Keep Precat or remove it? please advise

I installed Fabspeed headers and as you know they do not have precats. I got some CELs that I believe now have been resolved by using a pair of O2 extenders with built-in mini cats. If we’re to make a guess, if you rebuild the stock headers without precats for install on a North American market car, you may likely have CELs. But like me, the installation of O2 extenders/mini-CATs is an option to mitigate that.

Steve

 

Remove those precats, install 02 mini cat extenders and you will accomplish two things
1 way better sound and unrestricted exhaust and performance.
2 prevent that the mini cat gets loose, rattles inside, destroys itself and your engine ends up suctioning particles causing severe damage to your engine.


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I have swapped my OEM headers for a set from fabspeed. I have them encased in Capristio header blankets. Am very happy with the sound and performance. And I still have the OEM headers to make the car original if I ever wish to.

 

Its one of the best upgrades you can do on a US spec car... They rob power and can potentially detonate your engine!
Edit: *assuming* it's legal in your region

 

Steve, don't you have high flow cats as well, correct? THAT is what triggers a CEL. The removing precats but keeping OEM cats shouldn't trigger a CEL. It will have high emissions on start but should be fine form that perspective. It may be an issue in CA relative to visual inspection and passing smog.

 

I installed Fabspeed headers w/o precats as was happy with them, as I didn't want precats. I knew someone who had the material break up, and caused engine damage to the point of engine rebuild...

If you run w/o precats, you'll probably get a CEL. Mine triggered all the time, regardless of what Fabspeed said. O2 sensor extenders greatly improved that, but it would still trigger every 2 months or so. Reset is simple though, w/ a $20 obd reader.

 

I have stock cats and got CELs after installing Fabspeed headers ... which eliminated the pre-cats. The O2 extenders / mini-cat combos took care of the CELs

Steve

 

Thanks. I haven't been motivated to change but I didn't realize that would trigger a CEL. I guess I didn't read enough of those threads. Thanks.

 

Exactly the opposite
Removing precats is what triggers a CEL, installing high flow cats most likely would resolve the CEL
Why? Because the stock configuration has the downstream sensor BEFORE the bigger main cat. And with the hyperflow car you can install it after the main cat.
Please see my post #87 here
https://www.ferrarichat.com/forum/posts/145821856/


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It appears I was premature with my assessment that the mini-cats have resolved the CELs. Today, got the dreaded CEL again. Feralc might very well have the best answer to all of this. That is, the position of the downstream sensor is a key component.

Steve

 

I'm running fabspeed headers + sport cats with O2 extension. No CEL.

 

I swapped out the stock ones within the first month of owning the car just to be safe. These engines re not cheap!

 

Hmmm...well, if that makes you feel better.
But fine today may not be fine next year.

 

Keep in mind that Rifledriver has stated that he has never seen precat failure on an otherwise correctly running car. Ie, car is running poorly and owner ignores the running condition and keeps on going.....

 

I don’t doubt Rifledriver, but I know people who have tracked their properly running 360s, and while none has suffered pre-cat failure in the sense of having cat pieces sucked up into the engine, they have had them come loose, and on opening up the headers, have found that pieces had come off, with the remaining cylindrical portion rattle around inside the headers. Where the loose pieces went is anybody’s guess, but these examples show that a non-malfunctioning car could still suffer pre-cat issues if they are tracked and/or driven hard. It’s possible that the majority of Rifledriver’s clients don’t track or drive their cars hard enough to get the heat and vibrations up high enough to cause pre-cat problems.


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I don’t doubt your info or the possibility, just wanted to share another perspective.

 

Resurrection ...

Can I ask what CEL codes you guys were getting when the precat material failed? 0421/0431 (warm up catalyst below threshold), or 0420 / o430 (catalyst below efficiency)?
Can I also ask if you removed the precat, and install O2 minicats, does the minicat go on the upstream O2 sensor or downstream O2 sensor?
If you install sports cats (hiflow), do you then put the O2 sensor extender on the downstreams sensor?

 

I have been going through this rat race for a while now. I replaced the stock headers with Fabspeed headers. As you know, the stock headers have a pre-cat. The Fabspeed do not. The upstream O2 sensor installs near the collectors on the Fabspeed headers. But, now, you have less catalyst material between the upstream and the downstream O2 sensors.

