Row Row Row My Boat (4.3L Mercruiser, Bad Alternator?)
 

Ah... the latest in a string of mechanical problems. (Grrrrr.)

Here's what was happening last week:

1. At higher RPMs (above 3500 or so, typical holeshot), the engine smoothly revs up, brings the boat up on plane, then dies. RPM gauge drops almost instantly from 4200 to zero. Sometimes at 3500+ RPMs, it'll caugh, start up again on its own for a second, then die.

2. It restarts easily. On the next attempt, it may or may not do the same thing again.

No problems at idle, no problems at slow speeds, no problems starting or restarting.

Some sort of kill switch with an intermittent problem?


UPDATE:
The problem was definitely worse tonight. As soon as the boat would reach about 3000 rpm and plane out, the engine would kill. At one point, it seemed to be a little better, only to kill in the midst of a half-mile run at 3800 RPM. It would still start easily and run at no-wake speeds without a problem.

THEN...

[dramatic music]

We motored at no-wake back towards the slip. When shifting into neutral prior to entering a downstream channel, the engine died and wouldn't restart. Slow cranks, clicks, etc. Clearly, there wasn't enough oomph from the battery to start the engine.

So that $20 paddle on eBay came in real handy -- had to PADDLE THE FREAKING THING about 200 yards to the slip.

Any ideas? Would a bad alternator explain all this? I'm hoping that would explain the lack of battery power to start the engine, but also perhaps why it was dying at higher speeds. Did I kick a dog in my last life?

Help!

Re: Row Row Row My Boat (4.3L Mercruiser, Bad Alternator?)
 

Two paddles on our new-to-us-boat: One with the blade broken in half, lengthwise, and the other doesn't look a whole lot better. ISTM what would be really handy would be strong aluminum paddles with collapsing handles.

It would certainly explain the dead battery, but I don't see it explaining the engine dying at 3000 RPM--esp. as the battery still had plenty of juice to re-start the engine.

Jim

Re: Row Row Row My Boat (4.3L Mercruiser, Bad Alternator?)
 

I was thinking along the lines of other electronics in the system (fuel pump?) that might not be getting the voltage they need. Or am I revealing my total ignorance?

Re: Row Row Row My Boat (4.3L Mercruiser, Bad Alternator?)
 

That occurred to me, but I figured me taking WAGs wasn't going to do you much good :).

Jim

Re: Row Row Row My Boat (4.3L Mercruiser, Bad Alternator?)
 

I'll take anything at this point!

When the engine was dying, it felt very much like running out of gas... sort of a sputter, then nothing. At lower speeds, it was OK. So, my total noob theory is that a dying/dead alternator isn't ultimately supplying enough voltage to the fuel pump. At lower speeds, it's fine, but at higher speeds, the pump can't keep up with the engine's demand for fuel.

Re: Row Row Row My Boat (4.3L Mercruiser, Bad Alternator?)
 

I suppose it's possible. The thing that throws me off, tho, is, after dying, you had enough juice to restart. That takes a lot more current than running a fuel pump.

Either way: You know you have an alternator problem for sure. So fix that, put the battery on a charger to get it back up to snuff, put the battery back in the boat and see what you have.

Jim

Re: Row Row Row My Boat (4.3L Mercruiser, Bad Alternator?)
 

I totally agree, but my thought was that the starter motor only requires a short burst of power (relatively speaking) with a warm engine. In contrast, the fuel pump may work well enough at lower voltage and thus present no problems at idle or no-wake speed, but when the engine wants a larger stream of fuel, the increase voltage demand (by the fuel pump) can't be fulfilled by the failing alternator.

The alternator IS the original, so it's going on 18 years. I figure replacing that--even if the problem is something else entirely--is probably a good idea regardless.

Re: Row Row Row My Boat (4.3L Mercruiser, Bad Alternator?)
 

Also... for what it's worth, the boat's voltage gauge is reading just shy of 11 volts. (I know, I know, it's not the most accurate thing in the world. I'll borrow a tester.) But still.

Re: Row Row Row My Boat (4.3L Mercruiser, Bad Alternator?)
 

I don't know how accurate they are (they're relatively worthless if they're not accurate, btw), but 11VDC is definitely well below healthy for a 12VDC lead-acid battery. That battery is effectively dead. But you already knew that :).

It just occurred to me: These boats have no "idiot light" to warn you that the alternator isn't doing what it should. I regularly scan oil pressure and water temperature, but, in all honesty, pay little attention to that voltmeter. I think I'll add that to my list of gauges to scan regularly whilst under way.

I wonder what those battery idiot light circuits consist of...?

Jim

Re: Row Row Row My Boat (4.3L Mercruiser, Bad Alternator?)
 

Here's my plan to replace the alternator myself. I'm SOMEWHAT mechanically inclined.

1. Disconnect battery entirely (obviously).
2. Disconnect the two wires coming from the back of the original alternator.
3. Remove the original alternator by loosening/removing the two bolts.
4. Reconnect the wires to the new alternator
5. Put new alternator into place, making sure belt tension is appropriate. (1/4" to 1/2" with moderate pressure).
6. Reconnect battery.


