Remove Mercruiser catalyst
 

I have a Mercruiser 350 with the catalyst system on it. I am wanting a bit more power and was thinking of pulling the cats and maybe putting headers on it. Has anyone worked with this system yet? I don't want to make a mess of the system by pulling stuff apart before I know what I am doing.

I] I don't want to make a mess of the system by pulling stuff apart before I know what I am doing.[/
well... THIS puts you in a 1/2 of 1 % minority of people here...

before you do anything, get the FACTORY workshop manual .
have a quick look at where they put the lambda sensor if it has one... if it is before the cat , i would suggest you can dump them with no issue... if they are after then you are going to have to think how to make that signal correct without the cat. study the worksop manual pretty throughly and that will have a detailed explanation of the sensor array and operation and essentially tell you straight away if taking them off will screw you up. on the cars it was directly dependant on where the lambda sensor was...

The system has one sensor before each cat and one after each cat! The wires go back to the engine computer. A buddy has an 8.1 cat engine and his is set up the same way. He ran with the sensors disconnected and it threw fault codes! This is why I am asking.

If this is like an automotive setup...

THe sensor BEFORE the cat (between engine and cat) is the primary O2 sensor that does the work of telling the ECM what the air/fuel ratio is. This sensor you do not want to mess with.

The sensor AFTER (between cat and water) is there only to monitor the function of the catalyst. If you disconnect this, it will send an error code. If you pull the cat, it WILL send an error code. There are two options though to still be able to remove the cat and trick the computer. Both of these options have tons of history out there if you do a little searching.

#1 - use a spark plug non-fouler spacer to space the sensor further out of the exhaust stream. This will trick the sensor to send an incorrect reading that will tell the computer that the cat is still there and functioning. Here is a decent "how to"
http://www.audizine.com/forum/showth...-High-Flow-Cat

#2 - using radio shack components, build a sensor emulator that tricks the computer into thinking it is getting the correct reading. This will take a little more technical know-how and reasearch, but can also easily be done.

The third option is to pull the cat, and just live with the light. It should not effect fueling or performance...but simply tell you that the cat is missing (which you obviously know duh!)

I'm not sure how far along things have progressed with these systems, but what we'd do in the past with cat-delete systems is to replace the after-cat sensor with an appropriately-sized resistor which tricks the computer into thinking all is well.

You have to measure the current flow through the sensor circuit with an ammeter and do a little math to determine the resistance of the sensor when it's providing the correct reading under normal operation. From that measurement you can calculate the resistance using [R=V/I]. Replace the sensor with the desired resistor and you should be all set.

Changing the exhaust will not give you any signifcant power gains. Maybe 1-2mph at most.

thats true griff for sure as long as they are working but they make a lot of heat and when they foul at all its a bad deal and expensive... i would try to get rid of them just to make a cleaner cooler fractionally better flowing system if it can be done without screwing up the sensor inputs.

well... as mentioned accurately above, if it has after cat sensors you need to determine what that signal is and replicate it... sometimes ( again as noted accurately above) it is a matter of a resistor to put the reference voltage where it needs to be... but the factory manual will tell you this in the diagnostics for the sensor.

I like the Radio Shack option from above, but I am not an electrical guy. There must be something out there. Catalysts have been around for too long for there not to be!

The amount of time it saves you might be worth the extra $$..

http://www.cpperformance.com/p-16709...-computer.aspx

Haxby!
You 'da man!! Thank you very much. That was just what I was looking for! Have you used this yet? I think you are right about saving the time.

Has anybody out there tried it?

Thank you again, man!

exactly. the answer for sure

Well, there ya go. Plug 'n play, call it a day.
:cool:

Here is a MUCH cheaper and simpler "plug and play" solution.
http://www.afterthoughtsauto.com/o2sim.html

I would not mess with a plug in computer that adjusts fueling curves by modifying the O2 sensor readings...this simple solution above simply tricks the ECM that the Cat is still there.

