Mercury Outboard Cranks But Won’t Start 150 175 200 EFI

  • Information on this page pertains to motors that crank but will not start as a result of ignition system faults. Details and data provided herein apply to 2002+ Mercury outboard 150, 175, 200 electronic fuel injection engines with a starting serial number of 0T409000 and above.

An engine that cranks but will not activate and begin to work refers to when a motor’s crankshaft rotates but does not cause the internal combustion engine to turn on and start running. There can be dozens of reasons why a Mercury outboard cranks but won’t start. Some of the causes and solutions can simple while others fairly complex, and subsequently, require specialized tools to diagnose the source of the problem.

An engine that cranks but will not start up is often a result of a piece of equipment within the ignition system that has failed to function normally. That said, this write-up will only focus on ignition system troubleshooting as opposed to other possible causes for an engine that cranks but won’t fire up e.g. internal powerhead damage, low compression issues, water in engine, low or no fuel pressure, etc.

Take caution before troubleshooting ignition system

  • NEVER “spark” or briefly touch the marine battery terminals with the battery cable connections so as to check for polarity.

  • NEVER detach battery cables while the engine is in operation.

  • NEVER reverse the order of the battery cable connections. The marine battery negative cable is (—) ground.

Before you begin to troubleshoot the ignition system, inspect the following:

  1. Inspect the ignition switch and electrical harness to be sure it is not the source of the problem.
  2. Inspect that plug-in connectors are interlocked and the terminals are corrosion free.
  3. Check for disconnected, frayed or cut wires and for short and open circuits.
  4. Make sure all wire connections are tightly secure and corrosion free.
  5. Perform a thorough inspection of all electrical components, that are grounded directly to engine, and all ground wires to see that they are grounded to the engine.

Ignition Troubleshooting and Fault Chart

Mercury EFI Engine turns over but will not start running

Mercury outboard engine spins but will not activate the motor and turn on.

If your mercury outboard 150hp 175hp or 200hp EFI engine still cranks but won’t start after you’ve followed all of the above instructions, use the comment box below, provide me some details of what you have and have not tried, and I will do my best to provide you with more information so we can get your engine up and running again.

Dennis

Hey I am Dennis, an inboard, outboard and sterndrive marine technician with 5+ years of experience. Send me a question using the comment box on this page. If needed, I can post additional advice, diagrams or illustrations to address any question.

Dennis has 6 posts and counting. See all posts by Dennis

4 thoughts on “Mercury Outboard Cranks But Won’t Start 150 175 200 EFI

  • May 23, 2021 at 12:26 am
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    I have a 1999 Mercury 200 EFI. Rebuilt the short block 3 yrs ago and since only put 20 hrs on it. Ran good after the rebuild and every so often I would run it at home to make sure it still runs… this last time all it does it crank over but will not start. I checked for spark, good. I have a new battery. The fuel is good. I’m getting low pressure fuel to the high pressure tank. It seems the high pressure pump isn’t running. I removed the pump and tested it on 12v and runs good and quite. Also checked it for ground and is good. The filter is clean and have no water in the fuel anywhere. For some reason I’m thinking it has to do with the kill switch circuit. I can’t see the ECM going bad but I guess it’s always a possibility… any recommendations? Thanks!!

    Reply
  • June 24, 2021 at 7:00 pm
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    Hi there, I have a Mercury 150 EFI (‘99) and have a suspicion that it has been submerged owing to having found water in the starter motor. Do you have any tips/advice or even a workshop manual to assist in refurbishing the engine? Do you think it could still be worthwhile trying this?

    Reply
  • July 25, 2021 at 1:45 am
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    Hi Dennis, just installed a new graph in boat, had to fish wires up the side of boat. Took boat out after and it’ll crank all day but won’t start. I’m guessing we messed up kill circuit? We are still getting spark at spark plugs. Help us out!

    Reply
  • August 10, 2021 at 4:55 pm
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    I have a mercury Optimax 150, we were out for a ride and the motor stopped all of sudden. Started back up, ran for 15-20 seconds then stopped again, would not start.Motor turns over, trim works. No gauges work and the 4 light smartcraft gauge does not light up or beep when you turn they.Swapped out the relays and disconnected the killswitch…no difference. Thinking that it may be the ECM, hopefully not!

    Reply

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