Mercury 1998 250 hp efi

My 1998 merc 250XL EFI Is running so rich you can smell raw gas exiting the exhaust. I have replaced the map senser and adjusted the throttle positioning ind. But it has not done much good. I also fould plugs. I burn 26 Gal. an hour @ 4300 RPM. 2o mph. With my 25' cc C-Hawk. She will turn 5400 rpm WOT.. I cant seem to figure this one out. Can you help! A offshore trip running 80 miles round trip @ 4400 rpm 20 mph and trolling for 6 hours @ 1900 rpm 7 mph she burned 160 gal of liquid Gold. My friend burned 180 gal with twin merc 2000 model. same trip.. Something is Wrong!

Re: Mercury 1998 250 hp efi

I'll admit I'm not an expert on this engine but I'd start with a check of the fuel pressure regulator. A bad regulator in any EFI engine allows unregulated fuel to be pumped into the engine. That or some really bad injectors are the only way excess fuel can get into the engine. There is always the possibility the ECM or sensor(s) are bad but I would not suspect them until the regulator is verified good or bad.

Re: Mercury 1998 250 hp efi

One other thing is those engines still had a pulse driven fuel lift pump. If the diaphram is leaking on that it will put raw fuel right into the crankcase.

Re: Mercury 1998 250 hp efi

K I checked the fuel pressure, its at 38lbs.. book calls for 34-36.. I would not think 2 lbs will cause the problem.. My gauge might be off a little too. No leak in the diaphram... I will check the injectors today. Thank you..

Re: Mercury 1998 250 hp efi

Another sure way to check if you are indeed running rich is to get yourself a "color tune". Basically a glass spark plug. Any automotive spares retailer should stock it. It allows you to look inside the combustion chamber and observe the actual colour of combustion. Too light blue is too lean, and when it's orange it's too rich. There is a color chart with it.

Re: Mercury 1998 250 hp efi

Well I checked the injectors.. Visualy that is. They all seem to spray the same amount of fuel. I was surprised however to see haw much they sprayed. No leaks, Seals and fuel rail all was ok. The spark is jumping at 7/16" and all grounds have been cleaned. New plugs. I did find a spark plug wire that was falty. I have changed Them all. She runs a bit smoother but still a strong odor of raw gas.. Bleed system and check valves seem to be ok.. I did see a lot of gas in the bleed system. Thanks .. I will see about the glass spark plug thingee..And check that.. Thank yall for the help.. Bluefin tuna are here and I need to get fishing asap!lol

Re: Mercury 1998 250 hp efi

If the regulator diaphram actually holds vacuum there definitely is no leak. However, even a pin hole may allow it to regulate normally but still pass fuel directly into the engine. It would not hold vacuum if that were the case though.

Re: Mercury 1998 250 hp efi

I would still look at the lift pump. the rebuld kit is 20 or so and failure is common. takes maybe 15 min to rebuild it.its reccomended to do it every 3 years anyway.tony at shoreflyte or craig at wanchese marine will be happy to sell ya a kit and they come with complete instructions. but if the lift pump is faulty it will make it run pig rich, its also posible that the vapor seperator inlet needle is leaking, if it is remove the VST vent line that goes to the intake manifold and see if fuel is coming out. if fuel is coming out the vent the needle is leaking and will cause a pig rich condition as well.<br /> this motor will mostly trouble shoot itself if you let it.

Re: Mercury 1998 250 hp efi

Ok thanks for all the help.. I feel like we are on the right track.. I am going to see Craig and get that kit..Not sure where tha needle is but I saw fuel come out the bleed systym..