View Full Version : 2011 Mercury Optimax 150 no start with starboard temp sensor connected

07-22-2019, 05:38 PM
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.

07-25-2019, 04:39 PM
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?