Need some help Mercury 3.0 (250EFI) issue.....

**OldSchool III** · 04-13-2021, 11:20 AM

Reaching out to see if anyone has had this issue or opinions on what is causing it....
Was out running the boat a few weeks ago and the voltage dropped on one of my outboards. The engine kept running without issue and I got home, put it on the lift and took off the engine cover. Found a badly worn and broken alternator belt. Lack of maintenance on my part... No problem! I bought 2 new belts, threw them on and started the engine. It ran for about 5 seconds and cut out and then would not start. The other engine started right up as it always has...
Started diagnosing (to the best of my common sense ability). I had spark and I had fuel pressure at the tire-stem looking valve. Checked connections, changed plugs, etc... and it would not start. Started swapping parts off of the "good" engine. no difference until I swapped the fuel ECM from the "bad" engine to the good and it wouldn't start... I then put the fuel ECM on the "bad " engine. It started for about 5 seconds and then cut out. Of course, whatever the issue is, it phucked up the fuel ECU off of the good engine. I ordered one off of Ebay and I now have the "good" engine running again.

The big question now is, what is causing the breaking of the fuel ECM? Merc part # 830046 8

Could it be the wiring harness? That seems like the logical conclusion... but I just can't get past the fact that the engine ran and the only thing that I did was put a new belt on the alternator!!

Anyone have any ideas? I really want to avoid just replacing stuff until it's fixed! LOL

Craig

**Chaz** · 04-13-2021, 10:20 PM

Only thing worse than not enough battery voltage ... is way toooo much.

If it shredded the belt , either the alternator's bearings are stuck or the internal regulator is bad and spiking the ECM .
I use Palm Beach Generator .. but you can go to Advanced Auto Parts and have them test yours.
While the alt is off .. look in the nestle where it sits. Every one of them that left the factory has a weld dead center along the mold line. Early on they would leak there and shoot a stream of water into the alternator .. Sad but true ..

You will be able to see a water stain if yours has developed a leak .

You can find them on flee bay for around $100 bucks .

I usually take a hand full of alternators to the grump old &%^%&* at P B Gen and ask him to make me up a couple ~ three good ones out of junk.

Surprisingly he does , and for a reasonable price. And they last a dozen times longer than the chink knock~off's ..

If it over charged and cooked the harness , you'll be able to smell it .. Or unravel some tape and look for shriveled up wires. If ya find some , bust out the ohm meter and start pokin N prodden ..

The plug into the fuel ECU is low and not that waterproof. If the pins are green , go swipe one of the Mrs. nail files and give em a brush or two. Smear some dielectric grease on the receptacle plug it back in and tie wrap the boot ..

Let us know it that fixes it ...

**rdoaner** · 04-15-2021, 12:21 PM

Originally Posted by Chaz

Only thing worse than not enough battery voltage ... is way toooo much.
While the alt is off .. look in the nestle where it sits. Every one of them that left the factory has a weld dead center along the mold line. Early on they would leak there and shoot a stream of water into the alternator .. Sad but true ..

I'll be darned, mine has a ton of salt buildup right there. Was wondering what was causing it... how do I fix? I don't have a welder

**rdoaner** · 04-15-2021, 02:23 PM

BTW if you're around Deerfield Beach, Alternator and Starter Exchange can rebuild it. Their service is absolutely amazing, and prices are beyond reasonable. And another thing, if you find yourself breaking a lot of belts, DON'T go back to the OEM belt. Instead use a Gates V-belt with the 10mm top width, it's a MUCH better belt and will last a lot longer than OEM. I got a 29 inch one... you could probably get anything from 27 to 30 inches as long as it's 10mm top width

**OldSchool III** · 05-31-2021, 08:56 PM

Well... Got a new alternator and threw that on a on then put on a new (used) fuel ECU......and nothing. Turns over, but won't start. Back to the drawing board!! The worst part is that no one around here seems to have a scan tool or diagnostic program to see if there are codes. To be honest, it's a '99 engine, so I don't know if that would even help. For some positive news, there are no "water stains" around where the alternator mounts, so I've got that going for me. LOL

**OldSchool III** · 08-01-2021, 06:41 AM

Forgot to update this... but my boat is running again! LOL I couldn't figure it out, so I cleaned up all of the wiring connections (That didn't do it), Replaced the batteries (They were 4 years old), that didn't do it. I finally found a guy who had an old Merc diag computer, but that didn't really show anything. We put a spark board on it. The spark was a little weak and seemed to jump around a bit, so I ordered a new stator from Mercury on a whim. Thankfully, I lucked out and didn't open the box.... because when I pulled the flywheel off... wait for it... the phucking key on the crank was sheered off. No idea how it happened. I didn't hit anything and I never shift above idle!! Was able to return the $450 stator and spend $2.35 on a new key. Put it back together and she fired right up and runs like a champ. Weirdest thing ever!!