WOT issue

[sarbog]

Help. ’05 340 w/ 8.1 Horizons. End of last season I noted the port engine lagged (needed more throttle to maintain same RPM as strbd). Major maintenance year as risers and manifolds were changed. Also had the injectors cleaned. Test run last week and strbd engine good but port still only gets to about 4200. Starts and runs smooth. Everything on the engine checks in spec, just won’t get full wot rpm. At lower rpms (cruise rpm) it lags slightly but then slowly comes up and matches the strbd. I can not afford to just start replacing things willy nilly. It seems like perhaps a fuel issue. Suggestions on where to start. Want to resolve this before the season gets here.

 

[Espos4]

How about a fuel pressure gauge and an assistant to record the reading as you cruise around at different rpm’s, all the way up to full throttle.

 

[juggernaut1]

Could be plug wires and or plugs. How old are these items and when were thhey last replaced? I had a wot issue develop on one of my 8.1s and it was a plug wire - no tell tail signs otherwise though except for not reaching wot.

 

[hottoddie]

How were the injectors cleaned? Were plugs replaced at same time? How did the plugs look? Are the plug wires original from 2005? Age of fuel? Has it been treated? Water separators replaced?

 

[sarbog]

Full tuneup with new plugs, filters, etc. I honestly don’t know how old the plug wires are. Other than buying new ones and seeing if that fixes it, how can I check the wires?

 

[Espos4]

An ohm meter is one method.

Look for something Online for a reference on what the resistance should be.

Another option, run the engine in the dark. Look for spark jumping through the outer wire jacket.

You could even spray some water on the wires to help induce the spark if necessary, or if you’re really brave, feel the wires with wet hands while the engine is running!

 

[scoflaw]

CF3 issues. Is this why you had your injectors cleaned ? Replace those wires if they're original

 

[sarbog]

CF3 issues. Is this why you had your injectors cleaned ? Replace those wires if they're original

the CF3 issue came to my mind and the Service Dept at the marina is going to investigate the CF3 possibility. They have my engine serial numbers and will contact Mercruiser to verify my engines are among those affected. I will probably go ahead and replace the wires as I am the second owner and can not verify if they were ever replaced.

 

[JVM225]

Probably dumb questions but:
Are the tachs both accurate? What does the synch gauge tell you?
Either way, new filters, plugs and wires in a boat that’s new to you is always a good investment.

 

[sarbog]

SYNC gauge reflects the difference. I have had the boat 4 years and this is a recent development. In course of maintenance only the plug wires have never been changed.
In terms of using the boat it really doesn’t affect much. At my normal planing rpm, 3500+/-, all is fine. But there is clearly an issue that needs addressed. Just have to get to the cause.