I recently bought an '01 Mercury 25hp outboard (25M 4STR) knowing it had an issue. So here we go: starts very easily with electric starter or with manual start. Runs great -- on the hose -- at essentially any RPM, but w/in two or three minutes, it descends into limp mode. This is a carbureted engine. No signs of over heating, nothing unusual at all other than the limp. I have temporarily disconnected both the temp sensor and the oil pressure sensor, as well as the enrichener -- all in their turn -- w/o discernable effect. One at the time, being carful to hook 'em back up. Oil level is good, engine pees like a drunk sailor.
HERE'S MY QUESTION: what inputs other than temp and oil pressure persuade the ECM (if that's the correct term) to prescribe limp mode.
A bit of other information: I've long been a member of this forum, but finally gave up on the "forgot password" procedure. As to the motor: great fuel output from the fuel pump. No weird mechanical noise from the engine. It will idle until the cows come home. When it starts cold, it will run at any RPM. But if I just let it idle, it idles at about 2krpm, but slows down to what I estimate to be about 1krpm. Plugs look a bit smokey. Engine never in salt, all connections look good.
I may be using "limp mode' somewhat rashly. That's what it sounds like to me -- as if the ECM was limiting the engine to about 1400rpm or so.
An answer to my question above, and for that matter, any other on-point comments much welcomed. Of point observations gracefully tolerated.
Harold in Tallahassee, Florida. Home of good ideas!
HERE'S MY QUESTION: what inputs other than temp and oil pressure persuade the ECM (if that's the correct term) to prescribe limp mode.
A bit of other information: I've long been a member of this forum, but finally gave up on the "forgot password" procedure. As to the motor: great fuel output from the fuel pump. No weird mechanical noise from the engine. It will idle until the cows come home. When it starts cold, it will run at any RPM. But if I just let it idle, it idles at about 2krpm, but slows down to what I estimate to be about 1krpm. Plugs look a bit smokey. Engine never in salt, all connections look good.
I may be using "limp mode' somewhat rashly. That's what it sounds like to me -- as if the ECM was limiting the engine to about 1400rpm or so.
An answer to my question above, and for that matter, any other on-point comments much welcomed. Of point observations gracefully tolerated.
Harold in Tallahassee, Florida. Home of good ideas!
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