Intermittant engine miss?

[MARKM3144]

I have a 1995 Merc 225 carbed motor which has developed a intermittant miss.While running back in this past weekend it would run fine for about 10 miles and then start to miss and then run fine again, it did this for 35 miles. It sounded like a electrical problems.Any suggestions on where to start.I did notice a black carbon ring on the porclin around the edge of the boot on one of the plugs.

 

[dilligafda]

Re: Intermittant engine miss?

"I did notice a black carbon ring on the porclin around the edge of the boot on one of the plugs. "<br /><br />Carbon ring or tracking? Either way it sounds like a set of plugs and wires would be a good start. Give that a shot and keep us informed.<br /><br />Good luck!

 

[MARKM3144]

Re: Intermittant engine miss?

I went out last night to start motor put on the muffs but to no avail. It started ran rough for about one minute then died right away and would not start again.I am going to check with 50-1 mix in a spray bottle to see if it is fuel flow and also check for spark tonight. New plug wires are on the way but wont be here till the end of the week.Any sugestions?

 

[MARKM3144]

Re: Intermittant engine miss?

Checked for fuel flow last night and fuel flow after fuel pump looked good. Tried to start it one more time no luck. I sprayed a few squirts of 50/1 in the carbs just in case. No positive results.Turns over great but no fire at the plugs Sounds the same as When you forget the lanyard safty switch.I am going to get a spark plug gap tester this afternoon and check for spark but im sure there is no spark.

 

[MARKM3144]

Re: Intermittant engine miss?

Ok I think I found the problem. Merc techs let me know what you think please.<br /> Went and bought a spark gap tester waited till it got dark and started. I first tested the compression and it was fine 115 on 4 cylinders and 120 on 2 cylinders.I then tested all cylinders<br />with the spark gap tester set at 7/16" and all had spark except #5 so I decided to switch<br />the #5CDM and the #3CDM. When I removed the #5CDM the ground wire was so corroded there was no contact with the ground on bottom screw.The copper ground wire was also solid black instead of copper color. I put a new wire connector on the ground and switched it with #3.when I retested there was spark on #5CDM but not on #3CDM. I did realize that about two months ago I had to change the popett valve because of a leak in the diaphram.It is located within inches of the ground screw of the #5CDM.I would guess that this is why it corroded since I only use my boat in salt water.Anyway would lossing ground destroy the CDM or would it be something else? I will order a new CDM in the morning.Anybody feel that this is the correct diagnoses? The black carbon ring I mentioned earlier was on the #5 plug also.

 

[MARKM3144]

Re: Intermittant engine miss?

Anyone??

 

[KCLOST]

Re: Intermittant engine miss?

So based on your test. You regained spark on #5 CDM after moving it? And #3 lost spark....<br /><br />This doesn't sound like a coil problem... It's probably a ECU issue.... (or switchbox)...<br /><br />Your electrical feed into the coil is what is faulty, not the coil itself (based on your test). I would rule out the CDM, unless the ground lead is bad or you have no ground at all for the #3 cdm after you moved it...

 

[MARKM3144]

Re: Intermittant engine miss?

KCLOST <br />1.I found that there was no spark to #5 plug.<br />2.All other cyl had good spark.<br />3.I removed the #3cdm which had spark and installed it on the #5 harness and installed the #5cdm on the #3harness.I flip-flopped them.<br />4.Now the #3 cylinder did not have spark and the #5 had spark<br />I would think that the #5cdm would be the problem?

 

[KCLOST]

Re: Intermittant engine miss?

Ok, that's a much better description...<br /><br />CDM is at fault, not the ECU....

 

[MARKM3144]

Re: Intermittant engine miss?

Sorry about the previous confusing post it did sound like I just reversed #3 & #5 wires only. Sorry And thanks for the response

 

[MARKM3144]

Re: Intermittant engine miss?

Replaced suspected bad CDM this afternoon And noticed that the potting was seperated from housung on the #5 CDM after it was removed. After installation Motor fired up like it was brand new.I inspected the other CDM's and noticed that there are two others that show slight seperation.They are expensive but cannot afford to loose one 30 miles out.They will be replaced next week!!