2000 Merc 5.7 MAG MPI stopped running for no apparent reason

[2100V]

Hey guys,

I have a 2000 2100V with a Merc 5.7 MAG MPI engine, ~245 original hours. Well maintained. Today I'm out for my first run this season. Just changed the oil, seawater impeller, etc. last week and all was well. Today on the way back in we're cruising at about 3000 RPM and all of a sudden it's like someone turned the key off. The engine chugged and sputtered for about 5 seconds as it dropped from 3000 RPM to basically nothing, knocked/dieseled a couple of times, and quit. Engine temp, oil pressure, voltage were all normal. No weird smells, no smoke, no popping sounds, etc. Checked the oil and it's clean, water free, and at normal level. Plenty of gas. I turn the key off/back on, the fuel pump cycles, and the engine turns over but not even a hint of cranking up.

So, where do I start? Fuses? Check voltage on coil, pull distributor cap off and see if the rotor is spinning, take it to the dealer and let them rape me for the scanner fee?

Thanks in advance.

[mls6722]

fuel or ignition? It is fairly simple to check to see if you are getting a spark. If you have a timing light, hook it up to any of the plug wires and see if it flashes when you crank the engine. If not, pull a plug wire at the plug and insert a screwdriver into the wire. Hold the handle of the screwdriver and place the metal shaft near a metal portion of the block.
If you have spark, it is probably fuel related.

[TeamAllen]

Welcome to the site. Where are you located, maybe someone near you can help out?
Are you the original owner? If not, how long have you owned it?

[NICKYPOO]

Bad gas? 245 hrs is super low for a 2000. How long has it been sitting?

[2100V]

TeamAllen - I've had it since 2008 and never had a problem with the engine until yesterday. I'm in Knoxville, TN.

Nickypoo - The guy I bought it from never drove it, but that was 3 years ago and I've put ~75 hours on it since then. I put that tank of gas in last November, along with stabil, when I winterized it. It's run in my driveway a few times this spring and yesterday I got ~1 hour of run time on it before it shut down. I degreased the engine the other day but it ran fine after that and then sat in the sun with the hatch open for 2 days so I doubt I messed anything up with that.

[laserfish]

Take off your fuel/water separator/filter and pour it into a glass jar to see if you have any water in your tank. Don't forget to fill the new or old filter with gas before you screw it back on.

[boatwakes]

SPARK RELATED!!!! Get a spark plug adapter spark checking device from the local auto parts store. It plugs inline with any of the plugs/wires and allows you to visually see if it lights while cranking ($4 part). I'm going to go out on a limb and say it's the pickup coil in the distributor. It will probably fire up the first time you try on a cold engine but will cut out at temp and also show with no spark when it happens. Quicksilver part number 87-892150Q02, about $60 and mounts inside distributor, underneath the rotor, with two screws included with new unit. Start with spark and if you have one, a fuel pressure gauge. The port is at the actual front of the engine on the starboard side and looks like a bike air valve (scrader valve). It will most likely have a cap on it and is at the end of the fuel rail right next to the thermostat housing. Keep us posted on your progress.

[2100V]

Coil output: 12V with key on. Placed a spark checking device on the end of the coil wire between wire and distributor. While cycling the starter, no spark between coil wire and distributor.

Distributor output: checked 2 plug wires at the spark plug end, using the spark checking device. While cycling the starter, no spark in either wire (even stuck my finger in the end of it to make sure). Pulled the cap and made sure the rotor is making contact and turning with the starter.

Distributor ignition module: It is GREY. 10A fuse was NOT blown. disconnected the 2 wires from the ignition module and checked voltage on the fused ends coming from ECM, with the key ON. purple wire: 12V, pink wire: 5V (or was it vice versa). These are the voltages being presented to the ignition module by the ECM when the key is on but without starter engaged. Not sure whether they fluctuate during a start/run or what they are supposed to be.

So: no spark when starter is cycling, but with key on there's voltage being applied to the coil (12V) and ignition module (12V and 5V).

[boatwakes]

Okay, measure the resistance between the two wires on the distributor ignition sensor, if it's less than 100 OHMs, replace. Also, the jumper leads tend to crack (there's 2, one on each side of the sensor where it has the distributor shaft cutout, if resistance reads okay, this is another problem spot)and cause the same problem. The sensor provides an input signal to the ECM which then provides power to the coil each time a window on the rotor passes by. So when the engine is cranking, it is responsible for sending spark signal to the coil.
At this point, it's either the ignition coil or the sensor. If you have spare coil around, or pick up a cheap one from Autozone, see if it will run. If not, it's the sensor. Keep us posted!!!

[2100V]

I found an awesome diagnostic manual online for the MEFI-3 ignition system. Long story short, they tell me to unplug the lead that goes from the ignition sensor to the ECM, and with the key on, ground the ECM side of that wire and see if the coil throws a spark out. If so, the ignition sensor is the culprit. However I did this, and did NOT get a spark from the coil at all even though the fuel pump, etc. cycled every time I touched ground.

This tells me 1) the coil is fried, 2) the ECM is not sending the message to the coil telling it to fire. The reason I suggest the ECM could be the problem is: In theory, when I perform the procedure above, I am shorting the system and forcing the ECM to send a "fire" message to the distributor. But when I do this, there's no change in voltage at the white wire terminal on the coil, which is the wire coming from the ECM. Both wires on the coil (hot and ECM signal) are steady at ~12V even when I'm touching the ECM lead to ground. Shouldn't there be a change in voltage when I do that? Isn't that would signal the coil to fire?

Is the ECM even capable of malfunctioning on one specific task while functioning properly for everything else?

[NICKYPOO]

Sorry, this one is out of my league. I would like to see the manual you found though.

[2100V]

Google "Mercruiser Service Manual #24" and you should find a free download site on the first page or two of search results.

I just found another section in the manual that describes how to test the ignition coil driver circuit of the ECM with an ohmmeter so I'm going back outside to do that.

[lohe]

Is the ECM even capable of malfunctioning on one specific task while functioning properly for everything else?

In Short Yes.
Automotive ones do it all the time I have had many with water damage causing various fuel injection issues to coil issues but the rest of the system works.

[2100V]

Everything checked out with the resistance tests. No issues with the coil or ECM ignition circuits according to those numbers. The only question now is whether to buy a coil and ignition sensor anyway and cross my fingers, or save that $150 to put towards the down payment at the dealer. Particularly if they tell me it's the ECM, which is obselete and will have to be converted to a MEFI-4 at about double the cost.

[boatwakes]

There was a TSB about the early sensors and they were upgraded to have all their pots waterproofed and have an added ground wire. It's a $70 part and has been the culprit many times over. Obviously, it's up to you. Good luck!