2004 Mercury 75hp running on only cylinders 2 and 3

[baero]

Hey guys, I am knew to the forum and it looks like you guys know your stuff.

My father's 2004 75hp 4-stroke carb is only running on cylinders 2 and 3, we have ruled out the coil and ignition module. It sounds like it is an oil pressure issue by reading outher posts. However other people are getting a beeping and we are not getting any kind of signal and the rpms are not limited to 2000 RPMS.

Is it only the EFIs that beep and limit RPMS? Also, how hard is it to get at the oil sending unit?

Thanks for any replies and I will also complete this thread when the problem is corrected.

Thanks

 

[Silvertip]

Re: 2004 Mercury 75hp running on only cylinders 2 and 3

What oil pressure? If it were an oil "injection" issue it would affect all cylinders, not just one. How did you check spark? Have you squirted a fuel /oil mix in the carb for #1 cylinder to see if it picks up. If it does, rebuild carb #1 (and #2 and #3 as well since you are in the area). Have you actually pulled the plugs and compared them. How does #1 look compared with #2 and #3? Wet, dry, black, carboned, T-shirt white or ???? And just to make sure you actually have compression on that cylinder, have you checked compression and if so, what was the reading? And how did it compare with #2 and #3.

 

[baero]

Re: 2004 Mercury 75hp running on only cylinders 2 and 3

Answers in RED

What oil pressure? If it were an oil "injection" issue it would affect all cylinders, not just one.

Sorry, it is a 4 cylinder and 1 and 4 run off the same coil. The reason I ask this is that I have seen other responses that the motor will go into safe mode by shutting off cylinders 1 and 4, the same issue we have.

How did you check spark?

With a spark tester. We also have swapped coils and tried a second ICU

Have you squirted a fuel /oil mix in the carb for #1 cylinder to see if it picks up. If it does, rebuild carb #1 (and #2 and #3 as well since you are in the area.

Yes we have sprayed fuel/oil into cylinders 1 and 4 and the system does not pick up.

Have you actually pulled the plugs and compared them. How does #1 look compared with #2 and #3? Wet, dry, black, carboned, T-shirt white or ????

Yes we have, number 2 and 3 are brown, while 1 and 4 are black.

And just to make sure you actually have compression on that cylinder, have you checked compression and if so, what was the reading? And how did it compare with #2 and #3.

We have not checked compression yet.

 

[snapperman-nz]

Re: 2004 Mercury 75hp running on only cylinders 2 and 3

Hi there, once you have established the compression is OK. Get the carbis balanced. This is really done by a tech as they have the guages to setup and make sure the airflow and fuel is balanced between all carbs. This is critical for smooth operation. Is the motor running on all four carbs when the revs are increased?, if so the idle/primary circuits on those carbis are most likely blocked.

good luck

 

[Silvertip]

Re: 2004 Mercury 75hp running on only cylinders 2 and 3

OK -- the 75HP 3-cyl threw me off track and I missed the 4-stroke so I apologize for the "What oil pressure" comment. The two cylinders not firing appears electrical since adding fuel via the carbs does not pick things up. I don't understand, however, how you can have spark, add fuel and have no power unless something in the valve train is broken but that would show up in a compression test. That would be the next check. And spark should jump a 7/16 gap with a good snap so anythng less is not good spark. Have you replaced those plugs? Fouled plugs will not fire.

 

[baero]

Re: 2004 Mercury 75hp running on only cylinders 2 and 3

No problem,

When I said we checked for spark, I was implying that there was none on the 1 and 4 cylinder which lead us to check the coil, then the ignition module. With both of these checking out to be good.

After reading other's posts I have read issues where a bad oil sensor or pressure would disable these.

Sorry for all the confusion.

Right now on cylinders 1 and 4 we get fuel, no spark with the coil (swapped coils)and ignition module (tried new one) being good.

 

[saltfisher]

Re: 2004 Mercury 75hp running on only cylinders 2 and 3

So you say 1 and 4 plus were black? Is that normal? I just pulled all my plugs and all of them were black.