More MPI problems !

[QBhoy]

Hi all
So having not used the boat for a week or 2, I went down to start her today....not firing..
When I turn her over she doesn't even try to fire until......I let go of the key and then she sputters in a miss firing way, but no start.
Tried this a few times until the smell of fuel was ridiculous. Clearly getting fuel, but again only trying to fire who I let go of the key.
Now....she did this previously at the start of last season after winter storage. I cleaned the Mpi crap cap and away she went. One would think that this is the problem again, but I have only just replaced this in the last couple of months an after my other problems (just to rule it out).
So then, I have an idea...what if I turn her over on the key and when releasing the key (when she tries to splutter and fire) I then turn it back on again quickly ?
She then fires instantly with a quick grind of the starter. I then turn her off and try a normal start....no problem. Starts instantly.
What tthe hell is going on ? I have read that occasionally when damp, the battery may be low and not started for a while, the starter can take voltage away from the coil ? Surely not if she is turning over with a fair and normal pace ?
Thoughts please ?
I'm thinking this may be a good thing, but just wish she would stay broken to help me diagnose the underlying fault. The most recent of which was lugging at WOT as if there was a fuel restriction or lack of spark intermittently.
Thanks guys.

 

[alldodge]

Yo, what is the number one thing we need to know to help?

and I'm not going to go look for it

 

[QBhoy]

No idea AD....help me out ? The other faults historically ? If so, no idea how to relate to them....me and anything computer related just don't get on...

 

[alldodge]

You need to put your motor in your sig. We all look at so many post, just trying to keep them all straight is an issue and many times they get mixed up for me. So what motor are we discussing?

 

[QBhoy]

Really posing me off. Boat has been great for a sustained period of a year or so...then faults...then ok...then faults....then ok...then silly random faults, then super ok after a merc dealer reset....then it was flying for a full day, but on the return it started surging at wot...almost as if it was limiting electronically or had a blocked pick up from the tank.....then next time out she was 100%.
I then bought a jet ski (please don't judge me, haha) and have been concentrating on that for a while....went to start the boat and this happened ! I know she will start tomorrow, but just wish I could pinpoint the problem, instead of randomly replacing all the sensors until she stops her nonesense. Even then I can't be sure if she is just having a good spell or not !

 

[QBhoy]

Ah...got you now...ill have a go.. Is that in my profile ?

 

[QBhoy]

Can't see how to do that AD....in my profile i already have boat name, type and engines I've owned etc. Is there a way of getting it to display my boat engine details ?

 

[alldodge]

Go to profile

 

[QBhoy]

Good man !

 

[QBhoy]

Ah...won't work on the iPad !
Motor is a 5.0 Mpi merc.
Just had a horrible thought....please don't tell me that all these problems might be the battery ? It always cranks over fine and fires quickly...usually...surely it couldn't be that the battery (which has been in there for at least three years and is a tiny 85AH 630 cca) could cause all this ?

 

[alldodge]

surely it couldn't be that the battery (which has been in there for at least three years and is a tiny 85AH 630 cca

Yep'per it could be. If the ECU does not have enough voltage it can cause all kinds of issues, but could also be corrosion somewhere

 

[QBhoy]

Most instinct I have tell me it may not be the battery AD....but I am also aware that a battery will turn over an engine just fine and one would think the charge from the alternator would keep things in shape when running......but I also know that if a cell in the battery is jiggered (Scottish term for broken) then the alternator could just be throwing current to an open void....especially when at high demand like WOT. This may ring true with all the silly sensor fault I've been getting....most common of which are battery low voltage....even though it displays 14.1v on most occasions. Jeez, I don't think I've ever even had that battery on a maintenance charge...it's had a fair bit of work at it this year with compressor fridges and high demand stereo system.
What a fool I'd feel if that solved all my random problems ! It would ring true, especially after it not being used for a while....I shall invest in one and see

 

[alldodge]

The way to find out if it is a bat issue, is put a meter on the bat and see how low it goes when cranking. Then put the meter on the purple wire on motor or gauge and see how much it changes

 

[tpenfield]

QBhoy . . . your descriptions are a bit hard to follow . . . but FWIW . . . when I crank my engines over the first one takes the battery down to about 8 volts, but as I hear it starting to catch, I keep cranking a couple more seconds and then can tell it is ready to go, so I release the starter.

The second engine only takes the battery down to about 10 volts since the other one is already running. The thing is that they do not seem like they are going to run on their own until I release the starter, then they rev up and settle down.

Anyway, I am not sure what 'we' are trying to fix by reading your post.

 

[QBhoy]

Thanks Ad, I'll try that tomorrow.

Hi TP, thanks for your interest. Man it's a long story of intermittent faults...ill try and explain the matter today a little better...

The boat has been unused for 2 weeks...cold damp conditions here recently...not the ideal MPI territory !
I try to start it today...when turning her over, absolutely no sign of firing...she does turn over fairly healthily I must add...and stinks of fuel when doing so.
When I release the key after cranking...she sputters, almost has a miss firing attempt at starting and then nothing.
I did this around 8--10 times with the same result, except on the last attempt, when releasing the key and during the brief momentary splutter, I turn the key back to crank position and grab the throttle...she instantly starts, with a slight grind of the starter.
Clearly an electrical related fault. As mentioned she did this after winter hibernation a year ago, but cleaning the crap cap (perhaps coincidently) and running a generator with charging leads (because the battery went flat) as her fire up no bother...at the time I put this purely down to the diz cap.
More recently I have had all sorts of intermittent smart craft indicated faults which saw the engine loose power, go into an apparent guardian mode, then work perfectly, then restrict its self at wot, then work flawlessly again, and so on...second to last time out, it showed signs of fuel starvation and surging at wot or almost electronic limiting and surging...or both.
Nothing worse than an intermittent fault to diagnose...I've replaced the IAC, diz cap, leads, plugs and cleaned the throttle position sensor so far.