I've looked through some threads on the Forum about cat deletes, but I can't seem to get my questions answered.

I'm about to have to replace a pre-cat, so I was thinking of deleting both cats and just getting a good main cat.

Here are my concerns:

1. How much louder will it be? I like that my car is very quiet right now with the stock cats.

2. Has anyone done this and still been able to pass emissions? (I'm not talking about the visual inspection. I live in Texas.)

3. How do you keep the check engine light from coming on if you delete one or both of the pre-cats?

Thanks.

- Brian

 

I have an '02 Maxima GLE and I replaced the entire exhaust (manifolds to muffler) last year. If you like it quiet and legal, I'd recommend doing what I did, and replace everything with functioning parts. My '02 is my daily driver, so I chose to go the fix it right route.

My guess is that most people on the board that are in favor of deleting the pre-cats have two main reasons for deleting them: 1) it's cheaper to just gut the pre-cats instead of replacing as new ones are about $300 each, so it adds $600 to your bill unless you buy off Ebay or Rock Auto for slightly less. 2) gutting the pre-cats eliminates all chance of any of the honeycomb material inside the pre-cats from degrading and getting sucked into the engine and causing catastrophic failure.

Addressing your concerns:

1. Gutting the pre-cats shouldn't really make your car much louder or faster as long as you plug the O2 bungs with something.

2. Not sure what people do about emissions testing where they actually read the numbers from the tailpipe. Maybe the main cat can compensate for the lack of pre cats. I'm sure someone else can chime in...

3. From what I hear, there are two ways to keep the CEL off. 1) O2 Simulators which are illegal to buy, but available for sale online and simulate a properly functioning O2 sensor. 2) O2 spacers which move the O2 sensor back further tricking the computer into thinking that the emissions are normal.

Good luck which ever route you go...

 

Sanford7575,

Thanks for the info.

I've never heard of anyone worrying about the pre-cat pieces getting sucked into the engine. There's always positive pressure in the exhaust. The backpressure created by cats or smaller-diameter pipes is just pressure built up due to restriction, but it's still positive pressure. There should never be a vacuum in the exhaust.

The O2 bungs would be the route I'd have to go, I'm sure. Gotta figure out where to get those, though, because if I remember correctly, they have to be welded into the pipe at the right depth to work properly.

So what exhaust system did you get and how much was it?

How quiet is it compared to stock?

Thanks, man.

- Brian

 

Ill grab you an exhaust clip of my car. 03 6 speeds with all cats gutted and a slight exhaust leak

 

You can use O2 sims or an O2 extender (if there is room) to eliminate a check engine light. If all your state checks is for codes, you should be okay.

 

i thought both of these went together

 

Thanks for the info.

I never saw any of the threads where people were worried about cats getting sucked into the engine. It sounds absurd to me, but if someone has info on it actually happening, then I'll read up on it.

I'm curious how the car sounds with only a main cat.

 

For 3 years now, my '02 has gutted pre cats and the stock main cat and it is barely louder than stock. It only sounds a hint deeper in sound and no drone.

After the main cat, I have an OEM replacement Bosal B pip and Walker OEM replacement muffler. My original system rusted out and I didn't want drone so I went with OEM type replacements.

I love the sound and have no CEL because I have the o2 extensions. They screw into the o2 bungs and work perfectly.

 

That's perfect. Thanks!

What state are you in? Strict emissions standards?

I'll definitely go that route. I'll have to find those o2 extensions. Shouldn't be too difficult.

Thanks again.

- Brian

 

Is there a brand you recommend for the o2 extensions? Are they for the upstream, downstream, or both?

Thanks.

- Brian

 

New York, 2nd strictest state behind California.

for the spacers, you have 2 options. You can buy two Non-Foul plug spacers at an auto parts store and piggyback then and drill out the inner one, or go the lazy route that I went and buy the spacers on ebay. I think they are about $20 now for both (one for each downpipe o2 sensor).

