Mercury 150 efi overheated now sputters while accelerating & fouling port side plugs

Mercury 150 efi overheated now sputters while accelerating & fouling port side plugs

My 2000 Mercury 150 EFI overheated due to impeller breaking. I replaced impeller and complete poppet value assembly and engine now run cooler than ever, perhaps too cold?

The problem I'm having is during acceleration the engine sputters very badly at about 2800rpm and surges to about 3000 rpm then runs okay till it hits about 3800 rpm and it again surges to 4000 rpm. Then runs smooth from 4000 up.

I changed the plugs and fuel water separator and still have same problem. I pulled plugs and noted that all plugs on the starboard side looked good but the plugs on the port side were fouled badly especially 2 and 4.

Did compression test. All between 105 and 110. Did spark gap test all spark 7/16"

Not sure where to go next? Replace CDM modules? TPS adjustment? Engine tempeture sensor? Perhaps a stuck thermostat. Timing issue related to overheat?

Thanks in advance for your help and feedback!!

Re: Mercury 150 efi overheated now sputters while accelerating & fouling port side pl

Re: Mercury 150 efi overheated now sputters while accelerating & fouling port side pl

Any smoke? Can you get higher than 4000 rpm on the water? How hi? Its always a good idea to check all the sensors. It only takes seconds to do so. Any water in the fuel? Any water in the oil?

I would start with fuel rail pressure and regulator tests to rule out blocked filters and tired pumps, timing check to see if it advances with RPM, and then look to the injectors. Check them yourself, or send them out....

Re: Mercury 150 efi overheated now sputters while accelerating & fouling port side pl

Re: Mercury 150 efi overheated now sputters while accelerating & fouling port side pl

Thx Schematic. I don't have any smoke. I can get to 5000+ RPMs. Max at about 5500. I replaced the fuel water separator and poured fuel in bucket did not note water but probably should have used clear jar and looked closer. How would I check for water in the oil? I just filled tank with merc premium oil.

I tinkered with a few things today and it actually stopped the surging. It's kind of bitter sweet because I don't know what I did that would have actually made a difference so I'm nervous it will return. The biggest things I did was tighten a loose ground ( 2 ground wires that connect to the screw on the control module) and added a bottle of seafoam to the gas tank I also found a cut in the green wire that goes to trim motor (probably got caught when putting cover on). Also had not water tested since I did the compression and spark tests. On the bad cylinders I trimmed a little off each spark plug wire and reattached to CMD. I did not do anything major and did not replace anything so I'm not too confident in he fix yet.

Thx again. I will report back after I can get back out in a week or so.