350 Mag MPI Horizon died at sea, cannot find the problem.

[c1steve]

We had been running for an hour, engine appeared to be running well. Engine just stopped.
Checked for spark, nothing from the coil wire. Also battery voltage was low. Engine has 1800 hours on it, coil and both fuel pumps replaced 500 hours ago. 2006 (?) model, s#OM675521.

Was towed 15 miles back to the harbor. Charged the batteries, still no start. Used the Rinda software on my laptop, it showed no faults. Changed the crankshaft position sensor, still no starting. Fuel pressure was somewhat over the normal 43 psi, with the key on and obviously not running.

Any suggestions? I tried saving the computer information with Rinda, but that did not work. Thinking the Merc. computer may have a problem, am considering sending it out to High Tech Electro ECM, but I know nothing about their reputation.

Any suggestions?

 

[gm280]

When you finished "charging the battery", did you actually read the charged voltage? If the battery was not a high enough voltage, it could keep it from firing up. Other then that, I have nothing not being there and doing some testing...

 

[alldodge]

Agree check starting voltage

Check the 12V injector fuse
Check for 12V at coil Pink/White
Replace the distributor cap and rotor?

 

[c1steve]

12V injector fuse, I will have to find that, did not know it existed. Swaped in a used cap and rotor, no change. For the coil, put the probes on the white and pink wires? Connector has a pink plus two light colored wires. Starting voltage was back up to 12.7 volts, I have a Blue Sea digital panel meter, but can double check with my Fluke.

I tried pink and ground, got nothing.

 

[gm280]

I would be interested in actually cranking voltage instead of mere static voltage... JMHO

 

[c1steve]

I will be back at the boat on Friday, and will check the cranking voltage. Any idea where the 12 volt injector fuse is, if it has one? Looking at my schematic, I see that the two light wires in the coil connector are parallel. Will check the voltage there as well.

 

[alldodge]

There are 3 fuses on the motor and in most cases they are in one housing with a long rubber cover. Should be next to the ECM pins E and F

 

[c1steve]

Thanks, I will check those. Are they glass fuses or mini blade fuses?

 

[alldodge]

Mini blade

 

[c1steve]

The Fuel Injector fuse was out, thanks for the professional help. I did not know there were fuses under the cover...

Charging system worked excellently today. On the day the engine died, upon starting the boat the idle was too high, ~1100 rpm. I unplugged the IAC connector, engine died, but on start up idle was back to 600. Since then I removed the IAC and found it to be super clean. I had replaced it a year ago, trying to get my engine to run at 800 rpm for trolling. Perhaps pulling the connector damaged the fuse or a relay, and the circuit was overloaded, with the fuse going out an hour later.

Will take the boat out on Sunday, with spare fuses, and watch everything. I have separate Blue Sea panel voltmeters for the two batteries.

 

[alldodge]

Think you have an item which is starting to draw more current over time. From the previous drawing it can be anything which is connected to it. With the idle being incorrect and resetting when turned off/on that would be my thought, clean or not

 

[tank1949]

Check for the green crap (corrosion). Check battery posts.

 

[QBhoy]

Wish I had a dollar for every time an mpi Diz cap was the source of problems like this. Good chance this is another example

 

[c1steve]

Ran the boat for 35 miles on the ocean this Sunday, engine was reliable. Generally I clean the contacts inside the distributor 2x/season with a soft stainless wire brush in a Dremel tools. Otherwise corrosion builds up. This is an older boat where all the water drains into the bilge. I have two pumps but there is always some water.

I believe new crab caps/dist. caps come with an O-ring, I will install one next time. This distributor has no vents. I may change the main power relay, perhaps it is affecting the IAC.

 

[QBhoy]

Ran the boat for 35 miles on the ocean this Sunday, engine was reliable. Generally I clean the contacts inside the distributor 2x/season with a soft stainless wire brush in a Dremel tools. Otherwise corrosion builds up. This is an older boat where all the water drains into the bilge. I have two pumps but there is always some water.

I believe new crab caps/dist. caps come with an O-ring, I will install one next time. This distributor has no vents. I may change the main power relay, perhaps it is affecting the IAC.

Really need to just change it out. Learned this years ago. I’ve had 5 in mine now. This is the 6th year I’ve had the boat. Cleaning buys you time. But ultimately...not that long and will let you down. No o ring to change that I’ve noticed. They just get crappy easy. Especially in damp conditions. The thing is. Sometimes they will be ok. Sometimes randomly let you down. Sometimes won’t start at all. Usually at the worst of times possible.