The ad for the above site says that it does not work with the later vehicles (only up to 2003), so I doubt it works with the Mercruiser stuff. Also, I don't know if it will plug in.

I like the one from CP Performance because it is made for marine products.

Drivehard - How do you know that it adjusts the fueling? I don't see why it would need to.

Looks like the CPPerformance Maxvolt system may be the part for bypassing the system if it works with the Mercury ECM programming. CP can tell you that.

However, be careful here. check your engines warranty carefully. The new catalyst marine engine emmission systems are required by law to carry a three year warranty and it also has a bearing on the standard engine warranty. Not sure how yours is affected but if you have a warranty issue. If you have modified your exhaust and engine in any way your warranty is out the WINDOW!. Just a thought.

As for additional power I would like to see an actual dyno report on the 10-15HP gained from this system, what size engine etc. If you really get 10-15 HP on a small block that might represent 1 mph on your boats performance? NOt a lot so consider that before you go just changing exhaust or disconnecting this system.

You might be better of just considering the addition off muffler bearings or the alternator phase shift capacitors !?

Best Regards,
Ray @ Raylar

I'm not sure if it's changed but when I went to Merc school a couple years ago for the catalyst engines they were not running closed loop. There is a separate computer monitoring the exhaust /emissions system and it can talk to the engine ecm but it is not altering the fuel curve based on lambda readings. I would guess the MaxVolt deal just tricks the ecm into thinking the O2's are still there and doing their thing.

The rest of the story
 

Hi Ray,
I have tried polishing out muffler bearings before, but they just don't shine like a nice set of headers! :) You have helped me realize that a few horsepower may be nice, but what I really want is a better looking exhaust system. Thank you for making me think!

Haxby - What I have since learned about the Mercruiser catalyst system is that all of them run closed loop and it is self contained in the one engine controller. The part from Afterthought Auto will NOT work on vehicles later than 2003 because the engine computer does a test on the catalyst. I don't no what the test is, but the part from CP Performance runs the test as well as some other things that I did not pick up on.

Who is going to be the first to report on this device? Me?

It seems in the past that anything in a boat runs about 10 years behind the auto industry...figured that the marine injection system would be what the auto injection system was back about 2003. What does the second O2 sensor look like "post cat"? Is it a 4-wire?

Why would you have an O2 sensor pre-cat and not run closed loop? That seems odd to me...unless it is there only to compare values pre and post cat. Wow...that is a lot of cost just to monitor that the cat is there and functioning.

Maybe I am way of base here...but if I understand how the system works, this is what I believe is happening.

To answer the question about fueling...if I read the directions correctly, it is only making three connections PER SIDE of the engine.

One to the ECM side of the second O2 sensor
One to the sensor side of the first O2
One to the ECM side of the first 02 sensor

So...the connection to the ECM side of the second O2 sensor is simply to trick the ECM into thinking the second O2 sensor is getting the correct readings that the cat is still there. That sensor is no longer needed though...

The second two connections basically "condition" what signal from the primary O2 sensor that the ECM is seeing. The ONLY thing that little box can send to the ECM on that wire is the air to fuel ratio. It can not change anything else. So what I believe is happening is that the box is telling the ECM that the engine is running slightly lean from where it is really running...which makes the ECM dump slightly more fuel into the mix.

If the primary O2 sensor is not used for closed loop operation...I would call total BS that the box could effect operation AT ALL...other than to keep it from throwing a code.

If this is the case (which I totally believe is possible)...how could they possible have three different settings that would change the power output of the engine? I'm sure the main ECM would not change fueling or spark timing based on what the "cat computer" was telling it...so I would for sure call "BS" on this little box making any difference other than to keep that little dash light from popping on.

