Mercruiser 5.0 MPI backfiring and wont go over 500 rpm.?

[larsonboat21]

Good morning. I am also having issues with my 2005 mercruiser 5.0 mpi engine. I have checked everything. i bought the boat new and never had problems except iac valve and fuel pump relays. It idles perfect but i have the two beeps. took it for a drive, backfiring and wont go over 500 rpm. put it back in neutral. idles perfect. its a brand new iac. Today i replaced the map sensor. i turn the key on, and now i get the normal one beep. fires right up, stalls out. i unplug the map sensor, two beeps and it idles. any ideas? im lost on this one. thank you much

 

[Fun Times]

Sounds like it’s time to try a new distributor, cap and rotor and/or phasing in the distributor timing plus new spark plugs.

Do you have a wiring harness connector plugged into the sensor sticking out of the distributor assembly?… If yes, that is your CAM shaft sensor that might be an issue such as this…. That and/or a crankshaft sensor type issue too.
Also make sure all power and ground wires all over the engine is still clean and connected without corrosion buildup, etc..

https://www.offshoreonly.com/forums/attachments/general-q/577324d1652222576-350-mpi-horizon-base-timing-bul-2011-11r2-hvs-clocking.pdf

Mercruiser 5.0 Mpi issue

Hi all ! Has anyone previously known or came across a situation where the shaft on the distributor appears to be bent or off centre ? It was dark and not thoroughly looked at properly at the time. The boat is not currently anywhere near me and haven’t been back to it since. But a Quick Look at...

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