3.0L coil

[biggjimm]

I've got a '76 140 3.0L mercruiser & every season when we would first get it ready to go on the water it would not have spark & I would have to swap out the coil with a spare one & it would run fine all season until after it sat all winter & I'd have to swap back to the other coil to get it to fire the next season. I've since replaced the distributor & I think it's fine. The fuel pump went out shortly after changing the dist. near the end of last season & I'm doing the fuel pump & water impeller now but was wondering if anyone had any ideas what was causing me to have to swap coils every year. Like I said I think the new dist. fixed that but I'll know for sure tomorrow after I get the lower unit back on it & get it fired up. Thanks. Jim.

 

[Bondo]

Ayuh,.... A '76 should have Points,..?? Are ya changin'/ settin' the Points every year,..??

 

[biggjimm]

Yes it has points & I had changed the points the first year it wouldn't start & always checked the contacts & the gap every time after that but it always took swapping the ignition coil to get it to run. The distributor had some wear in the shaft bushings & the shaft & in the centrifugal advance so I replaced it & I can't remember how many times I had it out before the fuel pump went out but I think after the distributor change it was ok as far as the coil goes.

I've got the lower unit off replacing the impellar & housing (as soon as the mail man brings it) is it ok to clamp a hose on the copper water tube & run the engine or should I just wait until I get the LU back on it?

 

[thumpar]

You need to set the dwell also.

 

[biggjimm]

You need to set the dwell also.

Yes I guess I should have mentioned that I had set the dwell as well. Everything was as it should be except there was no spark present from the coil. As soon as I swapped the coil with the other one it would run great all season until it sat over winter & I would have to put the other coil back on it to get it to run again. I know it's crazy sounding & makes no sense at all but that is what I had to do. And even crazier than that, once I changed the coil & started it up, I could then put the coil that I just took off that would not spark, right back on it & it would work fine too until next spring. I thought maybe it was a ground problem or loose wire but I checked & rechecked everything several times & the only thing I found was pop the coil off & put the other one on & it would fire right up every time .Did that for about 4 or 5 seasons.

 

[biggjimm]

Okay, so I've been getting this boat ready to get back on the water, complete water pump kit in the lower unit, New fuel pump & cleaned out fuel tank & replaced fuel lines, carb cleaned, New plugs. Hit the key & just cranks. Pulled a plug wire & no spark! Haven't swapped the coil out yet but I'll almost bet the farm it'll fire when I do. Any ideas what is going on with this crazy boat?

Ps. Somebody school me a little here, as it's been a long time since I've fooled with a points ign. system other than changing the points. I'm going to go get my manuals from my shop tonight but until then..... I've got 12.94 volts on both sides of the coil with the key in the on position. Is this normal or has the dist. just just happened to have stopped with the points closed? I haven't pulled the cap off yet, I had to leave to get wife to work.

Pss. I'm reading DonS sticky on points ignition now.

 

[Bondo]

Pss. I'm reading DonS sticky on points ignition now.

Ok,.... I won't bother postin' the links to those threads,.....

The link to Don'S Adults Only section, is in my signature,....

 

[stonyloam]

If you want to check your coil: pull the center wire from the distributor cap and lay it about 1/4 inch from bare engine metal. Pull the distributor cap off, and put a piece of insulating material (dry paper or plastic will do) between the points. Turn on the key and with a piece of insulated wire briefly jumper across the points. You should get a nice blue spark out of the coil center wire every time you REMOVE the jumper. If you do, your coil is OK.

 

[biggjimm]

Ok stonyloam I'll be checking that soon as time permits. One thing, as I'm reading the sticky & checked my engine, I do not have a purple wire going to the coil. There is a light tan & medium brown wire terminated together on the + side of coil & two dark brown wires terminated together plus the single black wire going to the dist. on the - side of the coil. Am I missing the resistor wire for some reason?

 

[Eric 3.7LX Alpha 1]

If you want to check your coil: pull the center wire from the distributor cap and lay it about 1/4 inch from bare engine metal. Pull the distributor cap off, and put a piece of insulating material (dry paper or plastic will do) between the points. Turn on the key and with a piece of insulated wire briefly jumper across the points. You should get a nice blue spark out of the coil center wire every time you REMOVE the jumper. If you do, your coil is OK.

That test needs to be added into the:

how to test a points system....

