2008 5.0 MPI mercruiser wouldn't start

spdracr39

spdracr39

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Aug 30, 2010
Messages
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We were tubing at the lake today and everything was working perfectly. We stopped to swim and rest and when I tried to start it back up it would barely run for a couple of seconds and die. It seemed like it wasn't getting fuel pressure. I tried several times and the same result. It seemed if I primed the rail by turning the key on and of three times then starting it would run a couple of seconds longer before dieing. I called a tow and put away all the toys and ropes and tried one last time and it started perfectly so we ran back to the ramp several miles with no issues at 3000 rpm. It starts and runs on the muffs now every time without fail. I changed the fuel filter but I think it is the fuel pump. The pump doesn't sound right to me. Since the pump costs $400.00 on this motor I would like to be sure before I replace it. What are you guys thoughts ??
 
QC

QC

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Mar 22, 2005
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Re: 2008 5.0 MPI mercruiser wouldn't start

How hot was it? Ambient? See attached. No guarantee, but I think I have had exactly the same issue. Twice.
 

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  • Vapor Lock bulletin.pdf
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achris

achris

More fish than mountain goat
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May 19, 2004
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Re: 2008 5.0 MPI mercruiser wouldn't start

You need to put a diagnostic computer on and see if you have any fault codes. It could be something as simply as a bad IAC, but you won't know until you read the codes....

Chris......

EDIT: Just read QCs post and that's a really good place to start.... If your last fill at the end of last season was with 'winter' fuel, then a vapour lock is a very real possibility...
 
M

makonnen

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Apr 4, 2012
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Re: 2008 5.0 MPI mercruiser wouldn't start

I would mostly agree with achris, but remember fault codes rarely tell the whole story. For instance, if it is a fuel pressure problem, the fault codes won't tell you. The codes will usually only tell you when one of the sensors is out of range (coolant temp, manifold air pressure, air flow, IAC - not a sensor) etc...

Well the fault codes are definately a way to start.

Now for the editorial - in my very humble opinion - fuel injection doesn't belong on a boat.
 
achris

achris

More fish than mountain goat
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Re: 2008 5.0 MPI mercruiser wouldn't start

makonnen said:
...Now for the editorial - in my very humble opinion - fuel injection doesn't belong on a boat.
Click to expand...

Maybe we should all go back to sails and oars... ;)
 
M

makonnen

Petty Officer 2nd Class
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Apr 4, 2012
Messages
184
Re: 2008 5.0 MPI mercruiser wouldn't start

Carbs needs more TLC but no wire, sensor or ECM will stop a carb. Even if the fuel pump dies I'm sure I can rig up a fishwell pump or something. LOL

I'm a little biased having spent most of my career as a mechanic (GM dealer) fixing emission / injection / engine electrical problems.

I don't mean to hijack the thread but this is all I need to fix my 2BBL carb.
18933.JPG
 
C

cdiamond

Petty Officer 3rd Class
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Aug 20, 2008
Messages
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Re: 2008 5.0 MPI mercruiser wouldn't start

I'll wager - Vapor Lock
 
spdracr39

spdracr39

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Re: 2008 5.0 MPI mercruiser wouldn't start

QC said:
How hot was it? Ambient? See attached. No guarantee, but I think I have had exactly the same issue. Twice.
Click to expand...
This makes sense. The outside air temp was about 93 degrees. I will pack my IR thermometer next time out. Most of those improvements have been made from the factory but I was pulling a load and shut the boat off to pick up the tubers and just left it off. From now on I'll let it run a few minutes at idle first and run the blower to circulate some air back there.
 
spdracr39

spdracr39

Lieutenant Junior Grade
Joined
Aug 30, 2010
Messages
1,238
Re: 2008 5.0 MPI mercruiser wouldn't start

Went out today and after replacing the filter and started letting the boat idle for a couple or minutes before turning it off seems to have worked fine. We tubed for a couple of hours and no problems at all. It was about the same temp outside as yesterday.
 
C

cdiamond

Petty Officer 3rd Class
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Aug 20, 2008
Messages
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Re: 2008 5.0 MPI mercruiser wouldn't start

how much did i win on that wager ?
 
QC

QC

Supreme Mariner
Joined
Mar 22, 2005
Messages
22,783
Re: 2008 5.0 MPI mercruiser wouldn't start

Let me get this straight. I suggest vapor lock, you do a me too, and you get money? That hardly seems fair :facepalm: :p :)
 
C

cdiamond

Petty Officer 3rd Class
Joined
Aug 20, 2008
Messages
94
Re: 2008 5.0 MPI mercruiser wouldn't start

ok fair is fair
i'll split it with you
 
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