2003 Mercruiser 5.0 fuel pump challenge

[Alphawater]

I have a 2003 Bayliner I/O with Mercruiser 5.0 with thunderbolt V ignition control module and electronic fuel pump - not fuel injected. After third day on water in remote location, fuel pump would not run with ignition and kill switch on. Local mechanic helped confirm fuel pump was working but something was preventing voltage to the pump. Console fuses checked out fine. In order to get me home, mechanic wired a bypass from the fuel pump harness connection to the ignition coil and the battery ground. Motor worked great for 2 hour return home. Upon return and after reading similar forum threads, I have searched for fuses and relays from the bypass access point to the ICM - none found to this point. Local marine service doubted it is the ICM but backlogged so can't look at problem. Guidance help would be appreciated. Thanks.

 

[achris]

Hello and welcome to iboats.

Most likely cause of a lack of power to a fuel pump is the oil pressure switch. Either faulty, or most likely, corrosion on the terminals. The switch is located on the port side of the engine, below the exhaust manifold, down from #7 spark plug. There may be a tee piece there with the oil pressure sender (for your gauge) and the switch. The sender has a blue wire, the switch has 2 wires, a purple and a purple/yellow...

Chris........

 

[Alphawater]

Hello and welcome to iboats.

Most likely cause of a lack of power to a fuel pump is the oil pressure switch. Either faulty, or most likely, corrosion on the terminals. The switch is located on the port side of the engine, below the exhaust manifold, down from #7 spark plug. There may be a tee piece there with the oil pressure sender (for your gauge) and the switch. The sender has a blue wire, the switch has 2 wires, a purple and a purple/yellow...

Chris........

Thanks Chris for the info. I went ahead and tested the oil pressure switch and sender - switch defective but sender seemed okay - decided to replace them both. Having accomplished that today, in trying to start the boat, there is no power getting to the starter or solenoid when activating the ignition switch. 90 amp fuse on the starter checked out as did the fuses under the console - 50 amp breaker also okay. I do have power to the console gauges and to the audible warning sensor for low oil pressure that occurs at each start up. Confused about what to pursue next..

 

[dubs283]

Neutral safety switch?

 

[Alphawater]

Thanks for suggesting the neutral safety switch - I forgot to mention that in my last post - it was in the on position while trying to start the engine.

 

[QBhoy]

Bit of a strange one this. The description of expecting to hear a fuel pump run when ignition is turned on…would be normal for an mpi perhaps. Not a carb.
As mentioned, the fuel pump on a carb like this and it’s era…I’d assume would be triggered from the oil pressure switch when cranking.
If you aren’t getting to even crank the engine over…I might be suspecting something else other than the fuel pump for sure. Along the lines of a kill switch wiring issue or in gear interlock…perhaps even a poor connection somewhere even.

 

[nola mike]

Thanks for suggesting the neutral safety switch - I forgot to mention that in my last post - it was in the on position while trying to start the engine.

Different switch... The switch that is in the throttle that won't crank the engine if it isn't in neutral. You can wiggle the throttle a bit while trying to start.The other dead man switch (what I think you're talking about) will crank but not start the engine.

 

[achris]

Generally, deadman switch kills the ignition, but will allow the engine to be cranked with the starter motor, it just won't fire. That switch is usually on the outside of the gear/throttle control with a lanyard attached. Usually the DMS is after the instruments, so it will look like everything is fine, just no spark.

Neutral safety switch is usually inside the control box and will stop the starter motor from engaging...

I have recently seen variations of the above, so YMMV. (but always, the neutral safety switch will cut power to the starter motor.)

Chris....

 

[dubs283]

Thanks for suggesting the neutral safety switch - I forgot to mention that in my last post - it was in the on position while trying to start the engine.

Understood, as others mentioned the safety lanyard switch (run/off) on the remote/dash is for the ignition. Neutral safety is located in the remote for mcm/sterndrive applications. It's not a manual operated switch, the shifter mechanism engages it when not in neutral.

Check the stickies, top of forum page for the starting system troubleshooting guide

 

[Alphawater]

Thanks to all for the input on solving my boat problem. After checking on the suggestions along with rechecking wiring connections, switches and fuses with no success, I decided to remove and check the slave solenoid. The solenoid tested okay but in reinstalling the solenoid, I thoroughly cleaned the mounting bolts and attachment points on the engine. To my relief the starter engaged - then in starting the motor I could hear the fuel pump activate when the oil pressure increased and the motor is now starting up and running smoothly. Hopefully that is the end to this challenge. Thanks to everyone for helping out!