1979 Mercury 150hp V6 - Spark Issues

[epon]

Hi all... did some first-time troubleshooting on my new purchase. I'm getting no spark on any cyl right now and I've eliminated plugs and wires as problems. I think my trigger is working because those wires on the switch boxes are showing something on my multimeter.

So I put the motor down realizing there's a mercury switch and found some voltage on my inner and outer switch boxes (see image below), but some of the contacts fluctuate wildly while others are very small.

http://www.maxrules.com/oldmercs/Wiring/1966ona/53.jpg

So to eliminate if the problem is the switch boxes or coils, I need to know what voltages I should be getting at each contact point... I can't find anywhere online that lists what values (DC or AC) I should be getting on a multimeter.

Can anyone help me do some basic troubleshooting? I have the tools I need and I'm not afraid to get dirty, nor purchase new parts... I just want to make sure I purchase replacements on what's broken! Thank you very much!

FYI - my motor is I assume one of the later-models with a serial # between 5363919 to 5464484

 

[j_martin]

Re: 1979 Mercury 150hp V6 - Spark Issues

Any reading you get with a multimeter, either AC or DC is of no use. The specs are in P-P voltage, so you need a DVA, (Direct voltage adapter) which is a peak reading meter or adapter.

All the information you need is in the Mercury service manual. If you intend to do your own service, it is a priceless investment.

Quickies for now. Unless you know for certain how it is supposed to sound when cranking, get an amp meter you hold against the wire and check your starting current. It should be around 125 amps. If it's high, the starter is dragging and your cranking speed is slow. Without a real brisk cranking speed, it won't fire.

Disconnect the kill wires from both switchboxes and see if you get spark. If you do, there's a fault in the mercury switch or the kill circuit, which involves the kill switch and the ignition switch.

After that, you need a DVA meter.

hope it helps
John

 

[epon]

Re: 1979 Mercury 150hp V6 - Spark Issues

John thank you so much for the info. Going to see if my friend's shop has a DVA tomorrow. I know they have an amp meter (my dinky multimeter only handles 10A max)

I can say that the flywheel isn't spinning "brisk". My tach barely moves when the starter is spinning it. The battery is brand new but I've been cranking a lot so maybe it's starting to die on me. I have a trickle-charger that I'll put on it tonight that will hopefully help.

I did notice that the starter seems to be "stuck up" right now. The motor was sitting around for a year or so from the previous owner. He said it's a new starter (def looks new) but perhaps the axle is gunked up. I'll WD40 that as well and give it a little tap with a hammer to see if it releases down. I foresee that becoming a future problem if the thing ever turns over