8.1 warm start problem

Pierpressure1

Pierpressure1

Active Member
Sep 8, 2015
274
Richmond, VA
Boat Info
1998 400 Sedan Bridge
Engines
Cat 3116
I have a 2006 340 with twin 8.1s. Today we took a 30 mile cruise to Windmill point for lunch and when I started my Starboard motor for the return trip after about an hour it started right up and died in about a minute. After trying to restart with no success I installed a new IAC and after a couple attempts in started up and ran fine. At this point I felt I had fixed the problem and returned to our Marina. I let the boat sit again for an hour and restarted the motor and it died again after a minute. Eventually I was able to get it restarted and it ran fine again and would restart with no problem.

One thing I did not mention about the aftermarket IAC is that the gasket that it came with was not paper like the one I removed but a rubber double o ring which looked like it should go in a grove. There was no grove and the old gasket was stuck to the old IAC so I positioned it as best I could and tightened the valve.

Any my input on possible solutions will be greatly appreciated.
 
Could be a number of things, maybe the low pressure side of the fuel pump since its hard to start but runs fine once started which would be the high pressure pump while under a load. Just a thought.

Good Luck
 
Does it start ok after a cooldown - ie overnight? I would rule out vapor lock before you start changing parts.
 
BillK2632 said:
Does it start ok after a cooldown - ie overnight? I would rule out vapor lock before you start changing parts.
Click to expand...

It it starts fine after cool down and will fire up no problem after I eventually get it running. If it is vapor lock is there a way to avoid it or recover quicker?
 
The whole purpose of the Cool Fuel unit is to reduce / eliminate vapor lock. Only way to recover from vapor lock is to cool the fuel system down, one trick is to spray the fuel pump / lines with cool / fresh water, you wouldn't want to do this with salt water (obviously) and it's not a solution, just a way to get you going. Vapor lock is in simple terms when the fuel heats up and vaporizes in the fuel line around the fuel pump - the pump can't "pump" vapor. So anything you can do to cool the fuel down will eliminate the vapor lock. It usually occurs after shutdown, the engines / engine room tend to heat up for awhile after shutdown and that is usually when vapor lock occurs. You can google and find tons of information, I believe Mercruiser has a tech bulletin on it, but here is some general information. I've never had my 4.3 do it, but the 290 did it a couple of times, always happened in early summer when I still had winter blend fuel in the tanks - the spraying water on the fuel lines trick always go it running.

https://www.perfprotech.com/blog/articles/mercruiser-vapor-lock
 
Actually vapor lock can happen on fuel injected engines. I had it happen on my old boat - fuel injected - and an old dock mate had terrible problems with his 340DA, 8.1's. On the contrary I have never had it happen on one of my carburetor boats - not that it couldn't.
 
Last edited:
I was able to move the boat to the local Mercruiser certified Marina for them to check it out. Of course the engine fired right up and ran flawlessly during the 20 mile trip.

Will update the thread once I hear from them later this week. Thanks to everyone for their help.
 
Just picked up the boat this afternoon. They felt the original no start issue was a bad IAC and the second non start was the poor seal of the aftermarket gasket that came with the IAC that I installed. All fuel pressures checked out and the engine showed no codes.

I ran it 40 minutes back to our Marina and then let it set for an hour. It fired right up so hopefully this issue is behind me.
 
You must log in or register to reply here.

Forum statistics

Threads
113,253
Messages
1,429,366
Members
61,131
Latest member
VaBreeze
Back
Top