dougrainer wrote:
Older Chevy P 30 chassis that had dual tanks OR they had a vapor lock problem and the OEM installed a aftermarket fuel pump, they used one of the oil plugs at the oil filter block housing and installed a oil pressure switch that only when you had oil pressure would power be routed to the electric pump. Engine not running(no oil pressure) no fuel pump running. This is the easiest and a good safe way to power an Electric fuel pump. Doug
Doug brings up a point I forgot..
There SHOULD be an oil pressure switch between the pump and ignition switch.. The idea is if no oil pressure then the pump is not running, a real safety hazard is present if the pump continues to operate under certain conditions.
The ignition switch should provide power to the pump in RUN position, in START position the ignition switch will bypass the oil pressure switch for only the time of cranking over the engine.
Once engine has started the ignition switch should no longer bypass the oil pressure switch..
There is a chance that the oil pressure switch was replaced with an incorrect one and or bypassed.
There is a chance that the ignition switch is bad (ignition switch contains multiple switch contacts) and someone bypassed a few safety circuits on the switch to get the engine running..
The only way to know for sure is you will need to find the electrical schematic for your chassis and start tracing..
