1996 Mercruiser 4.3 electrical issue?

Swedefj40

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Hi from Northwest BC Canada, first post here :)

First, a little about me. I have been on commercial fishing vessels since I could crawl (it's in the family) and now some 40+ years later I bought my first pleasure boat, (I'm an Electrician now btw).

I recently purchased a 1996 Campion Victoria 215 with a Mercruiser 4.3 and Alpha one Gen 2 and 2 weeks ago was the first run. It overheated. I changed the water pump and risers (which were really plugged up) and ran it in the driveway for a half hour and was a solid 165 - 170 F. Problem solved.

The wife and I went out for a run today to test run the boat and do a little salmon fishing as well. Ran great aside from a little bit of surging at idle while trolling so I had to troll around 800 - 900 rpm. No biggie. We picked up the gear and ran around some islands and did some sightseeing and headed back to port all of which took about 45 minutes at around 3700 rpm. Ran awesome.

So... I wanted to see her top speed and opened her right up. I ran it full out about 5000 rpm for no more than a minute and brought her back down to idle. She smelt a little hot, almost an oil smell but not really. Smelt more like burning electrical insulation smell. But there was nothing obvious. We idled around in gear for about 15 minutes (all was good) then went to take off and head back to the dock and right away I felt a vibration and noticed that the oil pressure gauge was reading '0'. I immediately shut the engine down and popped the cover. There was a noticeable smoke coming from the engine. It was not hot at all nor was there any oil leaks that I could see. Bilge was good, just a little bit of water and no oil sheen at all. I noticed that the dip stick was out a little bit with a few drops of oil around the tube but that's it. Lots of oil in the pan too. Finally I went to try it again, started it up, put it in gear looked at the gauges and noticed that the Tachometer was being erratic and still no oil pressure so I shut it down again and limped home on the kicker.

So all you experts out there what's the issue? My experience with small boats like this is nil but I'm mechanically inclined and I'm not afraid to tear into something if need be but I just don't know these motors. Someone steer me in the right direction.
 

Swedefj40

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Thanks, will check that tomorrow. So I did some more poking around. Plug wires are good. I did see a broken terminal off what I think might be the oil pressure sensor around the lower back of the port side of the engine. Are there 2 wires coming off of the oil sensor? Or is this the oil pressure cut off switch?
 
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Swedefj40

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This is what I mean...
 

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Scott Danforth

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This is what I mean...

holy corrosion batman. not only are the terminals on the switch corroded off, the terminals on the wire are green and the block is rusty.

my guess this is a salt water boat.
 

Swedefj40

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Click image for larger version  Name:	image_294003.jpg Views:	4 Size:	1.73 MB ID:	10598048 Yup it is.

I haven't been able to do a compression check yet but I did find that not only was the oil pressure cut out switch faulty the oil pressure sender (I'm assuming for the gauge) had the terminal rusted off too which explains the '0' psi reading on the gauge. You can see it in the picture. This doesn't explain the vibration I felt though. If these leads were grounding out on the block would it have any effect on the ignition? Thoughts?
 

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alldodge

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There it is!!! the oil pressure sender. So you don't have an oil pressure issue, its a sender issue
 

Maclin

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I think this engine has an electric fuel pump, just wondering how it was getting power with that terminal off.
 

Swedefj40

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So the switch is wired to the Normally Open terminal which I assume will close once there is oil pressure.

So looking at a diagram I found, when the key is turned to the start position the fuel pump starts up because it's receiving power from the starter circuit to keep it running. While the engine turns over oil pressure increases closing the oil pressure switch which now begins to provide power to the fuel pump which is necessary because the key would've been released shutting off the starter circuit and interrupting the power to the pump. Is this right? If this is the case then the fuel pump should've stopped when the wire to the switch fell off. It didn't
 

Rick Stephens

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So the switch is wired to the Normally Open terminal which I assume will close once there is oil pressure.

So looking at a diagram I found, when the key is turned to the start position the fuel pump starts up because it's receiving power from the starter circuit to keep it running. While the engine turns over oil pressure increases closing the oil pressure switch which now begins to provide power to the fuel pump which is necessary because the key would've been released shutting off the starter circuit and interrupting the power to the pump. Is this right? If this is the case then the fuel pump should've stopped when the wire to the switch fell off. It didn't

Negative!

The 'primer' circuit comes off the outside lug of the starter solenoid. So while you crank the starter the outside lug provides power to the fuel pump.

As soon as oil pressure starts to come up the oil pressure switch then also supplies power to the fuel pump. The wire is literally Teed off from power side of fuel pump to starter and oil pressure switch. There is no other place that the fuel pump can get power. If your boat is wired differently then it is a good way to go boom.
 

achris

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... This doesn't explain the vibration I felt though. If these leads were grounding out on the block would it have any effect on the ignition? Thoughts?

Absolutely! That is the oil PRESSURE switch, the one that powers the fuel pump once oil pressure is up (or, more importantly, stops the fuel pump if the engine stalls and the key stays on). Look at the wiring diagram, you'll see that it's the same circuit as the ignition 12v... Ground that wire and you drop the voltage to the ignition system.... Hence your misfiring.

Just my 2c worth.

Chris.........
 

Swedefj40

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BTW, I have to say that you guys are awesome with the help!!! Thanks :)
 
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