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ive sifted through the net and came up with very little so i figured i would post here. i have a marine power MEFI 1 MPFI 350 and last year it had a problem with getting HORRIBLE fuel economy. i ended up sending the ECU to marine power after several talks with them for a reflash. seems the problem persists as i can see black smoke coming out the ass end at idle. this is only the second time ive had it out since the reflash. the first time it ran perfect and started perfect.
also yesterday while it was warmed up i tried to fire it up and it would not start. at first it fired then idled very erratically and died. i finally did get it to start with alot of frustration. we were heading back to the dock anyways so we went home. anyone have some definitive answers? i could just throw money at it and replace all sensors but im hoping to avoid that.
i saw in some other forum where a member said the IAC could cause the horrible fuel economy but could not find any other good forum info besides that. every other place said TPS, MAP, bad injectors, and vacuum leaks. which is pretty much everything but fixing the problem.

oconnor marine

just a shot here, have you checked the fuel in the tank for contaminants, change the fuel water separator filters?
cleaned the injectors?

Trash

What do you mean by horrible? What was your before and after comparison data so we can all start from the same baseline?

I wish you had posted first. THE LAST thing I would have done is a reflash. In fact I never would have done one. MEFI 1s are very robust (simple, yet robust).

The fact you have black smoke and poor fuel economy obviously points towards a fuel issue, and my 90% guess is you have an injector stuck open, or at least not fully closing. BEFORE you do anything else remove the injectors and get them cleaned and flow tested. I would lay money that's where your problem is. Has the boat been sitting for a while?

It is not the TPS and I have doubts the MAP sensor is bad. Vacuum leaks cause high idle problems not rich conditions to the extent you are seeing. If you can get a voltmeter read the TPS voltage output with Key On, Engine Off. It should be a smooth 5 volt sweep from idle (approx zero volts) to WOT reading of about 4.9X volts DC as you move the throttle. Having said that I doubt its your problem.

BUP

iTrader: (9)

Fuel pressure readings ??? , fuel regulator, stuck open injector(s), bad map sensor, problem of air restriction - And how dirty is your flame arrestor - when was the last time you cleaned It completely, can you see day lite thru it ???

Reflash of ECM ???? what tune ??? your problem ???

How well or not does this engine run and idle and power up ???

Scan the engine and note all parameters, does all look good there, any fault codes ???

, Ignition system producing correct amount of spark to lite the fuel mixture in the combustion chambers??? Battery voltage weak ???

Last time for a complete tune up - cap - rotor, spark plugs and wires and coil ???

Spark plugs gaped correctly ??? correct spark plugs ???

BUP

iTrader: (9)

bad MAP can cause very rich conditions.

Steve H

I would suggest getting it flashed again, back to OEM. Then start looking for the for the real issue: fuel pressure, injector, CTS, etc.

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it has a new fuel water separator on it but the injectors have not been cleaned.

horrible meaning i should easily have gotten 40 more miles out of the tank of gas i had. as it was i literally barely got the boat restarted and onto the trailer. i was damn lucky to make it back.
i guess i should have been more clear. the reflash was more of an "update". i assumed it was on the original program from whenever it was produced. as with everything electronic firmware and new programs become available. i figured it was a good idea to do.
this is a new to me replacement motor that came out of another running boat. so far is hasnt burnt a drop of oil. i will look into where i can take my injectors to have them cleaned and patterned.
i just happened to have a voltmeter and know how to use it. i will check out the TPS.

i have a FP guage that i need to install. just need a longer "nipple" to make it work. so as of now i dont have a fuel pressure reading for you guys. i will look into getting that done over the weekend.
the flame arrestor doesnt look terribly dirty but thats an easy thing to clean. i will do that as to eliminate any issues with it.
the engine ran smooth until this start up issue on saturday. before the "update" to the ECU i felt it was slightly sluggish. before i fired it up for the first time i did all the basics. new cap, rotor, plugs (proper ones installed and gapped correctly) and wires.
im assuming batteries are good. i have dual batteries and they are just a couple years old. they crank the engine over quickly. does not appear to have any ampacity issues.

thanks for all the replies guys. it is much appreciated.

oconnor marine

you could try taking off the fuel water seperator filter and fill it with techron black bottle, run the motor and see if that helps clear it up. if it does then i would say its the injectors. and if thats the case maybe remove them and send them to BUP.

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i did some prssure testing today with a rent a pressure tester. i jumped the high pressure pump and left the key in the "on" position as to activate the low pressure pump as i turned the battery selector switch off and on. it seemed to run about 42 psi which seems about right but i thought i read on marine powers website for the mefi 1 that the fuel pressure should be in the 30s. ill go look again.
yesterday just for good measure i cleaned the spark arrester too. ill keep updating. i might take the boat to the river this weekend.

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i should also note that i cannot fire up the motor unless the pump is in water. so i have no fuel pressure readings while the engine has vacuum on it.