90 hp ignition system diagnosis...inline six switch box.

O.K. fellas maybe someone can give me some help, but first a little backround info....I have a project 20 ft. penn yan that I have just about ready for the water. It has an inline six cylinder mercury 90 hp on it, I had a missing spark issue last season and narrowed it down to the switch box, which I replaced and it ran fine most of the season it got a little cranky towards the end so I just pulled it for the season. I rebuilt all three carburators this season and changed the water pump out and changed the lower gear oil and assumed I was ready to go.....aaaah nah! Same condition as last year missing spark on number 2, 5 and number three cylinder has intermitent spark....I know it's probrably the switch box again , but I think something must be the root cause of all this....as for me I am a former ase certified car and truck mechanic so I am pretty good at 12 volt electrical systems, I am new to this two stroke marine world lol...o.k. here's my question? Can you diag the ignition componants with a DVA the same way as with a cars system....ohm readings and such. Thanks for any info that you have to share...P.S. I have a maual for mercury , but I do not think its the right one...does have inline six info in it though...Thanks again people.

Re: 90 hp ignition system diagnosis...inline six switch box.

CDI will have a pdf of wht your looking for..

and yes a DVA is needed.

http://www.cdielectronics.com/downloads/troubleshooting guide/


Good luck!

Re: 90 hp ignition system diagnosis...inline six switch box.

Inline six motors used a couple different types of ingitions. One was a single switchbox, a single coil and a distributor. The other ign system was dual switchboxes, triple triggers and six coils. If you have the distributor ign, and have no spark to a couple of cylinders, it is likely the cap or wires. Rotors are not removeable and quite fragile.

If you have the non-distributor ign, one switchbox powers cylinders 1,3,5 and the other 2,4,6. The triple triggers provide spark for 2 cylinders each. So if you do not have spark on 1,3,5 or 2,4,6 it points to a switchbox or bias circuit.

Re: 90 hp ignition system diagnosis...inline six switch box.

canoemang said:

CDI will have a pdf of wht your looking for..

and yes a DVA is needed.

http://www.cdielectronics.com/downloads/troubleshooting guide/


Good luck!

Click to expand...

ok from car guy to car guy here is what I found. Since we are used to using power to ground testing and ohms with a manual ranging meter I can give some tips. ground your meter on the starter ground once the motor is running. now look at the rectifier (two yellow wires) make sure you have a charged power coming from them. Next move down to the switch box with the ground still on the starter, test each of the trigger side of each terminal to verify that you have voltage.

Next, (I cranked up my meter to max voltage) and looked at the output side of the switch boxes either you will have power coming out or not, If you do but still have no spark you are probably looking at coil packs, if no power coming out you have dead switch boxes.

Now I have replaced my switch boxes twice in 4 years, both with the same problems and symptoms. I asked on another forum where there is a Merc guru who seems to be pretty knowledgeable in this area what the root cause could be. He said that many times a loose battery connection would be the culprit causing fluctuation in the power and ground side of things in the circuit.

His recommendation was to use standard battery terminal clamps or stainless steel locking nuts to secure the battery leads, basically toss the wing nuts into the trash.

- Now here is where my car know how meets boat know how, I think...lol...
When we are dealing with high current drains in the auto world the first thing we look at is battery capacity, then move on to the "Big 3" This is where I am at now, as I can not up the current from my stator to force feed a smooth voltage to my switch boxes, I am going to do the next best thing, in my mind. I am going to be adding grounding straps from boxes to mounting plate, then plate to starter ground then separate plate to terminal ground.

I hope this works so that the next owner will not have the same issues that I have had with this electrical system.