merc diagnose

[yipster]

today i saw the future on our 6 cil '97 mercruiser magnum efi gen+ engines.

for stil unknown reason the alarm beep comes on and of so the marineman tested with the diagnose plug. strange enough it showed no errors (while the alarm went of) ok, i've got to take the oil pressure sender out, it gives no signal and maybe thats it. cooling, motor and drive oil are monitored by that alarm and i'm told the engine will shut off in case of malfunction. but i dont thrust it, asked for a new impellor and found that on merc's thats quit an operation, contrary to the only 6 screws i once did on our volvo sterndrive.

but what a magic diagnose box that is! it shows eng. hours, past errors etc you can even trotle up from that diagnose plug box! i was told it reads out in codes now but such a device should be on the dash i think. that amazing computer diagnose box has cartridges for various engines, ob's too.

still i wonder, replace oil sender and sail around hoping the peep stops?
anyone has a mercruiser forum adres or diagnose?

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edit
looking around on merc forums i learned these engines have two oil pressure sensors, one is the gauge the other the alarm switch.
interesting and will check! also learned what "boat" means: "break out another thousend"

[gonzo]

The dash gages have a set of senders separate from the senders the ECU uses. Also, depending on the model, the alarms may be on a on-off switch. The alarm is wired like a car horn; it has power all the time and the switch grounds it. A shorted wire can make the alarm go off at odd times. A faulty switch can also do it. One way to isolate the problem is to disconnect the low oil pressure or high temperature senders and run the engine. If the alarm goes off but the oil or temperature are OK. the sender is malfunctioning. It can be difficult and frustrating to troubleshoot, intermitent problems usually are. Good luck.

[yipster]

yes your rite it should be logic. was paging the manual as someone blaimed the eng wiring harnas eprom/computer. must confes i was really impressed with that diagnose box (that did not diagnose it).

from another forum i just got this reply:

Yes, the EFI engines with their computers are neat, but! Very seldom does the computer know what the problem is. I'm Volvo certified on Gas and diesel electronic engine control and EFI and usually the problem is basic mechanical problems other than electronic and the electronic parts that cause the problem usually won't set a code. Even when codes are set there is an extensive list of things to check that cause the problem. And normally they are dirty fuel related in my experience. Your alarm sounding can be from 3 things. Drive gear lube monitor low on oil, temp or oil pressure problems. The alarm switches are seperate units from the gauge senders. So while the gauge may read properly, the switches that provide information to the alarm system are complety different. Hopefully my rambilings will help you understand your engine and gauges a bit better.

Guess i was a bit lazy to dive in there yet once in the bilge i seem to enjoy myself. thanks again for the advice Gonzo, hope it wont be to difficult and frustrating to troubleshoot as intermitent problems usually are...

ps. did you hear of BIII couplers breaking after low hrs? happen to know a price on the steel aftermarket kits?
(forget it, i didnt ask, bet its expen$$$ive)