coil test results... is it bad?

[andyhoss]

I just wanted to confirm if you guys think my coil is bad.... Testing from the coil negative and postive terminals at Rx1 scale I get between .3-.4... according to the book it should be at zero. both of the other tests from positve terminal through coil to other side registers nothing, and lead out of the coil with ground registers nothing (not zero, ohmeter does nothing).. so do you guys think its bad since it is registering .3-.4 where it is suppose to be zero??? The engine is a 1970 mercury 650 4 cylinder.. Also if I wanted to confrim there was power to the coil could I just touch leads on switchboard to coil connection and turn it over?? should it say 12 volts?? <br /><br />Thanks a lot!!!

 

[andyhoss]

Re: coil test results... is it bad?

Ok after reading around on some of the other forums I did a few other things... I tried removing the tilt switch- no fire out of the coil... And I tested the red and white leads off the switch box the red one was 12.5 volts.... the white one was 12.5 volts when off and 9 volts when on.. Also the green lead from switch box to coil registers zero on or off.... any suggestions from anyone pleaassseeee?????? It must be either the coil or the switchbox just need to make sure I know which one.

 

[molsenice]

Re: coil test results... is it bad?

check out the thread "testing a coil from a late 60's merc, How can I tell if it is any good?" - need to know more about what the coil is from? serial #s and why you think it is the problem to begin with.

 

[andyhoss]

Re: coil test results... is it bad?

Serial # for enigine - 3073788...<br /><br />I've been running the engine for 2 years.. last time out stopped running now just turns over... first checked fuel line into carb- fine. No spark at spark plugs.. no spark out of coil.. power fine into switch box. Im no mechanic but seems like has to be switchbox or coil.<br /><br />Thanks Molsenice

 

[andyhoss]

Re: coil test results... is it bad?

If anyone could tell me whether or not I should be getting a voltage out of the green lead (from switchbox to coil) it would be incredibly helpful<br /><br />thanks

 

[andyhoss]

Re: coil test results... is it bad?

anyone? I'm pretty much stuck at this point....

 

[molsenice]

Re: coil test results... is it bad?

did you check out the above mentioned thread, "testing a coil from a late 60's merc, How can I tell if it is any good?" also, if when checking for spark, you turned the motor over, I have read, that will toast the switch box. Generally, coils are pretty tough buggers and you really cant hurt them. I'm no expert, but managed to get my engine running with help from these folks. Keep your head up, since the motor just stopped running, loose wires could be a possibility, corrosion / vibration of the wires behind the pannel, dependingon how you checked for spark, you may now need a switshbox as turning the engine over with the plug wires disconnected can eat those delicate little beasts, so I have read. Hooking the battery terminals up in reverse will do the same as I did. I managed to get a new coil/switchbox assembley from oldmercs.com, this at least covered two of my suspions and luckily it was right ($240.00). Will track down more info with the serial # and get back to you - good luck.

 

[molsenice]

Re: coil test results... is it bad?

one more thing, to properly test the coil, you need a known good one,identical to yours, to test and compare to - so a marina mechanic mentioned to me.

 

[molsenice]

Re: coil test results... is it bad?

If you need it, here is the part, www.oldmercs.com/197071Merc650.htm<br /> 332-2986K Aftermarket switchbox and coil kit replaces 332-2986A21 or 332-2986A27 switchboxes (above). Does not include sender for original style tachometers. $240

 

[andyhoss21]

Re: coil test results... is it bad?

i read the thread and I'm more interested in finding out specifically which part is failing rather than just replacing everything...I have the specs on my coil out of the shop book to test against.... also you said "if when checking for spark, you turned the motor over, I have read, that will toast the switch box" is there away to check for spark without turning the engine over?<br /><br />thanks for your help molsenice

 

[Motor Boater Bill]

Re: coil test results... is it bad?

