2017 Massimo MSU-500 Cranks but won't start.

[Tim Nelson]

Ok guys, my turn...

Working on my neighbors 2017 Massimo MSU-500.  Initial complaint was it would start and run for about 10 minutes and the just die.  He replaced the fuel pump and still had the same issue.  I stopped over one day to look at it and saw that it had codes flashing on the dash; 505, 336 and 337.  We decided to get a new stator/crank sensor.  Took it apart installed the new stator/crank sensor and nothing.  It won't even start.  I checked the pins on the crank sensor plug and one was in the wrong place, so I repinned it and it still won't start.  I double checked the connectors and all is good.  I checked the wires from the ECU to the coil, good.  It appears to have spark every once and awhile but not enough to start.  I replaced the coil with a known good one and still nothing.  I bought the cables and downloaded the ECU hardware and everything looks good.  I pulled the timing cover back off to check the flywheel keyway, it is good.  I checked the timing and timing chain, good.  I checked the valve lash, good.  I have to put it back together but just wanted to post in case there is something else I should check before hand.  I checked the 9 pin connector and it is clean.  I have battery voltage on the purple wire and pins 15 and 18 on the ECU.  I pulled the air filter off and I am going to put a new plug in it just for the heck of it.  What ECU inputs would prevent it from starting?  Why would it now not start at all after replacing the stator/crank sensor? It has to be something simple.  Any help would be appreciated.

[Tim Nelson]

the computer back up to it, I noticed I was not getting a RPM reading and was getting a CKP sensor error which meant it was not getting the correct counts. I took the flywheel cover back off to check the air gap. Not much movement but moved it as close to the inside as possible. I then compared the eBay special to the original and noticed that the wire colors were opposite of each other.  I put all back together and it still wouldn’t start. Just for the heck of it I switched the pins on the harness coming from the sensor and BOOM! She fired right up!  I would have never thought that the polarity of the sensor made a difference but it does. Just something to think about when you buy aftermarket parts.