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  1. #1
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    2011 Mercury Optimax 150 no start with starboard temp sensor connected

    Crank crank crank nothing...Unplug temp sensor on starboard and it fires right up and runs well. Seems to be rich, re-conencted temp sensor while running tuned off, and it restarts without a problem unless you let the motor sit for 5 mins, then no start.

    I replaced both temp sensors and have the same problem. I tested fuel and air, and they are 80 and 90 psi, my cheap gauges bounce but those numbers are the average without fluctuation with engine speed. They lower as the engine sits off. I had the fuel rails apart and both the tracker valve and the fuel diaphragm look good. O rings are good, cleaned the injectors and air injector.

    I hear the injectors clicking and the fuel pumps are both on, so something is killing the coils to create no start when the water temp sensor is connected until warm.

    Help, the lobsters are calling, mini season is in two days.

  2. #2
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    Gonna need a scan...

    83 V-King, 96 Mariner, 200 hp ff block 2.5 w/a 28p choppa
    We gotta clean this liberal mess up, VOTE TRUMP TO MAGA!
    Rebuild thread:
    http://www.screamandfly.com/showthre...-it&highlight=
    http://www.screamandfly.com/showthre...cs.&highlight=
    Videos

  3. #3
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    Update.
    The SB temp head sensor shares the Black/Orange (transducer ground) wire the goes to the sensors for port temp, air temp, TPS, crank, low oil, compress temp, smartcraft 8 pin plug, (2) block pressure. So I tested each wire that goes to the 32 pin PCM harness A, at pin #A15 to see if there was a break in resistance. Each tested .3 kΩ . No loss. I cross tested the same BLK/OR to each other at each sensor and there was no loss of continuity. Then I tested the Tan/Green from the SB temp sensor to the 32 pin PCM harness A to pin #A22 and it tested fine at .3 kΩ . Harness is good IMO.
    With the PCM on bench, tested resistance on pin 15 and 22 together, got 1.78 kΩ, same reading from #A15 and #A22 to pins #C15, C16 and C24 for Ground(-) on 24 pin PCM harness C connector. Temp Sensor is within spec at 12.5+- kΩ at 68 degrees.
    I hooked up all the sensors, PCM and zip tied...and the engine fired up..My son asked me what I did to fix it...response: "no idea"...Tested a few times before lobster trip, ran fine, left boat idling while we were diving for a few hours, spotter was in boat, and boat stalled at the end of the trip. Had a no start condition again. Pulled cover, disconnected SB temp sensor, engine fired right up. We tried to leave but engine stalled at 2000 RPMs. Disconnected SB temp sensor, started again, reconnected SB temps sensor and ran home (about 40 minutes at various speed) without issue. Got to the dock, turned off, and it fired up again, with everything connected. Tried again cold later in day. Fires up no issue.
    ANY suggestions for at next step?

  4. #4
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    The old unplug it and plug it back in

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  6. #5
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    Sorry, I am not sure what you mean.

  7. #6
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    Seems like a pin connection issue. Been a run of them lately.

    83 V-King, 96 Mariner, 200 hp ff block 2.5 w/a 28p choppa
    We gotta clean this liberal mess up, VOTE TRUMP TO MAGA!
    Rebuild thread:
    http://www.screamandfly.com/showthre...-it&highlight=
    http://www.screamandfly.com/showthre...cs.&highlight=
    Videos

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  9. #7
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    Quote Originally Posted by Findre View Post
    With the PCM on bench, tested resistance on pin 15 and 22 together, got 1.78 kΩ, same reading from #A15 and #A22 to pins #C15, C16 and C24 for Ground(-) on 24 pin PCM harness C connector.
    A22 is sensor gnd and A23 is +5. With a 33K series resistor on the input you should not be seeing 1.78k. The A15 input has a 33K series resistor and is pulled up with a 1K resistor so you should be measuring the resistance between A15 and A23 (+5) to test those resistors ~34K total. Cap is a .033uf so not likely to cause a problem but if you get anything less than ~30K there is a problem or the diagram is not correct..


    96 Cougar 23 MTR twin 300XS's. 100 something
    98 Laveycraft Sebring 20.2 Tunnel 280 90 something SOLD
    85 Baker RST 220 Laser SOLD

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  11. #8
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    OK, good stuff. Thank you!

    My instant issue is disconnecting the A15, allows the start of engine, so I do not think the problem is with A22.

    I see that A23 feeds 5v to the A15 circuit to both temp sensors (which do not relying on a feed from A23 directly) only as pass though residual voltage to A22 once powered through the TPS, (2) Pressure switches and MAP sensor. I have not tested any of the pass through voltages from them.

