removed cat - what about sensors?

[kr.k]

ok, now I have no cat just the pipe under my car. the question is - is there something that I need to do to the lambda sensors in the exhaust? I have been told that after removing cat my gas mileage will go bad cause ECU will get wrong information about A/F ratios etc. Please help me understand what to do, thanks!

 

[GhostBlk95]

the rear 02 sensor is the only one you gotta worry about...I've heard that wrapping it in tin foil and pulling it somewhere in the car *safe* will most likly keep CEL's off...thats what I will do once I get the high flow cat on....

 

[kr.k]

I drove around with just the pipe for about two days (before I had some serious engine problems and my car is at the shop right now) and it never fired any CEL-s... I have that rear 02 sensor still in exhaust.
My main concern still is the gas mileage as my car is stock daily-driven and it does take a little too much gas already. I can pull no more than 230 miles with full tank and I really don't want it to go any worse...
.. so would it be better for me to pull the rear 02 sensor out?

 

[98gstblk]

I am having the same problem...Once i put my Apexi N1 cat back exhaust on, the CEL went on and i am getting about 220 to 230 miles to the tank..(when i use to get b4 the exhaust close to 300)...i brought it to the a local shop and they said that it has somethign to do with the O2 sensor...when the O2 sensor is gettin a wrong reading it will make the fuel run rich wich it is doing and thats the cause for bad gas mileage...any solutions on how to fix this problem???thanks

greg

 

[nine5raptor]

a lot of misinformation... here's the scoop:

The 2nd o2 sensor solely checks for a working cat, it has nothing to do with fuel trims, tuning, or gas mileage.
if you have a highflow cat, you still have a working one, and the 02 sensor will know it, so leave it in.
if you have a test pipe, the ecu thinks the cat is dead and will most likely throw a cel. the foil trick might work, just taking it out might work, maybe neither. I had to buy an 02 simulator, as have many others, such as: http://www.importparts.com/importpa...1709a8e271d424d361a06ab/Product/View/ECG&2D28

 

[doug]

Just make sure you leave the ground straps attached or the O2 sensors won't work right.

 

[leet]

Originally posted by doug
Just make sure you leave the ground straps attached or the O2 sensors won't work right.

The braided steel strap which attaches to the exhaust pipe? Please elaborate, since I have removed my cat my mileage has been rather poor, but I have not received a CEL.

 

[truwarrior]

Maybe your turbo is spooling sooner causeing you to burn more gas since there will be more air....

My gas mileage sux if I mildly get on it.

Check your plugs and wires too.

 

[doug]

Originally posted by leet
The braided steel strap which attaches to the exhaust pipe? Please elaborate

Yes, that's the one. It grounds the O2 sensor. Without a good ground, the O2 sensor doesn't work properly, causing you to run excessively rich and decreasing your gas mileage.

 

[Omega]

I hope you don't think you can get Honda gas milage with a worked AWD. Lay off the boost and you should be alright, that said...

Is this a sudden drop in gas milage or has it been gradual?

 

[98gstblk]

yes ever since i put my cat back on my gas mileage has dropped greatly...so your saying it may be the steel strap and not the 02 sensor??...but the CEL says its the 02...i dont know what to fix/change?

 

[blinded]

Originally posted by 98gstblk
yes ever since i put my cat back on my gas mileage has dropped greatly...so your saying it may be the steel strap and not the 02 sensor??...but the CEL says its the 02...i dont know what to fix/change?

Which o2 sensor? A cat-back by itself will not cause a great drop in gas mileage or a CEL, unless the rear 02 sensor isn't plugged back in or was somehow damaged during installation. Even if that was the case, the rear 02 sensor won't cause bad gas mileage, it can only throw a CEL. That was my experience, at least. I drove around without a rear 02 sensor on my car at all after putting my exhaust on. CEL was on for 2 months straight. No change in gas mileage. Your problem must lie elsewhere if all you touched during installation was the cat-back.

A little over a month ago I made an o2 sim for about ten bucks. Here's the vfaq I followed, if anyone's interested. The CEL is gone. If you search this site, I posted about it in a test pipe/cel thread.

By the way, the ground strap is not on my car, and on my last tank of gas, I got 32mpg, driving on LA freeways in city traffic. Not saying that it can't help, just sharing my experience. I'll read the ground strap thread in a sec to see if there's anything new. This topic has been argued a million times.

nine5raptor, I saw in your profile that you put a 14b on your car for $30. Have you posted anywhere on how you did it? If not, can you start a thread? Or PM/email me? I have a 14b sitting here.

 

[Zex4g63]

I agree. You have other problems. I have the N1 system front to back and get 300+ with mixed city and highway and some whoop'ns in between. Ground strap was missing when I put the exhaust on and I never replaced it. CEL was on several times never effecting fuel mileage. Use the Vfac to trick it.

 

[DeezNutsForYou]

Will I have this same problem when I cut my cat out, being that I have a 1g I don't thinks I have that second sensor. Or do I

 

[Zex4g63]

No you don't

 

[nine5raptor]

Originally posted by blinded
nine5raptor, I saw in your profile that you put a 14b on your car for $30. Have you posted anywhere on how you did it? If not, can you start a thread? Or PM/email me? I have a 14b sitting here.

I have put the basics in a couple of threads. I will send you some info. and look for the other threads.

chris

 

[Zex4g63]

I have an idea here. The guys that are having fuel mileage problems, when was the last time you changed the primary O2 sensor? They do wear out. Over time they become contaminated and begin to react slower. When you remove your cat it makes the exhaust run cooler. This would amplify the problem. This would cause the o2 sensor to not give accurate readings. That is why many cars use heated o2 sensors. They need to be at a certain temp to work correctly. If you guys have never changed the primary I would recommend testing it, having it tested, or just replacing it now.

 

[DeezNutsForYou]

whats the cheapest place to get a primary O2 sensor?