Mercruiser Surge, Idle, die with 5.0 EFI

DESTINY200

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Joined
Aug 18, 2024
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This discussion (link here) defines the same problem I just had. Unfortunately, no solution was ever documented and it is now closed. I think I found the solution, which turned out to be quite simple so I thought I'd leave it here to save someone the frustration I experienced. I found a few old, closed threads that identified the same problem, but no solution was provided. But these threads were constructive in listing all the many things they tried. So, using these in a process of elimination, told me that the problem was likely that the computer was thinking the engine was cold when an attempt was made to start it after it had sat idle for 30 minutes or more after having been running at full operating temperature. So, I suspected the 2-wire temperature sensor, found on the top of the engine, opposite the single-wire temperature sensor feeding the temperature gauge on the dash. I found a new multipurpose temperature sensor at Autozone for under $25. After installing it, I have tested it twice and so-far-so-good! The old one looked pretty rusty and may have been an original. It appears that it was not telling the ECM that the engine was warm, so, thinking the engine was cold, it sent too much fuel causing it to surge and eventually flood out. I hope this helps someone!

Part I installed:

Duralast Multi-Purpose Temperature Sensor SU109

 
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