 

[alldodge]

Qbhoy, Agree they can go bad without warning but I have heard of no other which has needed to replace that often

 

[QBhoy]

Qbhoy, Agree they can go bad without warning but I have heard of no other which has needed to replace that often

AD. I think it really strongly depends on where the boat is in the world. What the climate is like and how it’s stored or used.
To explain further.
Here on the west coast of Scotland, we can literally go from +20 degrees Celsius one day to close to 0 degrees Celsius at the start or end of the season. But perhaps more relevant...over winter we constantly see change in conditions each few days to the next for the winter months. It can be cold, clear and dry for a few days...then mild wet and damp the next few days. For 4/5 months at a time during storage. Literally worst case scenario for encouraging damp and humidity. Same in summer really but higher up the mercury on the thermometer. It’s such an issue here for mpi flat caps that more than a few merc dealers now just change the diz cap as part of the annual service here.
I’d imagine in frequent use of an mpi might have an influence too. Especially in humid climates or varying changes in weather climates. Not sure. But the struggle is certainly real here on the west coast

 

[Lou C]

We get similar weather to what you have in Scotland but a periods of colder weather, combined with frequent dampness and hotter in the summer. So plenty of opportunity for condensation which is what causes corrosion. All distributors should have vents, there will be a screen in a marine unit.
Believe it or not I've had very little trouble with my stone age Prestolite points distributor, I have changed points & condenser maybe 3 times in 18 years, and the cap & rotor usually every other year, depending on how it looks. Some of the "improvements" on marine inboards have not been truly beneficial due to poor design of updated components, or cost cutting.
I feel the same way about throttle body fuel injection and EFI for inboards. They brainwashed us for years its better better better. Reading of the problems people can have and the cost of some of the components, and then when some parts become NLA, I don't see the "better, better better". The best technology is what can be made to work simply and backed up by the willing aftermarket. So in the future I'll take a Delco EST, because parts can be found easily but I'll stick with carbs where I have a choice of 3 I could use....Quadrajet, Holley or Edelbrock.

 

[QBhoy]

We get similar weather to what you have in Scotland but a periods of colder weather, combined with frequent dampness and hotter in the summer. So plenty of opportunity for condensation which is what causes corrosion. All distributors should have vents, there will be a screen in a marine unit.
Believe it or not I've had very little trouble with my stone age Prestolite points distributor, I have changed points & condenser maybe 3 times in 18 years, and the cap & rotor usually every other year, depending on how it looks. Some of the "improvements" on marine inboards have not been truly beneficial due to poor design of updated components, or cost cutting.
I feel the same way about throttle body fuel injection and EFI for inboards. They brainwashed us for years its better better better. Reading of the problems people can have and the cost of some of the components, and then when some parts become NLA, I don't see the "better, better better". The best technology is what can be made to work simply and backed up by the willing aftermarket. So in the future I'll take a Delco EST, because parts can be found easily but I'll stick with carbs where I have a choice of 3 I could use....Quadrajet, Holley or Edelbrock.

I get that Lou. Really do. Lots of guys think the same.
for me though, having worked out the wee issues and in control of them on my mpi. I just couldn’t go back to carb. So much more power and defo more efficient in standard factory like for like form. Haven’t had any issues for years now. Touch wood. A good coat of inhibitor spray on everything each winter seems to keep everything good.
the smart craft ability is a huge thing for me too.

 

[Lou C]

yep we all love electronic injection in our modern cars that run the same day after day, we never had that with carbs back in the '70s due to poor implementation of emissions regs. However when you grow up with Quadrajets, Holleys and Carters (now Edelbrock) it gets in your blood and you always have an affinity for them (well some of us do). Being able to get parts and repair common problems being totally independent of the robber baron pricing policies of Merc and Volvo, priceless lol! Long live the aftermarket, you can go out and buy a brand new Holley or Edelbrock for less than the cost of an electric fuel pump for a Volvo or Merc inboard engine and motor on if your old one is beyond rebuilding. I have the original 32 year old Quadrajet, that I am using on the boat now and a spare Holley 4160 4bbl I can use if something happens to the QJet. Replaced a 30 year old mechanical pump for about $85.

Plus knowing how to deal with carbs has a good side-benefit if you will, you can also keep all your small engine/yard equipment going. I have a 33 year old lawn mower (Briggs & Stratton 3.5 hp), a 22 year old 2 stroke snow blower, and 3 Echo 2 stroke machines (blower, weed wacker and hedge trimer) as well as a Husqvarna 2stroke chain saw all approx 10 years old.