Had new ecm's put in last weekend, no more black soot. NONE! It is finally clean after a run. Not sure about performance though, didn't really open it up.
Midrange punch seemed to be improved. My tech seemed to think there would be an increase in performance.

Rippem
Only problem i had on the mag was SOOT..Which cleaned up considerable after 50 hrs..Oil did get black rite away and was changed..After ecm swap no soot at all..Dealer said merc told them the problem was only on mag not HOs, I gues we know better..

Mine is much better since the change. I still had some soot after 3 days of running but compared to what was there before it was nothing. No performance change other than the fact that it was 20 degrees cooler than the last 2 weeks. I suppose that could have helped the soot as well.

Had the same soot problem on my 02' 496 mag. Called Merc and was told to take it to a dealer and they would send it in for reprogramming. Went to a local dealer who had not heard of the problem. They called Merc and a new PCM was sent out that day.
Date on new PCM is 8/29/2003. Part # 865364-001.
Time will tell if it helped the soot problem and what it did (if anything) to performance.
Anyone seen a service bulletin on this?

I was told there was NO service bulletin or recall of any kind...Thanks to this site we were able to get Merc to fix..

Is anybody other than merc doing this?


I know its a 4 yr old thread, but Im getting tired of cleaning now.

I've got an '02 496HO that still soots up the transom big time! I have a Raylar BCK103 kit on it with Whipple's Stage II ECU calibrations. Had hoped that Whipple's calibrations would take care of the soot problem, but no luck. I think they will do custom ECU programs (for a price) you could try them. I've also looked into Arizona Speed and Marine (they offer ECU programming also), but don't know much about them. I would love to lose the soot, but I don't want to risk leaning out the engine - it's running great and the spark plugs look good.

Were the only ones that can work with the PCM 555 on the Mercury engines. It's pretty hard to totally remove the soot, especially on some boats. We run 14:1 air fuel, far more spark and coil energy, yet it will still be there. Our Stage1 has less soot than stage 2 because it's lower hp and not as agressive for power.

Dustin

Dustin,
Can engine operating temperature affect how much soot is produced? I have a low temp thermostat (engine runs around 140 most of the time), I have been told that it might be too cool and the computer is going into "cold start enrichment mode" - causing some of the soot. What do you think? - Thanks.

Lower temp will typically increase soot, but also allows for more timing/compression which typically makes more power. The computer has temperature enrichment decayed out based off of time running and temp. Therefore, at 140deg F, even after firing, it only gives a small amount of fuel for a few seconds. At 60, it gives more fuel for longer periods. Thats is certainly not an issue. If it runs 160-180, it will have slightly less soot, but will be much closer to detonation, and if it detonates, it will use more fuel, as it uses fuel to try and stop detonation, along with timing retard. Now this does totally depend on how the driver drives the boat. If your running hard, the engine needs to run richer or closer to ideal AF for peak power and to keep cylinder temps down. If you cruise a lot, or have a boat that doesn't require lots of power to stay on plane/cruise, then it would be leaner and potentially have less soot.

Thanks,
Dustin