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crow
06-24-2009, 02:04 PM
I'm hoping that someone can point me in the right direction for what I hope is a relatively minor problem...

I have a 2004 Donzi 16 with a 5.0 MPI V8 Mercruiser. A few weeks ago, after a day of running (with several engine shut downs and restarts), after cruising for about 30 minutes, when I pulled the throttle back to near idle speed, the engine alarm sounded and then the engine stalled. The engine then would not start without giving it gas. We can now get the engine started only with the throttle partway open. The engine will run as long as I keep the RPMs above 900-1000, but as soon as we drop below, it stalls out. The normal idle on the engine is about 500-600.

Does anyone have any suggestions on where I should start?

Thanks!

fogducker III
06-24-2009, 02:19 PM
I had a similar problem a while back, also have MPI, not sure why it happened but to solve it I disconnected the battery for a few minutes, hooked it up and I assume the "computer" re-set itself and all was well.

Have you done any changes or "mods" to the engine lately?

Having stated the above, the engine alarm is a concern, from my understanding an alarm means: overheat, low oil and or oil pressure...?

gold-n-rod
06-24-2009, 02:34 PM
I'm hoping that someone can point me in the right direction for what I hope is a relatively minor problem...
I have a 2004 Donzi 16 with a 5.0 MPI V8 Mercruiser. A few weeks ago, after a day of running (with several engine shut downs and restarts), after cruising for about 30 minutes, when I pulled the throttle back to near idle speed, the engine alarm sounded and then the engine stalled. The engine then would not start without giving it gas. We can now get the engine started only with the throttle partway open. The engine will run as long as I keep the RPMs above 900-1000, but as soon as we drop below, it stalls out. The normal idle on the engine is about 500-600.
Does anyone have any suggestions on where I should start?
Thanks!

I had the same trouble last summer with my 5.0 mpi. You need a new IAC motor. IAC stands for idle air control. To find the IAC, remove the air intake cover (black plastic rectangle). The IAC is behind (to stern) of the air intake valve (formerly carb). It has 2 rubber hoses running to it and a wire connection. The Merc part is approx $120. You have to remove the motor from the valve underneath, replace the gasket (come with motor) and reassemble. Any idiot with a couple of tools (allen wrench and screwdriver, IIRC) can do it.

PS: Your Merc dealer will want your engine serial number to assure the proper part ID.

Good luck. Depending on how far away your dealer is, this is less than an hour's job, start to finish!

gold-n-rod
06-24-2009, 02:35 PM
Having stated the above, the engine alarm is a concern, from my understanding an alarm means: overheat, low oil and or oil pressure...?

His alarm sounded because the engine idled so low that the oil pressure became low enough to trip the alarm. No harm, no foul.

fogducker III
06-24-2009, 02:40 PM
His alarm sounded because the engine idled so low that the oil pressure became low enough to trip the alarm. No harm, no foul.

Great info, good to know, I thought the alarm sounding was strange seeing that it monitors heat and oil and the low idle problem doesn't point to that..........BTW. Do you know if my 377 Scorpion has an IAC?

mrfixxall
06-24-2009, 04:24 PM
How many hours? Try cleaning the throttle body and iac+ the passages also check and see if the flame arrestor is dirty,you may have to soak it in somesolvent then follow with brake cleaner in a can..

thescooter
06-24-2009, 05:10 PM
when is the last time you changed your fuel filters and put fresh fuel in the tanks. a

gold-n-rod
06-24-2009, 05:22 PM
Great info, good to know, I thought the alarm sounding was strange seeing that it monitors heat and oil and the low idle problem doesn't point to that..........BTW. Do you know if my 377 Scorpion has an IAC?

I believe that all mpi engines have an IAC. It has an auger that turns in an air passageway to regulate the flow of air into the air valve, based on inputs from sensors and calculated by the engine management computer.

Unfortunately, I don't know the location of the IAC on your motor.

gold-n-rod
06-24-2009, 05:25 PM
You guys who are throwing out guesses don't know that I just experienced the original poster's issue. My suggestions are based on first-hand experience.

Here's my offer. If my diagnosis is wrong, I'll donate $25 to the Registry. Are you other posters ready to put your money where your mouth is??????????

