8.1 Engine problem? Just shuts down.. Mechanics question

mnm99

mnm99

Well-Known Member
Oct 2, 2015
2,447
Long Island
Boat Info
2004 340 SeaRay Sundancer
Engines
Twin 8.1 Merc
Hey guys,
I'm working with a friend on this problem. 2003 496 8.1. Very weird. When he starts the engine and lets it idle it just shuts down at random times. Just shuts right off, no sputter or anything. Wait a min and starts right up most of the time. It could run for 5 min or 45 min without a problem before it shuts down. Twice it wouldn't start after it shut down then waited 15 min and started right up. Doesn't happen when cruising. He changed the crank sensor so far. No alarms or anything. Any Idea what it could be? Anyone have this problem?
 
No and it might set irrelevant codes when it dies.

Put a pressure gauge on the rail
 
Could that be iac related or is it off idle also
 
Does it only happen at idle
 
If the IAC doesn't do it, as I did that first also. When you turn on the ignition, listen closely for the fuel pump to prime. If it does not, and engine will not start, consider cleaning and reseating the power harness (2 connectors) to the fuel pump. Also, there are 4 relays on the top of the motor. One of them goes to the fuel pump. Figure out which one it is (disconnect one at a time, turn on ignition and listen for fuel pump) reconnect and retry ignition n see if fuel pump primes. After you have the respective relays identified on both motors, switch them and see if problem moes to other engine. If does - relay going bad. Does not - probably not the relay.
As I was having the same issue, I did the above and now it seems fine.(knock on wood). My guess is dirty/poor contact on one of the fuel pump connectors. The relay swapping was my mechanics recommendation. Didn't do the test bu t did get a spare relay to have. Minor investment @ 14.00.
 
Can he start it and get it slightly above idle? And then it stays running? Like 800 rpm? (assuming idle rpm of 600) That will point another finger at the IAC.
 
You didn't say whether the boat has one engine or twin engines, my assumption is one. If twin you can switch the IACs to see if the problem follows.
 
I’ll mention the relay and connection. Yes it has 2 engines. Already cleaned engine harness connections, swapped ECU (put back). Fuel pump runs when key is on / prime the shuts off. Normal. Will try IAC.
 
Would swap Iac before ECU
 
mnm99 said:
Hey guys,
I'm working with a friend on this problem. 2003 496 8.1. Very weird. When he starts the engine and lets it idle it just shuts down at random times. Just shuts right off, no sputter or anything. Wait a min and starts right up most of the time. It could run for 5 min or 45 min without a problem before it shuts down. Twice it wouldn't start after it shut down then waited 15 min and started right up. Doesn't happen when cruising. He changed the crank sensor so far. No alarms or anything. Any Idea what it could be? Anyone have this problem?
Click to expand...
I had the same problem with our Mercruiser, check the red emergency button top of the engine or maybe on the side, lose connection.
 
TonyV said:
I had the same problem with our Mercruiser, check the red emergency button top of the engine or maybe on the side, lose connection.
Click to expand...
Or replace it. From Hillsbrough to Key West our engine stopped 7 times., you wait for 30 seconds starts again. Since I replaced, problem solved. Good luck
 
What's your idle speed?

IAC is a candidate but before you check that, clean the flame arrestor and replace the IAC muffler - it's a tiny sponge in the throttle body. It should be white or light grey, it'll probably be revolting and black and sticky. It's like a three dollar part. And if you don't want to even do that, just pull the dirty one out with a pair of pliers and start her up. If it idles nicely then that's your culprit. But clean the flame arrestor anyway.
 
TonyV said:
Or replace it. From Hillsbrough to Key West our engine stopped 7 times., you wait for 30 seconds starts again. Since I replaced, problem solved. Good luck
Click to expand...
No red button on the 8.1's
 
You must log in or register to reply here.

Forum statistics

Threads
113,280
Messages
1,429,948
Members
61,150
Latest member
Wonderball2Swilm
Back
Top