96 merc 225 offshore series poor run condition

[fab9racing]

the proble i am having seems to be in my opion a fuel starving or timing issue, this thing will crank and idle fine when u first come off the trailer we have to go thru a nowake zone for about 10 min of ideling in gear motion then when u acclerate the boat for the first time it will take the throttle fine and after about 5 min at say 4500 rpm it starts an off and on surge not dropping cylinders but if feels like someting is retarding the timing up and down and you can stop the problem by moving the throttle either up in rpm or down it dont matter it just wont maintain a steady 4500 or even 5000 but step back or up just a little and it stops the surge,then when u are ready to stop u have to feather the throttle once it comes past 1200 rpm it feels like its straining to run and sometimes u can get by this spot but 1/2 the time it just dies and u think oh crap i have killed it then it will crank right up and idle fine but this time it wont take throttle if you put it in a bind the rpms will go to about 1200 and it feels like it is chokeing off and it will die then it will crank up fine, but when it gets at this point now i can hear a cylinder like detonation or misfire conditon but one is define backfiring behind the reeds if you squeeze the ball to check to see if its colapsing the ball the ball will be tight and everytime i hear the backfire i can feel the ball pulse back, now if u let it idle long enough with out trying to acclerate it will stop the mis and eventually u will get it to take throttle again and it will run with the surging problem at 4500 to 5500 or even 3500 but as soon as i stop again i have to repeat the ritual again to get it going, its never completley quit and not started, so far i have replaced the fuel ball,fuel filter,and fuel pump replaced the champion plugs with ngk and checked compression and its 125 across the board, was thinking about buying new crank sensor and some kinda sensor that is on the carb butterfly kinda reminds me of tps switch and if it has a temp sensor maybe that as well, any help or ideas will be appreciated

 

[sschefer]

Re: 96 merc 225 offshore series poor run condition

There are a couple of things that can cause the majority of your symptoms but since you mention detonation, then it's highly likely that you have water intrusion and it's likely on #4. Sometimes you can verify this by removing #4 plug and bringing #4 to the top of its stroke. You should be able to look at the top of the piston and notice that it is relatively clean compared to the others.

Another subtle symptom might be mild hydro locking where the engine sometimes feels like it's hesitating momentarily when you try to start it.

Here's how you might cure it.

The exhaust cover on the port side of the engine needs to be removed then the exhaust divider. The exhaust divider needs to be checked to see if it's flat and if not then it needs to be replaced. There are two different divider plates for these engines. If you need to replace it then make sure you replace it with the exact same one and make sure you order the gaskets for the correct divider by part number. Some gasket makers will send you a set for both plates make sure you read the instructions and use the right gasket for your plate.

It may sound complicated and difficult but this is actually a relatively easy job. Aside from waitng for parts the whole job can be done in about an hour. Less if you've done it before.

FYI, this is a very common problem on these 2+2 engines.

As a side note: A double firing coil can cause nearly the same symptoms but if you pull the plugs and look at the tops of the pistons and examine the plugs they will all look about the same. Hopefully you won't be as lucky as I was and have both problems. Nearly drove me nuts.

 

[fab9racing]

Re: 96 merc 225 offshore series poor run condition

thanks for your input, wouldnt the water intrusion thow cause the motor to try and hydrolock, it always cranks right back up fine and it dont spin over like its dragging a hole, update tho maybe some one knows this answer i was tinkering this weekend with the fuel enrichment valve and i noticed that when u first turn the power on there is a purple wire that goes positive, and since the yellow wire leads into the ecu could i presume that these motors have some kinda temp or rpm related ground system coming out of the ecm that triggers this fuel enrichment valve, with that being said i tried this i found that there was a yellow with black trace wire that was capped off, in testing it i found that that wire went positive when i pressed the choke button on the switch so i disconnected the purple wire that became hot when you turn the key on pluged the yellow an back wire in to the one that became hot when pushed for the swith, blocked the yellow and black lead coming from the ecm off and grounded the other side of the enrichment valve, now i can push in the button to activate the enrichment valve, havent been to the lake yet but it seems like the boat is ideling better, and i did notice that while in the factory wired system that when i unplugged the purple wire from the enrichment valve the idle would pick up 200 rpm.i am wondering if that was designed to be somekinda automatic type enrichment system for cold starts

 

[sschefer]

Re: 96 merc 225 offshore series poor run condition

Weird, I thought I posted that in response to another thread. It does not apply to a 225 it was in response to a 1999 100 2+2 problem. Disregard please unless you have a 100 also... LOL...:redface: