Mercruiser 5.0 EFI starting issues

[Pauli18c]

2000 Sea Ray 210 Signature series bowrider
Mercruiser MCM 5.0L EFI
Engine serial number: 0L641983

First off just want to say that this is my mom's boat which isn't local to me so trying to get a list of things to check / test before going. I was up there once trying to figure it out, but the starter gave out and blew the fuse so wasn't able to get very far. (dont believe it's related at all, changed the starter and fuse and it's back to doing what it was doing before).

Boat has been having issues starting randomly. Seems to start when cold fine first time of the day. She usually drives around a little bit, then throws anchor to float for a few hours. Outside temps in the 80s- low 90s lately in southern Wisconsin, so maybe it's still a heat issue even though it's sitting for a couple hours? Goes to start, and it just cranks. It tries to start but then sputters a little bit and dies. The more you try to start it, the worse it gets and then wont fire at all. Safety switch fine, it's in neutral, etc. Gets towed back to dock (4 or 5 times now). Lets boat sit for a couple more hours, then fires back up later on when she goes to put the cover back on for the night like nothing happened.

She's had a mechanic out a couple times now and he swears it was going to be fixed after the last time. He's replaced the ignition sensor, cap, rotor, and coil now so far.
Mechanic showed her how to look for fuel being sprayed, and she says there is

 

[alldodge]

Howdy, and thanks a bunch for the serial number

Can motor once warmed up, be shut OFF and restarted right away?

If it sits for 15 to 20 minutes will it restart?

If both the above are true and its only after it sits for couple hours or so, its probably vapor lock.

 

[Pauli18c]

Howdy, and thanks a bunch for the serial number

Can motor once warmed up, be shut OFF and restarted right away?

If it sits for 15 to 20 minutes will it restart?

If both the above are true and its only after it sits for couple hours or so, its probably vapor lock.

Yes, it will start multiple times over and over at the dock as I started it a few times in a row when I replaced the starter.
We went out for the day around 1pm, drove around for a while (45 mins), anchored for ~3 hours, went to start it and couldn't get it going. Towed back to dock. Fired back up about 730pm when when the sun was going down.

I will have them check the 15-20 minute time span.
What's the solution for that?

 

[Pauli18c]

I'll also add that she's had the boat for about 10 years on the same lake with no issues before. This year has been the first time

EDIT: after reading some on vapor locking this sounds like it may indeed be the issue. The piers were put into her lake early this year in mid April and she filled up the same time. Probably got bad gas that early in the year. I will report back after she refills with fresh premium.

Thank you for the suggestion, I would have never looked into that or thought anything of it

 

[alldodge]

Non-E gas does work better but isn't a cure all. As in the write up you posted many things can cause the issue to get worst

If you bring some wrenches, a rag and safety glasses you can cure VL quick. When it won't start, loosen the fuel line feeding the throttle body. Some air and fel will spit out, and may need to cycle the key once to clear the vapor. Re-tighten and it should fire up

To fix more so need to have the return line go back to the tank instead of the filter

 

[Pauli18c]

Non-E gas does work better but isn't a cure all. As in the write up you posted many things can cause the issue to get worst

If you bring some wrenches, a rag and safety glasses you can cure VL quick. When it won't start, loosen the fuel line feeding the throttle body. Some air and fel will spit out, and may need to cycle the key once to clear the vapor. Re-tighten and it should fire up

To fix more so need to have the return line go back to the tank instead of the filter

Ok thank you, I will have to give that a try with cracking the line loose to see if that's the issue.

Is there a write up somewhere on how people are routing the return line back into the tank? Do you need to drill a hole or something?

 

[alldodge]

Not to much on write ups, but this is how its done. The pis shows MPI but is the same for TBI. If you don't have an unused port in the tank, then a Tee fitting is made and placed in the fuel tank fill hose

 

[Pauli18c]

Thank you for the diagram