Mariner 200 EFI will not start

[Pond water]

Gentlemen,
i changed the 3 wire temp sensor. It didn’t help problem,
still will not start. I can unplugged 3 wire and will start. Just
Don’t seem like enrichment circuit working. But could be wrong.
Any ideas? Feel like I’ve checked everything. Any suggestions/help
greatly appreciate

[H2Okie]

That 3 wire temp sensor works together with the TPI to richen the fuel mixture until the engine reaches 90 deg F . I would say you should verify TPI setting for your motor . Manifold air temp sensor will richen fuel 10% if disconnected and reduce it by 10% if shorted out . Yellow/ red wire connected to the left side of the starter solenoid normally applies 12v+ to the ECU whenever the starter is energized to provide an enrichment signal when cranking the engine .

[Pond water]

Any help greatly appreciated. Had some things come up and had to put boat to side.
back on it now. I can spray mixed fuel in Intake and it will fire up. I can unolug
3 wire temp sensor and will fire up. (Unplugging sensor gives more fuel I read)
but with all connected engine will not fire up. No fuel on start up out of injectors
i had injectors cleaned also.

[Capt.Insane-o]

I have a 200 ecu that i have no need of if it ends up you need one

[tlwjkw]

look on tha starter solenoid.. should be TWO yellow/red wires on small start pole?.. one of those is tha enrichner circuit (goes to ecu).. it should fire a coupla injectors (choke/enrichner) every time you hit start..

[H2Okie]

That Yellow/ red wire connected to the starter soleniod operate coil runs through the engine wiring harness to the ECU connector plug on pin # 11 (Female pin) and then out to the ECU via # 11 (male pin ) .
You should be able to read continuity on that yellow /red wire from the solenoid to that female pin 11 with the ECU connector disconnected . I would make sure both pins are clean with no corrosion . Since you will have it apart inspect all of the pins for burns , corrosion, loose pins .

[half fast]

Have you looked to see what the throttle position sensors set on ? It has a lot to do with air fuel ratio and cold starting .

[Motv18]

I’m tempted out of curiosity to trace the temp sensor wires to discover why it doesn’t work connected, and does work unplugged.

To me this seams like a shorted wire

[Merc 2.5]

U have quite of few of the guru helping u out. I'd test what they say to test. They will get u goin

[rkmirage]

I'm having a simular problem, my motor spins over and has spark but won't fire. I can plug in my remote starter ( short harness with a key switch ) and it fires right up, then I plug the boat harness in and it starts right up. I think I've narrowed my problem down to the ign switch. Maybe something to try?

[billybob]

Yes replace that sensor, it should fix problem. Also you should know this. Mercury EFI are hard starting when cold. They will start and die, start and die. All you have to do is. After motor has started or almost starts. Turn key to cranking again. It richens fuel mix 15%, everytime it goes to start mode. If motor is running & wants to die, starter bendix flies up hits bottom of flywheel, & bounces back down, doing no damage at all, & motor will stay running that way. You can do it multiple times, until motor runs on it,s own. I have been doing this in the northern states, since 1989 when Merc. came out with EFI.

[Pond water]

1. Changed ignition switch. Same issue
2. checked continuity from start solenoid to pin 11 on the
yellow/red wire. Good continuity.
3. Can remove the yellow/red wire and supply battery voltage
will start and run. Remove voltage from wire engine will slowly
die.
4. It’s like ecu isn’t fire injectors. I can supply voltage to enrichment
wire at start solenoid and it will run. I can unplug temp sensor it will
run. Both are allowing fuel to engine.

[Pond water]

I did notice with ecu disconnected. Check voltage
at pin 11 enrichment circuit. While cranking only about 8 volts.

[H2Okie]

Sounds like you are supplying additional fuel to the engine to make it run that should be normally coming from the ECU pulse signals to the injectors . The ECU normally looks at the input values on all of the connected sensors (TPI , Coolant Temp, Manifold air temp, Manifold absolute pressure "MAP" , engine RPMs , cranking enrichment , & knock sensor if equipped ) and adjusts the injector firing rate based on a program in the ECU comparing the real time levels of these sensor inputs .

[Pond water]

Gents
i removed ecu and sent to brucato for bench test. Ecu
has been declared inoperable. Can ecu’s be repaired?
brucato had some new ones, just looking cheaper option
first.