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350 Mag MPI mercruiser Inboard loading up at idle

"I have 2001 eng serial# 0L671

"I have 2001 eng serial# 0L671768 with 360 hrs.
Purchased Ski Centurion tournament inboard new.
Any reason why no mercruiser inboard category? Most of the time it has run rich at idle causing back of my boat to get heavy black residue. I took it in once and they said the fuel pressure was way high. It was ok for a few months and symptom returned. i have never taken it in since. Recently, I had a mechanic come to the house to try and resolve. My luck, the thermostat stuck open and motor would not warm-up. Mechanic fooled around with it like this for awhile and it was really smoking badly(running very rich). I went and got a thermostat, we replaced it and it was much better. took it for a spin and it ran fine. He told me to put some mercury quick cleen in it and drive it hard. Next time I drove it I did just that with seafoam in it. While on the sand bar my oil pan rusted thru! Fortuneately, the oil leaked out while I was stopped and alarm alerted me on startup. After pulling and replacing the pan all seemed good. I found the problem with my speed control(ground wire) and then ran out of gas reviewing the system with my wife. Right before it died I commented how it was idleing rough. I decided to change my fuel filter while out of gas. It was terrible. rust on the top of the filter and orange looking fuel inside. Now, it starts right up but idles rough. hesitates when u accelerate and then runs ok(except idling). When u slow back down to idle it is worse than when 1st started. I changed spark plugs and noticed 2 plugs were badly fouled(black soot). No water on the plugs. I checked cap n rotor and they looked very good. It is obviously not burning all the fuel being delivered. I can see it in the water and smoke when idling. Not burning any oil as far as dip stick is concerned. Any way I can verify this is simply an electrical or injector issue and not something more serious caused from the Oil pan leaking all my oil out? exhaust manifold on one side is getting hot when boat is run hard. I drained block and exhause manifold and then left these out one at a time on each side and I observed same amount of water coming out. I put a new impeller in and found and removed old impeller pieces from transmission cooler. No improvement. The black plugs came from that side of the engine. So I have 2 issues. one exhaust manifold getting too warm(temp on gauge is ok - 175) and the big one is the rough idle. It's weird, The RPM is a little low but not bad. When I open the cover the motor isn't shaking but the boat is. If I am out of the drivers seat it shakes. Never did that before. Sorry for the long winded description but I wanted you to have as much info as possible about what has happened. I have owned inboards for 25 years and know how to take care of them. I HATE taking them into the shop and have rarely had to do so."
 
"Sorry, don't know what DD

"Sorry, don't know what DDT or CDX are but assume they are diagnostic equipment. So you think I need to take into a shop at this point? I was going to run 15 gallons through it to see if the Mercury Quick cleen injector cleaner would help before I give up and take it in. would be a cheap fix. But if there is a possibility I could be damaging the engine further it's not worth it. There is definitely raw fuel coming out of one side of my exhaust. i can see it in the water when I back into the boathouse."
 
considering im a certified mer

considering im a certified merc tech
i would plug it in
sounds to me the fuel pressure reg is shot or a sticky injector
or even a faulty sensor
 
Thanks Justintime. I apprecia

Thanks Justintime. I appreciate you sharing your expertise with me. You may be right on with the fuel Pres. Reg. since I have always had a problem with it running rich at idle. Is the regulator difficult to replace? Is it visible(not internal)? Where is it located? It may be worth it to just change that out. Thanks again for taking your time on this site to help people out!
 
I have found the correct part

I have found the correct part and located it within the fuel cooler. I think I can change that out no problem. What about a sensor you mentioned? Where is located? There is a fuel related relay switch that is located on the port exhaust manifold. This is where my speed control is located and I have messed around there just before this happened. if that connection were broke could it cause system to just deliver wide open fuel? This would really make alot of sense for the sudden change. Thanks so much for your advise!
 
"I'm in Milton Florida - n

"I'm in Milton Florida - near Pensacola Florida on BlackWater River. Checked and all connections located at the port exhaust manifold look good. However! while going thru that process I started checking the connections at the injectors. One of them was loose(wiggled up and down) where others did not. I wiggled it somemore and it broke off. Damn! I think I just messed it up. It was connected. Anyway I went ahead and ordered the injector and regulator from marineEngine.com. Anything I need to do before removing injector? release fuel pressure, etc.? Regulator looks like it just connects to throttle body vaccuum or fuel overflow return so should not be an issue?"
 
I removed the broken piece fro

I removed the broken piece from the injector connector taped it off with electrical tape and took the boat for a quick spin. It runs the same as it did before. I cannot really notice a difference. So my question is: Is it ok to use until I get the new injector and replace it?
For all I know it wasn't working before I broke it off. I just want to make sure I'm not going to damage the engine is some way I'm not aware of. Thanks!
 
"Guys:

I apologize. I am ne


"Guys:

I apologize. I am new to the site and have a different question regarding my 350 Magnum Inboard on my 310 SeaRay. I just replaced my port engine and it now has 40 hours on it. Ran great until last week. Now it will not hold RPMs. (Motor's RPM flutters and the synch gauge moves back and forth with the port engine surge. Temp is ok. Motor will surge under a load going from minimal throttle to full throttle unless I pull it back. I have to add throttle to get it to keep up with the starboard eng above 3,000 rpm but it is steady @ 2,000 RPMs or less. Do you think it is a fuel concern although same fuel for both tanks and the starboard engine runs porperly. Thanks again for taking time to reply. plb."
 
"Tim:

Sorry to have entered


"Tim:

Sorry to have entered my concern on your page. I am new to this.

I would like an e-mail or fax of the trouble shooting section. [email protected] or 904-565-7934. Thanks for your help Tim."
 
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