 

You only need to extend the o2 sensors that are after the precats to pull them further away from the exhaust stream to lessen the sensing/reading.

 

Cool. Just ordered two. I'll have the exhaust put on after I get the extenders next week. That's a big help. Thanks so much.

- Brian

 

There's a few across the internet. My thinking was the same about the material finding it's way back.
But that's also what I have read.
I'm also from Texas, and plan to gut out the pre-cats as well.But that's later on .Let us know how it passes.

 

I don't have to have emissions until August, but I'll try to remember to let you guys know how it goes. I figure as long as it passes emissions with the main cat, it shouldn't be a big deal. There's the heavy loaded main cat sold by Warpspesd that works better than the stock cat, so that's my back-up if they do tailpipe testing. However, here in Dallas, it's usually just an OBD2 scan and safety check and they're done.

 

I got rid of my pre-cat by using a Warpspeed y-pipe. The car was a federal emissions 2000. The y-pipe had the O2 bungs and I put the O2 sensors back in without extensions/foulers. Did not have any problems. Passed testing, but as stated above, we don't use the tail pipe sniffers here.

The exhaust was very minimally louder, a deeper, throatier sound.

 

Im thinking it'll pass.
I thought at the pre-cats were just for cali cars. Parts diagrams online show
also on Federal cars. Didn't realize a car needed so many damn cats.

 

Just texted a friend who works at a dealer. They test tailpipes for 96 and older.
Just throwing out some info.

 

With only 2 HO2 sensors?
Is it the same as 95 VQ30?
Also they can investigate you for no cats on federal level and apply for a search warrant to search your house and car!
Just a heads up!

 

They use the sniffer for '95 and older (OBD1 cars). '96 and up are OBD2 cars so the computer tells them the emission efficiency. No need to sniff.

I'm going to have my cats welded back on top of the pipes. lol Visual inspection should pass.

 

so they say.....but NY did away with all emissions testing in the past 2 years. I believe service stations were required to remove their old inspection dynos and couldnt even use the old sniffer if they wanted to. The state inspection is now strictly visual for obdI and obd II is a combo of visual and checking for any codes.

 

I saw the O2spacers at conceptzperformance.
​​​​​They have these for the 350Z.

 

You can get em predrilled on ebay for cheap, then buy an unmolested pair.

 

What can you get predrilled on eBay and what can you buy an unmolested pair of?

 

One last question: how does the exhaust sound if you just she'll the pre-cats instead of putting new tubing in? Sometimes, the large diameter of the pre-cats cause a crappy sound from under the engine bay in the exhaust.

- Brian

 

gutted precats, slightly... change the tone... barely noticable...

 

Heck, then I'll just try gutting the pre-cats first and using the extensions. That'll probably work fine. Thanks, man!

 

Not where I live in Texas. They check OBDII and the tailpipe. Maybe it varies by county.

 

I think that may just be your county. In Dallas, they just get you in and out as quickly as they can by plugging into the OBDII plug and getting their readings.

What county are you in? Maybe it's a Democrat county. lol They tend toward stricter emossions. Dallas is very Democrat right now but emissions testing has been pretty easy going so far...unless they've changed in the past year.

- Brian

 

Williamson County, but I made a mistake. I just looked this up, and Cephyr13 is correct. I previously had a couple pre-2000 vehicles that fell in the window for tailpipe testing. Apparently my 2000 GLE won't be subject to that. It hasn't had to be inspected yet since I've owned it, so I didn't realize it's "OBDII only."

 

Okay, good to know.

When you said they do tailpipe testing on an OBDII, that sounded like major overkill. A lot of shops will only do OBDII cars because they don't mind putting out the money for the OBDII testing computer and the tiny bit of time for an emissions test. But the sniffer machine costs a lot of time and money, so they don't even bother with it, and I don't blame them. There aren't many pre-97 cars on the road nowadays anyway.

- Brian