DrFeelgood,

Merc 496 Exhaust Assembly

So, where in this diagram would that unit go? I have an idea, but I’d like confirmation.

I’m assuming the water from the distribution tube goes into a jacket around the actual exhaust passage of the manifold, and is then introduced to the exhaust flow through the two hoses on either side of the base of the riser elbow….?

Also, since the 555 ECM doesn’t have provision for O2 data input, this addition would only be for test and tune purposes, then the sensor port would be plugged, right?

Assuming the additional height can be accounted for in the flexibility of the exhaust hose between the riser and the transom tubes….?

Also assuming it would be best to have these installed on both sides….?

Thanks. Brad.
(937)546-8991

You could permanently install a wideband O2 sensor with a gauge at the helm, if you wish to monitor on an ongoing basis. Doing both sides seems most logical but I'm sure there's some guys out there that arbitrarily just picked one side.

The stock manifold setup uses a wet joint at the manifold to riser joint. Most aftermarket setups eliminate that wet joint in favor of a jumper hose. In either event, there is no water in the exhaust gas stream at that point, it's just a matter of how cooling water gets from the outer cooling jacket of the manifold, to the outer cooling jacket of the riser.

DrFeelgood,

So it would go between the manifold and #15?

I wouldn’t be opposed to adding a couple O2 gages, just to monitor them, but I wouldn’t feel the need for them. I’m far more concerned with potential damage to those damned cast pistons if I’m running lean, but I also don’t want to be running overly rich, either. The transom soot is bad enough.

Thanks. Brad.
(937)545-8991

Based on that diagram, it looks like there's a dry joint with jumper hoses. Maybe Merc revised that with the 496, I don't know.

At any rate, 1 is the manifold and 7 is the riser. Ideally an O2 would go either in between those with an adapter plate, or in a bung welded into the riser.

496 exhaust is a dry joint from manifold to riser.
You could still use a plate between them or you could have a bunge welded in where the #7 is.

Guys,

Looking at IAC valves. Any reason not to buy the Sierra unit instead of the Quicksilver unit?

Thanks. Brad.
(937)545-8991

Get the ford motocraft one. Do a search, we have deciphered the part #.

Here is one such thread:
https://www.offshoreonly.com/forums/...iac-valve.html

SB,


https://cimg9.ibsrv.net/gimg/www.off...efba6309bd.png
Done did it. 😎

Thanks. Brad.
(937)545-8991

SB,

Finally got a chance to get the scan tool out and play with it a bit. I performed the IAC output test and got ZERO change in RPM from -100% to +100%. I'm assuming this is an indicator the IAC valve is bad. Since I already had the replacement part on hand, I swapped it out, but have not had the chance to get it wet again and fire it up for a final evaluation. Is it safe to assume the hunting idle will have gone away?

Thanks. Brad.
(937)545-8991