Merc 470 runs sometimes, sometimes not!

[Leori]

Been burying myself in the boat lately, trying to chase a problem that i keep running into. My boat had a merc 485, the motor ended up toast (cracked cyl and whatnot) so i managed to locate a 470 to swap in. The swap went beautiful, and she ran great on the water for night fishing the first night. Took her back out, and throttled up, she hit about 2800 RPM, started to come up, and it popped, like a muted backfire (though i've only been familiar with cars backfiring, so i can imagine that it was due to being in water) Since then, it's been all hell trying to troubleshoot why she won't start. Occasionally, i can go out, hit it, and she'll fire up for a bit. But it gets better

I still had the coil and points setup from the other boat, took the dist cap off, and found a corroded condenser, and a set of points that looked like more of a cup and nipple, rather than nice flat surfaces... went to the merc dealer and parted with the 8 bucks for a new set, and a new condenser, installed them, and set them. Turned the engine crank over till right before #1TDC and the cam for the points was at the peak. Used a feeler gauge, and set it at .20 to start (specs according to valve cover and manual call for between .18 and .25) Swapped what looked like an Accel automotive coil (giant yellow monstrosity) for the factory-replica newer coil from the old engine, swapped the wires for a new set of 8mm (overkill for the old ignition system, but should work) and regapped the plugs. I did notice that the old plugs were clean, smelled a little like gas (from me fighting with it to get her started before) but were dark, not shiny... went ahead and replaced them, regapped at .35 (also according to valve cover and manual spec) Replaced the small fuel filter in the carb, and the one under the bell assembly on the side of the engine, and put a new water separator filter on over by the gas tank. Pulled the big engine harness connector plug and cleaned it (learned to disconnect the battery first, steel wool can and will smolder quickly... threw that from the boat into the water where the muffs had soaked the driveway) spread the contacts just a hair with a small screwdriver, reinstalled it, and put a new hose clamp around the boot to keep crap out. This engine had a blown water cooled voltage regulator when i got it (that's why she was so cheap) so i moved over my alternator conversion kit from the old motor, (uses a Warner GM single wire type) and wired that to the battery (+) Terminal. Here's the kicker...

First time i got her to start, ran fine on the lake as above, second day out, took her for a spin, she did the backfire, and has been trouble ever since. Got towed back to dock, (nice guy with a jet ski dragged my 176 back) and got her home. Did all the cleanup, replacing stuff, and got her back together, tried to start in the driveway, and she'll spin like a top all day, but doens't want to fire... occasionally she will, if you toy with her enough, just at random when you are about to give up, you hit the key and it fired right up. The belt form the crank pulley to alt squealed something fierce, and i shut her down. The alternator pulley was too hot to even touch (now have a glassy spot on a finger) but had only ran for about 15 seconds? Alternator spins free, with belt off, tried to start, nothing, won't fire, sometimes will... i'm still trying to figure out what's going on!

On a hunch i noticed that the negative cable to engine had super hard insulation (old) so replaced with a new one, cleaned up the terminals, still nothing. I know the shift interrupt switch works, took the screws out and let it stay completely disengaged (doens't do jack on muffs anyway) that didn't seem to help at all. Traced the wiring under the helm, nothing out of the ordinary, all connections and fuses are clean, tight, and in good shape. Neutral safety switch is working fine, it won't let the starter kick unless you push the throttle only button all the way in and tilt it forward into Throttle only setting, or is in true neutral...

When it does start, she purrs, nothing abnormal at all, no RPM fluctuation, gauges all look good, gets to about 160 and levels off in temp, when you can actually get it to start.

My next thought was fuel delivery, but when you pump the throttle, it primes, and won't even stumble, acts like it's got no spark at all, or something... just spins like a top, and when the starter releases, just hear the compression release.

I'm a car guy, not a boat guy, and have had this learning curve hit me harder than a ton of bricks. I've tried tinkering with the points, to see if anything helps, from setting at .18 (minimum gap allowed) and .25 tried gapping the plugs a hair smaller (.33 instead of .35) and nothing.

Does anyone have any suggestions as to what is going on?

My thoughts, the alternator getting hot is really strange, but with it not even on the boat, sitting on the table, and starting her on battery alone, it doesn't make a difference.

Rotor and cap are like new, points are new, plugs and wires are new, condenser new, tried two different coils,

on a side note, i did notice that out of the engine harness at the electric choke, there are two wires plugged in, pink, and purple (what i can make out of it) and what looks to be a ground, that hasn't been connected in years? just a solid black wire that sticks up about 2 inches about 5 inches away from it coming out of the same section

also, the oil pressure gauge does not seem to work, though it did on the other engine, just read low (due to bad motor) will that have anything to do with this intermittent start issue? Also, in cleanup i have removed the old blown up water cooled regulator, wasn't even connected to anything anyway.

