Mercruiser mcm 350 magnum mpi hard to start.
 

I have a 2002 chaparral signature 240 that I just purchased, the boat
was bought new in Denver. When I try to start the engine I have to
turn it over for several seconds to get the engine started, when I say
several seconds I mean like 15 to 20. I can hold the key and let the
engine turn over about three or four times and let go and it will
crank but I have to use this procedure a dozen time before she'll
fire. After it starts it runs fine it's just a pain to get running.
I live at sea level so I was wondering if maybe the ECM wasn't
adjusting to the change in pressure. I don't have a scanner yet but I
am looking. I just thought maybe someone in the group may have had
this problem and can steer me in the right direction. Oh yes I called
Mercury Marine and one of the tech's told me that the MAPT sensor had
plenty of range to adjust to the change in altitude. I checked the
plugs and they were all very "wet" so I feel like the hard start
problem that I have is the ECM not adjusting to it's new surroundings
and still hasn't leaned out the mixture. The engine has 167 hrs. on
it, runs like a top if I can get it started, it's a mcm 350 magnum mpi
300 hp with bravo lll outdrive. Also while it's running if I hit a
large wake the engine "cuts out" momentarily could this be related to
the hard start problem? Any thoughts or help greatly appreciated.
electraglide
gulf coast

Hi,

I'm not real familiar with the Merc 350 magnum, although I believe that
it is the fuel injected version of the 5.7L Merc that is in my Maxum.

First thought would be to determine if you have spark during the
time that you are trying to start the boat before it fires. If you
do, then the next thing I would check would be the fuel pressure. The
fuel injection systems require a high working pressure, and any small
leak would cause it to depressurize. Could be the slow starting is
due to fuel pressure coming up.

Another good possibility is that one of your sensors is going flaky, and
giving the ECM bogus info causing it to give the engine the wrong fuel
mixture. Usually a rich mixture will cause the engine to start right
up, but then it won't run very well. A too lean mixture will give you
a hard time starting.

As far as the engine cutting out when you hit a wake... Could be a bunch
of things: Loose connector somewhere, Shift kill switch poorly adjusted,
etc.

After you get it running, can you kill it and easily re-start it? That
would be a big clue that the problem is fuel related. How long does it
have to sit before its hard to restart?

Don W.

Electraglide wrote:
I have a 2002 chaparral signature 240 that I just purchased, the boat
was bought new in Denver. When I try to start the engine I have to
turn it over for several seconds to get the engine started, when I say
several seconds I mean like 15 to 20. I can hold the key and let the
engine turn over about three or four times and let go and it will
crank but I have to use this procedure a dozen time before she'll
fire. After it starts it runs fine it's just a pain to get running.
I live at sea level so I was wondering if maybe the ECM wasn't
adjusting to the change in pressure. I don't have a scanner yet but I
am looking. I just thought maybe someone in the group may have had
this problem and can steer me in the right direction. Oh yes I called
Mercury Marine and one of the tech's told me that the MAPT sensor had
plenty of range to adjust to the change in altitude. I checked the
plugs and they were all very "wet" so I feel like the hard start
problem that I have is the ECM not adjusting to it's new surroundings
and still hasn't leaned out the mixture. The engine has 167 hrs. on
it, runs like a top if I can get it started, it's a mcm 350 magnum mpi
300 hp with bravo lll outdrive. Also while it's running if I hit a
large wake the engine "cuts out" momentarily could this be related to
the hard start problem? Any thoughts or help greatly appreciated.
electraglide
gulf coast

On Wed, 20 Jul 2005 01:24:22 GMT, Electraglide
wrote:

I have a 2002 chaparral signature 240 that I just purchased, the boat
was bought new in Denver. When I try to start the engine I have to
turn it over for several seconds to get the engine started, when I say
several seconds I mean like 15 to 20. I can hold the key and let the
engine turn over about three or four times and let go and it will
crank but I have to use this procedure a dozen time before she'll
fire. After it starts it runs fine it's just a pain to get running.
I live at sea level so I was wondering if maybe the ECM wasn't
adjusting to the change in pressure. I don't have a scanner yet but I
am looking. I just thought maybe someone in the group may have had
this problem and can steer me in the right direction. Oh yes I called
Mercury Marine and one of the tech's told me that the MAPT sensor had
plenty of range to adjust to the change in altitude. I checked the
plugs and they were all very "wet" so I feel like the hard start
problem that I have is the ECM not adjusting to it's new surroundings
and still hasn't leaned out the mixture. The engine has 167 hrs. on
it, runs like a top if I can get it started, it's a mcm 350 magnum mpi
300 hp with bravo lll outdrive. Also while it's running if I hit a
large wake the engine "cuts out" momentarily could this be related to
the hard start problem? Any thoughts or help greatly appreciated.
electraglide
gulf coast


Hmmm...I guess you would see wet plugs if the choked startup is
prolonged. So the problem could be either ignition or fuel mix.

Have you checked spark strength? Then ignition timing?

Brian Whatcott

On Wed, 20 Jul 2005 01:24:22 GMT, Electraglide
wrote:
First of all thanks for the reply's. When I run the boat and shut it
down I have the same start problem, slow to start. The spark and
timing is controlled by the ECM, timing's set to zero and then the
comp. takes over. I don't have a scanner to read the sensors real
time but I think that's gonna be my problem. Which ever sensor the
ECM uses for the starting process must be bad. The thing is I don't
know which one it is. I'm leaning towards the MAPT sensor but I'm not
sure. And yes the engine is direct injected so the start process
should be almost instantaneous when I hit the key I would think.
Once again thanks for the reply's I guess it's just a work in progress
until I get my hands on a OBD ll scanner.l

Sounds like the ECM is setting the mix too lean to start, which
like you think is probably a bad sensor somewhere. Yep, you're
going to need a scanner unless you want to guess & replace until
you get lucky. Fortunately OBDII scanners are not that expensive
anymore. I got a full up diagnostic kit that connects to my
laptop PC for ~$300. The handheld ones that just read the scan
codes are more like $60.

Good luck,

Don W.

Electraglide wrote:

On Wed, 20 Jul 2005 01:24:22 GMT, Electraglide
wrote:
First of all thanks for the reply's. When I run the boat and shut it
down I have the same start problem, slow to start. The spark and
timing is controlled by the ECM, timing's set to zero and then the
comp. takes over. I don't have a scanner to read the sensors real
time but I think that's gonna be my problem. Which ever sensor the
ECM uses for the starting process must be bad. The thing is I don't
know which one it is. I'm leaning towards the MAPT sensor but I'm not
sure. And yes the engine is direct injected so the start process
should be almost instantaneous when I hit the key I would think.
Once again thanks for the reply's I guess it's just a work in progress
until I get my hands on a OBD ll scanner.l

Thanks Don. Yes, my next step's going to have to be a scanner. To
replace sensors until I hit the right one would probably pay for the
scanner.
Thanks again for the reply.