Mercruiser 350 Mag will not stay running

[Wohlbergt]

Hello,

I just bought a boat off of a auction with a 2013 Merceuiser 350 Mag. Serial number 2A181660. The auction listing included a video of the motor running but when I received the boat it did not even turn over. I replaced the starter and was able to get the motor to start but the motor surges badly at idle and will not rev at all, it dies if you try to rev it. I started replacing maintenance items to see if it would clear up but nothing has work. I have already done the following

fuel filter, had water in the filter but the tank appears to be clean. It was empty when I purchased the boat. Checked pressure, reads high but seems to be thrown off by then surging.

replaced: cap, rotor, plugs, wires, coil with ignition module, IAC valve.

Currently the motor starts and still will only run with the surging idle. It is smoother than before I replaced parts but I cannot rev the motor at all. I have a MAP sensor or order but I am not sure where to head next. Please let me know your suggestions.

 

[tpenfield]

:welcome: to iBoats

MPI engine (right?)

You will eventually want to check for codes or any other operating abnormalities. As a next step, you might want to check to see if there are any loose tube/hoses that should be connected to the intake manifold/plenum.

It seems like right now you are throwing parts at it to no avail. Got a shop or someone who has the computer diagnostics?

 

[Wohlbergt]

Yes, my next step if you find someone to read the codes.

the parts I replaced all needed to be replaced sooner or later. I am thinking this boat had water in it at one point because of the corrosion I am seeing on these parts.

I just wanted to see if anyone had any ideas with my symptoms.

 

[Bt Doctur]

most likely was under water

 

[alldodge]

With the motor having CAT's you do need it scanned before doing much else. Doing things without knowing what the problem is can cause other things. Rinda makes scanners (Techmate and Diacom software)

Fuel pressure should be 43 psi and measured at the rail item 18 after removing cap

https://www.mercruiserparts.com/bam/subassembly/31758/15323/90

 

[Wohlbergt]

I do have a tube that is connected to the port rocker cover that is not connected to anything. I cannot see anywhere it goes to. It this tube supposed to be connected somewhere. It sounds like older motors would have this run to the flame arrestor.

 

[alldodge]

I do have a tube that is connected to the port rocker cover that is not connected to anything. I cannot see anywhere it goes to. It this tube supposed to be connected somewhere. It sounds like older motors would have this run to the flame arrestor.

Yes, its a tube which goes to the flame arrestor. Without it there would be no change for the motor

https://www.mercruiserparts.com/bam/subassembly/31758/15323/80