mercruiser 6.2 mpi bravo cold start problem

_vn_

Petty Officer 2nd Class
Joined
Apr 23, 2012
Messages
128
Hi,
I have 2004 merc 6.2 mpi with 540 hours on it, just recently replaced manifolds.
engine takes really long time to start on the ground. when cranking for 20-30 seconds and then let key go - engine actually turns over couple of times .. sort of, then spits out smoke out of flame arrester and stalls. last time it took me good 20 minutes to start it (with starting fluid).
once you get it started and actually run it - it will restart without a problem. rinda scanner didnt' pick anything up.
fuel filter replaced in may, fuel separator, oil filter oil, replaced just now.
spark plugs replaced 1 month ago with manifolds and risers.
 

tpenfield

Supreme Mariner
Joined
Jul 18, 2011
Messages
14,233
Maybe hook up the Rinda scanner while cranking.

Check to see if you are getting spark while cranking

Check the fuel pressure at the fuel rail before & while cranking.
 

QBhoy

Rear Admiral
Joined
Mar 10, 2016
Messages
4,706
HI
100% this is a poor battery. I’ve posted loads about this very issue with the mpi. Trust me. New or known good battery and it will go.
it’s definitely the problem. Won’t bore you with the reason unless you ask me to, but I’m certain of it. You might be lucky and catch it as you let go of the key by opening the throttle when it kicks. But basically you need a good battery. Typical mpi issue.
 

Lou C

Admiral
Joined
Nov 10, 2002
Messages
6,802
Weak battery may allow voltage to drop too far when cranking and/or a worn starter is pulling too much current out of the battery when cranking. In the old carburetor engines they would still start but MPI needs a certain minimum voltage to operate.
 

_vn_

Petty Officer 2nd Class
Joined
Apr 23, 2012
Messages
128
you might have a point there! my alternator is crapping out as the matter of fact, giving 11.9v but i did fully charge battery and it tested good with battery analyzer. anyhow, still need to replace that alternator for sure. i just wanted to winterize boat and look for alternator later or perhaps rebuild mine.
 

Scott Danforth

Grumpy old guy who plays with boats
Joined
Jul 23, 2011
Messages
33,384
you might have a point there! my alternator is crapping out as the matter of fact, giving 11.9v but i did fully charge battery and it tested good with battery analyzer. anyhow, still need to replace that alternator for sure. i just wanted to winterize boat and look for alternator later or perhaps rebuild mine.

a fully discharged battery is 12.0 volts
a fully charged battery is 13.6 volts

if your alternator is only giving 11.9 volts, that is lower than battery voltage. how are you reading that?
 

_vn_

Petty Officer 2nd Class
Joined
Apr 23, 2012
Messages
128
a fully discharged battery is 12.0 volts
a fully charged battery is 13.6 volts

if your alternator is only giving 11.9 volts, that is lower than battery voltage. how are you reading that?

reading off the alternator with engine revved up more than 2k rpm
i did get beeps and low voltage readouts on rinda previously. replaced one battery with fresher one also.
 

alldodge

Supreme Mariner
Joined
Mar 8, 2009
Messages
31,226
with starting fluid

Your not getting spark

What's your serial number?

Agree check fuel pressure

I would see if the tachometer is showing at least 300 rpm while cranking. If the tach doesn't show a reading then the PCM will not let the injectors fire.

Check the crank sensor, and if the distributor cap is original I would replace it. The flat caps are known to look good but be bad. If it isn't the cap then keep as spare because they go out without warning
 

QBhoy

Rear Admiral
Joined
Mar 10, 2016
Messages
4,706
It’s defo a battery lack of power issue. I’m certain of it. Especially now that you’ve said about your alternator perhaps being poor. These mpi won’t start with anything less than a good battery. As said above and in many of my posts...the cranking takes all the power away from the systems etc. They need so much power to start. Then when you let go of the key...for a moment it has enough power to fire a little, with the load being released from the starter. But ultimately not for long enough to fire. I’ve been lucky a couple of times when I left the fridge on at the beach one time. I managed to catch it when it kicks...by blipping the throttle open at that moment. But that’s a lucky strike mostly. First time it happened was the spring after I got the boat. Really confused the life out me that the battery was good enough to crank seemingly well..but it wouldn’t start. Makes you rule out the battery. But it was jusy that. I’ve proven the theory since.
 
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