cummins start and dies

[fracmechanic]

i have a Maxum 4600scr. it has twin cummins 6cta8.3 m-3 engines. when i start the starboard engine. i turn the key. the wait to start light comes on and after a few seconds goes off. i turn the key and it fires. the port engine not so much. i turn the key. the green wait to start light comes on and never goes out. i can turn the key and start the engine but it will shut off right away. oil pressure comes up and audible alarm will go off. green light still on. when it does start. the fuel shut off will open. starts then it slams closed and kills the engine. i went ahead and replaced the grid heaterecm and selinoids with harness. still no luck. the grid heater selinoid has power but i can't get a signal to operate heaters. they never come on. starting to think i have a sensor somewhere sending a false signal to the computer. any help with be great

[jparsons121]

Going off old memories here.
If I recall, the grid heater is driven off the air inlet temp sensor.
Assuming you have the 3-wire fuel solenoid, check to see if you have power to the Run circuit wire. Sounds like the solenoid is pulling in fine thru the start wire, but not latching when ‘key’ is released to the run position. I think it was a purple wire.
If there is 12v , then either the solenoid is failing or the linkage adjustment is out of spec.
The run coil in the solenoid isn’t as strong as the start coil and being off by 1/4” in adjustment will have it slam shut because it can’t hold it open. If you have no power to the run wire, it’s time to backtrack to see where the circuit is open.

Given you have two issues that both manifested after you changed out parts, I’d suggest tracing all connections in the harness and be sure they are good and tight.

[fracmechanic]

this was happening before i replaced the whole heater assembly. i traced the signal wire coming from the key as a orange wire. the funny thing about that is if i unplug the harness next to the engine(main wire harness). I have power on the orange wire. once i plug it together. i lose my 12 volts.

[jparsons121]

The orange wire should be your pre-heat indicator light signal from the engine to the dash. The 12+ to the engine will be the Red/Purple (Run) and the Yellow/Red (starting). These colors would be on the hull harness side of the connector...

[fracmechanic]

After checking the voltage at the plug for the fuel shutoff selinoid. I’m finding very low voltage. Kind of throw me because I have plenty of battery to crack engine over easily.

[jparsons121]

Ok, so that explains why it would start and then die. The start circuit is pulling in the solenoid when the started is engaged, but once running, the solenoid needs the run circuit to hold it open. Run circuit should be the purple wires.

I’d start tracing the issue by disconnecting the main harness and probe the hull side of the connector with key in run position. Black should be your ground, Red/Purple should be 12+ power and Purple should have 12+ as well (this supply’s power to the run circuit on the engine).