Hey i was wondering if the o2 sensor after the cat. can still mess up the engine. like does it still communicate with the PCM about the air to fuel mixture? or does it just tell us if the cat. is bad or not?

 

only the upper O2 sensor controls the air/fuel ratio, the bottom one just checks the effeciency of the cat and if its going bad.

 

Agreed!

 

oh ok so if i were to take out the cat and not touch the o2 sensor then all it will be is a bother to the check engine light?

 

bingo, just make sure you replace the cat with a straight pipe if you choose too, or another cat

 

You guys need to do a little more research on the downstream O2 sensor technology used by the Chrysler Corp. After '95 the downstream O2 sensor does, and will, affect the air/fuel ratios. Chrysler holds the patent on this technology. This is why places like Howell automotive and Modern performance carry the O2 sensor eliminator. This is used to fool the PCM into thinking the downstream O2 sensor is working correctly. It is well worth the money.

 

my Neon was made in 94 though...

 

I have a 98 DOHC and have ran my car without the downstream, car runs just fine with no change in performance. but I did so some research like you said, and I knew there was a reason why I gave the statement that I did because before I but my straight pipe in I did some research. you said that the eliminator is for neons after the years of 95 so for neoncrazy to buy one would be pointless. on the howell website the downstream is only for the years 99 and 2000, and on the Modern site they don't even sell one, So then I called to maybe see if it just wasn't listed but indeed they don't sell them. the howell site only has the Dodge neon optons, but the Modern has the chrysler,dodge and plymouth options I trust the content from modern more for the simple fact that all though the parts for the neons are vary interchangable, there are some differences, one in particular between the plymouth and dodge neon. and I found that out 3 weeks ago when I went to buy a belt but, I do understand what you are saying and have heard it somewhere else before. hope none of that was taken offensively because that was not what it was meant for, and hopefully it clears up some stuff.

 

No offensive taken. Let me explain how I came to my findings. On my '98 sohc, I decided to delete the converter. I had just put a header on the car, and put three inch pipe after the cat. The pipe ran back and out the drivers side just in front of the rear wheel. As everyone knows, the quickest way to delete the cat is to beat the guts out of it. (This works on converters too!) So this is what I did. I did not notice anything plus or minus in the power department as far as driving the car, however on the dyno I had lost about 8 hp.
After a little looking into the situation, I found that the NEONS do not like expansion chambers in the exhaust system. Luckily, the guy that owns the dyno here in Knoxville, builds Porsche rally cars. He explained in great detail about expansion chambers and how the Porsche engines love them, but most cars do not. Armed with this info, I rushed out and and removed the empty cat housing and replaced it with straight pipe. Back on the dyno and I had gained back about 5 hp.
With a quick email to Rick Ehrenberg with Mopar performance, I found out the information about the downstream O2 sensor affecting the PCM. I then employed a trick using a spark plug non fouler adapter and my O2 sensor. This trick leaves about 1/8 " of the O2 sensor in the exhaust stream which changes the catylist reading to the PCM, making it believe the cat is in place and doing its job.
After all this, I not only gained my lost HP back but gained an additional 7 hp on the dyno.
On performance issues you cannot always rely on track times, as they vary greatly with driver performance, or seat of the pants feel. Always use a dyno to tune with, if at all possible.
Also, based on neoncrazy's post, no one was to know if it was a question about performance, gas mileage, or just trying to beat the high price of replacing the cat or O2 sensor.

Fuzz, I was not posting a reply to be conflictual, but to give a better spread of information. This is a great forum for people being helpful and trying to help others with thier problems, but sometimes the Readers Digest condensed answer can/will do more harm than good. We never have the time or money to do it right the first time, but we find the time and money to do it correctly the second time. As I am an old man that has been building cars for a long time (back when you could still get a loan on a mid 50's model), I have found after alot of wasted time and money, it is better to understand the total dynamics and scope of the project and do it right the first time.

 

oh thats interesting... heres another question then... what size is the standard exhaust tubing on a SOHC Neon?