mercruiser mefi 3 discussion

[bud37]

OLxxxxxx...........

Edit .........mx6.2

[bud37]

What really throws me about this mefi system, is like in 405's case there, you have an engine running the way it is I guess, going by what we are told and there are no trouble codes, everything seems normal but clearly it is not.....must be difficult to deal with. Believe me I am just trying to learn, having two of these under the deck plates......

[km1125]

Here is a great pic to help understand the MEFI system. THIS MAY NOT BE EXACT TO YOUR ENGINE, but a good 'overview'. Not sure if yours has O2 sensors but if it does, those would be additional inputs on the top half. The top half is what the computer uses as inputs to know what and how to control the engine in the way of spark, fuel and air.

merc_ECM.jpg

The "discrete switches" would be things like oil pressure, outdrive fluid level (if applicable), trans temp, and coolant temp too high.

In your case, something like a clogged IAC passage or a sticky/slow IAC valve could cause the problem you describe. The IAC is trying to control your idle speed. As you move the throttle, or as load changes on the engine, it counteracts but can only do so in very small increments. Also, there should be some designed "leakage" past your throttle plate for absolute minimum airflow for the engine... if this is blocked (say, from a dirty throttle plate), then the IAC has to make up for that, but it can only do so much because it is a pretty small device.

[Viper]

Bud37, where are you located? Do you guys winterize there?

[Viper]

I did some digging with your S/N and nothing popped up that we haven't already discussed. See my question above.

[bud37]

Yup,I always have marina techs do the engines..... still 3' of the whitish stuff between the boats.....Just a guess here but if you ever worked for the place beside the old Dawsons you probably have worked on this boat.Was going to work on it this weekend but forecast has changed so that is out.......just saw your post, thats fine ,can't really do any more until things are working.......

[Viper]

You mean Crates with a "K" ?!!

I asked about winterizing because I've seen guys squirting fogging products into the throttle body as an easy way out. This will cause IAC system problems over time.

[bud37]

Thought so, were you there for the C or the K.....our guy put the solution in the fuel filter I believe......

[Viper]

Source of the post...were you there for the C or the K....

NO

[bud37]

Cool.....weather looks ok for next week, so we will have a look.....gotta get started soon....