triaqua

I have the 385-hp 454 MPI.I have had problems starting the engine after running it hard.The first time I start the engine,it fires right up and runs great until it is shut off and sits for a while.I turn the engine on and it stays on for a few seconds then dies.It almost sounds like if it's running out of gas.The problem is worst at altitude.

Outdrive1

Do you rev your motor up in nuetral? Ive heard that it does something to the ECU. You may need to reset it, I don't know if you can do it without a scan tool or not. You may want to have it serviced and have them check it for any codes.
How many hours? Ever changed the plugs? Fuel water seperator?
Somebody will chime in about the codes or the ECU.

scooby94

Check the IAC motor, it controls the idle. I have the same motor with the same problem, found out that the IAC was sticking closed. Ishopmarine.com was the cheapest around.

Dave1972

Could be any number of different things. Depending on the year of your motor, it could be a vapor lock condition typical of the VST tank EFI system. It could also be a clogged VST tank screen. As others mentioned, the easiest way to diagnose is with a scan tool. Let us know what you find out.

Magic Medicine

Ttt

WETTE VETTE

Magic Medicine is having a starting / idle problem with his 502 MPI. Sometimes it starts and idles like a top, and others it is very finickey. When it is acting up there is a swoosh noise coming from the engine compartment. It is changing in pitch like it is trying to compensate for something to keep the motor running. Almost every time that swoosh noise is made the motor dies. Is the swoosh noise the IAC motor? Is it bad or is there possibly a sensor there causing it to act up?

Dave_N

The "swoosh" is the IAC. It does not mean the IAC is bad. It means the IAC is attempting to keep the engine running at the desired idle speed, but there is a problem that is causing severe fluctuations in idle speed, so severe at times that even with the IAC wide open (swoosh sound) the engine still dies.

In other words, the IAC "swoosh" is a symptom, not the problem. Time to check for trouble codes, check for proper fuel pressure, and start figuring out what the problem actually is.

Dave

Magic Medicine

I have an appointment to run it on the Merc scan tool tomorrow. The Marina is going to charge me $45 to check it out. I didn't think that was a bad price since I did not buy the boat from them.

Any Ideas of what could be causing the idle fluctation???

GOODT

Great Price!!!!!!!!

Island Hopper

I agree with Dave. Sounds like a vapor lock. Next time it happens, check the fuel rail shrader valve. If air comes out, it is a vapor lock. Bleed all the air, and it should fire up. If you have the VST, that is where I would go next.