Dont just look at the connection joint where it k=hooks to the battery.....look at the cable strands where it goes into the connector.....if its green or black then id say replace the cables cause you don't know how far back the corrosion goes

My bet is fuel pressure-related.

I had an issue in the past that was similar. I had low fuel pressure due to cracks in the fuel feed hose coming from the tank. It wasn't leaking fuel, but was pulling air into the systema and in the end the engine wouldn't even run. Fuel pressure was down about 8 PSI and the plugs were black. The initial thought was that it was getting plenty of fuel but in reality the injectors were not atomizing the fuel properly.

You mentioned that yours will run fine until you shut it off; is this in a loaded condition or just on the hose? A no-load test condition will mask a lot and if it is a fuel pressure issue, it's important that you do not run it until resolved. It's easy to burn down an MPI engine - the injection system is rather basic and not smart enough to keep the engine from grenading itself.

*edited*

I was able to test the fuel pressure and it definitely seems to be the issue. When I first turn the key on it shoots up to 60psi and then goes down and holds steady at 18 psi. Would that be the fuel pressure regulator? If so what does everyone recommend? Getting an adjustable or aftermarket one or just sticking with oem?

Is that running?

No, that is just when turning on the ignition. When I first turn it on and the pump whines, it jumps to 60 psi for a second. When it stops whining, it drops down to 18 psi.

60 psi is higher than it should be capable of reaching unless the return line is restricted or the regulator is faulty. I'd be curious to see what pressure it supplies while the engine is running and the fuel pump is continuously "on".

Alternatively, you can jumper 12V+ to the gray wire at the fuel pump relay, this should allow for constant running of the fuel pump for testing purposes. The fuel pump relay is located in the electronics box at the top port side of the motor.

I haven't wanted to start the engine again as I really don't like using starter fluid. I just did it the one time as a test. I can try your suggestion and have the pump run continuously.

Understandable. shouldn't take more than 4-5 seconds of jumper-wire pump operation to see the needle stabilize at running pressure.

Id stay with the OE stuff, replace the regulator and pump if it was me...............if you boat in summer high temps and humidity you might want to consider an after market pump and regulator to eliminate the risk of vapor lock.

I live in Texas so it gets really hot in the summers here.

I did as you suggested and ran a red + wire to the grey wire to the fuel pump and let it run for about 5-10 seconds. After about 5 seconds it was holding steady at about 10 psi.