Running with 1 plug wire off???

[timmytes]

I'm trying to troubleshoot my engine. its a 1999 125 merc. classic. it starts fine, idles great, and for the most part, runs finie on high end. after it warms up and while running around 3500-4000 rpm, it will miss when you hit heavy chop. Can i pull off a plug wire, one at a time, to see if i can isolate a single cylinder that is missing. will the boat get up on a plane only running on 3 of the 4 cylinders??? If i can pinpoint which one is missing, it will help to troubleshoot the problem!!<br /><br />thanks

 

[WillyBWright]

Re: Running with 1 plug wire off???

This would work much better. Connect an inductive pickup timing light to each plug wire (one at a time) and run the motor. As long as the light is flashing, that sparkplug is firing. You can see misfiring and non-firing cylinders as you're running this way. Running with the plug lead removed can damage the CDM.

 

[timmytes]

Re: Running with 1 plug wire off???

would that work even if the miss is for about 1 second. it will miss, then run fine for a little, then miss again whe you hit chop. if it missed on a cylinder for a brief second, would you be able to see it with that device your talkin about??

 

[fatpratt1996]

Re: Running with 1 plug wire off???

Do you have any loose wires on that motor that would cause the speratic misses when in choppy water? Just a thought

 

[timmytes]

Re: Running with 1 plug wire off???

none, been through it over and over. i'm at the point where i just need to start replacing components in the ignition system. what would you recommend first. idon't know what else to do!!!

 

[Barnacle_Bill]

Re: Running with 1 plug wire off???

Something is loose somewhere or, you can try diconnecting the mercury kill switch on the motor and see if that solves your problem. In case you are not familiar with it, it is the little mercury activated switch that keeps you from starting the motor when it is tilted up. If they haven't changed the color code on your new engine the wire going to it is black/yellow.

 

[WillyBWright]

Re: Running with 1 plug wire off???

You can see if the cylinder isn't firing by the lack of a flash, even for a second. You can see it on the timing light and hear it on the motor, especially when it kicks back in. You might also want to check for water in the fuel. I'm not sure they used mercury switches on the 4-cylinder models, but they certainly did on the older inline sixes.