I was responding to Snowrunner about his 500EFI issues.

However, I will always listen to any feedback on the PF-4 system. My main concern is O2 sensor failure rates. I get about 8-10 hours before they fail. I am sure it is moisture in the exhaust post shutdown. I have the sensor in the dry part of the system, but 18 inches after the sensor is the water dump. Dry pipes are an option, but would have to build a very custom one-off as I have side exhaust. Thru transom is not an option.

Also, the engines were dyno'd extensively before installation, so Im pretty sure Ive got 80-90% tune dialed in. Most of my tune issues left are now on idle issues, and hot start issues. Which I think is related to the moisture in the exhaust, messing with the O2 sensors. I placed the bungs just above the elbow flange (about 2 inches down pipe). the goal was to be at least 18 inches from the water dumps. All the pipes are flowing down from the elbow, and into the internal mufflers. But I bet that just holds the wet in the pipe and takes out my sensors.

I tune alot of boats on the water using WB02 sensors, have you installed these directional innovate HBX-1 extenders? They are directional, they protect the tip from reversion but in my testing on water and on my dyno they absolutely did not change 02 readings, slow down response etc. I tuned a 322 baja with lightning headers, thing went thru 02 sensors in record time, these made them last night and day longer.
does your prfolow 4 look like a open plenum intake with 4 bbl TB on top or like a tunnel ram with a monoblade on front, the proflow 4 XT is one I was referring to making signifigant gains with (front mounted tb), Smitty
https://www.ebay.com/itm/27498899266...iABEgLQBfD_BwE

So this heat sink looking bung does that thread into the exhaust manifold and then the o2 sensor threads into that?

I use the 4150 throttle plate style, and a large K&N marine 5" tall air cleaner/arrestor. The XT was tested on my motors and gains were slight at best. I think with a bigger cam motor, these would make more power. I have big cubes but mild cam for low and mid-range torque, so the XT was not any better at these lower RPMs. I almost put them on because they are also pretty cool looking!

I like the bung extension. I think I will look at these as a possible solution. many thanks!

-jeff

yup, sounds similar.

Mine is hibernating in storage for the winter, will be a spring project now.

let me know if you find anything

Yes, and its directional, I have shimmed them with spark plug gaskets, filing brass washer comes with it, etc, they work, Smitty

Yeah whole different setup than the proflow4 XT's ive been modding/using, they are a mini tunnel ram with monoblade tb, they work very good, great hp on top once modded, unfortunately, not at all like a proflow 4 so my results are irrelevant to yours, Smitty

Will do last night I changed the throttle positioning sensor and another sensor on top of the manifold parts changing try to chase this issue and in the spring I’ll change fuel filter I swear i am moments away from pulling this set up out and building a dart block set up with an EFI carburetor and calling it a day I just can’t handle no tuning and no modding of this motor mercruiser has a cease and desist order on tuning for all catalyst engines tell me your thoughts if you don’t mind.

Hey if i had to start over, that is the route I would go also. 16 is too many injectors to go wrong in my opinion. Only reason i am staying put with Mefi3 MPI is I've already bought 16 new OEM injectors 3 years ago and so far, plugs look real even. But one goes off and you can lose a motor quick. Not the way to go. I like your idea.

I presume you have the cat converter? That was the most ignorant thing - adding those. So much money and takes up valuable room, and adds weight. For what - to REDUCE emissions. Over a whole season I bet on a boat that DIFFERENCE in emmisions would be about what an 18 wheeler puts out in probably one minute. Follow..... the ..... money I always say. . Not what was is the smart thing to do, or the right thing to do..

Well that's been the unspoken standard at the OEM level forever. The OEM's have been trying to thwart tuning forever.
But with you saying that, is it hearsay or have you seen something in print from Mercruiser?

Are you having troubles with O2 sensors surviving in an OEM catalyst situation?