Be sure to have a good look at all your wiring before you start replacing parts. Some 1970 Mercs had a bad reputation for insulation falling apart. <br /><br />I've read different things about what will and won't toast a switchbox--hard to say. It should be okay to test for spark if you have the plug out, connected to the wire and the base of the plug grounded. Electrically, that is no different than the plug being in. Or you could use a spark tester that goes between the wire and the plug and has a clear barrel in which you can see the spark.<br /><br />This motor takes a different coil than Molsonice's, and just the coil is $132 bucks, the switchbox is $350, so I can't blame you for wantind to find out what the problem is! It does like it would be able to use the aftermarket kit for about half that price. But I don't know beans about this motor, so keep posting! If you don't have any luck here, try John's Old Merc Q and A board:<br /> http://pfs-ware.com/kwast/mercboard/index.htm

 

[andyhoss]

Re: coil test results... is it bad?

couple of things<br /><br />1 - when testing the voltage coming out of the white lead on the switchbox it dropped from 12.5 volts to about 9 volts.. could this be enough of a drop to cause no spark??<br /><br />2 - should there be voltage from the lead going into the coil?? i'm getting nothing<br /><br />thanks for your help guys

 

[Ben Konopacky]

Re: coil test results... is it bad?

HI ahoss; your primary coil appears to check ok with that.3-.4 on the rx1 range, the secondary coil appears to be open with no reading,re check the secondary on the rx100 scale ,should read 9-12between towerand grd. that is 900 -1200 ohms. hope this helps a little.

 

[andyhoss]

Re: coil test results... is it bad?

thanks ben i rechecked on the rx100 scale and its not registering anything??? what do you think?? is that possible for it to read absolutely nothing...<br /><br />a couple more things that might be helpful<br /><br />1 - the last time it was running I did notice a kind of buzzing sound coming on and off from the engine.. definately a new sound almost like a short...<br /><br />2 - I have located a short somewhere in the red cable from battery to engine.... It wouldn't turn over at all earlier and after shaking that cable it starting turning over again..<br /><br />Im mainly confused about that green wire from switch box to coil.. if coil was broken would there still be a voltage reading from switchbox...<br />be cause like I said it is dead on or off<br /><br />I wish I had taken some of my electrical engineering classes by now...lol<br /><br />thanks for the help guys, means a lot to me

 

[andyhoss]

Re: coil test results... is it bad?

hate to ask a million questions at once.<br /><br />but does anyone know how interchangeable these old mercury coils are? I have found a couple of really cheap used coils on ebay.... 2 of them are off of merc 4 cylinder engines on 73 80 HP engines and the actual coil LOOKS EXACTLY the same.... just wondering cuz if I could try throwing one of those in to see if it fixes the problem I woul

 

[Motor Boater Bill]

Re: coil test results... is it bad?

You can cross reference the parts by going to the mercuriser site and checking the part numbers between the motors:<br /> http://www.mercruiserparts.com/selectModels2.asp?type_id=MERC <br /><br />Or you can go to oldmercs.com and see if they show the same part for both motors.<br /><br />Also ask the seller on eBay for the part number.<br /><br />Good luck!

 

[andyhoss21]

Re: coil test results... is it bad?

so are the green and black wires both grounds that come off of the coil... I was reading that most coils have a primary and secondary ground

 

[andyhoss21]

Re: coil test results... is it bad?

to see a picture of what my coil LOOKS like go here: <br /><br /> http://cgi.ebay.com/ebaymotors/ws/e...1284&item=4556956705&sspagename=rvi:1:3v_home <br /><br />can anyone tell me if there should be voltage going into the green wire when the engine is turned over???????

 

[Ben Konopacky]

Re: coil test results... is it bad?

andy ;the green is the hot leg to the coil,I beleive the voltage is high and pulsating NOT a steady voltage source.CDI ,don't think it can be meas. w/ d.v.m..the pri. & sec. coils are com. to grd. internaly,like an auto ign. coil.back to the ? of testing the coil w/ohme meter, if you had NO reading on the secondary (grd. to tower 900-1200)you have an open coil. less confusing ?

 

[andyhoss]

Re: coil test results... is it bad?

and sorry but im really confused... if the coil is open it is no good??