My first problem (Check Engine Light) is the same as many others experience ... I got P0421 / P0431 codes ... Warm Up Catalyst Efficiency. This means that the downstream O2 sensor has detected that the the converter is not working as efficiently as it should. This kind of makes sense because the downstream O2 sensor is stuck into the center of the catalytic converter -- not behind it. And since the stock headers were replaced, there is is less catalyst between the downstream and upstream sensors. This would be the same code that someone would get if they deleted the cats altogether.

For many (some) the solution is to install O2 sensor extenders or small mini-cats into the bung on the stock cats and then install the O2 sensors into the extender or mini-cat. I have tried both without success. Others have reported doing this resolves the issues, but not on my 360. Well ... I suppose it depends how you define success.

The P0421 / P0431 codes have gone away ... replaced with P0139 / P0159 codes ... O2 sensor circuit slow response. Now, I am not sure what could be causing this. I have tried replacing the O2 sensors but that did not help. Some other things are:

• Excessive fuel in exhaust stream ... but, I do not have other symptoms that would indicate this.
• Bad O2 sensor ... but, I replaced them.
• Leaks in fuel system or exhaust. Tested for that and do not believe it is this.

My thought is that if I install the O2 sensors as they are meant to be, they are in the exhaust stream and then the ECU thinks the converters are not up to snuff. If I put extenders on, then the O2 sensor is backed out of the exhaust stream and the ECU thinks they have slow response time.

So now, I am thinking of having the shop install a bung on the downstream side of the converters. Just past the last bit of catalyst material before the converters mate to the pipes to the silencer. My thought is that I will then install the O2 sensor directly into the exhaust stream ... same as original ... but, now, I have re-introduced more catalyst between the upstream and downstream sensors. My hope is that the ECU will once again believe the converters are back to snuff and with the downstream sensors back into the exhaust stream they will not be suffering from slow response times.

I surely hope this resolves everything. Keeping fingers crossed.

Steve

 

Does your shop have a emissions analyzer? You might try just checking to be sure you don't have a weak plug or coil and the car is actually running a little rich. What extenders did you try the 90 deg or straight? Moving the bung should help as long as its something else causing it.

 

What a PITA. You've been at this forever....
If you don't solve this, it might be easier for others to just replace old headers with new stock headers if you think the age of the precat is a worry. Life is short !
I had success with the decat on my 355 using extenders and was hoping you would find a solution for the 360.

 

I am fighting the same codes but with a different cause. The catalyst material on a US 360 CS is in 3 stages:

Upstream O2 sensor
Precat
Thin cat
Downstream O2 sensor
Main cat

In the stock configuration, there are Precat and Thin cat stages between the two o2 sensors.

Due to a broken internal cat, bot cats were rebuilt by Fabspeed, BUT and this is a big BUT, they only put back the main cat, without any thin cat. Therefore there is only the precat material between the up and down stream o2 sensors.

So, as soon as the drive cycle is complete, the two codes 0421 /0431 (heated cat below threshold) show up. BAM.

I am thinking a Minicat extender may solve this issue. But the last time I tried it on bank 2, the slow cat signal CEL came up due to the large right angle dead space of the minicar extender.

If the Minicat does not work, I might want to add a bung after the main cat but that is a large piece of cat material and there has to be a reason why Ferrari put the rear O2 sensor after the thin cat, as opposed to the very end. Maybe it will also throw a slow signal CEL too.

In the end, the bullet proof solution is to go back to the stock cat converters with thin and main cat materials. No real solution yet....

 

yes you are correct that the stock configuration is upstream 02, precat (these two on the headers), thin cat, downstream 02, main cat (these three on the cats)
And you mentioned that your stock car was rebuilt by Fabspeed and they only put back the main cat so you only have the precat between 02 sensors.
You have very little scrubbing material between 02 sensors.
The extenders might help, I resolved my issue when I removed my stock headers along with the precat, BUT on my case I have high flow cats so the main cat is BETWEEN both sensors (that is more scrubbing material than stock)
The bung after the main cat will fix it for sure, early 360s and Euros are this way.


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Yes, I have little scrubbing material between the 2 O2 sensors, and old cat material at that.

So in your case, fabspeed headers, fabspeed sports cats, fixed the CEL issue? Is that correct?