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My boat stalls when at idle, but only once the engine is hot. I have a merc 502efi. The dealer said that this problem is common with the 502. It may be common but there must be a way to fix it. Has anyone had this problem before? What was done to fix it?
My 95 Formula will do this after it sits for the week. The mpi's are known for this, some idle rough when cold. This happens because the fuel evaporates from the fuel rail. Cycle the key a few times before start up.
You need to know how the "IAC" motor is working/or not. It's a round electrical piece, held on with two screws to hold it on the throttle body. You need to use a "DDT" or a "Merc laptop CDS" to 'look' at your systems. Those will tell you 'what the engine computer is seeing and ordering the IAC motor to do', but not actually READING any feedback from the "IAC". The system may be telling the "IAC" to open and the "IAC" is not operational. 454 MPI's have a slight open position on the throttle plate, a 502 has that same setting and a small hole in the throttle plate. Those physical settings along with the "IAC" motor control the airflow at idle on your engine. The engine computor also controls idle speeds with spark timing, fuel pulse width, and the afore mentioned "IAC" motor. This is my view of your problem without any other input from you. I assume the motor runs well at all times and speeds other than your "question of idle" problem. Put it on a DDT and test it!
Has anybody had to scrap the VST system on their 502? One shop told me to eliminate the VST and add a fuel pump and a fuel bypass instead of adding a cool fuel system. Which is better?
That is the cause of you "stalling at idle"?
well for proper feul atomization you need it warm.a few years ago they used to put a burner if you will in the center of the intake manifold on the heavy duty trucks which was located inside the intake of course