O2 spacer to avoid CEL from no cat-- bad mileage?

[Mike431635]

I'm getting a downpipe from a 2gnt member soon and also a gutted high-flow cat. I don't want to get a CEL for a missing/inoperative cat so I'm thinking about doing something a lot of the 1.8T VW guys have been doing for years. It involves using spark plug non-foulers to space the O2 sensor out of the exhaust path and prevent the CEL.

Searched and searched all over the net, found some very interesting stuff, but most of it pertained to "tuning" the amount of oxygen the sensor sees, causing the ECU to recognize a "rich" condition and lean out the mixture and boost fuel economy. That's not what I want, obviously, but I understand a stock ECU makes the car run a bit richer than needed as a safeguard so it SHOULD be ok.

The car in question has been getting terrible gas mileage-- 13-15mpg, so I just replaced both the front & rear sensors a couple weeks ago. Mileage has gotten a lot better, hitting 20-22 in the city which I consider pretty good. I don't want to lose this and revert back to the terrible mileage I was seeing before just to avoid a CEL. Does anyone here know what the effect is on gas mileage by using a spacer like this to avoid a CEL? Theoretically, using some kind of O2 simulator does the same exact thing only with an voltage signal, so I'm interested in knowing the effect of such devices on mileage as well.

 

[toofast82]

Give it a try! Using a non fouler might actually be a cheap and easy fix.

 

[Mr Peepers]

The rear o2 sensor doesn't have any control over fuel trims which are what would affect mileage. Its only purpose is to check if the cat is working.

 

[xsboost]

if the non-fouler method doesn't work you could try this.

O2 sensor bypass

It's really cheap and easy. I don't know if it's the same for N/Ts but it's worth a look.

 

[Mike431635]

Chrysler is the only company which specifically states the rear O2 sensor has nothing to do with fuel management. Other companies have admitted the rear O2 is responsible for up to 2-5% of fine tuning. In reality, studies have shown that ALL manufacturers' vehicles use the rear O2 to some extent for tuning fuel management.

At least this is what I have gathered from my research. I'm pretty certain the non-fouler will work to prevent a CEL, my only question is-- will it hurt my gas mileage? I guess I could always test this on the car before I go turbo since it's still NA right now. If the rear O2 really has NOTHING to do with fuel tuning and the same driver is using the car under the same operating conditions, fuel mileage should vary little or none. Hmm.. maybe I'll check it out.

 

[Gamble97]

I have used the non fouler method on my spec v. I only needed to use 1 of the foulers and it worked great and didn't affect gas mileage. Go for it.
Also if your car has high miles try some seafoam that has helped out my integra bit. I'm still on my first tank but I'm getting like 2mpg more.

 

[Mike431635]

Yeah I used Seafoam before I changed the sensors and the oil at the same time

Thanks for that tidbit on the gas mileage-- thats really what I was getting at with this thread. Did you drill the fouler out to open up the hole and allow more flow to the sensor, or leave it alone and use it as-is?

 

[Gamble97]

Drill it out some so the o2 threads in more than a few turns.

 

[rich3389]

Chrysler is the only company which specifically states the rear O2 sensor has nothing to do with fuel management. Other companies have admitted the rear O2 is responsible for up to 2-5% of fine tuning. In reality, studies have shown that ALL manufacturers' vehicles use the rear O2 to some extent for tuning fuel management.

At least this is what I have gathered from my research. I'm pretty certain the non-fouler will work to prevent a CEL, my only question is-- will it hurt my gas mileage? I guess I could always test this on the car before I go turbo since it's still NA right now. If the rear O2 really has NOTHING to do with fuel tuning and the same driver is using the car under the same operating conditions, fuel mileage should vary little or none. Hmm.. maybe I'll check it out.

Where did you get this information?

 

[Mike431635]

Can't recall exactly, but I read a large amount of information. One document was a statement from Chrysler which said (paraphrased) "the post-catalytic converter O2 sensor in Chrysler vehicles is not used for fuel management, but soley to indicate the presence and proper operation of the catalytic converter"

Got my exhaust in yesterday. I'm gonna install it next weekend with a drilled-out fouler on the rear O2 and give results soon.

 

[Mike431635]

Just wanted to update this..

I installed my exhaust, been running it for a few weeks now. I didn't use a spacer cause I was short on time and didn't want to run to the store and get the foulers and just delay it longer. I'm not throwing a code at all, even with a gutted cat. I'm getting like 220-230 a tank (10-11 gallons to fill up, even though its a 15 gallon tank-- I think the fuel level sender is fubar), so mileage is definitely up. I may have a restriction in the stock exhaust before the cat as well, so when the turbo setup goes on I may see the bad cat CEL. I'll update later.

 

[rpalais]

Sounds great! Can I use this method for the downstream, or rear 02 sensor in my '97 GST? I recently bought my mint 54,000 mile '97 GST and have been upgrading for the past month. I do not see a cat in the car and I have yet to see how the rear 02 senbsor has been handled. I do not have any CEL at this time, fortunately. Please advise ASAP if I can use this for the rear 02 sensor.

Also, my car has been running butt-rich. I just put in an aftermaret fuel rail with an adjustable fuel pressure regulator. I turned down the fuel prssure just a couple of pounds and it ran great according to my wideband air/fuel gauge. Felt a lot better with crisper response as well. But then it started running butt-rich again later in the same day (yesterday). I am now going to replace the upstream or pre-cat 02 sensor and see what happens. I do suspect a bad 02 sensor. Please advise any other suggestions ASAP. Tune seems to be good as it did run great (14.3 on the wideband under light cruise) most of the day before going butt-rich again. Thank you! RKP

if the non-fouler method doesn't work you could try this.

O2 sensor bypass

It's really cheap and easy. I don't know if it's the same for N/Ts but it's worth a look.

 

[VelocitàPaola]

This is the 420A section. You're better off asking your question in the Newbie Forum.

 

[brian9397gsx]

As a technician who has attained level 3 status in Chrysler drive ability I can tell you we do use the downstream 02 in calculating fuel trims, however it's impact on fuel trims some of the time is minor.(dont know exact number I suppose I could consult my old obd2 training book) I understand this thread is old but wanted to clear up some mis information