Re: help electrical problem 1993 5.8 omc
Interesting, I have a similar problem with my 1993 5.8 as well.
Mine would cut out occassionally with little warning. It would restart with a lot of cranking but would then only run rough at best (stumbling) and I would have to feed it lots of throttle so I wasn't able to get it in gear. It would die as soon as I brought the throttle to neutral. So far I've tracked it down to the fuel pump control circuits.
I made up some monitoring LEDs on straight pins that were pushed into the wires to the two fuel pumps. When everything is running properly, these LEDs would be glowing a solid red, but when stumbling they would flash indicating to me that the fuel pumps were being turned on and off rapidly (about four times per second).
The fuel pumps are connected in parallel and engergized by a small relay mounted just to starboard of the foreward (low pressure) pump. I've just mounted an LED across the coil of this relay too see if it is picking up properly but so far the boat has been running just fine.
For reasons unknown, if I shut the battery off and totally power down the system the engine will start normally. This doesn't seem to make a lot of sense unless it is somehow re-setting whatever is causing the fuel pumps to pulse on and off.
When you read seven volts, your volt meter may be interpretting a rapid on/off as a steady seven volts. Do you measure an AC voltage across your fuel pump? If yes, you're probably having the same pulsing as I am and you may be able to start the engine by giving it more throttle.
Does any one have a schematic of what controls the relay that picks up the fuel pumps?
