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failing at decceleration


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I guess this is a tricky one, need the valuable help of the crew.

LXi Response 2003, Monsoon 335, 250 hrs, engine fails when deccelerating until killed, especially if done quickly and not always. Looking to the back of the boat there is black smoke coming out from the exhaust what seems to be excess of fuel. Difficult to start, with the lever moved forward following flooded engine start up instructions until finally starts. It can be controlled by reducing speed slowly but requires skills, therefore an annoyance for anyone with less experience to sense the engine.

Many things have been checked, temp sensor, injectors serviced, distributor cleaned, no code appears with the scanner.

As a background, and this may or may not have anything to do with the problem, few months back the ECM failed and was replaced. The effect of the failed ECM was that it was opening some injectors continuously flooding the engine badly. After replaced, and with new spark plugs, we started to notice this last fail. Otherwise, the engine runs nicely at any speed and condition.

Hope this is clear for testing troubleshooting skills, thanks for your support !

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First it would be good to know what the fuel pressure is it should be around 38- 42 p.s.i. if your getting black smoke your running rich for some reason most of the time its a bad fuel pressure regultor it located under the pleutum its bolted to the fuel rail has a gas line going to it and a vaccum line going to it if you pull that vaccum line off and then turn the key on just to the on postion don't start the running the fuel will do a 5 sec. prime and if you get fuel coming out of the vaccum line the regultor is bad. Also when they came out with the 335 monsoon they had a problem with them stalling or idling erraticly when you brought them back to idle quickly there is a calibation out there to correct this problem but if the boat is over fueling and it doesn't have this cal it will do exatly what your desrcibing

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First it would be good to know what the fuel pressure is it should be around 38- 42 p.s.i. if your getting black smoke your running rich for some reason most of the time its a bad fuel pressure regultor it located under the pleutum its bolted to the fuel rail has a gas line going to it and a vaccum line going to it if you pull that vaccum line off and then turn the key on just to the on postion don't start the running the fuel will do a 5 sec. prime and if you get fuel coming out of the vaccum line the regultor is bad. Also when they came out with the 335 monsoon they had a problem with them stalling or idling erraticly when you brought them back to idle quickly there is a calibation out there to correct this problem but if the boat is over fueling and it doesn't have this cal it will do exatly what your desrcibing

if you add robertiux's 'replaced ecm' to malibu guru's new 'calibration' requirement i would bet a trip to the dealer to re-flash the ecm is the fix.

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The idle flair calibration would have been done already if the ECM was replaced within the last year. And that cal fixed idle flair, not sure if this is anywhere close to the same issue.

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Sticky or bad IAC valve may be worth a check, I had this on my last truck, would stall on rapid deceleration, there was some carbon build up. I dont think this would address the rich condition but worth a check, and easy to do. Mine cleaned up fine with carb cleaner and worked fine after that. I'm with the fuel pressure check as well.

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Thanks for the very fast response ! The ECM was replaced end of 2009 and since then this problem remained, it makes sense that the ECM calibration is not updated. I'm checking with Paul from Bakes if he can confirm, he helped me with this ECM.

In the meantime, we are checking the fuel pressure and regulator.

Thanks,

Roberto

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