I have twin Mercruiser 4.3L MPI V6, 2004 (OW065549 and OW065554) that are hard to start when hot/warm.
They will turn over but will take several minutes to fire. When they do eventually start, the exhaust smells rich for a few moments.
The workaround is to start in neutral at WOT then quickly throttle down. Both engines start straight away with this workaround.
The issue occurs in both engines, after they have been sitting for between 5 minutes to about 2 hours after use.
Both engines start straight away when cold.
The engines show no fault codes when plugged into the computer and compression is fine.
I have found the Service Bulletin 99-7 (
http://www.boatfix.com/merc/bullet/99/99_07.PDF) regarding vapor lock. I do not believe that it is however as I have tried, all without any improvement at all:
- blowers
- idling after running for several minutes
- opening the engine hatch
- never using fuel with ethanol.
I have replaced the IAC values on both engines but no improvement.
I suspect that it may be one of the following:
- Temperature Sensor - even though there is no fault code, the sensor may have some fault which tricks the computer to think that the engines are warm (when they are not) and to inject more fuel than necessary. I think this because the hard starting is cured with WOT starts.
- MAP Sensor - again for the reasons above, an incorrect temperature reasoning causing more fuel being injected than necessary.
- Low pressure Fuel Booster pump - I don't think so, because the engines start fine at WOT
- Fuel regulator - Maybe if the regulators are impacted by temperature......
Before I start throwing parts at it, any thoughts?
Any assistance would be great.
Thanks all in advance.
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