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JustinLCurrie

Major Timing/Backfire around 1,800 RPM - 2006 C4 Avalanche

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Been having issues with boat for 18 months now (owned for 5 years) and have spent $10K at boat mechanics/dealers (new CPU, new top end, new cap/coils, various sensors) and still not working.  Always starts and no issues at idle.  When under load around 7 mph/1,800-2,000 rpm starts to misfire badly and will repeatedly do this - very heavy timing/misfiring when bumping up against this rev range.  Sometimes it will get through the issue after 15 -30 minutes of trolling and trying to get on plane - seems like it just catches and timing issue goes away - maybe crazy but it seems that if water is rougher or going over wake it allows it to catch more easily.  Once through the issue will  run absolutely perfectly until stopped.  Very rarely (but usually when been out on a bouy it will start and run just fine immediately but after 2 minutes then goes into limp mode and then the same issue happens.) Local dealer/mechanics are stumped - (Vancouver, Canada) - and I don't have a limitless budget.  Basically we have nice looking floating slow moving island/tanning bed but no surfing.

Really want to get this sorted out. Still love the boat and wave when it works so would love to figure out what the issue is.  Have the time this off-season to investigate issues. 

Wondering if this could be related to fuel pump/corroded wires? Other ideas or suggestions would be welcome? 

2006 Avalanche C4 Storm Series 

New core put in 2017

Approx. 300 hours on boat 

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jtryon    14

black scorpion 330?  are you getting good constant 14.2-14.3 voltage with the motor running?  have you checked the fuel pressure?

there are two fuel pumps from what i hear, one in the tank and one at the rear port side of the motor (black scorpion anyway) near the raw water pump.  i'm assuming you've done the easy stuff first like fuel filter, plugs and wires since you also did the cap and rotor?  if not i'd do all that as well as the IAC valve and maybe the CPS.

Edited by jtryon

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beau t    8

Have the injectors been cleaned or replaced, do all of the spark  plugs look the same as in is 1 black or a different shade than the rest. I didn't see anything listed about this above. with a car you can do a distribution test to check the injectors and should be able to do it with a marine engine to but i have not got to play with a computer that hooks up to marine engines to verify. this is just throwing out ideas since you have a long list above of stuff thats been done. Also can you free rev the motor and it not cut up?

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