Drivehard-
I agree. The pre sensor is still driving the fueling via running in closed loop control at the slower speeds. The stock system on cars and boats go rich when you go to WOT. And yes, the post sensor is now gone, but the pre sensor has to stay in the system. That is why you can now buy headers with a sensor hole in them. And that is for both sides of the engine.

All four sensors are identical and they are 4 wire sensors.

They are not saying there are three settings, they are saying you can use it in three different applications: headers without cats, stock exhaust without cats, stock exhaust with cats but without the post sensor.

I have heard that there are a lot of post sensor failures with the stock setup.

I haven't spent the money yet, but I did speak with a few different people at CP. They said they have sold some kits, but they would not tell me who or what engines they went on. They said they have not had issues with this system.

So, who out there has tried this system? Someone has!

The issue is that this device is recognized by the Coast Guard as an electronic device specifically designed to illegally modify a complient engine in many areas. It's a fine or impounding waiting to happen. They have bulletins infroming them to look for these units. If you install them you must hide them and then the issue of the cat being missing. There may be an after market device that looks like a cat but is a thru pipe of sorts.

If the cats are missing and the Coast Guard asks some will answer the engine is modified and makes over 500 HP. A cat is not required. They will look for a blower sometimes.

If the light is on after pulling a cat off and the Coast Guard now is checking for this. You get friend.

I know a couple guys who just got their boats factory new and ordered the boats without cats and stated intended use in areas outside the US. No questions asked.

A paralegal said that if the vessal is retitled (aka straw deal) it slides through where autos or trucks would not.

Next boat I get will simply have 525's in them as the engines have headers and no cats.

The Coast Guard has no jurisdiction regarding emissions, so I don't know where this device is "recognized" by them. Do you have a copy of one of these bulletins you speak of?

If a stock Merc exhaust system is used, but the cats are removed, there is no way to tell by looking at the system from the outside other than the Check Engine light being on; it would have to be disassembled. This device is suppose to keep the light off.

Only the Federal EPA and CARB have emissions jurisdiction. The EPA and CARB are so broke they hardly check cars anymore, never mind boats! I have had the Coast Guard check for safety gear like an anchor and life jackets. I have heard of them doing noise testing on small lakes. I have never heard of them checking for emissions. Other than pulling an engine and putting it on an emissions bench, I don't see how they can replicate the 5 mode emissions test in a boat.

What make/model of boat are you wanting to try this on?

I would like to see it tried on any marine catalyst engine, but preferably a V8 Merc.

Engineer:

This is your thread and you're the "engineer", so why don't you buy this system, put it on your boat and report back to all us interested parties if it works properly and you have good results.
My personal opinion is that it is not the cats on the new engines that are keeping you stock power down, but the special camshaft profiles, fuel mapping and tuning that must be run to keep the engines in the emissions compliance numbers the EPA is requiring on these engines.

If you reaaly want and need more power you will have to change the camshafts, remove the cats for a better power producing exhaust and completely re-ECM the engine for the proper fuel and spark mapping that will support and work correctly with these power adding modifications. If you get somehow nailed for these illegal modifications then that's your issue to deal with. If you choose to do it and have great results and never have compliance issue then you're the ultimate winner!

In other words, just eliminating the cats from your stock engines is not going to add squat to your available power from those engines! Unless you are prepared to go into the engine and do the real power increase upgrades, why even bother with the cats!?

Best Regards,
Ray @ Raylar

WOW! Why the hostility?

As a marine engine builder, I am surprised that you didn't know that the camshafts are the same between the cat and non-cat engines. Also, if you look at the fuel flow (or injector pulse width) and ignition advance at WOT, you will see they are almost identical between the cat and non-cat engine.

Lastly, my issue has to do less about power and more about the way the engine looks. If dumping the cast gets me a few extra horsepower, then great.

It may be my thread, but I am just looking for info before my warranty runs out. I am sorry if my questions annoy you.