Am I missing anything here?

Re: Row Row Row My Boat (4.3L Mercruiser, Bad Alternator?)
 

Not that I can see. You only need to disconnect the negative side of the battery, tho.

Jim

Re: Row Row Row My Boat (4.3L Mercruiser, Bad Alternator?)
 

Okay, so is it just me or does this sound like water in the fuel or a failing fuel pump.. It is possible that the week battery could actually cook an alternator if it was being asked to carry the full load. The engine stopping while at higher RPM can point to a fuel pump running at lower pressure than it is suppose to. At idle the low pressure wouldn't show up but as the rpm and the volume requirement of gas increases the low pressure situation can cause the motor to die as you bleed the fuel out of the primed line. Just my pennies but I have experienced a similar issue with a fuel pump and a plugged seperator..

Re: Row Row Row My Boat (4.3L Mercruiser, Bad Alternator?)
 

A weak battery can't really kill an alternator, but a battery with shorted plates can over time burn up the rectifier diode inside the alternator (not related to this gripe). In normal operation, the battery is only used for starting. After that everything runs off of the alternator, along with it charging the battery. Now if the alternator is failing (bad brushes/windings/voltage regulator/rectifier), the battery is forced to step in to provide the current to run everything which means it is no longer charging. With everything working correctly, battery voltage with the engine running should be right around 14 volts (12.8 - 14.7 is the acceptable range). The range takes into account variables like heat (higher temps increase a battery's charge capacity, but also increases resistance in the alternator's windings which can drop voltage output).

Re: Row Row Row My Boat (4.3L Mercruiser, Bad Alternator?)
 

Depending on the complexity of the voltage monitoring, it can be as simple as a few resistors, a transistor and a lamp/LED. The easiest solution is a ready made voltage monitor/gauge. Here's a couple made for motorcycles, but should work just fine in a boat:

http://www.customdynamics.com/LED_battery_gauge.htm

Another option is an actual digital voltage gauge. I went this route for one of my bikes since I had one left over in the garage from a stereo install I did a few years ago (I had blue on hand, but they also make them in red):
http://ecx.images-amazon.com/images/...XL._SS500_.jpg

Re: Row Row Row My Boat (4.3L Mercruiser, Bad Alternator?)
 

Excellent points. BUT... instead of a failing fuel pump, doesn't it make more sense that the pump (which is electric on my 4.3L Alpha One) isn't getting the voltage it needs to output a higher fuel volume? Or that other parts of the fuel delivery and/or ignition systems would sputter due to lack of adequate voltage?

Plus, a failing fuel pump wouldn't explain the dying battery very well either, although I suppose that is possible. And water in the fuel would cause problems across all RPM ranges. I haven't put a multimeter tester on it yet, but if the voltage gauge on the dash is even close to accurate (it's reading just shy of 11 volts regardless of the engine running or not) it would almost certainly point to the alternator, wouldn't it?

I'll have the new alternator in by tomorrow night, and I'll report back.

Re: Row Row Row My Boat (4.3L Mercruiser, Bad Alternator?)
 

Its possible it is due to low voltage, the the motor should be set to run at 12V's so 11 aint that bad.. You should not pretty quick once the alternator is in...

Re: Row Row Row My Boat (4.3L Mercruiser, Bad Alternator?)
 

UPDATE:

Well, it looks like I have two concurrent problems.

First--bad alternator. I put the new one in tonight, and immediately, the running voltage returned to a normal range--13.0 to 14.0 or so. Previously, both the running voltage as well as the voltage at the battery when the engine was off was about 11. The new alternator is providing nice voltage and--*gasp*--actually keeping the battery charged! I used a multimeter to test this. I'm also pleased to report the voltage gauge on the dash is very accurate, too, and the new alternator is definitely a little more quiet than the old one.

Second--the bad news. The new alternator did not solve the problem of the engine stalling at 3000+ RPMs. Just like before, the engine starts easily, and runs fine at idle and slower speeds. Then, whether slowly accelerating or hammering the throttle, when it reaches 3000RPM or so, just after planing or just as it's about to plane, it dies -- the tach needle drops to zero pretty quickly. It sure feels fuel-related.

So I guess I was half right, and I'm certainly no worse off for replacing an 18-year old alternator that clearly was having problems. But man... I'm just DYING to hammer this thing and finally fly across the lake! I have a service appointment at an authorized repair place on Tuesday.

If the fuel pump turns out to be the culprit, I'll owe 22empire a nice 12-pack of quality brews for the accurate insight!

Re: Row Row Row My Boat (4.3L Mercruiser, Bad Alternator?)
 

Do these motors have coils like car motors?
I had a similar sort of problem with a car I had once, it would rev up ok out of gear, then put it into gear it would go ok at idle but die if i put my foot down a bit.
Turned out the coil was pretty much had it, put a new one in and problem solved.
Just one idea for you mate.
Good luck.

Re: Row Row Row My Boat (4.3L Mercruiser, Bad Alternator?)
 

