Both engines died at the same time...

I have a 2001 400 DB with 2 454’s.
Last weekend we cruised to an island and hang out for a couple hours and as I was backing out of a cove both engines stopped at the same time…. It took me several attempts to get one engine running again and we started our journey back on one engine. During our cruise back I tried about every 15 minutes to start the second engine and after a few attempts the second engine finally started, I was already mentally preparing to back her into my slip with one engine…. About an hour after successfully parking the boat I tried to start the engines and they both didn't start and I tried that over a couple hours…. The next day,everything worked as always, both started right away. The one thing what is really strange is that both engines do the same thing but they are completely independent from each other, right?
Could that be vapor lock? If yes would it help if I add a third blower what pushes fresh outside air into the engine compartment, close to the air intakes?

My guess is the batteries were discharged during the time you were "hanging out". The second engine fired up after the batteries recovered their charge. Assuming you were plugged into shore power overnight, the batteries again were able to recharge and this allowed the engines to start up right away the next day.

For both engines to quit running like that I would guess some kind of fuel issue. Perhaps water in the fuel?

I had that happen to me last year with my 330SS 454mpi Formula with both engines. They both started and while I was pulling up they anchor they both died and would not start back up. It was a hot day and previous to that only the port engine had ever vapor locked. I cracked the hatch and ran the blowers for a half hour and they started again and ran flawless. This seamed to happen after recently fueling the boat on land and only did it that one time so I'm not sure if the fuel itself played a roll or not.

Avenger said:

I had that happen to me last year with my 330SS 454mpi Formula with both engines. They both started and while I was pulling up they anchor they both died and would not start back up. It was a hot day and previous to that only the port engine had ever vapor locked. I cracked the hatch and ran the blowers for a half hour and they started again and ran flawless. This seamed to happen after recently fueling the boat on land and only did it that one time so I'm not sure if the fuel itself played a roll or not.

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I'll try that next time when it happens. I used fuel from a gas station up the road in January as well.... I don't trust the fuel at the marina, a lot of people had bad experience with it...
If I get more airflow into the engine compartment, that should help...

Juergen said:

I'll try that next time when it happens. I used fuel from a gas station up the road in January as well.... I don't trust the fuel at the marina, a lot of people had bad experience with it...
If I get more airflow into the engine compartment, that should help...

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And there is your answer. You bought gas from a gas station in January. That station was selling winter blend fuel. Now 6 months later you are running in hot conditions, and the winter blend will vapor lock.

Typically gas sold at a station is good for about 6 months unless you put something like Stabil in your fuel.

So old gas that is a winter blend being used in summer. There is your problem.

CaptRonn said:

And there is your answer. You bought gas from a gas station in January. That station was selling winter blend fuel. Now 6 months later you are running in hot conditions, and the winter blend will vapor lock.

Typically gas sold at a station is good for about 6 months unless you put something like Stabil in your fuel.

So old gas that is a winter blend being used in summer. There is your problem.

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We have a winter grade diesel in the north but have never heard of such a thing for gas. Is there something added in the south for heat in the summer?

Thornton69 said:

We have a winter grade diesel in the north but have never heard of such a thing for gas. Is there something added in the south for heat in the summer?

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Google "winter blend gas" and you'll find several articles on it.

I’m reposting this for those who have vapor lock, I posted it previously on another post.

Been there, fixed that!
What you have is vapor lock, it happens after a hot engine sits in a hot engine compartment causing a “heat soak” where the engine actually gets hotter instead of cooling down. I tried opening the hatch, no good, it still would not start. Hitting the key on and off didn’t work because the fuel pump could not “push” the air through the lines.

The excessive heat causes vapor lock because the fuel sitting in the fuel line vaporizes which causes a “air gap” in the line that the fuel pump cannot “pull” through to the fuel rail. Most mercruiser EFI engines need either 39 psi or 43 psi, any less and it ain’t startin’!

The permanent and CORRECT fix is this, and it will never happen again. Mercruiser makes a low psi “push” pump. The kit comes with: pump, wire harness, fittings. Simple to install, just install it inline between the fuel tank and water separator filter. The wire harness is plug and play and the pump only comes on when your other fuel pump is on. These “kits” are found online or through your Mercruiser Dealer and any brass fittings you may need are available at HD.

The other fix is this: Go online and find aftermarket 5 psi fuel pumps, make your own harness. Then pray you don’t blow yourself up because either you or the backyard mechanic who installed it didn’t do it correctly!

The reason fuel vaporizes faster at different times of the year because the fuel companies add ingredients to increase “Rapid Vapor Preasure “ (RVP) in the colder months.