No Hostility on my part here, just a little head scratching trying to understand if you already know all the information, have already done all the research to identify the same camshafts, same injector pulse width, same timing advance, you must already have some pretty sophisticated equipment becuse there are few if any companies or individuals outside Mercury and their owned ECM company that can read this newer ECM family,those pulse widths and timing with standard industry scan tools. So it sounds like you are way ahead of anyone on this forum on this cat-versus non-cat information, data and knowledge and from your own research, what the hell are you waiting for!
No that's not hostility its just wondering why you are on a budget technical forum asking for confirmation of your already gleened knowledge and expertise in this matter.
I know what you really want I think in my opinion is someone else to be your guinea pig, buy the expensive parts avaiable and tell you whether it works or not so you don't have to put yourself out to do it or spend the money if it does not work. If this opinion makes me seem hostile I am sorry but that's just the way I feel after reading your previous posts and discussion. If you really have done your homework, you know it will work and you really want to see if you will get more power and you like the look of taking them off and adding an aftermarket exhaust, then by all means get busy and do it. We would all like to know of your success and improvements.
Not hostile, just waiting to hear of your success with this project.

Best Regards,
Ray @ Raylar

Ray - You're kidding me! Right? What are you going to do when the only engines you can get have catalysts? This guy sells products to read just about ANY marine ECM. There is no magic here. For a shop as big as yours, you need one of their products:

http://www.rinda.com

I am not looking for a guinea pig, just want to know who has tried this box from CP Performance. At some point, my warranty will be over and I will want to look at a set of nice headers. Perhaps by then you will have this figured out and will be able to guide customers and sell product.

Ray, my apologies. I should have told you the whole story. The camshaft part numbers came from a call to the Merc dealer. They looked up the parts and said they were the same.

Regarding the fuel flow and engine timing, that came from a guy who had a pair of catalyzed 8.1s and a Rinda Technologies tool. We compared the numbers to another guy's boat with a pair of 8.1 without cats. Part throttle, the cat engines burn less fuel, but at 5000 rpm they are about the same. And this makes sense as they both make about the same power.

I think Raylar knows about the Rinda scan tools since we have been using them since 2001 and referring performance boaters for just about as many years. We have the most recent software scan version on our laptops and computers. Just so everyone else here knows, there is no Rinda scan tool to my current knowledge that reads or displays injector pulse widths and if you graph and record on the tool you can follow the timing advance if you make full consistant rpm power pulls, but if these are not done on a dyno with loads or in the boat with loads, these readings just reving the engine are pretty much useless.
Yes ,I do know a little about marine ECM programming and systems since we do that everyday for a living and we have reporgrammed hundreds of Mercury ECM's and many Delco Mefi ECM's for hundreds of marine engines.

There have been so few new performance boats built and equipped with these new engines, let alone performance versions that there is no demand or resonable need at this point that will support product development or investment in upgrading these engines let alone trying to keep from breaking laws with respect to tampering with the systems and keeping them in some form of allowable compliance.

When it comes to the new marine catalyst equipped engines I do not know specifically all models build specs or OBD-M controls and tuning in detail and I do not consider myself yet an expert in these new catalyst equipped engines because we have not made that a priority in our offerings at this point.
I do know that when we come out with our products, kits or builds for some of these specific emmission engines it will be done right and they will perform properly although they will probably not always be emissions compliant.

Good luck with your research, I hope you achieve success and accomplish what you are trying to upgrade.

Best Regards,
Ray @ Raylar

Rinda does show injector pulse widths on many engines but ole' triple nickel does not share his data and it is therefore a parameter that is "not available" when connected to a 496.

Every 350 boat I ever scanned (which is about 4 engines) did show injector pulse width as well as many other parameters that Mr. 555 does not give up. That software actually adapts itself to the unit it's talking to as to eliminate mass confusion for guys trying to read an item that is not displayed.

Of course, most of this selective data display is based on the menu item you chose when you first connect..

