Mercury Fault Code 312 - Port side pre Cat oxygen sensor slow to respone

[Searay205]

Hello,
Pulled Mercury fault Code 312 this my Rinda after the alarm went off. Mercruiser 5.0 mpi with Catalyst (puke). Boat runs flawless and oxygen sensor was replaced 2 years ago. Tested oxygen sensor with multi-meter and heater leads had 9.5 ohms and open connection between signal wire s and heater leads. So by the book it shows good. I made a home made circuit tester using some old o2 sensor leads with 1.5 volt AA battery. RInda showed signal as 1318 which is well below 1955 BUT all other o2 showed the same 1318 so that test was inconclusive. I not getting codes on other oxygen sensors so how can they have the same ready as suspect and not show code.

Any help would be greatly appreciated. I

 

[Searay205]

More information. Rinda pretty nifty tool. I found the freeze frame data and it only hit one time. Ran an additional 3 hours with no more codes. On the flip side I hit the over rev 19 times, LMAO!!! I love it. 5.0MPI in searay 205 sport crazy. I swapped stock 3 blade with 5 blade. Boat was dangerously fast with stock hit 62 mph felt like black ice. with high five solid 56 doesn't matter if 1 person or 7 person on board. pull tree off shoreline with torque

 

[Noidea44]

I am experiencing the same code on a 2010 350 Mag. I brought it to a mercruiser certified mechanic and even called mercruiser and no luck on resolving. I purchased a Rinda over the winter and now beginning to self diagnosis.

any insight is much appreciated.

 

[Searay205]

The RInda is powerful but requires brain power. It much more than a code reader. i got a used service manual #49 off eBay for like $25. priceless. goes into detail on how the entire PCM operates. The first think you will learn is don't buy a mercuiser with catalyst. Incredibly complicated. The PCM is constantly looking for faults. The smartest thing I did was buy the CP performance catalyst emlimantor and removed the rear o2 sensors which corroded through every 2 years. Horrific pathetic design. I also removed the catalyst. So now what can get hurt with a rich or lean fuel mixture nothing. I also used a .25 cent connector to disable the siren (which i have tape over speaker) to unplug when a useless code pops up and enjoy the rest of my day. note the guardian system is still in play and can reduce power to prevent damage.

Back to our code. Mine hit once (first time out this year) and not again even though i ran another 3 hours. If I would have known that i would have erased and gone on with life. Again spend time learning the tool. If i knew then what i know now i could have seen the reaction time that instant and determined what the problem is. you really need the manual #49 as the rinda instructions are pretty lame. My guess is the O2 sensor had a blip, who knows. again get rid of the cats with the CP perfomamnce o2 eliminator and you just removed 4 headaches (2 o2 sensors and cats), only two left are the from O2 sensors which are usually pretty bullet proof. they are away from the exhaust discharge and stay dry.

Don't see an error for a sensor and think sensor bad think what is causing sensor to read bad. for example it you have a misfire that could cause this code, leaking injector, bad PCV valve. anything that cause engine to run rich. obviously could be bad O2 sensor. fk mercury get a wagner sensor have the price.

Keep in touch good news is what you learn on your boat is directly applicable to your car.

 

[Searay205]

oh i much rather smell unhurt fuel than skunk smell which is what the cats discharge. keep you cats they are worth money. i put mine in sealed bags in the attic. inboards are dead EPA killed them that's why you see all boats our size with outboards these days, rumor is EPA will require cats on those and they will be fed

 

[Searay205]

i also have the mercury service manual supplement with emission control again like $25 used. it show you all the pin outs for the CPU and cooling system. Not as important as #49 but with those two you know more than 99% of the idiot mechanics out there. the key is develop a understanding of what the live data looks like and find the variance. After about 3 hours of study i pretty sure i know more than 99% if the mechanics working at marine max...

with the pin outs you can take an ohmmeter and check the circuit in about 3 seconds. it identifies what and where all the fuses are.. truth be told once you learn it once its not that complicated

option two is buy a 350mag non-cat and be done with it. even if my 5.0mpi cratered i would go back with a 350mag non cat. holy hell that would be fast

 

[blcmcck]

FWIW, that code is often associated with a leaky fuel injector. Easy fix may be as simply as cleaning your fuel injectors.

 

[Searay205]

Makes perfect sense thanks blcmcck. Rinda will tell you pulse width of injector but can't tell you if injector is leaking, it just relays the signal the PCM is sending. First time out after sitting 6 months it makes sense this could be it. Plan on going tomorrow so with my new found knowledge will see what i can screw up, lol.....

