidence to conclude that the instructions were incorrect in that the pump should have been powered continuously.

To paraphrase Paul Harvey, “And now, the rest of the story”:

There are two types of e-pumps currently available in a 6 volt configuration. One design operates somewhat like a solenoid with a set of points to cut the power feed when the core nears the end of the stroke. The whole mess operates as a spring/mass system cycling as long as external power is available. These pumps are available from Airtex, and allow the engine’s mechanical fuel pump draw through them with no apparent difficulty.
The second design is a rotary vane pump, without springs to bias the position of the vanes, which becomes important detail on whether the engine’s mechanical can draw through the e-pump. If the e-pump is installed per the manufacturer’s instructions most of the time when the power is cut the vanes relax enough to allow the engine pump to ‘draw through’ the e-pump until something disrupts the position of the critical vane . . . like a sharp turn. If the vane disruption blocks the fuel flow that’s ‘game-over’ the engine will run out of fuel. If however the disruption increases the most critical flow area the ‘game-continues’ with the driver completely unaware that anything has occurred. Some have used a rotary vane pump in conjunction with a bypass loop with a check valve, all of which allows the e-pump to be de-powered after priming.

My ’48 had a rotary vane pump, no by-pass loop, and the description I got from the previous owner was to use the pump as if it was a solenoid type pump. That car got so predicable on which turn it would ‘quit’ I would turn the e-pump on to avoid the possibility of stalling. I temporarily installed an electric fuel pressure gauge, and amazed myself when the fuel pressure when to zero on one of the notorious turns. I tore-down the vane pump and confirmed the blockage hypothesis. During one experiment the pump was reassembled with the critical vane positioned well out of the way. In that configuration it was quite easy to blow air through the pump, but when the pump was positioned so gravity pulled the vane into the minimum area position the flow became quite restrictive.

There is a very long list of what could make an engine stop running, but your comment about the previous owner installing an e-pump brought back memories. Please identify the e-pump design and plumbing details.

dp