This could have changed over the years for the 555 with DTS??? I'm not sure bout that.. Going back to the 0308 it holds true

Digging this back up. Has anyone done a cat bypass?

Came across this thread now. I installed the O2 by-pass (link below) and it works perfectly. I kept the 4 catalyst and 2 - O2 sensors boxed it and ditched the cast iron. All 460 lbs for both engines. Then I purchased IMCO manifolds and risers. A
https://cimg4.ibsrv.net/gimg/www.off...476f103b4d.jpg
pair weighed 36 lbs. So I **** canned around 380 lbs. That's the weight of around 65 gallons of gas. I noticed a notable performance change which I contributed to the weight loss.

What I had to do is buy 4 brass plugs, drill, tap and install in the backs of the manifolds for the temperature probe. I also changed out the thermostat housing

http://www.cpperformance.com/p-16709...-computer.aspx

Mercruiser 5.0 MPI - Bypassed Downstream O2 Sensors with CP Performance Max Volt
 

I'm aware this is an old thread, but I'm also aware that a lot of people are still reading it (like I was a few weeks ago) trying to figure out how to correct an emissions error on their Mercruiser and/or bypass the downstream O2 sensors (which are prone to corrosion and failure, and arguably serve very little purpose).

I had an emissions error code on my 2011 Merc 5.0 MPI, and a very annoying repetitive alarm on my SmartCraft gauges.

I troubleshot it with a Rinda scan tool and determined it was my downstream bank 1 (port) 02 sensor. I actually replaced the sensor, cleared the code, and ran the boat for several hours to confirm it was fixed and I was starting off with a clean slate.

A few weeks later, I installed the CP Performance Max Volt Module to bypass the downstream O2 sensors. I have run the boat for several hours and it runs perfect. There are no issues. The CP Performance module is truly plug and play and if you can use a zip tie, you can install it without any issues.

The CP Performance module (at least in this application) does not alter your fuel mixture or have any settings that are changeable - all it does is bypass the downstream O2 sensors by simulating their voltage/resistance for the ECM. Since the downstream sensors only monitor the post catalyst exhaust gases, they have no impact on fuel mixture or engine performance.

Where a slight performance gain may be had is by removing the catalyst from the exhaust (it no longer serves any particular purpose, since my downstream O2 sensors are literally unplugged). I intend to remove the catalysts the next time I do manifolds and risers. I don't expect massive horsepower gains, but it common sense says it should open up the exhaust and run a little cooler. It also shaves a few pounds of weight from the stern of the boat, and it's a $1500 part (x2) that I will never have to replace!

Of course once you eliminate the downstream O2 sensors, you also have the option of upgrading to headers or some other aftermarket exhaust for even more gains (overkill in my case).

VesselView Mobile
 

Could VesselView Mobile be a solution?

In FAQ in the mobile app under "How Does The Fault Code Information Work?"
It says it's possible to
"Select the Active Fault notifications to turn off (set to silent) or turned back on (alert) at the user's discretion. This is useful it your engine repeatedly gets the same fault, for example, an optional sensor is not installed."

Sorry I can't bring a picture since I have not posted 10 replies yet. But check under FAQ in the mobile app, no need to have the hardware for reading in the app..
// Retro2

From a purely legal standpoint,...is it legal to modify the exhaust this way?

It is illegal…

https://www.epa.gov/sites/default/fi...etampering.pdf

The above civil enforcement document (from 2020) includes emission controlled marine engines as “in scope” (see section 213 of the EPA’s Clean Air Act).

Will they go after individuals? Probably not. But the shops that are selling and installing similar are getting hit with huge fines per instance (look into what some diesel tuners have run into… seen some of it on YouTube).

Example… https://www.thedrive.com/news/another-diesel-tuner-nailed-with-1m-fine-for-emissions-tampering

Probably not enough to go after in the marine marketplace as of now, but so long as the climate police continue to gain ground, eventually, they’ll start looking in that direction.