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Jason
Jason, Marine Mechanic
Category: Boat
Satisfied Customers: 15353
Experience:  Degree in Marine Technology. Gas and diesel marine mechanic.
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I have a 2001 Mercury 50hp. It is 3 cylinder. It is running

Customer Question

I have a 2001 Mercury 50hp. It is 3 cylinder. It is running very good on 2 cylinders can't get the top cylinder to run. Have reworked the top carb it is getting fuel. replaced the spark coil and checked all connections.
Submitted: 2 years ago.
Category: Boat
Expert:  Jason replied 2 years ago.
Hello, my name is ***** ***** am I speaking with?
Have you checked for spark the top cylinder with either an adjustable gap spark tester, or a timing light?
Also, can I get the serial number on the engine, that way I can run it and see which ignition system you have.
Customer: replied 2 years ago.
My name is***** have only checked for spark visually. ot220452
Expert:  Jason replied 2 years ago.
Hey Frank. Are you near the engine now to try a few things?
Customer: replied 2 years ago.
I am inside the house Engine is outside
Expert:  Jason replied 2 years ago.
Those ignition coils are called CDM modules. What I want you to do for me is get a marker and label them 1 2 and 3 from top to bottom so there is no confusion on them.
Swap the 1 and 2 modules, and let me know if you get spark on #1, and loose it on #2. Start with that and let me know what happens.
Customer: replied 2 years ago.
Have tried that. don't see any difference still have spark. also tried replacing the top cdm with a new one
Expert:  Jason replied 2 years ago.
There are only 2 ways to properly check for spark, either with an adjustable gap spark tester or a timing light. Any other way might show spark when the engine really doesn't have it.
have you checked compression yet, and if yes, what the your numbers?
Customer: replied 2 years ago.
No I haven't tested compression yet. I have to get a new guage mine is broke.and yes that is a very important test and should have done it before I talked to you
Expert:  Jason replied 2 years ago.
There are no time limits here, do you want to check it and get back to me?
Customer: replied 2 years ago.
Yes. It will be later today. How do I get back to You?
Expert:  Jason replied 2 years ago.
Each time I reply the website sends you an email letting you know I reply, and in those emails there are links back to the website. Follow this links and reply back to the website. Do not reply back to the emails, reply back to the website.
Customer: replied 2 years ago.
OK Thanks!
Expert:  Jason replied 2 years ago.
You bet.
Customer: replied 2 years ago.
Sorry it took so long. Had business to attend. The compression test was top 125, center 125, bottom 128. The spark test changes the problem it shows very low spark on all 3 cylinders. I know you are offline so I will check back tomorrow for your response.
Expert:  Jason replied 2 years ago.
Hello. What do you mean by "very low spark" What kind of test did you do?
Expert:  Jason replied 2 years ago.
It looks like you read my response and logged off. Did you try to send a reply back, as I did not receive one.
Customer: replied 2 years ago.
It's just an inline spark tester. The intensity of the light reflects the strength of the spark. All 3 barely lit the bulb. So I would call it weak or none.
Expert:  Jason replied 2 years ago.
Got it. Click this link to pull up a picture.
https://xfer.mercmarine.com/pximages/partscatalog/COMMON//5264_500.gif
Locate #5 on the picture. That is called a rev limiter. It is optional and not on all engines. Check to see if you have one. If you do, disconnect it. Does spark get any stronger?
Customer: replied 2 years ago.
Yes I do have one I will try it.
Expert:  Jason replied 2 years ago.
Okay let me know what happens. Also, do you have a digital volt/ohm meter, do you know how to take basic resistance meaurements?
Customer: replied 2 years ago.
The spark is stronger. Yes I have a vom and can use it.
Expert:  Jason replied 2 years ago.
If it is stronger can you get the top cylinder to run now?
Customer: replied 2 years ago.
Maybe I over choked it but it won' run at all right now. I checked the spark just now while only cranking the engine.
Expert:  Jason replied 2 years ago.
If spark got a lot stronger the rev limiter is definitely bad, there is no question on that. You don't actually need it and when we get bad ones in the shop we throw them in the trash.
Take the boat out and see what happens. I'm sure it will run much better. If it still gives you problems just post back at any time.
Thanks,
Jason

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