 

[biggjimm]

I'm going to try & find a wiring schematic online as I'm not going to make it to my shop to get a manual tonight. But now I've only got less than 1 volt to the coil w/ the ignition switch in the on position so I don't know what's going on with this wiring & I can't manage to download the power point file in DonS sticky about troubleshooting the points ignition. Not a good day today I guess.

 

[stonyloam]

here is a diagram: http://boatinfo.no/lib/mercruiser/ma...ser3.html#/366 Yeah the colors on the older Mercruisers are a little different than modern engines. BTW this manual should cover your engine, you should be able to print out pages you need.

 

[biggjimm]

I'm getting ready to run thru the troubleshooting sticky but I do know that I have no voltage on the tan wire going from the little post on the starter to the + side of the coil now. I thought I had power when I tested it earlier, but I'm not 100% sure. And I'm guessing that testing the coil as stonyloam directed above is useless if I have no power going to the coil???

 

[biggjimm]

Ok apparently I've got 2 separate problems going on here.

1st is I have no voltage on the + side of coil (tan wire on this boat) & there is no voltage at the little terminal on the starter that supplies the coil 12v during cranking (if I'm reading everything right) Does this mean the starter has issues in the solenoid???

And 2nd is that I tested the coil per DonS sticky on troubleshooting the points ignition, which said if there is no continuity between the tower on the coil & the + & - posts, then the coil is bad. I have no continuity on either post. So sounds like the coil is bad as well???
But what about #1 & the starter issue???
All the wires on the slave solenoid & the other wires on the starter are doing as they are meant to, I'm just not getting voltage from the little starter terminal to the coil. Thanks for your patience in helping me muddle through this. Jim.

 

[stonyloam]

OK there is only voltage on the starter terminal when the starter is actually turning. You could try running a temporary jumper directly from the battery + to the coil + to see if you can get it to run. Or for the coil test I mentioned above.

 

[biggjimm]

Let me ask this real quick, the tan wire going from the starter to the coil + is terminated with the tan wire that is apparently the resistor wire, they are both in the same ring terminal that was put on at the factory. Should I separate those & put them on separate ring terminals so I can verify the voltage of each one independently?

 

[biggjimm]

Oh ok, so when the starter is running I should have 12v to the coil but it should be the resistor wire (4-9v) the rest of the time. If I could get that darned file from the adults only sticky on "how the points ignition work" to download I would probably have read that.

Now I guess I still have a problem with the resistor wire because I've only got 0.24 volts at the coil + but I'll run that down tomorrow now that I know how the one from the starter works.

I figured I'd test the coil per your method with a jumper tomorrow as well. Thanks Terry, you've been a great help!

 

[stonyloam]

A quick explanation: the coil is a transformer that steps up the voltage from 12 v to 20,000 v or more, and the distributor feeds that voltage to each plug at the proper time. The points are opened and closed by a cam on the distributor shaft and control current flow through the coil. The coil has 2 sets of windings, a primary ( few windings) and a secondary (many, many windings). When the points close current flows through the primary, generating a electromagnetic field. When the points open the current stops and the field collapses. The collapsing field generates the high voltage in the secondary windings which are connected to the coil center wire. The " spark" travels through the center of the distributor into the rotor and jumps to the plug wire terminal that it is pointing to, on to the plug wire and jumps to ground across the spark plug electrode. The bypass wire from the starter provides battery voltage to the coil during starting for a "hotter" spark because the draw of the starter reduces the battery voltage and the engine is cold. When the engine is running the resistance wire reduces the voltage to the coil to limit current flow, to keep it from getting hot. The dwell is the length of time the points are closed, in degrees of rotation of the distributor. Too short dwell the coil does not fully charge, too long too much current flows and the coil could overheat. That is pretty much how it works.

 

[biggjimm]

That's pretty much what I thought. Thank you for that info Terry.
Here's where I'm at now, I'm getting somewhere, I think.
Took the main harness connector apart, the big one that goes up to the helm, & checked all that out- had no power on the white wire coming from the key switch that feeds the resistor wire, checked at the key switch & gauges & everything is fine. Fiddled with the main harness connector some more & plugged it back in & I've got voltage on the resistor wire (it fluctuates from about 3.5-7.0v) but only when it is disconnected from the coil. Hook it up & the voltage is gone. Take the + wires back off the coil & the voltage is present again. I'm going to jumper the coil & check it per your earlier instructions. Thanks. Jim.

 

[biggjimm]

Checked the coil with a jumper wire & got a faint yellow spark. Not the big bright blue spark that I wanted to see so I guess I'll go to town & get a coil this afternoon. Thanks Terry. Jim