CAT bypass pipes with no CEL's ? (5.2)

Spacers will not work alone, out of range

Make a box that sends a regulated voltage to the signal I remember about 1.2 volt and a 20 ohm resister on the heater circuit and your good to go no CEL. Basic 02 stuff you can find anywhere on the web

 

I've never seen this addressed on FChat, but is the post cat O2 sensor only monitoring cat performance or does it fine tune fuel trim as it does on other cars?

 

The system needs to read different values from the front and rear O2 sensors. The front sensor needs to slowly oscilate between rich and lean as the ECU manipulates the mixture, while the rear O2 sensor sees an essentially constant oxygen percentage. In addition, the read O2 sensor needs to read rich durring warmup.

This is outlined in the WSM. I'm sure a EE with some meters could figure out how to trick the system.

 

It seems to be more than that. The rear O2 sensor is looking at post cat exhaust gases and is used to further correct the mixture in conjunction with the front sensor. For this reason I have never understood how a car with bypass pipes can run right unless the ECU is reprogramed. The ECU is expecting to see post cat gases and without cats it will be seeing the same mixture as the pre cat sensor. It's not just telling the ECU the cats are or are not working. It would seem you can do what you like to fool the ECU from throwing a cel but if it isn't sensing the actual post cat gases it will not be sending the ECU the correct signal. I.e., you can send the ECU a fake signal that tells it ever thing is in range when in fact the mixture isn't correct. The rear O2 sensor is in the fuel trim loop and bypassing the cats has to make it see wrong exhaust gas composition and throw off the trim. Just another reason to own a 95.

 

Great post John. I've wondered the same thing myself. They sell those "O2 simulators" on various racing-oriented sites, but as you address above, the 5.2 Motronic systems seem too complex for this to provide an actual fix.

EDIT

I've only heard of one group that has been able to crack the code on the 5.2 Motronic units for reprogramming purposes.

 

I have a reprogrammed Motronic 5.2, and I am very pleased with the fact that I don't have to play games with it.

No CEL codes for CATS, Air Injection, SDECU, or the bypass valve, which I don't have. Downside, it was $2,000.

Mark

 

Where did you purchase it?

 

I am also interested in straight pipes for my 98 but I cannot rationalize the $800 Fabspeed price. As others have pointed out, its just pipe.

Could an exhaust company create these from stock T304 for substantially less? Maybe we could group buy with a ceramic option, etc. Just having trouble with the price...

 

Had it done through fabspeed.

 

I think Larini has pipes for about 300$ but I can't remember where I saw them.

 

Folks this is so easy to do, grab a couple sections of tube, some flanges from vibrant and weld it up or have your favorite welder weld it up. No thought involved here just get your ass up and do it. You can get a cheap welder and the parts for less then what you would pay for them

 

I rather make things but again thats what I do for retirement at the toy shop. Maybe 3-4 hours at most including lunch and a trip to the chronic lounge

 

I'm not sure why you want to run straight pipes is it not cheaper to just buy hyper flows or something similar and let the computer do its thing.

 

Guys,

Here's my take on this. Its just based on my logic so if I'm wrong, please explain it to me.

Keep in mind, the '95 355's don't use a rear O2 sensor and they work just fine at maintaining the proper fuel/air mixture. But, for the sake of argument, let's suppose we have an original design without any cats at all. The O2 sensor is there to monitor the fuel/air mixture and send appropriate signals to the ECU to adjust the fuel flow through the injectors as needed. Obviously, a second O2 sensor couldn't tell the ECU anything new and would be totally redundant and unnecessary.

Now we add a cat into the system. The cats only purpose is to oxidize any unburned fuel to comply with current pollution control standards. It serves no other purpose whatsoever. If its new and working correctly, nothing extra would be needed since you can't adjust anything in a cat. The 95 355's are an example of this.

But, a cat's ability to do its job slowly deteriorates over time so what was needed to guarranty minimum standards was some way to monitor the cat's performance in real time. The post cat O2 sensor was that solution. Its purpose is to measure the exhaust stream and, if its above the minimum threshold set by the pollution control standards, to notify the ECU to throw a CEL.

If a change in the fuel/air mixture for optimum performance and efficiency is needed, that's done by the precat O2 sensor. Now let's suppose the post cat sensor detected something amiss. Its only choice would be to ask the ECU to further lean out the mixture below what the precat sensor had set for optimum performance in a vain attempt to help a failing cat, not something I would want my car to do.

Logic tells me this is the only reason for the second sensor. If you don't have cats, you sure don't need one. And if you do (like with the 95's), you still don't need one unless you want to monitor the cat itself. And then, its addition is likely to only reduce engine performance (I'm talking horsepower here, not pollution control efficiency) as the cat nears the end of its useful life.

OK, guys. Tell me where I'm wrong.

 

HJP is correct. The secondary downstream O2 sensors main purpose is to tell the OBDII system if there is an issue in the Cats for the purpose of diagnosis and safety (a plugged cat CAN generate enough heat to burn a car down). If it does no see a reading withing the parameters it is expecting, it will throw a code. If you trick it because you are running test pipes, that is fine, but if you trick it and are still running cats, you are asking for trouble.
As for the 5.2 systems making any adjustments based on the downstream o2 sensors, I don't know for sure, but in most systems I've seen, the only think they can do is trigger a fixed map limp home mode, not a fine adjustment. (Disclaimer) BUT I DON'T KNOW FOR SURE ON THE 5.2!

 

Not correct. It's in the fuel trim loop for the 5.2 as indicated by the WSM. {edit} Understand that the wording is typically Ferrari "unclear". The ECU is looking at both O2 sensors all the time. It has no idea how old the front sensor is. It is making adjustments based on info from both, but if the front sensor is working as intended little further adjustment may be required.
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Spacers alone work just fine for me, but you have to use the "L" shaped spacers not the straight ones. Been nearly 3 years and 5k miles with no CEL. Even passed emissions inspection.

 

With all due respect Johnk, I think this still supports my contention here.

Not to be argumentative but, since there are two identical sensors, of course the ECU monitors signals from both, just for different purposes.

Clearly Ferrari is saying the post cat sensor's first and main purpose is to monitor the condition of the cat. Then they say if the first sensor is misbehaving for some reason, the ECU would then correct the mixture from comparable signals received from the second sensor. After all, its just another O2 sensor. But if the front is working fine, the second just continues to do its primary job, monitoring cat performance. In other words, its a redundant check on conditions to help preserve cat performance, not better engine performance.

I still contend this is all about the cat, nothing else. You don't need to adjust the fuel/air mixture twice if the first sensor is working correctly. Of course I concede there's nothing wrong with having a back up. But I believe that's all its second function is for, just a back up.

 

Nope, no issues at all. No heavy gas smell or burning. Just pure exhaust sound and flames