Help With DDIS ignition

[jnk111]

91 mercruiser 3.0LX


I was getting gas in the oil, a rather large amount. After searching the forum it seemed to point to the fuel pump. I replaced that, all seems OK now with that anyway. I replaced the plugs last week because of fouling, they were black and wet. That leads me to this.

New plugs in #1 and #4 were black, #2 and #3 were just like new. This was with only about 15 minutes running on muffs. I hooked a timing light up to each plug wire to check for spark. #1 and #3 had a consistent flash, #2 and #4 seemed to flash twice as much as the other two. What would cause this or is it normal with the DDIS ignition?

Compression was also tested all four were right around 165 (warm).


Thanks

 

[Maclin]

Re: Help With DDIS ignition

I do not know if that is normal for DDIS but that is usually an indication of spark being picked up by induction, can happen if two wires run real close to each other for a long distance. It can also be arcing within the cap, or across wires on top of the cap. If you can run it at night you may be able to see arcing. If it is arcing within the cap then once the arc has been established then that path wil be there forever, stealing some of the energy from the plug that needs it.

 

[Maclin]

Re: Help With DDIS ignition

Maybe DDIS does not even have a cap! But the arcing can happen with bad boots in any system.

 

[jnk111]

Re: Help With DDIS ignition

Yeah, there is no distributor cap in the DDIS system. The boat runs good, a little rough when cold though. I can run 45mph at 4400 rpm GPS verified, its a 17' sea ray open bow. It really doesn't seem to be missing, that is what is perplexing about it.

My theory was that the gas was thinning out the oil and allowing to get past the rings. That would account for the wet, black plugs. The "double" firing (the best way I can describe it) does however seem to be in line with the firing order. 1-3-4-2.