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-   -   Back fire on start stock 496HO (https://www.offshoreonly.com/forums/do-yourself-boating-budget/356120-back-fire-start-stock-496ho.html)

BUP 08-18-2018 01:28 PM

Post 8 have no idea what happened. fixed now here

describe runs fine after start up ? can you reach full rpms at WOT ? 5000 rpms HO mag and 4800 for mag 496 is WOT

I would not rule out CRANK SENSOR here either for starting issues. That signal and cam sensor have to sync for start up among other things


FIXED from earlier mishap

BUP 08-18-2018 01:35 PM


Originally Posted by 38fountained (Post 4644444)
Thanks BUP, you’re a life saver. 300 hrs total. New plugs the ones you recommend and wires about a year...crank sensor and cam sensor come up as code on the Rhinda. Will do more testing. Bleed down on fuel pressure?


A really good reply from me would be --- I bet the crank and cam sensor fault codes are NOT real fault codes --- they happen for a reason and that is common as to why they happen. Anyone want to take a guess why ?

Even without a real fault code I would not over look the crank sensor. They become an issue even for a hard start for a mild issue to even 300 lost rpms for a medium issue to a complete stalled engine to a no restart and no tach signal for the worst ends of a completely failed crank sensor.


BLEED down fuel pressure - I would really look at the issues here. and what is fuel pressure while the engine is running ?

38fountained 08-18-2018 02:13 PM

WTO, well I went out the other day to test and just as I cleared the canal the steering system puked out every drop. Sea Tow to the rescue.

VoodooRob 08-18-2018 09:19 PM

Man your having a hell of time with your boat right now. We have all been there.

38fountained 08-19-2018 09:20 AM

Oh just wait, Major leak in the bellows on that engine found when drifting awaiting sea tow. Leak in drive motor lines. Super tight shift cables. And I just had my shoulder joint completely replaced. Life’s great, Boating’s Great.

SB 08-19-2018 09:32 AM

Hey BUP -Ican't remember, do the 496's have wasted spark ? Prob not because individual coils,but still worth the ask. :)

BUP 08-19-2018 10:00 AM

sequential injector firing with 8 coils near plugs. DIS

early coils gen 1 were prone to fail here and there.

gen 1 crank sensor more prone to fail than the later version without the ribs. And the rib crank sensor ( early version ) can even break when pulling it out. Not common but can happen

crank and cam sensor signals are very important

2 versions digital throttle n shift and mechanical throttle n shift.

early years 10 pin wiring harness later years 14 pin wiring harness

IAC can play a role for stalling as well.

more than half IAC failures come from lack of proper maintenance.

More than half PCM repair that I see have a bad IAC circuit. ( H bridge) for PCM 555 and ECM 555

beaver 3 08-20-2018 08:06 AM

are you sure the coil harness is on correctly. my buddy put his on wrong one time and had the same issue it sounds like your having. it would run just a touch rough and afterfire out the exhaust while idleing.

38fountained 08-20-2018 09:12 AM

Coils have not been touched, but maybe connections need to be checked...

HPHQ 08-20-2018 01:16 PM

We have had this come through the shop before and kept getting a cam sensor fault. Throw a sensor at it and problem disappeared for awhile but always returned. Changed crank sensor 3 years ago and no more issues. Seems the computer cant tell where engine phasing is so it will constantly throw a cam sensor fault if the two dont match up. Good luck!!


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