Any advice on where i can go from here is MUCH appreciated!

 

[Lyle29464]

Re: Merc 470 runs sometimes, sometimes not!

Think I would run a jumper from the + on the battery to the+ on the coil and try that. If that fixes it you need to trouble shoot the ignition system ( 12 volts)

 

[telstar1]

Re: Merc 470 runs sometimes, sometimes not!

!.Determine spark quality out of coil.Is it blue and bright. Should jump 1/4 inch or more.
2.Pull plugs.Try spark at plugs. Still good?
3. Probably flooded. Remove all plugs,roll eng. on starter ior awhile. Blow out cyls with compressed air.
4. Reassemble, observe choke is it closed?
Try to start. Dont roll over for more than a few times with choke fully closed,or itll flood. Try holding choke open with a screwdriver etc. pump throttle. During all this it should be starting or trying to start. If not you need to look for other causes.Sudden stop like that,Id guess spark related.

 

[stonyloam]

Re: Merc 470 runs sometimes, sometimes not!

As telstar says, the first thing to check is the spark. OK on to the choke connector. There should be 3 wires. A purple wire from the ignition switch, a purple (might have faded to pink) wire going to the coil plus, and a black wire that is the ground for the electric choke. 1) if the ground (black wire) is cut, then the choke is not functioning (could be the po has it jammed open) and that could be part of the problem. Might want to substitute the choke module from the other engine 2) check the connector on the coil end of the purple resistance wire. Measure the voltage there with the key on. 3) Your coil gets its voltage from the slave solenoid when starting (purple/yellow wire), so check the voltage at coil + while cranking, then check battery voltage when cranking, should be the same. Let us know how that works out. BTW what is your engine year and sn?

 

[Leori]

Re: Merc 470 runs sometimes, sometimes not!

Swapped carbs and choke from the old motor to the new one (carb was rebuilt about two months ago on the old engine) and rebuilt the connectors, i noticed on the old harness that the wire that had been cut, was in fact the ground for the choke.. hooked everything back up, and fixed the new harness and installed the entire thing, even swapped the throttle linkage over. Put a new set of filters in it, just to be on the safe side and went on troubleshooting.

Got the spark tester out, and had NOTHING, clamped the spark tester on several different grounded points, with the #1 cyl wire, and no dice, no spark.

So i decided to try the hot wire from positive cable to the coil, fired right up, no hesitation. Started to rev more than i'd like on the muffs, so i walked back to the boat after the key didn't shut it back down (due to the wire) and took the wire back off the terminal.

Here's the kicker, now... set up as normal, she doesn't hesitate to start at all? Hot or cold. Doens't even need the wire from positive to the coil to run flawless every start? But nothing really changed?

Went about the business, and found out that the alternator pulley was slightly out of alignment from the balancer pulley, and that i had WAAAY too much tension on it... got that all adjusted back correct, and no swueal, not getting hot! Used a volt meter to check voltages and here's what i found

Pos to Neg, the battery between terminals shows 13.12-13.23 volts
With engine running, alternator post on the back of the alt to the battery negative reads 14.28 volts
Engine running, Alternator cable end on the battery, to the battery negative, reads at 14.21 volts
Engine off, alternator post to the battery negative reads 13.11-13.24 volts
Coil positive to the battery Negative reads 12.01-12.2 volts (key on)
Coil Negative to the battery positive reads between 4.13 to 8.19 volts (key on)
didn't want to leave the key on for long, as i read something about the points if closed will fry the coil if you leave it on too long with engine not running...

So i'm baffled... what the hell happened? Is the voltage for the negative coil terminal supposed to be that low? Is it possible that the coil is just weak? Or that there is a problem in the engine harness? Definately dealing with a spark issue, we know that now, even ran a bit smoother on the other carb, so i'm leaving it on there... want to get the starting issues down before i start messing with getting the carb and timing adjusted

On a side note, the low RPM is idling on muffs at about 950 rpm, in water ususally that sits her at about 700 in gear, i did notice when i installed the alternator again that the rpm idle dropped about 200 rpm, i am assuming this is the drag of the alt on the engine, so i adjusted to put it back where it was.

I'm still trying to wrap my head around why this problem somehow resolved it's self? Not sure that i trust it yet, and that it's out of the woods yet...

I did find that the hour meter was unplugged, and it WILL NOT start with it plugged in guessing the hour meter is toast.


Engine is a 1981 470 I'll grab the S/N once it stops raining buckets

 

[stonyloam]

Re: Merc 470 runs sometimes, sometimes not!

