My 8.1 Mercruiser 2007 STBD was...

[Vinster]

My 8.1 Mercruiser 2007 STBD was running fine. Just this weekend, the engine started, warmed up, but stalled after 20 minutes at 1100rpm in channel. It restarted at slip that same day, but now, it stalls after 5 minutes of run time. It will not restart immediately after a stall. New CF Filters, Batteries checked OK. Fuel is Rec 90 only. Genny on same batteries & runs perfect. 393 hours on engine. No fault codes on vessel view. Thinking next step is check fuel rail pressures, verify cables and connectors, clean or replace IAC, and possibly replace alternator. Any advice on diagnosis?

[FIG]

Vinster- those are the typical symptoms of the Cool Fuel Module problem. Raw water is used to cool the fuel pumps via a chamber next to the fuel pumps. If the pumps overheat due to the chamber being clogged, it will cause vapor lock. The easiest thing to do is to replace the whole unit (about $1300). If you have basic mechanics, skills, you can do it yourself.
In addition, due to ethanol, paint particles inside your Cool Fuel (Fuel Pumps) come lose and clog your pumps, fuel pressure regulator and eventually your injectors.
Replace those things ASAP, trust me, I’ve done both of mine.
Hope this helps.

[keokukone]

I'd contact Mercruiser through a authorized service provider first. Mercruiser may offer to supply the parts for you. Modules are $1300 each, injectors are around $200 each!

[Grand_Crew_II]

You need to flush your engines with fresh water. You most likely have a salt build up in your fuel cooling lines

[Vinster]

Thanks for the replies! In troubleshooting, step by step is the cue. Checked the fuel pressure, replaced fuel filters idle at 40psi, at 1500, 44psi. Last year, CF had paint issue, back then, I replaced and cleaned injectors. For this recent issue, Checked all sensor plugs and hoses. Spark plugs were ok. Did find slight corrosion on main ground lug connectors, under starter, on engine stud, so removed them (3) and cleaned all up! Ran engine 45 minutes at varying idle so up to this point, one of those things helped. Next day, got engine up to 3500rpm, 24.2 mph at 14.1gph. All was good until voltage on vessel view mobile started to fluctuate from 14.1 to 12.9. GPS sounded low voltage alarm. Ramped down to idle, started generator, put on charger and bam, back to 14.0 charging. From that point, no other issues. So, that "chirp" in the video has to be the bearing in alternator. That may be causing " momentary" power loss during engine electrical demand causing ECM 5 volts to drop leading to engine rpm drop. Next step: alternator change and verify all wires/connectors on this charging circuit are in good condition! Stay tuned!

[gregk]

Good observation, hopefully that was it, watching thread...

[Vinster]

Found two things caused the starboard engine to shut down. First, the charge volts have always been lower than the port at idle. 13.7 vs 14.1. Give starboard some rpm and it settled at 14 on anything over 1100rpm. Second, the isolator on starter is right where I put the front of my shoe to get over the engine when work is needed on starboard side. The isolator was loose causing intermittent voltage to the ECM causing the engine to shut down slowly. The fix was to replace the isolator, and clean up the stud with the orange charge wire from the alternator. The other part of this issue, was the low charge voltage during low rpm. That was resolved by replacing the alternator.

[gregk]

Nice job, thanks for reporting. Be careful on the routing the orange wire, my 2003 350Mag had a recall for incorrect routing of this wire.