merc 4.3 starting problem

[HLM1996]

Electic fuel pump will not always power on. If the engine sits overnight and you turn the key, 80 % of the time the fuel pump will not power on. The 20 % of the time that it does power on the engine starts fine. If I pour fuel in the carb it will start and run fine all day. I just read some more of the previous postings and it sounds like it may be an intermittent oil pressure switch ?

 

[Don S]

Re: merc 4.3 starting problem

On Mercruisers, there is a wire from starter solenoid that powers the fuel pump while the starter is engaged. If that wire is defective or loose or the solenoid on the starter has problems, it will not power up the fuel pump.
Here's a wiring diagram of how the fuel pump is wired.

 

[Don S]

Re: merc 4.3 starting problem

I just read some more of the previous postings and it sounds like it may be an intermittent oil pressure switch ?

You were "Editing" while I was posting.

IF the oil pressure switch was not working, it wouldn't keep running.

 

[180shabah]

Re: merc 4.3 starting problem

Possible bad pump - that is exactly how mine failed. With 12v applied directly to the pump, it only opperated 1-2 times with 20 attempts. Replaced the switch and installed a momentary switch to prime the system after sitting and now it starts on the first try, everytime.