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2007 Monsoon 340 no rpm on tach while cranking


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I have a 2007 Wakesetter 23LSV with the 340 Monsoon engine. Yesterday on the lake it gave a small pop while accelerating then died. I couldn't get it restarted. It would crank, but never even tried to start. The fuel pump runs and it has a new distributer cap, rotor, coil, and spark plugs. I noticed that there is no RPM indication on the tach while cranking. On another vehicle of mine this was due to the crank position sensor failing so the ECM didn't know the engine was turning over. I don't know much about the 340 monsoon motor. I assume it won't start with a bad crank position sensor, but I'm not 100% sure what this ECM uses the signal for. Will it register on the tach if crank position sensor is bad? Or does the ECM get that signal from the distributor? Also not sure what the camshaft position sensor does on this engine either. I plan to go out there this afternoon and start diagnosing the problem but want to have some idea of where to start looking so I don't spend too much time in the 110 degree heat.

BTW, it didn't set any fault codes and unplugging the sensor had no effect and didn't set any codes either, although I'm not sure if the ECM can recognize a missing or bad crank position sensor.

Thanks.

John

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John, I probably have the same 340 Monsoon engine in my 2005 LSV. Unfortunately, I can't really help regarding your crankshaft position sensor questions, but I don't think the tachometer will register when just cranking (the engine is only turning at a few revolutions per minute, which is probably too slow for the tach to register). Regarding not throwing fault codes, what Diagnostic Scan Tool are you using?

BTW, I'm also having an issue with my Monsoon, which appears to be heat related. If the boat sits for an hour after use, it won't start. It cranks easily, but acts like there's no fuel, or no spark. If I open the engine hatch for about 30 minutes (to help it cool) it will typically start. However, if it doesn't get cool enough, it will only start for a few seconds, then the RPM jumps to around 1,200 and it immediately shuts off. The engine will start during normal use, meaning I can turn it on and off pulling wakeboarders, but if it's shut it off for more than an hour, then some component or sensor gets too hot in the engine bay. Any suggestions where I should start troubleshooting?

Thanks, Scott 

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On 7/8/2024 at 1:08 PM, jhh67 said:

I have a 2007 Wakesetter 23LSV with the 340 Monsoon engine. Yesterday on the lake it gave a small pop while accelerating then died. I couldn't get it restarted. It would crank, but never even tried to start. The fuel pump runs and it has a new distributer cap, rotor, coil, and spark plugs. I noticed that there is no RPM indication on the tach while cranking. On another vehicle of mine this was due to the crank position sensor failing so the ECM didn't know the engine was turning over. I don't know much about the 340 monsoon motor. I assume it won't start with a bad crank position sensor, but I'm not 100% sure what this ECM uses the signal for. Will it register on the tach if crank position sensor is bad? Or does the ECM get that signal from the distributor? Also not sure what the camshaft position sensor does on this engine either. I plan to go out there this afternoon and start diagnosing the problem but want to have some idea of where to start looking so I don't spend too much time in the 110 degree heat.

BTW, it didn't set any fault codes and unplugging the sensor had no effect and didn't set any codes either, although I'm not sure if the ECM can recognize a missing or bad crank position sensor.

Thanks.

John

On modern ECM engines it is common to inhibit spark until the crank sensor indicates a few hundred RPM, so the tach probably won't show anything until the engine decides to add spark.  If you have a crank sensor it needs to work properly for the engine to run.

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2 hours ago, MalibuGA said:

If the boat sits for an hour after use, it won't start. It cranks easily, but acts like there's no fuel, or no spark. If I open the engine hatch for about 30 minutes (to help it cool) it will typically start. However, if it doesn't get cool enough, it will only start for a few seconds, then the RPM jumps to around 1,200 and it immediately shuts off.

This could be a condition called vapor lock, where the engine bay is hot enough to allow the gasoline in the fuel system to vaporize and essentially cavitate the fuel pump.  It is much more common with ethanol fuel than with real gasoline.  Try wrapping a cold towel around the fuel pump and surrounding lines when it happens to see if you can get it to immediately start and run.  If so, a low-pressure pump at the tank should help, as will leaving the engine hatch open during long rests.

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13 hours ago, justgary said:

This could be a condition called vapor lock, where the engine bay is hot enough to allow the gasoline in the fuel system to vaporize and essentially cavitate the fuel pump.  It is much more common with ethanol fuel than with real gasoline.  Try wrapping a cold towel around the fuel pump and surrounding lines when it happens to see if you can get it to immediately start and run.  If so, a low-pressure pump at the tank should help, as will leaving the engine hatch open during long rests.

Yes, that is vapor lock.  I'm struggling with this on my 06 LXi with the extreme heat we have here is Florida.  The answer for me is to run the blower often and to open the engine cover if sitting a bit to help release the heat from the engine compartment.  I'm also going to try Marine Stabil with next fuel up.

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11 hours ago, Mitchellm said:

Yes, that is vapor lock.  I'm struggling with this on my 06 LXi with the extreme heat we have here is Florida.  The answer for me is to run the blower often and to open the engine cover if sitting a bit to help release the heat from the engine compartment.  I'm also going to try Marine Stabil with next fuel up.

Just as an aside, I'm in Florida and it doesn't ever happen on my boat.  I don't use ethanol fuel, so maybe that's it.

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15 hours ago, justgary said:

Just as an aside, I'm in Florida and it doesn't ever happen on my boat.  I don't use ethanol fuel, so maybe that's it.

I do think it's the ethanol fuel.  Unfortunately, I do not have easy access to ethanol free where I keep my boat.  I'm hoping the StaBil additive will help.

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