Offshoreonly.com - 502MPI - Intermittent Crank, No Start

Offshoreonly.com (https://www.offshoreonly.com/forums/)

- General Q & A (https://www.offshoreonly.com/forums/general-q-20/)

- - 502MPI - Intermittent Crank, No Start (https://www.offshoreonly.com/forums/general-q/258807-502mpi-intermittent-crank-no-start.html)

I'm taking it out tonight to see what happens. It's hot and humid today, so should be a relative test. I'm planning to take my spark tester, Fluke, and the service manual. I'm almost hoping that it does exhibit the condition so I can get to the bottom of this.

I appreciate all of the advice - I'll report back with the results.

Quote:

Originally Posted by supercat (Post 3463596)

Even though ambient air had cooled off, the engine compartment stays hot for a looooong time. And after the vapor lock has pushed the gas back to the tank (assuming you don't have a check valve) you still have to crank like you ran out of gas. Try running slow with hatch open slightly for a little while before shutting it off or running blower for a while after you shut it off and see if problem disappears. My guess is it will.

Like was mentioned before, If the battery has enough to crank engine normal speed there is most definitely enough voltage to run ecu/fuel pump and injectors. If it were a hot electrical component problem then jumping would not help. When my hp 500's do it I crank and it fires for a split second then quits and I know I just ran the little bit of fuel in the fuel rail out and have to crank and crank and crank to prime again. Oh by the way, the reason they added the mechanical pump in front of the electric high pressure pump on my hp 500's was because they had vapor lock issues and the high pressure pump sucks (pardon the pun) at priming.

UPDATE: Took the boat out Wed night. The only changes I had made at that time were cleaning the connections with a wire brush. The boat started in the driveway and started at the ramp. We drove about 10 mins at top speed, then parked at a beach. Sat around for a couple of hours - boat started, then died. Tried to start again, and just cranked - no start. So, we sat around for about 20 more minutes with the hatch open. Tried to start again, and the engine started - no jumper cables.

So, I'm starting to the think that maybe this is vapor lock.

While having the hatch open and the blowers on, I discovered that the starboard blower was inop. Replaced that last night.

So my plan for the weekend is to run the blowers quite often prior to beaching and starting (obviously) to see if that improves my no start condition. I appreciate all of the suggestions!

.....more to come, I'm sure!

Quote:

Originally Posted by easyrider1340 (Post 3465355)

there are correct ways to fix this which i am sure will be discussed but in the short term, as you approach where you are going and when you come off cruise and go to " no wake zone" speed etc. crack the hatch open as much as you can as you trundle in so the engine compartment temps come down to something less than the surface of the sun. once you park, let the motors idle for a few minutes with the hatch fully open and let everything cool down and once you shut it all off leave the hatch open for a few more minutes to let everything cool down relatively quickly and not heat soak.. this will increase your chances of getting started again quite substantially. the real fix is relatively simple in concept but a bit involved in execution.

Found bulletin in the Formula forum for this same problem. I don't know how to post in here but go there and read it is Mercury's vapor lock bulletin.

Post Weekend Update:

I had the boat out on Friday night, Saturday, and Sunday. As I approached our usual anchor out or beach locations, I turned the blowers on and opened the hatch about 1'. The boat started each and every time I needed it to ! I was quite happy!

Thanks for all of your help. I'd be happy to hear about the permanent solution to fix this (if there is one). If you prefer email, try easyrider1340 (@) gmail dot com