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8.1 starts then stalls when warm.


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Daverdown

2006 247 LSV

8.1L engine

1400 hrs

When my engine gets hot, it starts, but immediately stalls. Then to start it, I have to neutral throttle, and feather the throttle back. If I neutral throttle and go straight back to neutral, it stalls again. If I leave the starter engaged, it fires, stalls, then fires again. After the second fire, I can release the key and she purrs like a big loud kitten... 😂😂 Any suggestions?

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When did you last do a tune up? 

Did you measure the fuel pressure? 

Does it run OK when cold? 

If so, does it die by itself when it gets hot, or run OK until you stop it and then it won't start?

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Daverdown

I did spark plugs last year. Injectors the year before. Haven’t checked the fuel pressure. It runs great cold or hot. Plenty of power. Doesn’t skip a beat.. Just after we’re out for a while, when I turn it off to pick up a rider and re-start, it stalls right after it fires. Crank, crank, vroom, die..... If I keep the starter engaged, it goes crank, crank, vroom, crank, crank, vroom and runs perfectly. 

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Has anything else changed recently? 

I'm not sure if this model is susceptible to vapor lock, but it could be what is happening.  The next time you go out and turn off the motor, wrap a cold rag around the fuel pump before you try to restart it. 

You might also try cleaning the throttle body.  Sometimes the gum builds up on the butterfly edge and the IAC pintle.  Cleaning it can really improve starting and idle. 

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Daverdown

It definitely vapor locks when it’s hot at Lake Powell and we’ve been surfing for a few hours, but only when I’m dumb and don’t leave the blower on or the engine compartment open when we stop and it sits for 30 minutes or so. I cleaned the throttle body last year a few times with no change. I changed the thermostat to make sure it wasn’t heating up. Always locked on 160 when it’s running. Change impeller every year.
 

It so strange that if I keep the key in the start position for 5-6 seconds, it goes through the fire/stall sequence then fires a second time and runs perfect. If I forget to keep the starter engaged it stalls, then won’t fire when I try to start it a second time without giving it some throttle, and even after it fires, I have to slowly work the throttle back down until it decides it’s going to idle. If I go straight back to idle, it stalls and I have to repeat the process.. But same thing, once I slowly work it back to idle, it runs perfectly. I can’t be the only person who’s ever experienced this... 😂😂

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9 hours ago, Daverdown said:

It definitely vapor locks when it’s hot at Lake Powell and we’ve been surfing for a few hours, but only when I’m dumb and don’t leave the blower on or the engine compartment open when we stop and it sits for 30 minutes or so. I cleaned the throttle body last year a few times with no change. I changed the thermostat to make sure it wasn’t heating up. Always locked on 160 when it’s running. Change impeller every year.
 

It so strange that if I keep the key in the start position for 5-6 seconds, it goes through the fire/stall sequence then fires a second time and runs perfect. If I forget to keep the starter engaged it stalls, then won’t fire when I try to start it a second time without giving it some throttle, and even after it fires, I have to slowly work the throttle back down until it decides it’s going to idle. If I go straight back to idle, it stalls and I have to repeat the process.. But same thing, once I slowly work it back to idle, it runs perfectly. I can’t be the only person who’s ever experienced this... 😂😂

I'm not sure if you have a MEFI 4 or MEFI 5 ECM in that year model.  A scan tool is definitely your pal when diagnosing issues like this.

In any event, the big block ECMs use an Intake Air Temperature (IAT) sensor.  The value of the temperature at turn on has to be within a few degrees of the Engine Coolant Temperature (ECT) sensor.  You can check each one with an ohm meter by disconnecting the harness and reading the sensor directly.  Check them with the engine cold and again with it hot.  The IAT sensor should have tan and black wires.  The ECT sensor should have yellow and black wires.

ECT at ~60*F should be about 4,000 Ohms, and at ~160*F about 400 Ohms.

IAT should read the same values at the same temperatures.

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I have seen a quite a few vapor lock crank-no-start or stalling at initial start and/or idle issues with Indmar engines that use a single engine mounted fuel pump that were built prior to 2008.  I don't know if adding the low pressure inline fuel pump kit would help with your starting issues, but I have seen it help on many other boats.

A faulty check valve in the fuel pump could allow pressure to bleed back quickly at key on and cause hard starting, but that would usually happen more often when the engine is cold.  A faulty pressure regulator can cause excessive fuel in the cylinders which would cause noticeable starting or idling issues when the engine is warm.  Try a fuel pressure test to determine if further diagnosis is needed.

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