oil pressure dropped, now wont start

[cpoint]

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Hi All,
Back with another never ending problem. Took it out Saturday. All was sounding great. All indicators were good (engine temp, oil pressure) on both engines. After about, maybe 30 minutes, I noticed starboard side, oil pressure dropped from 1/2 indicator to 1/4 indicator. Everything still sounded fine and functioned fine, so I returned back to dock to not do any damage in case there was some serious problem. I was not sure if it was just the dash board display. But got side tracked and did not restart the engine after docking to see if it would pop back to normal. Anyway, then I proceeded to change oil on both engines, as it was on add mark. yes I had neglected changing timely matter and checking. after changing oil and filter (correct oil and filter as recommended by mercruiser ), I started the starboard engine, at least attempted. nothing happened. did not turn over. when i listened i the engine room, there was a wining, ticking noise. after a friend of mine checked around, notice sound and vibration was coming from, i believe fuel pump. see picture attached. I had the fuel pump replaced 8/2016. did not put that much time between than and now, so not excessive used, I suspected oil pump, or oil pressure switch or something. I will talk to my mechanic tomorrow, but any ideas from anyone here, what it may be. by the way port engine, oil change was success, all worked, and that's my usual troubled engine. thanks in advance for your input. also this is a mercruiser 7.4 mpi. 200 model.

[390Express]

You may have a safety mechanism on your fuel pump, that precludes it from getting power when your oil pressure is reading low. Try jumping out your oil pressure safety switch, or replacing the oil pressure sending unit (or check the connections on your oil pressure sending unit, if you experienced a sudden drop of a 1/4 of the gauge). Oil pressure sending unit is fairly cheap (around $22). I just picked one up myself.

Unless you had a sudden spike in temperature, or a mechanical failure somewhere, you shouldn't see a sudden change in your oil pressure.

[km1125]

Did you check to make sure it's in neutral?

[cpoint]

Thanks, I like the encouraging news, hope that's the case with mine. I'll try to figure out if it is something I can do easily. Sending unit cost is not so bad, if I can replace it. If it is not the case, at the most I would have new sending unit. Did yours make noises when switching the key on though? The water (engine) tempetarue gauge was normal (same on both engines) all the way back to dock. The oil pressure range stayed on the 1/4 mark all the way. Not sure if distance was great, if it would have dropped to zero. At this point I have the new oil in the engine. But not turning over so....

[cpoint]

Source of the post Did you check to make sure it's in neutral?

Yes, I am not much of a mechanic, but that I know . Minor things I can do mechanically. But when its over my head, or if too difficult of an area, I let go and get a mechanic.. Also as mentioned, there is no sign of turning over in the helm. But if you are in engine room, you hear kinda wining and clicking noise from that unit that I placed a picture of on top of the posting. Looks like that's where fuel pump is I believe.

[km1125]

Simple things are sometimes easily overlooked.

If it won't even crank over, that's a simpler system to troubleshoot. You were in there messing with oil and filters, could you have knocked a wire or connector loose on the neutral-safety switch or solenoid?

If it won't crank, theres's few things to consider;
battery-cables-breaker-ignition switch-neutral safety sw-solenoid-starter

[cpoint]

I was pretty careful not to bump into things. 100% sure I did not mess with anything, but granted something by coincidence may have come undone. But still the oil pressure fell to 1/4 mark before doing anything, so problem started at that point I believe. Also, repeating, there is something happening in that unit(in earlier pic I posted). noise and vibration in that black plastic box when engine start is attempted. Is the oil pressure switch in this (pictured)? I am checking online, but can't find exact model of my engine. Looks like an easy, cheap fix to try replacing oil pressure sensor trip. Does anyone have any idea on 2000 carver 356 (starboard engine), where it is located? picture would be fantastic. I seen enough videos today on replacing, seems easy, maybe difficult area to get to at most.

[bud37]

I believe there is an oil pressure switch and an oil pressure sender......sender may have ( Lt blue wire) only ground to block......switch may have ( Lt blue/tan) wire only ground to block.This according to Mercury parts for 2000 or so 7.4 MPI.
Hard to focus right in , but your pic appears to be the fuel pump.

[cpoint]

Bud, thanks. Yes I believe thats the fuel pump, which was replaced 8/2016. So potential bad fuel pump? with the noise coming from it. Or you think still the oil pressure switch/sender causing problem, which is making fuel pump to make the noise? Or if oil pressure switch/sender have problem, would fuel pump even not try to come on? I will look around when I get back to it more.

[km1125]

Please be clear on your symptoms. If it won't even crank then it's not your fuel or oil pressure. If it cranks but doesn't start, then it could be one of those things.

The fuel pump SHOULD make a sound when you turn on the key, so it primes the system. If it make some unusual sounds, then it may have an issue, but that shouldn't stop the engine from being able to crank. It will only run for a few seconds without oil pressure, so if it started and then dies, then I would suspect oil pressure or a problem with the fuel not being able to pressurize.

You can have no oil pressure, no fuel pressure and no fuel but the engine should still crank. If it doesn't, fix the crank problem before you look at anything else.