This is not to cast doubt on Mr. Fixall's expertise. He's a great mechanic. He simply hasn't experienced this issue first-hand. Experience is the best teacher.

fasttrucker
06-25-2009, 02:38 PM
when is the last time you changed your fuel filters and put fresh fuel in the tanks. a
I try this first,would not hurt to change the fuel filter.

blackhawk
06-25-2009, 05:10 PM
You guys who are throwing out guesses don't know that I just experienced the original poster's issue. My suggestions are based on first-hand experience.
Here's my offer. If my diagnosis is wrong, I'll donate $25 to the Registry. Are you other posters ready to put your money where your mouth is??????????
This is not to cast doubt on Mr. Fixall's expertise. He's a great mechanic. He simply hasn't experienced this issue first-hand. Experience is the best teacher.

I agree it is probably the IAC but it may not need to be replaced. I have experienced this twice and I simply cleaned it.

gold-n-rod
06-25-2009, 05:24 PM
I agree it is probably the IAC but it may not need to be replaced. I have experienced this twice and I simply cleaned it.

That would be nice. I cleaned mine and it was still, "no go." This situation is the manifestation of Merc sourcing cheap "made in China" parts. Save a nickel here, a nickel there, increase profits and descrease reliability. Sad. :frown:

mrfixxall
06-25-2009, 06:03 PM
That would be nice. I cleaned mine and it was still, "no go." This situation is the manifestation of Merc sourcing cheap "made in China" parts. Save a nickel here, a nickel there, increase profits and descrease reliability. Sad. :frown:


Ill chine in again! whyle cleaning the iac, you need to! start the engine,whyle its running unplug the iac motor or it will retract when you shut it off. theirs 2 torx screws holding the iac in,remove them,watch out for the little o-ring cuz you can loose it and the iac will pop out.. whyle cleaning the iac theirs a spring loaded plastic cover that goes over the shaft,slide it back and spray some carb cleaner then blow it clean with air,,the shaft has steps in it and that what binds them up and makes your engine die when you come off plane and it dies because the iac is stuck closed..

Dont worry about setting a pcm code when you unplug it,it will reset after few key starts.

gold-n-rod
06-25-2009, 06:41 PM
I agree it is probably the IAC but it may not need to be replaced. I have experienced this twice and I simply cleaned it.

Oh, BTW, are you putting up the $25?

gold-n-rod
06-25-2009, 06:44 PM
Ill chine in again! whyle cleaning the iac, you need to! start the engine,whyle its running unplug the iac motor or it will retract when you shut it off. theirs 2 torx screws holding the iac in,remove them,watch out for the little o-ring cuz you can loose it and the iac will pop out.. whyle cleaning the iac theirs a spring loaded plastic cover that goes over the shaft,slide it back and spray some carb cleaner then blow it clean with air,,the shaft has steps in it and that what binds them up and makes your engine die when you come off plane and it dies because the iac is stuck closed..
Dont worry about setting a pcm code when you unplug it,it will reset after few key starts.

No O ring, plastic cover or spring that I remember. Valve on the bottom, motor on top and a gasket in between.

You in for the $25??????? :wink:

mrfixxall
06-25-2009, 07:23 PM
No O ring, plastic cover or spring that I remember. Valve on the bottom, motor on top and a gasket in between.
You in for the $25??????? :wink:

I dont gamble!:) do you have this style?

http://www.mercruiserparts.com/Show_Pictures3.asp?dnbr=884712&ivar=images/COMMON/1359.png&inbr=7585&bnbr=80&bdesc=Throttle+Body

this one is differant then the one i talked about (ford type in the pic)

Junk junk junk replace it!

crow,if this is your type also make sure theirs no cracks or loose rupper line going to the housing that the iac is mountd to

gold-n-rod
06-25-2009, 08:35 PM
I dont gamble!:) do you have this style?
http://www.mercruiserparts.com/Show_Pictures3.asp?dnbr=884712&ivar=images/COMMON/1359.png&inbr=7585&bnbr=80&bdesc=Throttle+Body
this one is differant then the one i talked about (ford type in the pic)
Junk junk junk replace it!
crow,if this is your type also make sure theirs no cracks or loose rupper line going to the housing that the iac is mountd to

Yessir, Mr. Fixxall. Here is the made in China culprit:

http://www.mercruiserparts.com/images/mer/5892.jpg

crow
06-27-2009, 11:07 AM
Yessir, Mr. Fixxall. Here is the made in China culprit:
http://www.mercruiserparts.com/images/mer/5892.jpg

So, if this is junk, where do I go for a better quality replacement?