Raw Fuel coming out of the exhaust

[PicoPico]

Hi, I have a mercruiser 7.4 MPI EFI 1999, after changing manifolds, spark plugs, gaskets, cleaning the inyectors, etc (overall service). one of the engines passes fuel directly to the exhaust, the engine does not misfire and seems to run very well, but when i get to destination I leave a massive spillage of fuel in the water, in fact , at minimun you can see the fuel poping out in patches, what could tha be?

 

[gnealon]

Are you sure that it's not your trim tab actuators leaking? I had this issue with my old 280DA, it looked like fuel in the water, but it was in fact the trim fluid. Even without using the tabs, I still had leakage.

I agree... had same issue on my 280 da. Looks just like fuel... it wasn't until my drive stopped going up did I realize. Good luck

Sent from my ADR6300 using Tapatalk

 

[PicoPico]

Are you sure that it's not your trim tab actuators leaking? I had this issue with my old 280DA, it looked like fuel in the water, but it was in fact the trim fluid. Even without using the tabs, I still had leakage.

Thanks Scott, we did have the same leakage from the trim tab and solved it, but funny, I had both issues, I now have only the fuel problem and it is definetly fuel as you can smell it.

 

[AKBASSKING]

Is all cylinders firing? If you have raw fuel coming out of the exhausts, then it isn't all being burned. Fouled spark plug?

 

[PlayDate]

The fast answer is to pull the plugs on that engine and see which one(s) have fuel on them. I am very suspicious of the "cleaning of the injectors" and how they did it.

Normally "stuck" injectors cause the engine to have a noticable miss. A "partially leaking" injector could cause the problem you describe because it would be leaking fuel during the exhaust stroke which would show up as individual fuel patches on the water.

-John

 

[gregkjones]

My right engine suddenly developed this problem last summer. I looked at everything I could but all seemed fine. With all the computer stuff on engines now, fuel metering and airflow sensors; I dont have the right merc software to read the engine codes and whatnot. So I called a mechanic hoping it wasnt a bad cylinder or something else terminal. Mechanic hooked up the computer and all was good, no codes, except that fuel flow was about 5 times higher than it should be. Amazingly the engine was running fine but the raw fuel and blue smoke was present.

Now I dont know what this part was, but it was a silver cylindrical looking doodad right under/next to the distributor. It has a couple vacuum lines coming out of it. I had mentioned to the mechanic that one of those lines had fallen off earlier. It was the line that runs down to the fuel pump/cooler. Even though I reconnected it, the silver thing (whatever it is) was stuck. He disconnected the line and blew into it and then sucked a few times and heard a click. Started up the engine and the fuel flow dropped dramatically and no more raw fuel out the exhaust. Didnt even replace the part, it has never done it again. Mechanic said the line was probably off for awhile and the part just got stuck from lack of cycling for so long apparantly. The blue smoke was instantly cured as well, and the reason for it the mechanic explained, was that with all the extra fuel, it was striping oil off the cylinder walls. In 10 minutes the fuel flow was perfect, no blue smoke and engine running perfect. I am usually curious, so I dont know why I didnt ask him what the part was called but I was just so relieved that it wasnt a blown engine that I think I went into a daze for a while. I can call and ask him if you want to know what it is.

 

[PicoPico]

Thanks John,

The mechanic has taken the injectors out once again for another look, I will take her out this weekend so i will keep you posted on the outcome.

PicoPico

The fast answer is to pull the plugs on that engine and see which one(s) have fuel on them. I am very suspicious of the "cleaning of the injectors" and how they did it.

Normally "stuck" injectors cause the engine to have a noticable miss. A "partially leaking" injector could cause the problem you describe because it would be leaking fuel during the exhaust stroke which would show up as individual fuel patches on the water.

-John

 

[PicoPico]

Great point greg,

I know the lines you refer to, in deed we conected those back on as they were not properly attached the first time, the thing the mechanic did not do was to blow the line to ensure it was working properly, I will definetly mention it to him this weekend.

great tip!

g

My right engine suddenly developed this problem last summer. I looked at everything I could but all seemed fine. With all the computer stuff on engines now, fuel metering and airflow sensors; I dont have the right merc software to read the engine codes and whatnot. So I called a mechanic hoping it wasnt a bad cylinder or something else terminal. Mechanic hooked up the computer and all was good, no codes, except that fuel flow was about 5 times higher than it should be. Amazingly the engine was running fine but the raw fuel and blue smoke was present.

Now I dont know what this part was, but it was a silver cylindrical looking doodad right under/next to the distributor. It has a couple vacuum lines coming out of it. I had mentioned to the mechanic that one of those lines had fallen off earlier. It was the line that runs down to the fuel pump/cooler. Even though I reconnected it, the silver thing (whatever it is) was stuck. He disconnected the line and blew into it and then sucked a few times and heard a click. Started up the engine and the fuel flow dropped dramatically and no more raw fuel out the exhaust. Didnt even replace the part, it has never done it again. Mechanic said the line was probably off for awhile and the part just got stuck from lack of cycling for so long apparantly. The blue smoke was instantly cured as well, and the reason for it the mechanic explained, was that with all the extra fuel, it was striping oil off the cylinder walls. In 10 minutes the fuel flow was perfect, no blue smoke and engine running perfect. I am usually curious, so I dont know why I didnt ask him what the part was called but I was just so relieved that it wasnt a blown engine that I think I went into a daze for a while. I can call and ask him if you want to know what it is.

 

[PicoPico]

Hi Guys,

I finally went to the marina this weekend and took her out, thanksfully NO more fuel coming out of the stern drive, the mechanic said that the fuel injectors were all ok and also tried blowing the vacum line, so it all pointed that the fuel was not fuel after all, it was the trim oil from the trim hose that was a bit lose, so you guys had it spot on!
Many thanks.
PicoPico

Great point greg,

I know the lines you refer to, in deed we conected those back on as they were not properly attached the first time, the thing the mechanic did not do was to blow the line to ensure it was working properly, I will definetly mention it to him this weekend.

great tip!

g