troubleshooting 85 merc 50 hp motor

I have posted and a few times and have been researching on iboats. I know now more about outboard motors than I ever thought possible. My problem is engine bogging while going WOT. I found that cylnders 3 and 4 are not getting spark. I have found the cdi electronics webste to have good installation and trouble shooting guides. I have made a DVA and will begin troubleshooting the ignition system. My question, do any of you veterans have a suggestion on where to begin. Here is my plan. Please tell me if you have any suggestions or the steps are out of order.

Check stator for resistance and voltage
Check the Trigger for resistance and voltage
Check switch box for resistance and voltage
Check ignition coils on plugs for voltage

Also, should I check the rectifier first? I'm not sure. But it does sound like a pretty eary test. I just bought a new starting battery, since I needed one and wante to eliminate that as a possibility.

I appreciate all of the knowledge and experience. I'm sure I will have more questions, but this has been a great learning experience.

thanks

Re: troubleshooting 85 merc 50 hp motor

I go a different route on the 4 cylinders. I swap the stator leads around on the switch box and check fire with a tester without sparkplugs in. Red swap with red/white and blue with blue/white. If it fires on 3 and 4 and not 1 and 2 the stator is bad. If there is no change the stator is good. Do the same to check trigger and coils. Take a wire loose on one that is firing and swap with one that is not. Seldom a trigger on 2 cylinders and hardly ever 2 coils at once. Bound to be switch box or one side of the stator bad.

Re: troubleshooting 85 merc 50 hp motor

Thanks, egeodale,

Good idea. I will try that and see what happens. I'm guessing the stator or switch box as well.

mark

Re: troubleshooting 85 merc 50 hp motor

On a single switchbox system as used in the in-line 4 cyl, swapping the stator leads simply switches the hi and low speed windings and will not restore spark anywhere. Totally different than swapping leads between TWO switchboxes as used on the 6 cyl motors.

The simple fact that the 4 cyl HAS spark shows that the stator IS producing voltage to operate the switchbox.

DVA testing is necessary to properly identify the fault of either the trigger or the switchbox.

When testing the triggers remember to disconnect the throttle cable and move the throttle/timing levers throughout their range of travel to see if trigger voltage fails, indicating a possible broken wire somewhere in the flexing wires.

Since the firing order of the 4 cyl is 1, 3, 2, 4, it is unlikely that the trigger is the fault, More likely it is the switchbox but you must PROVE the fault as there is NO RETURN on electrical parts.Make sure of the bad part to prevent ordering unnecessary parts.

Edit: Too early in the morning, haven't finished my pot of coffee. With the firing order of 1324, the triggers (2) each fire 2 cyls, 1 & 2 share a trigger, and 3 & 4 share a trigger. So it IS entirely possible for the problem to be EITHER a trigger or the switchbox. BOTH need DVA testing to be sure which is at fault.

Re: troubleshooting 85 merc 50 hp motor

Thanks Commander. I did some checking today and I'm stuck. Here is my situation,

I checked DVA on the 4 coils. No voltage on any coils

I checked DVA on low and high speed stator with the following results.

high speed within range dva (42) Resistance 144, within range
Low speed DVA 1.4 V, 10.8 resistance - is definitely bad

I checked the Trigger DVA
Purple to White wire 5.9 V
Brown to Black 0

I'm stuck

First , I do not understand how I am not getting ANY voltage at the coils. None of the coils is receiving power. Would the bad low speed stator readings or the 0 reading on the trigger black/brn wires?

Second, could the failure of the low speed stator test, cause the trigger test to read 0 on brwn, black wires?

Third, is it possible or should I say likely to have more than one component go bad at the same time.

Also, what is the best way to test the rectifier?

thanks for any helo
mark

Re: troubleshooting 85 merc 50 hp motor

If there is spark on two cyl's then the DVA test of switchbox output to the coils was faulty, it should read on the two coils that had spark.

The DVA test of the stator may have been faulty, since the two cyls have spark the stator MUST BE generating voltage.

Repeat the DVA tests only this time disconnect all wires being tested as an internal short in a switchbox can skew the results.

Another possible test is to switch the trigger wires on the switchbox, place 1 & 2 on 3 & 4, retest for spark. If the spark moves to the 3 & 4 then the trigger is bad, If the spark stays on 1 & 2 then the switchbox is bad.

Rectifier is tested with an Ohms meter, test each yelow to red then reverse the leads and again test yellow to red. You should read continuity only one direction and no reading when reversing your leads.