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4.5 engine quits

A

AlJ

New member
Howdy all, Am trying to figure out why my merc 4.5 dies after about 45 minutes of running fine. Started after about 94 hrs on meter. Was brand new, all new out-drive and harness and controls, steering and a few gauges. its in a 99 22 ft trophy. I have replaced the starter switch, thinking maybe it went bad, All new cables to batteries, good grounds, etc. Wont restart after.. 1 or 2 cranks and that's it.. normally cranks for 4 or 5 times to start engine. ( auto start?? my truck does this dame, cranks till it starts even if you let off switch.) Doesn't throw any codes for computer checking to pick up.. wondering if fuel related? but why did it wait for 94 hrs to crop up? Fuel injected.. is there a relay of some sort that could over heat and then switch on again when cooled enough.. not sure of restart time frame.. usually don't get to it for a few days later and then restarts ok. Any ideas welcome. Amy slightly bald now with hair pulling.. Ö
 
could be crud collecting on the pickup tube, especially if the tank in the boat wasn't flushed out when the new drive train went in...could also be the vent line is clogged...
 
makomark said:
could be crud collecting on the pickup tube, especially if the tank in the boat wasn't flushed out when the new drive train went in...could also be the vent line is clogged...
Click to expand...
But why would that stop it from starting again.. ie.. cranking over. only 1-2 turns then stops.. ? normally it would crank 3-5 times until it fires. Feels electrical... it doesn't sputter to a stop.. off.. like a key switch.. if clogged then wouldn't ever start and have to replace tube? dunnio.. ty for input.. Fuel for thought.
 
crud cover screen and blocks fuel flow...engine cuts off and vacuum holding crud dissipates and crud falls off...

If the engine dies and then will not crank over....or cranks over slowly, pull the spark plugs and check for water collecting in the cylinders...also good idea to check the dipstick to make sure it isn''t over FULL ...
 
Any update I have a 2021 m22 Monterey 4.5 250hp doing something similar. I have put a new fuel pump module and spark plugs runs great perfect plug readings then dies. has a 822 code for 02 sensor heater on port side 1. Hooked up to scan tool all perfect readings across the board then an hour or so later won't restart just cranks. 315 hours also leaning towards vapor lock ran fine at 95 degrees out for hours then a few hours at 117 and the problem occurred but hasn't restarted since with cooler temps outside?? This one's really throwing me through hoops
 
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