    Should A23 and A15 be tested powered up? or asleep (no power)? My first thought is if I am doing it powered up, I should unplug everything and put power directly to A1 and Gnd to get a correct value from these pins.

    I agree that the issue is with resistance value of A15, but finding the correct method to measure the resistors and cap, without opening the unit, is where I am stuck. 1.78K was asleep between pin A22 and A15 only on the PCM pins and SB temp sensor plug.

    Only thing can think of is to use disconnected A15 Tan/Green wire SB temp sensor plug to A23 Purple/Yellow wire on plug for either TPS, (2) Pressure switches and MAP sensors disconnected to get a A15 and A23 value. If I get ~30-34, then I have to think its as simple as a pin connection (credit XstreamVking with Occam's razor).

    Sorry for the confusion. Thanks again.


    Quote Originally Posted by luv2gofast View Post
    A22 is sensor gnd and A23 is +5. With a 33K series resistor on the input you should not be seeing 1.78k. The A15 input has a 33K series resistor and is pulled up with a 1K resistor so you should be measuring the resistance between A15 and A23 (+5) to test those resistors ~34K total. Cap is a .033uf so not likely to cause a problem but if you get anything less than ~30K there is a problem or the diagram is not correct..
    Last edited by Findre; 07-26-2019 at 05:36 PM.

  12. #9
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    5.092 kΩ at Pin A15 connected to A23 with MAP, TPS, pressure sensor and 8 pin smart craft disconnected. Strange part is the engine still fires right up even with low resistance. I guess I need to see what the resistance is when it won't start.

    Dang gremlins.

  13. #10
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    The measurement I recommended is with the sensor disconnected and power off to test the internal resistors in the pcm. I didn't know your reading was with the sensor connected. Your number makes more sense now.


    96 Cougar 23 MTR twin 300XS's. 100 something
    98 Laveycraft Sebring 20.2 Tunnel 280 90 something SOLD
    85 Baker RST 220 Laser SOLD

  14. #11
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    5.092 is without sensor connected. It's the plug for tn/gn wire to another plug purple/yel wire.

    That is a direct connection to the a15 and a23 with no other sensors connected. So we are <30k.

    What do you think?

    Quote Originally Posted by luv2gofast View Post
    The measurement I recommended is with the sensor disconnected and power off to test the internal resistors in the pcm. I didn't know your reading was with the sensor connected. Your number makes more sense now.

  15. #12
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    That reading is directly on the pins of the ecm? The schematic shows a 33k series resistor so the reading has to be > 33k with nothing connected


    96 Cougar 23 MTR twin 300XS's. 100 something
    98 Laveycraft Sebring 20.2 Tunnel 280 90 something SOLD
    85 Baker RST 220 Laser SOLD

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  17. #13
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    That is what I thought. I had a brain wave while sleeping. I will compare the other two temp sensors resistance plug wire separately A16 then A17 to A23, as they have the same 33k spec on the schematic and compare. Or I'll just pull the 32 pin plug and test.....duh, still early.

    Easy to test and I really don't want to crack the ECM open unless totally sure the resistance is bad. So I'll compare and rule out bad spec given on the schematic.

    Of course Mercury said, just replace the ECM. Ah what's $2000 to them.

    Quote Originally Posted by luv2gofast View Post
    That reading is directly on the pins of the ecm? The schematic shows a 33k series resistor so the reading has to be > 33k with nothing connected
    Last edited by Findre; 07-27-2019 at 08:51 AM.

  18. #14
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    I had a no start condition and pulled the ECM plugs and tested a14,A15,A16 and A17 to A23. All 4 pins pairs tested 5.092k.

    Does this mean that they are sharing the same bad resistors? or is the resistance value number wrong in the schematic?.

    I pulled the connector on A15 and it started right up once reconnected ECM plugs. This seems to blow the bad A15 theory if the other I'll inputs are the same.

    Am I dealing with software issues and not hardware issues??

    Quote Originally Posted by Findre View Post
    That is what I thought. I had a brain wave while sleeping. I will compare the other two temp sensors resistance plug wire separately A16 then A17 to A23, as they have the same 33k spec on the schematic and compare. Or I'll just pull the 32 pin plug and test.....duh, still early.

    Easy to test and I really don't want to crack the ECM open unless totally sure the resistance is bad. So I'll compare and rule out bad spec given on the schematic.

    Of course Mercury said, just replace the ECM. Ah what's $2000 to them.
    Last edited by Findre; 07-27-2019 at 11:47 PM.

  19. #15
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    I am starting to think there is voltage drop to ECM when boat is starting. Batts and wiring are new. Engine starts when charger is connected or was recently turned off from being charged. If it sits, it wont start.

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