RESOLVED! Tach Jumping & Boat Backfiring Under Load

Hi, Not sure if you can still see this. I have a 502 Mercruiser EFI that is having the same problem. Is this switch the same at the neutral switch? If so what would it have to do with the tach and backfiring. I hope this is my problem as well. Just curious?
 
Thanks for the reply. I read that last night after I posted this. Thanks. Just thought it was strange that I am having this same symptoms with the backfiring at load and tach bouncing.
 
Would a crack on both sides of a spark plug in the porcelain part cause something like this?
 
Hi H2Oski, saw your video I have exactly the same problem, had it for 3 years now caused stress & confusion out on the water, almost threw the towel in for boating. My mercruiser mechanic could not find the problem he took the boat out 4 times. I hope the switch does the trick, maybe I may get enthusiasm back to go boating. Hope your boat is still running well.
Regards.
 
Sea Ride I had the same problem as H20. After many trials and tribulations I took your advice and had a mechanic change the Shift interrupt switch. "It cured the problem". Thank you so much. The Dealer was so happy also they didn't charge me anything for putting it on. They thought I was a genious. It was a summer of great boating. I have not responded earlier due to computer and log in issues. Thanks again.
 
Mark,

Glad to help and thanks for letting us know problem solved. Enjoy and have a great season this year.
 
I had to set up an account just to say thank you Sea Ride! We bought a new boat, and when we started having backfire problems my mind went to the worst after changing everything timing and fuel related. I wish I'd found your post before changing a bunch of parts, but she runs awesome now! Thanks again.
 
SD,

You are welcome. I always thought this was a. extremely rare issue - perhaps not!

Enjoy your recent purchase and stick around as CSR had lots of good information.
 

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