Currently rebuilding my 8.1 Volvo Penta Gi-BF which is stock with no oxygen sensors. New Stock Iron heads, Block with forged pistons and rods. Sainless Marine manifolds and risers for an all FWC system. I'm not trying to win any races but in automobiles, 02 sensors make the engines better. Should I bother with adding 02 sensors? Will it help with fuel economy, power, or healthier engine? If so, how is this done? New ECU?

If your EFI system can be tuned, you can use the O2 sensors to help you dial the tune in, or get a newer aftermarket EFI.

Stainless Marine manifolds often have O2 bungs from factory. Otherwise you'll have to get your riser/tails modified for an o2 bung.

No matter the fuel distribution system, ams O2 sensor is always a good idea.

I currently have the stock Volvo Penta EFI/ECU for the 8.1 which did not come with o2 sensors. How do I know if my ECU can support two oxygen sensors?

Is there a guide?

Not sure if they're supported or not...but you can use stand alone O2 sensor meters to tune the EFI, even if it cannot directly receive data from it. No different from a carb.

it does not support 02 sensors.

Is there a plug and play ECU that does and can be turned?

I see no reason to add them to a stock engine.

Imannyr,

Holley makes a couple systems that will do everything your ECM will do and more, but they are not cheap. I just got my Merc 496 back online after doing just this with a Holley HP. If you get the right harness for it, it will be about as close to PNP as you're going to get. You'll have to splice in all the matching connectors, but they'll all be there. Even then, you'll use the WBO2 to tune it, the disconnect and remove the WBO2 and run it in closed loop, like your OEM ECM did before your rebuild. Running WBO2 in closed loop is widely discouraged in a marine application because the water in the exhaust stream will sooner than later kill the WBO2.

The most economical and practical way of doing this is to use the WBO2 socket(s) already in your manifolds, install the engine and build an AFR table with the boat in the water, send your ECM to someone who knows how to tune it, then remove the WBO2(s). If you have not made any significant changes to the engine that would change the fuel demands, this might all be a waste of time and resources. That said, Merc left a lot of performance on the table tuning the PCM555 to protect the "wet biscuit" hypereutectic cast pistons. Assuming your VP was the same, since you've gone with forged pistons, you can remove some of that neutering through tuning.

Thanks. Brad.