*Running O2 Sensors Properly Without Cats?*

[whiplash473]

I'm looking for a way to run my O2 sensors correctly with long tubes and no cats. I have a couple friends that have thrown MIL eliminators on their Mustangs to make the computer think the O2s are reading correctly (I don't have to go through emissions with my Mustang so no cats) but I'm wondering if there's other options on there I can use. '98 Silverado with a Vortec 350.

Thanks.


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[kennythewelder]

I keep writing on how to do this, but everyone ask this question differently, so here we go again. Like you, I wanted to gut my cats, but I knew I would get a CEL, and the ECM would be in limp mode. So here is what I did last year. My truck is a 97 Silverado C1500 with a 5.7 L Vortec I have shorty headers, with true dual exhaust, with 2 old school glass pack mufflers, no restrictions what so ever in the exhaust system. I made 2 mini cat simulators, with some spark plug spacers, and I took some of the honey comb that I removed from the cats, and ground it round (on a bench grinder, and it makes a lot of dust) to fit inside the bottom spark plug spacer between the exhaust pipe, and the 02 sensor, so that the exhaust gas would have to pass through the honey come to reach the sensor, like it would if there were still cats on the truck. This only needs to be done to the 2 sensors behind the cats of course. I have been running my truck sense last year, with no CEL and the ECM thinks there are still cats in the exhaust, because of the simulators. Here is a web sight where you can buy some simulators ready to be installed, but you will need 2, one for each rear 02 sensor.http://bigdaddiesgarage.com/ And here is what you need to build your own, but you will need to add a small piece of the honey come you remove from the cats when you gut them. The honey come will need to fit into the bottom undrilled spark plug spacer. It will be only long enough so that the 02 sensor can still fit into the top SP spacer. I cut mine with a hack saw after I ground it round to fit inside, and cut it to about 1/2 long with a hack saw, but you have to cut in the direction where the teeth face away from you. If you try to cut with the teeth (pushing the saw) it is to aggressive and brake the honey comb. I tried to use the SP spacers with out the honey comb, and it gave me a CEL.

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[kennythewelder]

I had to redo this pic, but here you go. Remember this is the back 02 sensors only. And no this is not my truck.

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[whiplash473]

Well I guess I know what I'm making at work tomorrow, gotta love being a toolmaker. Thanks for the in-depth reply, honestly. This guy a few weeks back at the gas station told me to just put a bunch of washers under the head of the sensor and I really couldn't picture how that would work, at least for my problem.

EDIT: And they want $50/ea. There's no way I'm paying that for something I can make 2 of in an hour.

 

[kennythewelder]

Y.W. I wanted to do mine for a long time. When I gutted my cats, I knew I would get a CEL. After I saw the bigdadys simulators, I knew I could make my own. I have been a welder for a very long time, and I can make anything, well within reason anyway.

 

[whiplash473]

Y.W. I wanted to do mine for a long time. When I gutted my cats, I knew I would get a CEL. After I saw the bigdadys simulators, I knew I could make my own. I have been a welder for a very long time, and I can make anything, well within reason anyway.

Y.W.?

Blue collar work has it's advantages.

Have you worried about the honeycomb falling out or did you make it just big enough to have to press it in some?

Is the thread 18x1.5?

 

[kennythewelder]

It cant fall out, because the SP spacer with the yellow line, its hole is to small for the honey comb to fit into, and the HC is just long enough so that the 02 sensor hold it in place. It is just a little loose inside the bottom SP spacer. If you try to force it into place, it will brake and crumble. I wore a dust mask to grind the HC, because it makes a lot of dust. If you brake some of it, no big deal, because there is a lot inside of each cat. I would guess that I ground the HC to just under 1/2 inch around, where it would just fit inside the bottom SP spacer. Then I cut it to length. I put the hacksaw in a bench vice, and drug the HC in one direction to cut it just long enough so that the 02 sensor would not quite touch it. I then put the HC inside the undrilled SP spacer, and installed the 02 sensor with the drilled out SP spacer on it. I could shack the unit and hear the HC shacking around inside just a little bit. The HC can not be so tight that anything will smash it, because it is brittle, and you will cruse it, then it will not get any exhaust flow. Once you grind and cut the HC you will see what I mean. After it fits rite in the SP spacer, blow off the dust with an air hose. Keep in mind that the exhaust has to flow through the little holes in the honey comb. I gained 1.5 MPG and a little more WOT power after this mod. The OE cats are restrictive. LOL it makes up for the 1 MPG I lost with the shorty headers and true dules, but I do have a lead foot.

 

[kennythewelder]

Oh you can always have your ECM tuned to not need the rear 02 sensors anymore, but a tune is expensive when you can just trick the ECM for maybe $10.

 

[whiplash473]

Oh you can always have your ECM tuned to not need the rear 02 sensors anymore, but a tune is expensive when you can just trick the ECM for maybe $10.

That's what I was trying to avoid since I really don't need it besides the exhaust issue. Really thanks all your help, I appreciate it. I'm gonna make two of them tomorrow but it's gonna be a bit until I can install them since I'm still driving it every day. Once winter hits I'll be driving the beater and I can tear into all of this.

 

[kennythewelder]

That's what I was trying to avoid since I really don't need it besides the exhaust issue. Really thanks all your help, I appreciate it. I'm gonna make two of them tomorrow but it's gonna be a bit until I can install them since I'm still driving it every day. Once winter hits I'll be driving the beater and I can tear into all of this.

I tuned my truck with a jet programmer (set to max) but you can not delete the rear 02 sensors, so that is why I did this.