Mercruiser 3.0 issues

[countryboy26047]

Hi all... been a long time since I've been around, but haven't had a boat on the water in a few years either... anyhow, I just recently purchased a 1985 Citation 19' open-bow with a mercruiser 3.0 I/O. I know it's an older boat, but the thing looks great and up until my trip before last, it ran great too... after our second trip out with it, I decided to fix the gas gauge that was not working when I bought it... found out that it was the resistor spring inside the tank that was stuck.. I pulled the assembly and cleaned it up and the gauge started working.. At this same time, I also pulled the plugs and checked/cleaned them as well as pulling the dist. cap to check the contacts. I should add here that the previous owner installed an electronic ignition conversion to the motor. Anyhow, the very next trip out as well as the trip after that, it ran great for the first 15-20min running around 2500-3000 rpm's at a fast cruise speed... all once everything is warmed up, it starts to misfire, and eventually backfires through the carb and dies and won't restart until everything cools off... Today, after replacing the plugs, wires, dist. cap, coil, fuel filters, and removing, stripping and cleaning the entire carb as well as adding dry-gas and a dose of sta-bil 360 marine, I thought I got it worked out as it was running great the entire time in the driveway... however, once I put the dogbox back on, about 10min later it started acting up again. It acts as though it's something externally getting hot as it didn't act up as long as I had that air movement with the dog-box off.. I talked to a guy I know that works on them and he said sounds like it could be the ignition module, however I can't locate it on my motor.. Also, just another little thing I discovered was a small pool of oil inside the distributor after I removed the cap and plate. Any advice would be greatly appreciated!

 

[alldodge]

Hi all... been a long time since I've been around, but haven't had a boat on the water in a few years either... anyhow, I just recently purchased a 1985 Citation 19' open-bow with a mercruiser 3.0 I/O. I know it's an older boat, but the thing looks great and up until my trip before last, it ran great too... after our second trip out with it, I decided to fix the gas gauge that was not working when I bought it... found out that it was the resistor spring inside the tank that was stuck.. I pulled the assembly and cleaned it up and the gauge started working.. At this same time, I also pulled the plugs and checked/cleaned them as well as pulling the dist. cap to check the contacts. I should add here that the previous owner installed an electronic ignition conversion to the motor. Anyhow, the very next trip out as well as the trip after that, it ran great for the first 15-20min running around 2500-3000 rpm's at a fast cruise speed... all once everything is warmed up, it starts to misfire, and eventually backfires through the carb and dies and won't restart until everything cools off... Today, after replacing the plugs, wires, dist. cap, coil, fuel filters, and removing, stripping and cleaning the entire carb as well as adding dry-gas and a dose of sta-bil 360 marine, I thought I got it worked out as it was running great the entire time in the driveway... however, once I put the dogbox back on, about 10min later it started acting up again. It acts as though it's something externally getting hot as it didn't act up as long as I had that air movement with the dog-box off.. I talked to a guy I know that works on them and he said sounds like it could be the ignition module, however I can't locate it on my motor.. Also, just another little thing I discovered was a small pool of oil inside the distributor after I removed the cap and plate. Any advice would be greatly appreciated!

:welcome: back

What kind of ignition system is installed?

 

[countryboy26047]

Not sure honestly but the coil that's on it is a flamethrower II all I know is its an electronic ignition lol.

 

[alldodge]

Not sure honestly but the coil that's on it is a flamethrower II all I know is its an electronic ignition lol.

Sounds like you have the Petronix ignition system. Here is a link

http://www.pertronix.com/support/tips/default.aspx

These things work great until they don't then there is very little help to figure out what is the problem. Need to find out if you have the igniter , igniter II or igniter III

 

[countryboy26047]

Thanks buddy.. I have the igniter II inside the distributor... I've been thinking about this and is it possible that heat isn't necessarily the culprit, but rather the oil I found in the distributor? I'm wondering now if instead of it being heat related, if it's actually the time it's taking for more and more oil to build up inside the distributor base, causing the timing advance to not function properly or make the proper contact? Again, I'm fairly confident in my mechanical knowledge, but this is my first experience messing with an I/O boat engine, and granted they are a standard automotive engine per-say, there are obviously differences in how they operate. Thanks again for the help as my forehead can't take much more pounding on the concrete lmao

 

[alldodge]

Don't think it would be oil unless the distributer is getting soaked inside. The marine distributer uses mechanical fly weights to advance timing, no vacuum. You know we keep looking at an electrical issue when it might be fuel. If an engine runs lean it will back fire and cough. Running for a while on a hose in most cases doesn't cause this but its worth looking into. Do you have a vacuum fuel pump pressure gauge to test pressure? It should be 4 to 7 psi.

Could also be a dirty fuel filter, bad gas, restriction

 

[countryboy26047]

No I don't have a pressure gauge to test it.. I did find that bad fuel filter in the pump and got it changed and while it did help some, it didn't clear it up. The reason I keep going towards electrical is because it runs beautiful for the first 15-20 min or so then all hell breaks loose lol. One thing to note is that the day before this issue arose, I did have the fuel sending unit out of the tank because the gauge wasn't working. I also messed around with wiring under the dash to trouble shoot the gauge issue. And to top it off, I adjusted the idle as it was idling very low when I got it, and I accidentally adjusted the wrong screw (adjusted the screw on the right side of the carb at the base which I guess is an air/fuel mixture screw?) Is it possible that something may have gotten shaken around in the tank and got into the pickup line? I've considered that but I was thinking if that was the case, it would cause a consistent problem rather than only happening after a good warmup but I've been known to be wrong before, just ask my wife! lmao

 

[alldodge]

Running good for 15 to 20 is long enough for a worn pump to start giving up, choke starts opening up, starts to lean out. You could also have a filter or screen behind the carb inlet fitting, would need a engine serial number to verify.

The air mixer screw is at the base, and crud in a tank clogs filters quite often.

 

[countryboy26047]

Well, whenever I pulled the carb apart to clean it all up I did check the "inline" filter on the input of the carb and it was good. I guess my next coarse of action is to find a pressure gauge to check the fuel pressure. Just seems so odd that this all started the very first trip out after I messed with all that crap but I am the king of coincidence I guess lol

 

[alldodge]

The good thing is they only cost around $20 and you can also use it to adjust the air/fuel mix buy looking at the vacuum side.
http://www.harborfreight.com/fuel-pump-and-vacuum-tester-93547.html

As before it still may be electrical but a couple items are causing me to rethink the issue

 

[countryboy26047]

I'll definitely check into getting one of those.. either that or I'm thinking just buying a pressure gauge to put in-line permanently.