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Cant figure out 3.0 181 Merc with dst still misfiring

mateoaba

New member
i recently took my boat out (1997 maxum 1900 sr with the 3.0 4 cyl) out on the water everything was running just fine and no issues then boat fell on its face out of nowhere under WOT and kept misfiring/ pinging and wouldn’t run past 1800 or so rpm. let the boat sit start it and is just fine. went out one more time had no issue then same issue pops back up again, i’m stumped since boat runs just fine on all other occasions
 
If this has electronic ignition, my thoughts are,
1. Distributor gear roll pin broke causing loss of timing causing miss fire and loss of timing advance. Have to pull distributor to confirm.

2. Timing belt/chain went south causing similar to above.

3. Ignition control module failed causing all of the above..
 
how long have you had it??? who winterized it last fall??
i winterized it fogged carb along with cylinder walls, antifreeze in the block, wrapped up in shrink wrap and stored inside a garage, have had the boat for five years just yesterday did new cap, plugs, plug wires and coil. tried it out again did the same thing and idling back to the dock started running just fine again no misfire.
 
If this has electronic ignition, my thoughts are,
1. Distributor gear roll pin broke causing loss of timing causing miss fire and loss of timing advance. Have to pull distributor to confirm.

2. Timing belt/chain went south causing similar to above.

3. Ignition control module failed causing all of the above..
i’m really stumped i could see those being the cause but when on dry land not under load will idle all day no problem, go thru the entire rpm range, moment it’s put under a load starts to miss
 
Temporarely disconnect the shift intrruptor switch. That shorts ign to ground and if faulty may be doing so intermittenly
 
Temporarely disconnect the shift intrruptor switch. That shorts ign to ground and if faulty may be doing so intermittenly
will definitely look more into the ignition system, just been very confused on where to look since the engine runs just fine on land and for all about 10-15 min or even two hours then starts to miss and in some cases when doing back will just randomly stop missing
 
You seem to be looking for the easy answer. There may be NO easy answer without some troubleshooting, doing things and presenting the feed back here so we can review.

Unplug any connectors and blow out, Maybe add a little dielctric grease and reconnect-Maybe a intermitten contact on a pin

What ignition do you have? Points or electronic? If electronic which one?
Whats your plug type/number and gap?
Do you have a timing light? If so hook it up and see what the timing looks like at different rpm and if its steady or erratic.

WHat parts did you purchase for replacement? OEM Mercruiser or aftermarket?

The condition you describe sound like a timing malfunction of some kind but also could be coil/distributor related. hard to tell from a keyboard.

Also running good and then bad and then good ONLY while in the water under load could also be fuel related. Possibly the fuel tank pick is getting clogged intermittenly which could appear to be an ignition problem but really its your running out of fuel. You would need to pull the sender off the tank and look with a flash light to see if there may be something floating near the bottom. This issue would not be the first ime for this to be a cause of running issues.

Anyway there are some more suggestion and needed feedback from you.

Remember, Details and complete information helps as well as a good description which you did good with. now need more.
 
might be worth investing in a spark tester or a timing light, mine will vapor lock on a hot day, and run kind of like you describe under load until it gets its self worked through it, if you can check for good spark then it is a cam/valve train/fuel/?? issue. hows the oil pressure? could it be collapsing lifters? have the valves been adjusted? might be out a little and floating at rpm but not evident until under load, timing advance coming it or sticking at rpm? choke all the way open?
 
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