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Old 09-02-2013, 01:27 PM
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FourFourty FourFourty is offline
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Join Date: Nov 2010
Boat: 2018 XStar that's trying to be a 40th.
Location: Northeast
Posts: 2,141
Originally Posted by [email protected] View Post
The only way an ECM can compensate for a difference in air flow is to have a sensor in the trailing edge of said FAE which there is not, therefore the ECM is NOT adjusting for the FAE and only operating only to oem specs.
If back pressures are higher, Manifold absolute pressure will be higher as well. The ECU would compensate for that. With a "Speed Density" fueling system, like our boats have, the MAP sensor measures intake manifold pressure, in order to make fueling adjustments, based on the load, and flow of the engine. If you restrict the exhaust flow, you reduce the efficiency of the "pump", and the inlet side will have a corresponding change in pressures.

Not saying that the corresponding changes will be as "spot on" as the normal parameters on an engine without FAE, however, it does compensate for things like that.

Originally Posted by DHPRO View Post
O2 sensors should adjust to account for changes in flow (again, I have no idea how marine sensors differ from cars). Those OEM spec'd boats would be interested to see if they have any diff mapping in the fuel tables or timing as a result. If not, then I'd feel lots more comfortable adding it to mine.
O2 sensors will only make microscopic changes to an engines fueling, and ONLY under a sustained, low throttle, cruising condition. The O2 sensors are ignored, by the ECU, under any kind of load above 1/8-1/4 throttle. They are also ignored at idle. They would not help compensate for an FAE at all.

Same goes in a car engine- You are cruising along at 50mph on a nice straight, flat, highway. Your foot is just barely pressing the throttle, and holding it steady. At this time, the ECU will take a look at your O2 readings (goes into closed loop), and make 1-3% changes in the short term fueling of the engine. As soon as you either let off, or put any kind of load, above 1/4 throttle, the ECU immediately ignores O2 readings (switches to open loop), and uses MAF, (or MAP sensor, depending on fueling type. Some engines run both), Intake air temp, engine temp, RPM, and throttle position, to make adjustments to fueling.

Because of the way boats are used, and how they are constantly under heavier loads, an O2 sensor is ignored 99.9% of the time.

Originally Posted by [email protected] View Post
How could O2 sensors adjust for added exhaust tubes, changes in flow etc. when they aren't even there (after the FAE). BTW the "sensors" on engines don't compensate for air flow or the like, the characteristic (or flow) of an engine is preprogrammed in the ECM, the only thing an O2 sensor does is measure the amount of Oxygen in the exhaust gases and reports to the ECM then the ECM makes adjustments to the air/ fuel mixture, flow has nothing to do with it.
You are right about the O2 sensor, however, like I said above, they absolutely can compensate for changes in air flow. They absolutely have to, otherwise, you would have to rewrite the ECU, with another program, every time you changed elevation, or even temperature outside....... Not to mention, the flow characteristics, of an engine, change over its lifetime.

Flow has EVERYTHING to do with it. Changes in elevation, outside temperature, engine temperature, backpressures, and intake restrictions (dirty air filter), all effect the FLOW of an engine. They are designed to deal with a wide range of changes. And sure, there is a limit to what it can compensate for, but they leave a pretty healthy cushion.

With all of that said, no way did the FAE take that connecting rod out.....
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