Ahhh the joys of owning a boat LOL. Who knows, maybe the points were a little glazed over and are making better contact now. Sounds like the voltages are OK, don't know about the coil voltage, but it will be lower due to internal resistance of the coil. Your idle should be about 650-700 out of gear. Here is a link to the Mercruiser manuals for your engine and OD, #3 and #6 respectively: http://boatinfo.no/lib/library.html Have fun

 

[Leori]

Re: Merc 470 runs sometimes, sometimes not!

I highly doubt the points were glazed, they are only a day old, have less than 15 minutes total run time on them.

So, i let her sit overnight last night, and no dice, can't get her to start at all.... tried a little gas down the carb, nothing, seems like no spark, i'm guessing the coil may be on it's way out, so i'm replacing it again, guess somehow i have two bad coils? Took the accel monster to napa, they tested it, and aside from "a little dirty, shows no resistance and checks out"

engine Serial # is 5689256 Drive Serial 5606190 valve cover has serial number 5689256 as well 224CID timing 8 degrees BTDCsays RPM range 3800-4200 plug gap .035 point gap .019-.025 dwell 28-34 88 octane minimum, model is MCM-470

Still at a loss to explain it, it's like, once the coil gets warm, it runs okay? and will start every time now, but once it cools off enough it's a no dice, i am also thinking choke related, so going to replace the choke and reset it as the next go.

Any other suggestions? Or things to troubleshoot? I'm running low on causes

 

[Eric 3.7LX Alpha 1]

Re: Merc 470 runs sometimes, sometimes not!

Those voltage numbers were when it is running or having issues?

You have a mult meter... does it have an Ohms setting? You can test the coil yourself easily and eliminate it as a possible cause.

The specs for testing the coil is in the manual link that Stonyloam gave you.

 

[stonyloam]

Re: Merc 470 runs sometimes, sometimes not!

OK try this: Remove the cap and rotor, pull the center wire out of the cap and lay it about 1/4 inch from bare block metal, Take a piece of insulating material and place it between the points, so they do not make contact. Turn the key to run and with a piece of insulated wire briefly jumper across the points then remove the wire. You should get a strong blue spark out of the coil every time you remove the wire. If you do your coil is OK. Now remove the insulator and crank the engine over, you should get the same blue spark. If that checks out them your ignition should be OK.

 

[generator12]

Re: Merc 470 runs sometimes, sometimes not!

"...So, i let her sit overnight last night, and no dice, can't get her to start at all...."

Have you since tried (again) to start it with the jumper from batt + to coil +..? As I read this, it worked when you did that. If it starts with this in place, you've got an intermittent wiring problem somewhere in the harness.

I've got a 470 and had a wiring problem (documented in prior posts here) that caused my engine to shut down without warning. Turned out to be something with the wire to the tach. Not the tach itself, nor the shift interrupter switch that's on the same line, but the wire. What's more, the problem with that wire doesn't show with a multi-meter, voltage or resistance to ground, engine running or not.

So I repeat, if you haven't tried to start her with that jumper in, do so. If she runs, you'll have to run a new wire from the ignition switch back to the doghouse to replace the original.

 

[Leori]

Re: Merc 470 runs sometimes, sometimes not!

Damned wiring! I gave up on the points, and decided screw it, replaced the entire system again, and upgraded to the electronic petronix style (sierra) ignition, new cap, new wires, fresh plugs, and went to start it, no dice...

Tried, with the coil hot wired, and BAM she runs! and continues to run and start every time, 10 bucks says as soon as i back her in the lake, she won't start... so i'm running a new wire from ignition to the doghouse in the back. According to the wiring diagram, the ignition coil runs off the "I" terminal on the starter solenoid, with a purple wire w/ yellow stripe. I ran a second wire from that terminal, to the coil + and all is good! Guess it just had a terrible connection when cold in that harness somewhere, engine heat would warm up the harness, and get her to connect is all i can figure. For now, the other wire works, and until i have the engine out the next time (at which point rebuilding the wiring harness is on the list) Running a new one in it's place seems the best fix! If i had known a 3.00 spool of wire, and a couple eye terminal ends would have fixed it, coulda saved a CRAPLOAD of cash!

On the bright side, there's a lot less to do at the end of season maintenance, as she'll only be out a few more times before it's too cold and we winterize her.

 

[rock doc]

Re: Merc 470 runs sometimes, sometimes not!

Probably a long shot but did you try unhooking your tach?

 

[stonyloam]

Re: Merc 470 runs sometimes, sometimes not!

Check to make sure you are getting 12V to the coil from the slave solenoid (r/y wire) when it is cranking. Sounds like that is where your problem is.