I have recently removed catalytic converter and it seems that the MPG went down a bit. The car runs fine, even better then before and no CEL.
There are no regulations in my country for the emission so it is not illegal to remove the catalytic converter.
I have read on these forums, that on some wranglers downstream O2 sensor does not do anything except monitoring the catalytic. Some say that it will run rich and cause the low MPG.
The wrangler is 1997 4.0 with 3 speed auto trans. And the question is:
Does the downstream O2 Sensor affect the fuel/air mixture and cause lowering MPGs ???
I am also not a fan of emission crap on my car, but....
Your state may not have mandatory emission inspections, but your catalytic is a federal requirement and when you sell the vehicle you as the owner are required to make the vehicle compliant.
if you read stuff from those who have done a lot of tuning on Jeeps and other Chrysler vehicles, you find reports of the downstream O2 sensors have an affect on A/F ratio. Sometimes as much as 20% away from stoich. The downstream O2 sensors will tell the computer to lean or richen the mixture based on the efficiency of the catalytic converters.
The computer monitors/maintains cat efficiency by heat. Cats need to be up to temperature to work properly, so the computer will heat up the cats by richening the A/F mixture. This dumps more fuel into the exhaust stream, where it basically breaths fire into the cat...and this heats them up. Once they are up to temp, the computer moves things back to stoich.
If the cat(s) are removed, your computer will constantly being trying to heat up the cats. Eventually the computer will recognize something is wrong and trip a CEL for the cat's being below efficiency. How quickly that CEL is tripped is based on exhaust flow, O2 sensor readings, and how smart the computer is at figuring these things out. TJ computers are really stupid, especially the older ones.
if you read stuff from those who have done a lot of tuning on Jeeps and other Chrysler vehicles, you find reports of the downstream O2 sensors have an affect on A/F ratio. Sometimes as much as 20% away from stoich. The downstream O2 sensors will tell the computer to lean or richen the mixture based on the efficiency of the catalytic converters.
The computer monitors/maintains cat efficiency by heat. Cats need to be up to temperature to work properly, so the computer will heat up the cats by richening the A/F mixture. This dumps more fuel into the exhaust stream, where it basically breaths fire into the cat...and this heats them up. Once they are up to temp, the computer moves things back to stoich.
If the cat(s) are removed, your computer will constantly being trying to heat up the cats. Eventually the computer will recognize something is wrong and trip a CEL for the cat's being below efficiency. How quickly that CEL is tripped is based on exhaust flow, O2 sensor readings, and how smart the computer is at figuring these things out. TJ computers are really stupid, especially the older ones.
Your TJ or LJ does not monitor the cat's temperature. It has no idea what the cat temp is. It is simply comparing the downstream O2 readings with the upstream readings, to see if the cat is working. If there isn't enough difference, it throws a code. It is not adjusting your mixture based on downstream readings. It is not dumping extra fuel into it to heat up the cat.
So yesterday i have fit the simulator to the O2 sensor. Something like the spacer...
Many people told me here that it would help and on other brand vehicles it works too.
The CEL was not lit and is not lit now.
It is impossible to buy catalytic converter here (new one), so i have to buy from USA. then the price for transportation and for levy, so the catalytic will cost 400 dollars for me... I would like to get a freeflow or high flow catalytic but...
Also i am planning to swap the transmission to AX15. And I will change the ECU with the older one (YJ), which actually has one upstream O2 sensor...
Makes zero sense to enrich mixture for inefficient cat as that would add to pollutants in fuel so no one would come up with self defeating plan like that
More like I think this happens so I'll make up something to explain it
The newer iterations of the TJ do have issues with effects of downstream nut not his 97
Lots of guys replaced cats with test pipes back in the day and it did not hurt gas milage
Back in the day.....
My 94 yj has no converter....
Originally I smashed it on a rock and had to gut it on the trail to get back....
Drove it that way for a year or so... had more power but got worse mpg's.... I eventually put a new cat on it... less power but better mpg's.... smashed it again n replaced w a straight pipe..... power is back and so is the reduced mpg......
Must be a coincidence lol
Well just install three cats in series light to get mpg lights me a hybrid
You just solved the effiency crisis and can be in Gore's next book
Course on the same page with the gal in my basic intro to engineering who figured that just putting generators on front wheels and electric motors on back wheels here electric cart could run forever without a battery
With your basic heated narrow band oxygen gradient based voltage generating upstream oxygen sensor all the computer can do is attempt to regulate mixture to keep the sensor voltage bouncing back and forth across the sweet spot and the computer is not tuned for a CAT, that is magical thinking at its best
Hook up a monitor and watch how quick it goes closed loop well under 2 minutes long before engine fully warms up
It goes closed loop that fast and uses heated sensors to satisfy the tighter emissions standards and artificially enriching the mixture (to heat up the cat) would add unwanted tailpipe emissions totally defeating the required results
The downstream were added to trip a cel and fail for poorly functioning cat
Adding a test parameter to ignore readings not meeting criteria until readings are out of spec for a specified duration keeps from tripping a cel without artificial enrichment with the associated increased tailpipe emissions
The intentional enrich to heat up cat is not plausible and would be counter productive in the emissions arena
Cold engines do run richer open loop as an enriched (choked) mixture is helpful or necessary to get a cold engine running
Year or so ago I played around with my 98 by attaching the temp sensor plug to a sensor not installed sitting in ambient air
It started ok when cold and despite a cold sensor it still went closed loop in about one minute
However after running for a couple minutes with the engine warmer if you shut it off the warm engine, it would not restart with a cold sensor, crank fine but not start
Hook up the warm sensor and it started fine
My guess is the cold sensor reading caused excessive enrichment so that the warm engine would not start
Like trying to start a warmed up carb engine at full choke
Ok I've been watching this and thought I would add my experience. both my jeeps are 2.5's, not same year 97,00. 97 had cat removed when I got it. 00 has complete exhaust. 97 the down stream sensor was just hanging under the jeep. mileage was bad, about 12 and blowing blackish smoke. had a cat eliminator pipe installed and just screwed the hanging sensor into bung. It took about a week of driving to notice any difference. my mileage did get better and the blackish smoke went away. mileage never got what I would call good for a jeep, but better. I didn't put the pencil to it, but I could run farther on my odometer than before. I know what everyone is saying about the down stream, but this is my experience.
No idea on a 97, but on my 2003 the downstream O2's do in fact affect fuel mixture. I've got a supercharger installed on my jeep, and use an O2 fooling device to enrich the mixture under boost. At first I only connected the forward 2 O2 sensors, and while it had an effect, I had to crank up the change to max. After adding in the rear sensors as well, I had to back the change back to about 25%. I have no idea what chrysler's intention was for using the rear o2 in mixture adjustment, just know that they do.
Please be advised, removing or disabling emission control equipment on any vehicle is illegal in all 50 states, regardless if an emission test is required.
This thread violates federal law and therefore is now closed
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