 

[Searay205]

Another data point above 3500 rpm the PCM goes to open loop and uses a fixed program and the Oxygen sensor isn't used to adjust fuel trim. Mine engine would ping if I held above 4500 rpm's Unless i used 89 octane. After pos catalyst removed i use the cheapest fuel on planet 86 octane zero ping, oh my manifold temps are 139F when its 95F outside also..... loose the cats they do nothing but harm and cause grief and future regret. If you put fuel injector cleaner you may cause them to explode causing the planet to start rotating backwards and we would all get younger

 

[Searay205]

To bring closure another 4 hours running no code. My o2 response times were .09 rich and .06 on Port side and 0 on starboard side well below the .920 allowable. I did find cylinders 1 and 3 had 4 and 5 misfire respectively, I assume that is count since for that drive cycle overall engine misfire percent is zero. That is suspect since they are on the Port side and would cause that bank to run rich. I will pull the plug wires make sure no corrosion on terminals I had a similiar misfire on the starboard side and found the spark plug terminal corroded but it count was in the 100's. I pretty sure i put dielectric grease on all of them. Another note to fully clear the codes I had to go into freeze frame data and clear the codes there in addition to faults. if i just cleared the faults the codes came back.

Again 5.0 mpi in a searay 205 is a beast of a set up. The battery test gave erroneous results for whatever reason. it led me to believe there was a communication issue when there is not. Maybe resistance through CAN connector who knows. Pretty cool the Catalyst simulator definitely sends an fluctuating signal to the CPU I love it!!!!

 

[Lou C]

I give you guys a lot of credit that you have the patience to deal with this nonsense. In the future I’ll have nothing but outboards and most likely an Evinrude because it can meet the emissions regs without a cat converter. I don’t mind cats on vehicles but on boats they have no place; neither inboards or outboards. I’ll keep my Chevrolet in a hot rod!

 

[vortmaximum]

I am experiencing the same code on a 2010 350 Mag. I brought it to a mercruiser certified mechanic and even called mercruiser and no luck on resolving. I purchased a Rinda over the winter and now beginning to self diagnosis.

any insight is much appreciated.

Same engine. Same issue. Currently my port side post cat O2. Called dealer where I bought the boat used in 2015. Mechanic said bring the boat in. LOL hundreds of miles away. I asked can you just give me some starting points? Bring the boat in. Not possible, went nowhere. I have the techmate, I can read the voltage at all four O2s. I've replaced them, moved the around, cleaned them. Same result. Either terminal temp too high, Fuel too rich or too lean. Boat is running smooth as butter. I've noticed that when engine is cold, that post cat port side 'D' sensor is reading as it should. Within a couple minutes in drops off to zero while the rest are reading properly. The alarm inevitably goes off within an hour or so of run time. Bring to the dealer it says, not possible to original dealer. And a local mercruiser dealer to dx and reset alarm it is a minimum of $100. No one near me seems to have a clue to the mercrusier EMC system. So i clear the fault to not have to listen to the beeping. With the techmate I can also see the injector functions, they are all reading the same values, so I assume they are good. Frustrating for sure. I have new rotor, cap, plugs, wires within the last 2 years, so that is not the issue. At this point and after a few years of dealing with it, I assume it is just a poor designed system. The techmate and ability to read fault codes and clear them as more than paid for itself. Also have a buddy with a 2020 sea ray mercruiser and he also gets the same issue with the O2 sensor alarm If you figure it out please share. I'll do the same...

 

[Searay205]

Same engine. Same issue. Currently my port side post cat O2. Called dealer where I bought the boat used in 2015. Mechanic said bring the boat in. LOL hundreds of miles away. I asked can you just give me some starting points? Bring the boat in. Not possible, went nowhere. I have the techmate, I can read the voltage at all four O2s. I've replaced them, moved the around, cleaned them. Same result. Either terminal temp too high, Fuel too rich or too lean. Boat is running smooth as butter. I've noticed that when engine is cold, that post cat port side 'D' sensor is reading as it should. Within a couple minutes in drops off to zero while the rest are reading properly. The alarm inevitably goes off within an hour or so of run time. Bring to the dealer it says, not possible to original dealer. And a local mercruiser dealer to dx and reset alarm it is a minimum of $100. No one near me seems to have a clue to the mercrusier EMC system. So i clear the fault to not have to listen to the beeping. With the techmate I can also see the injector functions, they are all reading the same values, so I assume they are good. Frustrating for sure. I have new rotor, cap, plugs, wires within the last 2 years, so that is not the issue. At this point and after a few years of dealing with it, I assume it is just a poor designed system. The techmate and ability to read fault codes and clear them as more than paid for itself. Also have a buddy with a 2020 sea ray mercruiser and he also gets the same issue with the O2 sensor alarm If you figure it out please share. I'll do the same...

