8.1 Mercruiser Problems

Final Update (I hope)
New CFM finally arrived. I rebuilt the raw water pump and replaced its hoses due to accessibility while CFM and exhaust system removed.
Installed new CFM and put everything else back together. Put fuel pressure gauge on fuel rail. Ran pump. No pressure in fuel rail. Cycled pump ten times. No pressure. Getting worried. Checked fuel line connections. Ran pump about 10 more times and it finally primed and showed /held pressure in the fuel rail.Started and hunted idle for awhile. Took out for test run and ran flawlessly through all rpm ranges.
As Paul Harvey used to say “and that’s the rest of the story…”
 
Nice work! Hope you are done......I hate boats..lol.
 
Congrats on getting the boat back to running correctly. I went through the whole CFM myself and replaced and cleaned all injectors, fuel rail, wires, etc., etc. Finally just had both CFM's replaced by the marina and it solved everything. This diagnosis and fix was also over a period of months and many disappointing test runs that each failed. I have to say that even 2 years later I'd slightly cringe each time I'd put the hammer down to get on plane waiting for the pop-pop-pop sound I was getting with the bad unit.

I'd say that if you're a 2003-2006 (or more) 8.1 boat owner there's a VERY high chance you'll need to replace the CFM's at some point. It almost becomes one of the first points of failure to consider. I'm not sure Mercury is still doing this but for me I got the units for free but had to pay the marina for the labor. Not bad coverage for a boat that was 13 years old at the time.
 
Bad news.
I launched the boat today for first time this year and the problem has returned. Very hard starting , lumpy idle , then quits. Took me about 10 tries to get it to run and would only do so when I cracked the throttle 50% to get it to run above 550 rpm. Exhaust water is very white and has an aeration look to it. Took it out for a few miles hoping it would clear itself. It did not. Managed to keep it running with excessive throttle but ran horribly.
I really thought this problem was solved when the boat was put away last September. Ran like a top after the CFM module replacement.
Any ideas?
 
Checked the IAC valve? It’s a very common problem that could be related.
 
Sorry about that. Just read the original post. I see you’ve tried a bunch of things. Checked the high pressure fuel pump as well?
 
superwa
Brand new CFM. The high pressure pump better be good. I have done no diagnostics yet. Just parked it and left. Frustrated does not begin to describe how I feel, after spending all last summer chasing this issue. Was looking forward to trouble free summer.
First thing I will do is check fuel rail pressure...
 
scoflaw
I wish I could. Getting anyone to do that around here requires a 4-6 week wait. Begging does not help. Same thing last year which is why I proceeded on my own going down numerous rabbit holes.
 
Buy one you might need it again. 1st thing I do when I buy a boat, worth the money
 
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.
 
Could be an intermittent valve issue... Sticking valves will cause this, are any plugs fouling or showing uneven burn?

You should have a leakdown test done on the engine to rule that out... With all of the other work you've done that is exactly where I would go. Running the motor with a valve issue could cause catastrophic failure. A valve job takes a week once you find a shop and will be about $1000 for the actual work done. Maybe another $7-800 for R&R of the heads from the motor.
 
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You mentioned swapping cam shaft sensor. Did you also try swapping the crankshaft position sensor?
 
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Mig22
No we did not but discussed doing so. The techs felt that since the engine is firing but not catching that the CS is most likely good. I guess they are a work/no work type part. I think a bad CS would have shown up in the diagnostic scan also.
jmac572
I hear what you are saying but I think it is very unlikely. I am capable of doing that work myself but really don't want to tear that engine down until I am positive all other possibilities are eliminated,
Today I am going to start at the vent valves , work to the fuel pickup , then the solenoid valve , ensure long fuel feed line is not compromised and then to CFM. If I have to , I will switch CFM's out again from good engine to bad on the off chance I got a bum CFM last year.
Unlikely , but desperate men do desperate things...
What really puzzles me is that it started and ran perfectly before I put it on the hard at the end of my season in September.
 
Update
Took the fuel solenoid out of the equation. Connected line from tank and line from CFM with an angle fitting. Before I did that blew into fuel tank line and no obstructions. Could hear bubbles at end of fuel pickup. Blew compressed air through disconnected fuel line from solenoid to CFM. No obstructions. Disconnected fuel vent line and blew compressed air backwards through vent hose. No obstructions
Left solenoid connected electrically so there would be no ECM problems. Took fuel filter off of CFM and cycled fuel pumps. Lots of flow. Attempted start. Same results...no go.
This afternoon I am going for a Hail Mary and am going to switch running starboard engine CFM to bum port engine.
 

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Update
Switched CFM's. No go.
sprayed fogging oil into throttle body to get things moving. No firing. Hmmmm...
Engine always fires with that stuff unless ...no spark. Checked for spark on both cylinder banks...none. WTF?? 2 days ago techs said no faults after scan. Also said crank sensor was good.
Switched out crank sensors. Still no spark. After 10 hours working in bilge chasing supposed fuel problem , It now appears I have a spark problem.
Spent a few hours on forums last night but really have little idea how to proceed.

scoflaw...if your'e out there it appears you know your electrics. Any guidance as to where I start in tracking down no spark condition?
 
Begin checking the mini fuses, they are around the PCM typically in a wire harness end that has a cover or some are in the small black blocks. Also verify the 50amp red push button fuse isn’t tripped. Sometimes you have to give those a good push to reset. Then check for loose grounds and all harness connections. (The crank sensor can cause a no ignition issue but sounds like you ruled it out as when placed in your other running motor it does not create the same condition…)
 

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