You will spend a lot more to do it correctly, but if safety is important to you do it right the first time!

I hope this cleared it up, it took me months to figure it out and all Mercruiser techs I spoke to could not figure it out or have a cure.
Good luck with this,
Bow Tie

I'm glad this was reposted, because I had a crappy weekend!!! Story.....2006 380 Sundancer 8.1 Mercs with Cool fuel gas pumps. 675 hours on motors. Both motors start right up, run great, starboard motor dies. Cranks but won't restart. After sitting all day, motor starts right up again. Go out on the boat, starboard motor dies. Cranks but won't restart. Again, after trolling my way over to a mooring, sit all day, boat starts right up. Sometimes the motor dies after 15 minutes of run time, sometimes after one hour of run time. One time out it didn't stall at all. All posts lean to vapor lock or crank sensor. Mechanic puts scanner on motor and gets codes for crank sensor and cam sensor. He says he's never seen the cam sensor having to be replaced. Suggests that its the crank sensor. BTW the mechanic is well respected and a friend of mine, so he's not looking to make money off of me. Who else would come out twice on the weekend!! I suggest lets swamp crank sensors and see what happens. We do and again starboard motor dies after ten minutes of run time. On the return trip doesn't stall until we are docking. No audible alarms sound. I replaced fuel filters already. So, if it's vapor lock, a crank sensor shouldn't come up on the scanner, right?? Our next step is to swap the ECM's and see what happens. Very frustrating, and I'm glad I didn't run out and by the crank sensor.
Any input is greatly appreciated as I have boat vacation booked and thinking of pulling the plug on it!!
Thanks everyone in advance!

searay495 said:

I'm glad this was reposted, because I had a crappy weekend!!! Story.....2006 380 Sundancer 8.1 Mercs with Cool fuel gas pumps. 675 hours on motors. Both motors start right up, run great, starboard motor dies. Cranks but won't restart. After sitting all day, motor starts right up again. Go out on the boat, starboard motor dies. Cranks but won't restart. Again, after trolling my way over to a mooring, sit all day, boat starts right up. Sometimes the motor dies after 15 minutes of run time, sometimes after one hour of run time. One time out it didn't stall at all. All posts lean to vapor lock or crank sensor. Mechanic puts scanner on motor and gets codes for crank sensor and cam sensor. He says he's never seen the cam sensor having to be replaced. Suggests that its the crank sensor. BTW the mechanic is well respected and a friend of mine, so he's not looking to make money off of me. Who else would come out twice on the weekend!! I suggest lets swamp crank sensors and see what happens. We do and again starboard motor dies after ten minutes of run time. On the return trip doesn't stall until we are docking. No audible alarms sound. I replaced fuel filters already. So, if it's vapor lock, a crank sensor shouldn't come up on the scanner, right?? Our next step is to swap the ECM's and see what happens. Very frustrating, and I'm glad I didn't run out and by the crank sensor.
Any input is greatly appreciated as I have boat vacation booked and thinking of pulling the plug on it!!
Thanks everyone in advance!

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How old is the fuel in the tanks?

I'm on my second fill up of the summer.

Do the cool fuel mercs with low and high pressure pumps in the module get vapor lock? I've run mine in 40 plus degree C temps on the plane for hours and never had restarting issues. I run in the ocean though so water temps are generally coolish.

Exactly!! They aren't supposed to. But if crank sensor comes up on the scanner, and it's not the crank sensor, sounds like vapor lock.

Unless the cool fuel module has internal corrosion restricting water flow contributing to vapor lock. I've replaced one of my cool fuel modules due to corrosion when I first bought the boat.

Good point. But the crank sensor alert kind of muddies that thought process. One more piece to the puzzle I should have added. While diagnosing, we looked at the white fuse block that sits on top of the motor. One corner of the "white" block was brown where a fuse for the fuel pump is located. Indicates over heating. Spoke to a Merc tech who suggested checking the relay for the fuel pump to make sure it isn't overheating, and also checking the fuel pump pressure to make sure it is correct. Again, makes sense, but why the crank sensor alert, unless there are two issues. I'm also supposed to check the circuit for the crank sensor.....where the hell is that??!!

Juggernaut 1, you hit the nail on the head. I don't want to blow my trumpet early, but I think I've figured out the problem. I took the water lines off of the cool fuel system only to find out that the bottom nipple adapter is totally clogged with this gluey, silicone type of junk. I was scraping it out with a screw driver. Went to unscrew the blue drain plug and that snapped off also. So my question is, how do I clean the block that the water goes thru. I really don't want to take off the cool fuel module. Thinking muriatic acid, forced air or forced water? Also, why the crank sensor alarm on the mechanic's scanner?