Engine Trouble... anyone got any ideas??

[salvagefirst]

i thought mine was a fuel problem,my black max would start skipping ,sputtering wouldnt idle. went through everything your doing, than i went through the electrical. Replaced the stator, crank trigger, finally i replaced both cd boxes( they have to be replaced as a set) and that cured the problem. Les

[CaptScottNC]

finally i replaced both cd boxes( they have to be replaced as a set) and that cured the problem. Les

CD boxes? Go by another name? not that familiar with Mercs or outboards in general but I'm sure learning a lot day to day. The shaking of the boat making the engine die is what's really bothering me.

[salvagefirst]

Hate to say it but it is starting to sound more and more electrical. check your grounds especialy the grounding areas where the cd boxes ground to the block. A weak set of batteries or jump starting a merc will screw up a cd box faster than anything. The merc shop manual says fuel systems are the most often blamed but least likely to fix the problem. Les

[CaptScottNC]

What exactly are the CD boxes? and What is the best way to rule out the CD boxes and trouble shoot those? I don't yet have my manual for working on this engine to take me through the trouble shooting steps. Going to try and find one today.

Thanks everyone.

[CaptScottNC]

OK... Have a little more information. All cylinder are sparking although some appear to be sparking "weakly" and not near as strong as the others. All of this is at idle on the hose. I put a screwdriver in the plug wires and checked for the arc to the engine block or spark plug top. I will try and show a text diagram of the results unplugging each wire had on the engine idling. I unplugged each one at a time and recorded the change. This is from top to bottom if you were looking at the back of the engine.

Port Cylinders

Moderate change

No change or
maybe very little

BIG change

Starboard Cylinders

No Change

BIG change

Moderate change


Ok.. now what do you make out of this? Also, All plug wires zap me if I unplug them at idle by hand even through the insulation except for the middle port cylinder and the top starboard cylinder wires.

Electrical problems are so much fun. I hope to fix this today if I can figure out where to go next.

[CaptScottNC]

OK..another update. Just switched CDM from the number 1 cylinder that was so weak and had no change when pulling the wire and swapped it with the CDM from the number 3 cylinder just below it. The spark was stronger on the #1 cylinder but it still had no change when I pulled the wire on the engine idling. The spark was not as strong from the CDM I put on #3 but still had a significant impact when I pulled the wire and it ran rough. Is it possibly the #3 cylinder is just more "vital" for idling then the #1 and I still could have a faulty CDM??

I did not switch the CDM from #4 and #6 yet but I suspect I will have the same results. What is upstream from the CDM that I have to check?? and how do I troubleshoot that? or is it still possibly a CDM problem?

[salvagefirst]

the cd boxes are on the starboard side, they are stacked together one on top of the other, lots of wires going to them . some merc dealers say they have a tester to check them but most just replace both boxes then test the motor in the water.This is usually the first thing they do because they are 90% of the electrical problems on a merc. also look at the stator, it is located under the flywheel, you can see the bottem of it between the flywheel and the block , look for any spots that have got hot , the paint burnt off, or black tar hanging down. the stator is your charging circuit, low and high speed windings. most of the wiring along with the crank trigger wiring and other block sensers goes to the cd boxes wich control the firing of the coils. Remember if you replace a cd box you need to replace both as a set because a new one will usually burn out the older one. There is also the chance of a damaged flywheel or crank trigger that might of gotten damaged during impact. Les

[Bigshrimpin]

"CD boxes? Go by another name?"

I've always heard these refered to as "switch boxes"

[salvagefirst]

Bigshrimpin,your right, switchboxes in a CDI system. Les

[salvagefirst]

Capt Scott heres 2 great web sites with troubleshooting help outboardparts.com has the best prices and quick shipping and maxrules.com has the best troubleshooting info. Les