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Tan
Tan, MerCruiser Certified Technician
Category: Boat
Satisfied Customers: 10701
Experience:  40 yrs. experience with complete engine repairs both inboard/outboard and MerCruiser Certified Technician.
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I have a1997 5.7 mercuiser with a knock sensor that i just replaced and after the boat is

Customer Question

I have a1997 5.7 mercuiser with a knock sensor that i just replaced and after the boat is running for a while it starts to ping I changed the spark plugs and they looked fine
Submitted: 1 year ago.
Category: Boat
Expert:  Tan replied 1 year ago.
Hello. My name is***** you checked the timing? How old is your fuel?Have you done a compression test?Could I get the engine serial number please?
Customer: replied 1 year ago.
the fuel is fresh the timing has been checked i dont have the serial number handy the boat runs fine i get it up to operating temp before i leave the dock all the way out it is fine it only happens on the way back in after a few hours
Expert:  Tan replied 1 year ago.
Have you check the fuel filters for water in the fuel? Have you done a compression test?
Customer: replied 1 year ago.
I have checked the water separator no i have not done a compression test i was leaning more towards the module
Expert:  Tan replied 1 year ago.
Ok we need to check the timing when the engine is running. Watch to see how much advance you are getting when the engine starts knocking.
Customer: replied 1 year ago.
ok the mariner set the timing last year when the problem started
Expert:  Tan replied 1 year ago.
What did he set the timing at? If you have an ignition module acting up it can cause the timing to advance higher than it should. The timing in your module is 22 degrees+ 8 base timing giving you a total of 30 degrees. If the timing is advancing above 30 degrees it will cause pinging. To determine how much the engine is advancing you have to use a timing light with the advance degrees in the light. The timing marks don't go that high on the engine.
Expert:  Tan replied 1 year ago.
So you don't know that the base timing is correct?
Customer: replied 1 year ago.
correct although i do believe he told me had it set to 8 so the module could cause this ?
Expert:  Tan replied 1 year ago.
Correct. Now this statement here tells me he did something if it started after they worked on the engine."ok the mariner set the timing last year when the problem started"
Expert:  Tan replied 1 year ago.
Ok what I would do is check the timing make sure it is set at 8 degrees BTDC. If it is then the module is the problem. Now to verify this check the timing where the engine starts to ping. If the timing is advancing beyond the 30 degrees then the module is bad. Now the module is very expensive $ 485.73 for a Alpha drive and $454.93 for the Bravo drive engine. Now there is an alternative to the module and it is cheaper.Would you be interested in the alternative? Some people want to keep their boats original.
Customer: replied 1 year ago.
i would be interested in an alternative
Expert:  Tan replied 1 year ago.
Ok you can go with the EST ignition system they use on all the new motors. You can get the complete kit for $ 369.00 plus shipping. Here is the link to the complete kit. http://www.michiganmotorz.com/delco-voyager-marine-electronic-distributor-p-119.html That should take care of everything you need. Now if you need further assistance pleas ask. Thank you.....Tan
Expert:  Tan replied 1 year ago.
Please don't forget to positively rate me as that is how I get credit for helping you.
Thank you........Tan

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