Mercury 280 Missing/Fault Issue

[rankink]

Had a recent issue with my low hour 280 which I had not encountered before and was hoping for insight on what it might be. ROS ECU on stock electronics

On cylinders 2-4-6 I could feel the engine missing. Checked the plugs and you can see below the brown soot all over #6 piston. Engine was running fine (3500-5000 rpm run) before this with good temp, good fuel pressure, no other faults on the DDT. Plugs were new as well. EGTs dropped on the 2-4-6 bank vs. 1-3-5 bank with this issue too.

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Below are the 6-4-2 plugs (#6 on left) and as you can see the same brown soot on the plug very heavy causing it to miss and an ignition fault on the DDT.
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[stoneman]

It looks like water intrusion on #6

Have you run a compression test?

[rankink]

It looks like water intrusion on #6

Have you run a compression test?


This was one of my fears and doing a comp test tomorrow. I did change the o-ring gaskets when I opened up the heads and this one was broken when it came out.

[kellytheaker]

I have posted info on this before - not the water intrusion but on the DDT - FAULT - miss . Of course do your initial compression checks and such but look into your history on the DDT and see if the frequency of miss is showing a fault - usually on the face of the DDT it will light red but further investigation it will show a miss frequency .
The coils can go bad after even low hours but having 20 year old coils s..
if left it will take down the ECM and it can be sent to Simon Motorsports. So that's what I know and have found if compression check is good and water intrusion is okay as well . The DDT is a great tool and make sure the plugs are correct as well. I don't have that info in front of me so use the search . It's your friend as well .
Hope this helps sir

[rankink]

Thanks for the input. To be clear, stock 280 electronics with ROS ECU. The DDT history has been good (as in no faults) for a while and this just came up last time out. (I will check further into the readings per your suggestions). Coils are always a concern, and have others to switch out as well. I have a second ROS ECU that i can always switch out as well. Plugs are correct as well.

[kellytheaker]

Good - you have spares . I thought you had seen a history in the DDT . So back to your basics - compression and water intrusion . You seem to have the tools - DDT is a great companion as well as the spares . You can't do any better other than asking here about frequency of known owners and their experience with their 280 s . Your on the right track sir - always know the TPS is set at the correct setting. And that the fuel setting and what it's set at - hopefully you have the DDT manual so your useing it to its full potential but it can be learned easilly on how to get to the histories of certain parameters with ease .
All I was saying initially was a history check on the coils/ miss frequency usually means a coil is going and will wreak havoc with a driver in the ECU and overheat a pot and will need looked at and fixed by Simon . Which was my issue and did take the ECU down . You did mention a bad oring on the head so continue on that basic .