Ok your issue is different did you say "port side post cat O2" ??? the only purpose for the after catalyst O2 sensor (in manifold after cat) is to tell if you cats are working!!!! Nothing else, hope you don't have a bad Cat as they are $$$$$. I told you guys once loose the Cats, get the simulator. The precat o2 sensors are very important they determine air fuel ratio below 3500 rpm. again without the fragile cats who cares if it runs rich, with cats the pre cats o2 sensors better be working right. Do you notice your engine cranks a little before starting? vs a non cat engine. Reason is mecruiser cranks engine before firing injectors so its not a rich mixture and harms their precious little cats. Anything related to post cat is easily solved (so O2 sensors or catalyst) can be eliminated with simulator. I ran a year without cats and without simulator boat ran flawless just didn't have alarm siren since i disconnected it.


Again your problem sounds like a weak Catalyst converter since it is post and you moved sensors around and it came back to that one. I think there $1200 new. The post O2 sensors does zero except tell computer catalyst is working. Crazy a simulator is $400 and it removes both cats and both o2 sensors and tons of nuissance alarms.

 

[vortmaximum]

Ok your issue is different did you say "port side post cat O2" ??? the only purpose for the after catalyst O2 sensor (in manifold after cat) is to tell if you cats are working!!!! Nothing else, hope you don't have a bad Cat as they are $$$$$. I told you guys once loose the Cats, get the simulator. The precat o2 sensors are very important they determine air fuel ratio below 3500 rpm. again without the fragile cats who cares if it runs rich, with cats the pre cats o2 sensors better be working right. Do you notice your engine cranks a little before starting? vs a non cat engine. Reason is mecruiser cranks engine before firing injectors so its not a rich mixture and harms their precious little cats. Anything related to post cat is easily solved (so O2 sensors or catalyst) can be eliminated with simulator. I ran a year without cats and without simulator boat ran flawless just didn't have alarm siren since i disconnected it.


Again your problem sounds like a weak Catalyst converter since it is post and you moved sensors around and it came back to that one. I think there $1200 new. The post O2 sensors does zero except tell computer catalyst is working. Crazy a simulator is $400 and it removes both cats and both o2 sensors and tons of nuissance alarms.

Thanks for response. Yes engine cranks for a few seconds then fires. Runs beautifully.
Yes post cat O2 sensor, port side. Sensor ‘D’ reading goes to zero or flashes single digits shortly after starting.
After I bought the boat in 2015, I had similar issue on starboard, but that cleared up by replacing O2 sensor and running a little cata-clean through it.

I hope not the cat either, $1200 part? Erg.
When guardian trips, it doesn’t reduce power, so I assume not damaging the engine.

 

[Searay205]

What is your exact code. I cannot find the code for post catalyst o2 sensor slow to respond. Makes sense as again the post o2 sensors do not have the ability to change the oxygen fuel mixture so how could they be slow to repspond....

 

[vortmaximum]

What is your exact code. I cannot find the code for post catalyst o2 sensor slow to respond. Makes sense as again the post o2 sensors do not have the ability to change the oxygen fuel mixture so how could they be slow to repspond....

Will let you know exactly what it says next time out.

 

[vortmaximum]

What is your exact code. I cannot find the code for post catalyst o2 sensor slow to respond. Makes sense as again the post o2 sensors do not have the ability to change the oxygen fuel mixture so how could they be slow to repspond....

I had an opportunity to get out on the water. I took the port side post cat 'D' O2 sensor out and put one of the old ones I had replaced back in. It alarmed again. The smartcraft only says 'System fault' Oxygen sensor not working properly. I reset and turned off boat. A couple hours later when I started up I watched all four O2 sensor data on my Rinda. Upon start they all read in the 400-500ish MV range. Then during the next minute or so the 'D' sensor started climbing higher, rose steadily up to 2000 mili volts. Then basically froze there. A short while later the smartcraft went off. The rinda fault said it was indeed the post cat O2 sensor on port side, sensor D. The readin went to zero. The message was the terminal temperature is too high. So it appears as the engine warms up, the milivolts/temp on that post cat 02 goes too high.

 

[Searay205]

O2 sensor may have a bad heater. Surprised yours don't Rott out every other year like mine used to. You can check resistance across the O2 sensor terminals or pick up a new one. Again post o2 sensors are just an annoyance, no affect on how boat runs.