They do. They're really not all that different from an automobile engine. Some marinized parts to resist the constant exposure to a hostile environment; backfire flame arrestor on the carburetor, instead of an air filter; raw (sea/lake) water pumped through the engine, instead of a closed radiator system with a fan (tho some do have a closed cooling loop, with the radiator cooled by raw water); and, on most boats, "used" cooling water mixed with the exhaust. If you can wrench on an automobile engine you can wrench on these.

Jim

Re: Row Row Row My Boat (4.3L Mercruiser, Bad Alternator?)
 

I'm having the Mercruiser techs look everything over on Tuesday, and I'll report back.

Place your bets:

A. Fuel pump
B. Coil
C. Something else

and

1. Less than $100
2. $101 to $499
3. $500 to $800
4. Pull the plug and turn it into a fresh water reef.

Re: Row Row Row My Boat (4.3L Mercruiser, Bad Alternator?)
 

You left out "All of the above" :D

Don't be ridiculous--it's a boat we're talking about here.

This would be my guess, but it's a boat we're talking about here, so...

Distinctly possible.

Too expensive. You'd have to strip her of all pollutants (engine, gas tank, outdrive, anything else), first. Probably the upholstery, any wood (it's no doubt all treated), probably all the wire and electronics, as well. ;)

Btw: Before invoking the expensive option, I'd consider obtaining a replacement coil and trying that, first.

Or... Do these engines have electronic ignitions, or are they the old points-and-condenser systems? It's been a long time, but... this is kind of sounding like a condenser problem, maybe?

Jim

Re: Row Row Row My Boat (4.3L Mercruiser, Bad Alternator?)
 

I'm going with C and either 2 or 3 since you are taking it in. My actual guess as to the cause of the gripe is a combination of fuel/water separator filter and carb inlet filter.

Re: Row Row Row My Boat (4.3L Mercruiser, Bad Alternator?)
 

So why doesn't my boat stay running past 3000 RPMs? Why does it run OK at idle and at no-wake speeds, but die shortly after getting up on plane?

After a careful inspection, the Mercruiser techs are saying...


(wait for it)


Badly corroded carburetor.

As in, "it's really pretty bad. It shouldn't be rebuilt, but replaced." As in, "there's been a lot of water in the gas over the years." As in, "the previous owner may have messed it up, or used a lot of gas with ethanol because this was years in the making."

So there you have it. Another $900 bucks. :shakehead: At least the shiny new (well, remanned) carb will match the shiny new alternator.

Re: Row Row Row My Boat (4.3L Mercruiser, Bad Alternator?)
 

That's why I started using Sta-Bil marine formula right off. Ethanol and (older) boats are Not A Good Mix.

If you haven't seen it: Tell EPA to Wait on Ethanol Increase. Summary: EPA, at the urging of ethanol producers, want's to increase ethanol in gasoline from the current 10% (E10) to 15% (E15), without first researching the possible side-effects. E10 was a disaster for the marine industry. You would have thought they'd take that into consideration. But I guess not when Big Money (ethanol producers, in this case) is speaking. So much for "Change You Can Belive In," eh? :rolleyes:

*Ouch*! That really is a case of Bring Out Another Thousand!

Well, at least the problem's identified and relatively easily fixed.

Jim

Re: Row Row Row My Boat (4.3L Mercruiser, Bad Alternator?)
 

At least you have gotten to the source of the problem, and a valuable lesson learned for all others out there.
Now you can get out there and enjoy your summer :wink_thumbup:

Re: Row Row Row My Boat (4.3L Mercruiser, Bad Alternator?)
 

Hmmmmm....Summit Racing has a package. 600 CFM Edelbrock 1409, K&N flame arrestor, and new studs for $420. You need the 1485 kit with metering rods and jet kit for the 4.3L. It's $17. You might need an adapter too depending on your manifold.

-Chris

Re: Row Row Row My Boat (4.3L Mercruiser, Bad Alternator?)
 

I have to agree: $900 for a stock (I assume) 4-bbl. Rochester or Webber carburetor does seem kind of steep, even installed. Replacing a carburetor is trivial, labour-wise. Back in the day I thought nothing of regularly tearing 'em off, rebuilding 'em and putting 'em back on.

Jim

Re: Row Row Row My Boat (4.3L Mercruiser, Bad Alternator?)
 

Apparently, in this case, it's about a $600 part (I verified this at several parts places online), and a total of about three hours of work -- 1 hour for initial testing and diagnostics, 2 hours for replacement.

Not saying I agree with this, but I guess I understand it. :shakehead:

Re: Row Row Row My Boat (4.3L Mercruiser, Bad Alternator?)
 

You gotta pay to play...

Sorry to hear the not-so-good news. Hopefully, it'll be all fixed soon.

I would wager as you as soon as you drop the hammer for the first time out, the thoughts about the incurred costs and headaches will all disappear.

People always give me that old "Two best days in a boat owners life... " line. I tell them it's nonsense. I can never get that ear to ear grin off my mug every time I punch it to get up on plane... :yes_grin:

Re: Row Row Row My Boat (4.3L Mercruiser, Bad Alternator?)
 

Given the cost, I ask myself this question:

"It's $900. Your boat could be mechanically flawless. Would you rather have two hookers and a bottle of scotch?"

No. Probably not.