Is it the Switchbox??????

[CSkjerven]

I have a 1988 100hp 2+2 Mercury Motor. I only fires and runs on the bottom two cylinders. We flipped the plugs, the plug wires, the coils, and the stator wires and the same problem persists. It never switches to the bottom 2 cylinders We believe this eliminates these parts as possibly defective. The compression has been tested and is good. Our limited knowledge leads us to believe that the problem is a faulty switchbox. Before I spend the $250 to order a new box, I would love some reassurance that this is probably the problem from someone that knows more than my dad and me. Is there a chance it could be the trigger or something else? I would really appreciate a quick response or two because I have the next 2 weeks off, the fish are biting, and I am itching to hit the water. Thank you very much!

 

[Faztbullet]

Re: Is it the Switchbox??????

Explain a little better what your trying to troubleshoot and engine symptoms are. The 2+2 motors run on the top 2 cylinders at idle and up to about 1800 rpm then the bottom cylinders will kick in. At idle rpm you can pull the lower plug wires and will see little to no difference in rpm as they are getting just enoungh fuel to lube cylinder but not make any power.

 

[CSkjerven]

Re: Is it the Switchbox??????

We have been at this problem for a long time and it has caused us a lot of confusion due to what you just explained about the motor. It is not running, sparking, or idling at all on cylinders 1 and 2. The motor is somehow compensating by idling (though very poorly) on 3 and 4 where there always is good spark. The boat will go but only 12mph topped out. It seems very strange, because like you said 1+2 are suppose to do the idling and the low speed work. We have done a spark test and even ran the motor with the plug wires off of 1 and 2. It runs though has trouble idling at low throttle. We have tried all of this flopping to try to get 1 and 2 to spark but nothing has worked. Hopefully this seems possible to you. I know we were very surprised to find out problem was 1 and 2 because we were under the impression it wouldn't start or run at all without them. Thank you for your time. I hope my explanation makes sense.

 

[CSkjerven]

Re: Is it the Switchbox??????

By 1 and 2 I mean the top 2 cylinders are the ones that are not firing.

 

[CharlieB]

Re: Is it the Switchbox??????

A DVA meter and testing the ignition following the well laid out directions in the Ignition Troubleshooting Gujide available for free download from the Support pages of CDIElectronics.com will confirm the defective part.

You may also try switching the trigger wires 1 & 2 for 3 & 4 to see if spark switches cyls. If so, the switchbox is good and the trigger is bad. Do NOT attempt to start the motor with the triggers switched.