O2 Sensor in a boat exhaust
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O2 Sensor in a boat exhaust

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    Senior Member kurtis500's Avatar
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    Default O2 Sensor in a boat exhaust

    I purchased the Holley HP MPFI system and just went to the lake with it. The O2 sensor burned out immediately. I stopped by Bergeron on my way back to the lake and he said they have never found a good way to run O2 sensors in a marine exhaust. He had one there that was ran on a dyno then the fuel map was set and shipped back. On my system I machined in the O2 sensor right between the snail and the manifold of a BBC. Phil said water will still get up over the snail and knock out the sensor. Maybe my manifolds had a leak on the inside between the snail and log?? Has anyone ran an O2 sensor in an EFI on a marine engine? What exhausts are the best? I would REALLY prefer to run this brand new holley EFI system in closed loop and not set the fuel map and use the O2 sensor as only a sensor..

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    gn7
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    Phil is right. You will still get some water on the engine side of the snails, mainly at low Rs. It may not be enough to cause problems with the way the engine runs aor even make into the cylinders, but it is enough of a mist to take out a O2 sensor. With over the transoms you might get away with it if the water is introduced at the very very end, and the O2 is mounted right at the log. But you still risk a little water running back at low Rs.
    If there is a fool proof way to mount a O2 using a set of logs, I never seen it.

    It doesn't take cylinder filling type water. Just steam is enough to knock one out.



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    Last edited by gn7; 05-30-2011 at 05:40 PM.

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    New here Beer:30's Avatar
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    Any exhaust down at engine level or lower will definitely get at LEAST some steam.

    My Lightnings have a bung welded through the water and into the dry exhaust area at the collector. Being near the highest point of the header and not any reversion issues, the O2 will work just fine in these apps.

    Aftermarket headers are pretty much the only safe way to run an O2 sensor.
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    Or Seth, either one Budweiser's Avatar
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    Just a rumor. Never tried it myself or know anyone fwho has, but...

    If your heads have the port for the exhaust crossover under the INTAKE manifold, you can (reportedly) drill and tap the intake manifold for the O2 sensor, probing right into the "emissions"...err... port... thingie

    Just a little outside the box thought fer ya.

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    I've seen O2 sensors in water jacketed headers that have worked fine for years.
    You just need to take some time to make sure you put it in a dry spot.
    Maybe relocating the water dump to somewhere farther downstream would be an option too.

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    Senior Member kurtis500's Avatar
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    Thanks guys. Does an yone have a pic of the O2 sensor in their exhaust? I found this in the instruction manual for the older commander 950 system. Look at the bottom..

    http://www.holley.com/data/Products/.../199R10226.pdf

    I really thought between the snail and the log was good enough.. maybe not?

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    gn7
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    Quote Originally Posted by Unchained View Post
    I've seen O2 sensors in water jacketed headers that have worked fine for years.
    You just need to take some time to make sure you put it in a dry spot.
    Maybe relocating the water dump to somewhere farther downstream would be an option too.
    The problem here Mark, isn't that the exhaust is wet, its that it is a log setup, with snails. There just isn't any place in a system like that, that you can reasonably guarantee water or at least steam won't get to the sensor. With jacketed header type system it is doable.
    I think Budweiser has the best idea. Not sure how accurate it is located there, but it by far the safest place.
    But any low slung log system with snails and dumps exiting the transom is questionable anywhere in the system, even with the mildest of cams.



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    cfm
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    Most water jacketed header manufacturers (Lightning, CMI, etc) will install 02 bungs in their headers for extra money.

    Most manifold systems (EMI, Gill, etc) one can make a plate to go inbetween the manifold and riser to install an 02..........many DIY's do this.

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    Senior Member kurtis500's Avatar
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    Taking a look at the holley manual I am thinking about drilling and tapping the front exhaust port on the log for the O2 sensor. Maybe going all the way to the front is the way to go?

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    cfm
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    THen you have to determine if you want 02 readings from one cylinder, or in the case you just mentioned mostly one cylinder, average of 4 cylinders on one bank or the other, or average of all 8 cylinders.

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    gn7
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    No worse than taking the reading in the intake manifold cross over. The very front would be the safest place. But it is going to be a little tricky. Some logs have water up to just short of the port. About your only location is in that short area from the log to the port face. Not sure how well the sensor likes being that close to the port. Your talking flames at that point, and it will definitely have an effect on the reading. Those "flames" are still consuming O2 that would otherwise not be read by a sensor in the correct location. Could show a lean condition when in fact it really isn't.

    If you mount it in the log area itself, you'll have to penetrate two walls, and weld in a tube to cross the water jacket. Welding the tube to the outside of the log is easy. Welding it water tight on the insider wall that seperates the water from the exhaust, that could prove to a little more difficult.



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    Last edited by gn7; 05-31-2011 at 03:09 PM.

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    Quote Originally Posted by gn7 View Post
    No worse than taking the reading in the intake manifold cross over. The very front would be the safest place. But it is going to be a little tricky. Some logs have water up to just short of the port. About your only location is in that short area from the log to the port face. Not sure how well the sensor likes being that close to the port. Your talking flames at that point, and it will definitely have an effect on the reading. Those "flames" are still consuming O2 that would otherwise not be read by a sensor in the correct location. Could show a lean condition when in fact it really isn't.

    If you mount it in the log area itself, you'll have to penetrate two walls, and weld in a tube to cross the water jacket. Welding the tube to the outside of the log is easy. Welding it water tight on the insider wall that seperates the water from the exhaust, that could prove to a little more difficult.
    I agree. At that point, he might as well drill all 8 and go with pyros instead of O2. At least he could see all 8! A pyrometer is meant to live in flames (longer, anyway) and would be the next best reading. I don't think the injection would read it, but he could at least go open-loop and tune accordingly per pyro readings. Still not optimal.

    How about GETTING RID OF THE LOGS?
    Quote Originally Posted by gn7 View Post
    EFI is the wave of the future. There can be no denying it. Electronics have been on the leading edge of our entire lives. Not only os the magneto dead, but the standard issue CDI is wavering. Its all about total fuel, air AND spark control. Anybody that thinks its not has their head up their ass.


    2001 SleekCraft 30' Heritage SSB, open-bow mid-cuddy. 496HO / Bravo-I.

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    Senior Member kurtis500's Avatar
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    i thought about it, but after $3400 on an EFI alone and an entirely new rigged boat Im having a hard time forking out another 2000 for an exhaust when I may just do an open loop...

  16. #14
    Boat Nut sleekcrafter's Avatar
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    My buddy machined up a set of spacers I sketched out for him. They are about 4 inches long, in-line between the log and manifold. They have been working out well for a few years now.
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