Poor cold idle and cold start Merc 5.0 Mpi

[nauticool]

Hi, Have a 5.0mpi 2005 and alpha one outdrive 1990

model mcm 5.0L mpi

serial ow385827

engine will not start unless throttle is advanced slightly and wont idle until warm, around 5 mins after start.

Things ive tried so far;

use fresh gas from clean container
change iac valve genuine merc
change iac muffler genuine merc
charge batteries fully
change spark plugs
change fuel filter/seperator genuine merc
clean flame arrestor

the problem started about 18 months ago when it would start cold but would "hunt" up and down around 200-300rpm and if batteries were not fully charged would die.

once engine is warm it runs, idles and wot is fine

i could live with this as when i let it run cold at 1000 rpm for 5 mins it is fine after but i dont like it not being 100%. Also if it came to selling im sure the buyer would like to see it start from cold.

Thanks in advance guys!

 

[Bondo]

Re: Poor cold idle and cold start Merc 5.0 Mpi

Things ive tried so far;

use fresh gas from clean container
change iac valve genuine merc
change iac muffler genuine merc
charge batteries fully
change spark plugs
change fuel filter/seperator genuine merc
clean flame arrestor

Ayuh,... Myself, beyond the Basics,...
Before I start throwin' parts at a 'puter driven motor,...
I go find a guy with the Mercruiser diagnostic software, 'n pay 'im to run it, 'n See what it says...

I guess that's why I like good ole Carb'ed motors.....

Did ya find any debris, or other hints in yer travels through it,..??

 

[nauticool]

Re: Poor cold idle and cold start Merc 5.0 Mpi

Thanks Bond-o. No didnt find any debris or anything else that didnt look as if it should. The engine has only done 100hrs but is 4 years old.

May have to get the dealer in but may not bother as im not sure it will throw a code? Most parts changed were part of service anyways.

im not 100% my batteries are good even afer full charge and load test, could this be an issue after starting? I know the mercruiser computer has a safe cut out if it reaches low volts

 

[troman9]

Re: Poor cold idle and cold start Merc 5.0 Mpi

Nauticool:
I'm very interested in how this pans out for you. I have this exact same engine, and same year. Since I first fired up the engine this season, I've seen very similar symptoms. When the engine is cold, the RPMs go up and down from about 400 to 600 while it's cold. Last time I started it up cold in the water, it stalled several times until I ran the throttle up a little, then it was OK, and once it's warm it's OK.

All I've done is clean out the IAC valve, and that didn't help so I've ordered a new one. I hope that does it, but I see you've already tried that, so it might not. Anyway I'll be very interested if you find the problem, and likewise I'll report back what I find.

Tom

 

[Don S]

Re: Poor cold idle and cold start Merc 5.0 Mpi

Welcome to iboats Tom, why don't you just start a new thread of your own. It's possible that the original poster of this thead never replies again, or his problem is for a different reason.