4.3 electrical issues (intermittent is a nasty word!)

[ShoalSurvivor]

2 intermittent issues, at this stage, after engine removal and reinstall. Goal today was to fire her up and hopefully adjust idle/timing.

What keeps happening (Twice, this self corrected after about 45 minutes and I was able to try again. )

1) Gauge cluster loses power
2) bypassing oil pressure switch to test fuel pump fails

the details:
- I undressed the engine after replacing seals and oil pan; new filter and oil, and refinished the block.
- I disturbed the balancer while the distributor was out, so I have reset to 8ºBTDC after pressure on cylinders 1, and set distributor to cylinder 1.
- checked all connections on starter. Red and Orange circuit complete
- check alternator - Orange circuit complete
- ground from battery to flywheel cover is good (starboard), grounds (through engine) to flywheel cover (port) to wire harness (3 wires) and transom bracket are all good.
- 50Amp fuse - hot on both sides
- Starter solenoid: hot on red side, not on yellow!
- trim pump working, but thats on a dedicated circuit.

When the gauges are on, the starter kicks, engine cranks, but she wouldn't start. Sounded like lack of fuel, so I check for fuel in the carb and found none.

then I jumped the oil switch with ignition switch on, just to make sure the fuel pump was working. it was. reconnected the oil switch, and tried to start, and noticed the gauges were out again, and now the fuel pump bypass isn't working either.


Seems like there is a fuse blowing (and resetting itself) (not the 50Amp) to the gauges and other component, but the starter, alternator and red port of solenoid all remain powered when the other stuff goes.

Hoping for some clues or steps to take. Thanks.

 

[Fun Times]

What year engine model? Serial number handy.

Decent chance you have a bad connection at the Main wire harness 10 pin cannon plug at the engine… With the key on wiggle the wire wire harness and watch the gauges. See if they turn on and off.

If not, leave key on and start carefully wiggling all wires at engine, ignition key switch and wires under the dash make sure the lanyard switch is in the up/on position by physically touching it, etc.

 

[ShoalSurvivor]

What year engine model? Serial number handy.

2004 'ish 4.3 with Reman engine. Have been told it's:
MerCruiser 4.3L (Gen+) (4Barrel) Reman
No serial number.

I did disconnect the connon plug (as well as everything else). Will try the wiggle and dance test now. Thanks.

I tested the female side if the Cannon and found only one port was hot (7, it think). I was trying to figure out where the gauge power originates from the block.

 

[Fun Times]

See if this may be of help to you…

https://www.perfprotech.com/blog/articles/mercruiser-engine-harness-schematic?srsltid=AfmBOorM3GXaFmZEIgjkM2qTQwBKwePP_BIEHm4OESV2fjmT8Ee1iJJ8

 

[ShoalSurvivor]

More detail:
solenoid jump test kicked starter
getting power and ground to entire console cluster including ignition
verified starter connections, again
fuel bypass still not working. I assume that should fire when oil switch jumped and key on, like it used to, but not now.
wiggled and jiggled but no change.

i will check power at starter from ignition when I can get help.

I sanded a cleaned all grounds. Tested bolts and the ground seems solid

thanks.

 

[ShoalSurvivor]

also, will pull console and test ignition switch.

 

[ShoalSurvivor]

also, will pull console and test ignition switch.

Interesting. Ignition switch continuity passed for both accessory and ignition position. Switch is good.

i pulled the red/yellow ignition wire from the starter solenoid and tested 12v power to switch. Failed. Checked fuse and it was blown. Replaced fuse, now working as expected

checked red/yellow ignition wire at solenoid with ignition switch and it passed.

removed oil pressure switch and jumped it. Fuel pump runs as expected.

pulled jumper and plugged oil pressure switch in and it immediately blew the ignition fuse.

I could probably run through a box of fuses trying to figure this out, it appears that plugging the oil pressure switch is blowing the 10A ignition fuse. does this indicate anything obvious?

 

[ShoalSurvivor]

I tested and there is no continuity between the leads in the switch side of the oil pressure switch, so I’m confused at how plugging it in would blow the fuse. Also, I blew the fuse again when measuring the voltage at the oil pressure gauge (between the purple and ground) with a multimeter.

im going to disconnect all purple wires and reconnect them one at a time to see if i can isolate a short.