8.1 Mercruiser Problems

Thanks Mig22...went down all those roads already. Checked 50A fuse for continuity too. Have read that they can be bad even when they look good
 
There was a another member in Sarnia….”Jimmy Buoy” who had, I believe, a mechanical background…maybe reach out to him for an opinion.
Hope you find a solution soon…sounds like a nightmare btw.
 
Do a voltage drop test when cranking. Starter will spin with 9.5 volts but not enough juice for the pcm to fire the plugs.

Did you clean the block grounds and the connection at the 90 amp fuse.
 
scoflaw...affirmative to both. I will do the voltage drop test.

timeflys...I have read his posts but do not know who he is. Maybe I'll ask around.
 
Do the drop at the 50 amp breaker and the negative side as well, battery to block
 
sejensen737 said:
Update
Two techs double teamed the port engine for 2 hours. Diagnostic revealed ZERO faults. IAC checked OK. All injectors checked OK. Tried swapping the cam sensors...no change. Checked for contaminated fuel...OK.
Remember , the port engine ran flawlessly after CFM replacement last August and now won't run after spring launch.
Click to expand...

"Two techs double teamed the port engine for 2 hours. Diagnostic revealed ZERO faults"

Sorry, but you got the wrong "techs"
 
scoflaw

Starter voltage drop .75
Battery to block voltage drop .30
50A breaker voltage drop .30

I also tried a start with the emergency system. Never done that before. Noticeably faster starter action but still no start.
 
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So your dropped voltage is over 11 at the 50 amp breaker while cranking and you have no spark ?
Does your tack read over 300rmp while cranking? Did you change the cam sensor?
 
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Switched cam sensors ...no change...i was very hopeful on that one...would have made sense...paid special attention to that connector and harness
rpm while cranking looks to be 100-200
checked voltage drop between terminals on CB while cranking. About .30

I am in bilge now looking for broken/corroded wires or connectors. Everything looks quite clean. The boat has been in fresh water for 12 of its 18 years.

There are 4 relays on top of the engine. Appear all the same 882751. Is it worth switching all 4 from starboard to port?
 
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100 to 200 isn't enough. Change your crank sensor.
Your not saying what the cranking voltage is. Fresh batteries and did you replace the 90 amp fuse ?
 
Replaced batteries last year. They are good.
Switched crank sensors last week. Made no difference on bad engine (port). Left port crank sensor in starboard engine and it runs fine.
Checked 90 amp fuse for continuity. Its good.
can't check cranking voltage right now...I'm alone...when i had help and checked voltage drop cranking that value should still leave lots for PCM , no?
I can try switching 90A fuses. One of the few parts I have not switched.
 
You still don't mention what that voltage was. Continuity isn't a good test for that fuse it's carrying a large load. If it's original I would replace it.
 
switched fuses...no change...still cranking about 200 rpm
i will try and find some help for a cranking voltage test
frick
 
That's enough voltage but 200 rpm's on the tack isn't enough. What's the rpm reading on the good motor?
 
IMO yes. Not an issue IMO. It cranks a little faster when I use emergency start which I would expect
 
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