350 Mag MPI questions

All,

I have a 2002 Four Winns Horizon with a 350 Mag MPI (OM254958) and a Bravo 3 drive. The past couple of times we have been out the engine has been hard to start after its been running. So I did some searching on possible causes to see if I could check a couple items and noticed that some people have a check valve in the coolant line to help with vapor lock. I looked in my service book (mercruiser #24) and no where in there is a check valve referenced. I also checked the mercuiser online parts manual and it does not show one for my serial number either. I checked the boat and it does not have the check valve before or after the fuel cooler. Is there a kit number that I can use to install one? I have also had a high pitched whine coming from the throttle body at low rpms. While checking into the hard start, there where several recommendations to clean the throttle body, IAC, and replace the IAC muffler (which it sounds like is the cause of my high pitched whine). I looked in the parts manual to locate it and get a price on a new one and no where does it show the IAC. It shows the throttle body with it installed but not the IAC separately. Is there a reason it is not listed separately? One final questions, while checking the engine I noticed a plug with a purple and black wire on one side and a white wire looped to itself connected to the other end of the plug. I have attached a pic. Any idea what purpose this plug serves and is it supposed to be connected like this?

i also have a 2003, 350 Mag, Bravo iii, i have had similar issues. however my fix was to replace the distributor rotor and cap. mine is almost a yearly change. i usually buy the mercruiser part. This doesnt come with a gasket. i believe the Sierra version comes with a seal. So next time i will try the Sierra brand. i also just change the starter solinoid. boat starts right up.

Just so you're aware, the serial number you posted (OM254958) is coming up as an Alpha transom assembly so you'll want to reconfirm the numbers.

Your engine being an 2002 does not utilize the IAC muffler....That started a bit later in 2003 with the small block engines.

Also being a 2002, it did not come with a water check valve system as again that came standard on some engine model a year later.

Being a Bravo drive, the wire plug shown needs to be there as that is for the mercruiser shift interrupt switch system "had" you had an Alpha stern drive...The bravos need to be jumped like that so the ECM/ignition will work properly.

For past vapor lock info for closer to your engine model, see the following links,
http://www.marineengine.com/boat-forum/showthread.php?390380-Vapor-lock-or-what&highlight=Vapor+lock
http://forums.iboats.com/forum/engi.../7758108-2000-350-mag-mpi-fuel-pressure-issue

Here would be the booster fuel pump kit to consider using, http://www.marinedepo.com/product-details.php?id=150
http://www.iboats.com/350-MAG-MPI-ALPHA-BRAVO-0L331599-THRU-0M299999/dm/view_id.1691793

Boat Tech, I saw that one of the parts vendors listed that serial number
as an Alpha, yet another (if you look under the 350 Mag MPI Alpha/Bravo, and then the serial number) shows the s
ame serial number and the correct parts breakdown. However, both of the the 350 Mag MPI parts breakdown showed both styles
of Mufflers. I also had planned on tuning it up with cap, rotor, and wires first. I did put a fuel pressure gauge
on it today and did a key on/engine off reading of 28psi. That reading slowly started dropping. Within ten minutes
it was down to 20psi. I am going to pull the injectors and see if one of them is leaking. Thanks for all the help!!