250 efi fouling plugs

[bucsfan1973]

1998 250 efi ser#Og548757 purchased boat last year, lots of headaches. 1. motor had no thermostats. 2. Had 5 cdms replaced. Been to 2 mechanics and neither have totally solved my problems. Last wknd, could not get on a plane, motor cutting out. Brand new plugs were installed that day champion QL77CC at .035. Got back to dock plugs were fould after mins. Wet black/oil gas mixture on plugs. it seems this motor is tricky because the computer does not diagnose everything. One mechanic suggested the stator could be bad, notgetting enough volts. Or a map sensor. Stator needs needs ohm test not a volt test right? Any advise, very frustrated merc owner

 

[jaybirdtx]

Re: 250 efi fouling plugs

The throttle position sensor (TPS) setting will cause a rich or lean condition if it is not set right. The stator can be ohm'd or voltage checked. With the engine running and the 2 yellow wires disconnected from the rectifier/regulator you should have 14 volts AC.

 

[aalleykkatt]

Re: 250 efi fouling plugs

Originally posted by bucsfan1973:<br /> 1998 250 efi ser#Og548757 purchased boat last year, lots of headaches. 1. motor had no thermostats. 2. Had 5 cdms replaced. Been to 2 mechanics and neither have totally solved my problems. Last wknd, could not get on a plane, motor cutting out. Brand new plugs were installed that day champion QL77CC at .035. Got back to dock plugs were fould after mins. Wet black/oil gas mixture on plugs. it seems this motor is tricky because the computer does not diagnose everything. One mechanic suggested the stator could be bad, notgetting enough volts. Or a map sensor. Stator needs needs ohm test not a volt test right? Any advise, very frustrated merc owner

 

[aalleykkatt]

Re: 250 efi fouling plugs

You might want to check that you have spark that will jump a 7/16" gap before you start messing with the stator..Yes he is right tha tps could be out also,You will need a wire harness to hook up a multimeter part #84-825207a1.I do not think tps would make it run that rich .I set mine by ear at idle. The smoothest setting is where I set mine. Check fuel pressure. pressure regulator may be bad. The pressure shoud be 34-36 psi . If higher to much fuel is going through the injectors. I have had the same problem with my 250 EFI. Lift pump diaphram was bad in mine.. Maybe you should change it anyway.. I am told lift pump should be rebuilt evey couple years anyway.. The kit is about $40.00

 

[aalleykkatt]

Re: 250 efi fouling plugs

Forgot.. The mapp sensor is about $200.00 So I would check out other things first..

 

[rodbolt]

Re: 250 efi fouling plugs

its to easy to do a running voltage test on the CDM's and is highly reccomended. <br /> setting the TPS by ear is idiotic and ill advised as the TPS is the main determinant for ign timing on that engine and an icorrect setting may lead to a detonated piston.<br /> make sure all CDM's are fireing, check your compression, then check the fuel pressure regulator,VST needle valve and the fuel recirc system a fuel system(rail) pressure test is needed as well. that can find a bad,stuck shut, regulator and any leaking injectors. while the ohms test is nice I always run an output voltage test as well. and its possible you have another failed cdm,<br /> find a merc dealer that has the merc efi tester.<br /> it can quickly rule out whats not wrong so you can concentrate on what is wrong. a bad low pressure pump diaphram can cause all sorts of problems, blown powerheads included, and I always just kit them every 3rd season or so.