2003 Mercury 200 HP EFI -wildly Surging idol, rich mix, etc.

The boat is currently in the hands of a mechanic but I don't think I'm much closer to knowing what is going on. The boat would not plane up and eventually died on the last outing. SeaTow took us back to the slip.

I went through the fuel system (right up to the final filter), cleaned up the plugs and got it started. The idol is low and rough and the RPM's surge wildly from below normal to and aggressive rev. It will choke out and stall if I try to give it a little throttle to bring up the idol. When the idol surges a very rich oil mix is evident in the exhaust.

The mechanic initially thought the diaphragm was the culprit (torn) but this has since been ruled out, so has the TPS sensor . The fuel pressure is fine and the computer shows no codes (of course).
Anyone have any ideas? I?m stumped, I hope the mechanic isn?t but I don?t get the feeling they have any idea at this point.

I hate boats.

Re: 2003 Mercury 200 HP EFI -wildly Surging idol, rich mix, etc.

Unless tha tha oil injection is totally screwed up that gunk your seeing is an unburnt fuel/oil mixture. This could be injectors and/or electronics. That motor is a cdm motor and tha electronics control a lot more than tha earlier switch box motors and can cause all kind of wierd things to happen. They might retest and set tha tpi. Check tha stator very close. It does a lot of things not normal on a regular stator. Also tha ECU and ECM. This is one thing thats really hard ta help with on a computer with tha newer electronics....................JMO

Re: 2003 Mercury 200 HP EFI -wildly Surging idol, rich mix, etc.

One thing I did notice while trying to troubleshoot this myself is that at least once or twice the gas prime bulb felt never ending. What I mean by that is usually two pumps on the primer an it is solid...can't squeeze it anymore. After 5 or 6 pumps I felt like I was pushing fuel into a bottomless pit. Now I guess that would make sence if one of the fuel injectors were stuck open.

Could that have been a fuel injector stuck open?

I'd rather be dealing with fuel injectors that the computer.

Thanks for your thoughts!

Re: 2003 Mercury 200 HP EFI -wildly Surging idol, rich mix, etc.

Sounds like the MAP sensor is stuffed,

Re: 2003 Mercury 200 HP EFI -wildly Surging idol, rich mix, etc.

I?m told the map sensor tested ok. They are pulling the fuel injectors today?.

Re: 2003 Mercury 200 HP EFI -wildly Surging idol, rich mix, etc.

The MAP sensor on my 2007 EFI 150hp tested ok as well according to the DDT. Changed it anyway as no other faults were found and the motor then ran as smooth as the day I got it. Fuel economy went from 32 litres per hr to 24 litres per hr.
The shop who did the testing had a pair of 2003 EFI 250hp on the back of a big CAT that were coughing and fouling which they could not find a fault with. So they did the MAP sensors on those as well and the problem was fixed.
The Techs were suprised no faults showed for the MAP. The shop now carries them in stock

cheers,

Re: 2003 Mercury 200 HP EFI -wildly Surging idol, rich mix, etc.

Thanks for all the input. I just got the boat back today. The problem was the fuel injectors. The difference between the pre and post service bench tests showed a 39-50% increase across all six injectors. It has never run so well.