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 Post subject: Catalytic Converter Removal Effects. . .
PostPosted: Sun Mar 19, 2006 7:11 pm 
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I have a DOHC car, that has had a rather annoying rattle in the exhaust. It's my experimentation car for the moment, until I figure out exactly what I want to do.

Anyway, I took the converter out to confirm that the catalyst block was rattling around in the converter housing, and it was. Since I've never really been a fan of converters, and I figured I could just plug my wideband into the down stream O2 sensor hole if the converter was out of there, I replaced the converter with a 2.25" straight pipe. I did a careful job to make sure all of the junctions were nice and smooth on the inside, and everything is good.

This car has a pacesetter, 12s, ported intake manifold, auto TB, AutoZone turbo muffler, 3.0 tube intake, and a Mopar PCM.

So, here's another ugly confirmation that these cars like converters -- Not only did the car sound as crappy as everyone says, it lost something like 12 HP, and lost power across the entire power band.

I was using my MR Dyno, with updated correction factors for every run, and doing 2nd gear pulls from 15-59 MPH. I use the same locations, and do pulls in both directions at those locations. The results are very consistent and repeatable.

With the rattling converter in the system, these pulls were taking, on average about 5.3 seconds, with an un-smoothed peak of about 154 WHP @ 7400 IIRC, and a smoothed peak of about 148 WHP in that same RPM range. Without the converter, that time stretched out to an average of 5.75 seconds, and the top end drops off a LOT. Exactly what I wouldn't have expected to see. . . .

If anyone would like to host it, I can send you a screen shot of the MR Dyno graph comparing the two averages. Maybe it would be nice to have a little more solid data like this than I have seen on this topic before. The results are kind of shocking to me since I always figured that the loss of power people suffer is because they just gut the cat and leave it in the system hollow, like a big untuned expansion chamber.

Does anyone have any plausible explanations for why this would be the case?

Thanks,

Thad :?

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Last edited by Tjabo on Tue Mar 28, 2006 11:55 am, edited 4 times in total.

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 Post subject:
PostPosted: Sun Mar 19, 2006 7:23 pm 
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Maybe your exhaust is so small you are slightly restricting flow. The heat from the cat might have had a "suction" effect on removing hot exhaust from the exhaust ports.

Whatever the case, I bet if you went to 2.5" exhaust you'd make more power without the cat.

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PostPosted: Sun Mar 19, 2006 7:31 pm 
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Well, I hadn't really thought about it that way. . . . I've got a 2.5" Dynomax exhaust on the shelf I could probably throw on there with my stock location 2.5" glasspack (long style) to see what would happen.

I'm guessing as soon as I got it tested, I'd feel compelled to take it back off the car, because that would be one LOUD setup! Still, it might be an interesting data point.

Thanks!

Thad

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PostPosted: Sun Mar 19, 2006 8:19 pm 
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unless you are running a stand alone you should leave the cat, as you can see neons don't respond well with chryslers downstream 02 sensor in the mix

get a high flow 2.5 and slap the dynomax piping on, then you will be happier

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 Post subject:
PostPosted: Sun Mar 19, 2006 9:04 pm 
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Interesting idea about the down stream, but from what I understand, the open loop mode encountered during WOT just looks up values on maps, and does what they say. No feed back.

Makes you wonder, doesn't it?

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PostPosted: Sun Mar 19, 2006 9:08 pm 
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If the PCM is actively trying to protect the cat due to the feedback in closed loop, it can probably use different open loop tables as well.

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 Post subject:
PostPosted: Sun Mar 19, 2006 9:50 pm 
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I'd love to see the dyno sheet where it says you lost power.

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 Post subject:
PostPosted: Sun Mar 19, 2006 9:59 pm 
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super8neon wrote:
I'd love to see the dyno sheet where it says you lost power.

Check your e-mail. It's on its way.

Thad

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 Post subject:
PostPosted: Sun Mar 19, 2006 10:03 pm 
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MCarp22 wrote:
If the PCM is actively trying to protect the cat due to the feedback in closed loop, it can probably use different open loop tables as well.

I suppose that makes sense. If so, then maybe I should try the resistor trick, or plugging the down-stream bung and leaving the sensor out in the air?

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 Post subject:
PostPosted: Sun Mar 19, 2006 10:32 pm 
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I'm not a fan of these electronic dynos... there are way too many factors that can adjust/ change each run.

I bet you lost a little low end torque, but probably gained a bunch up top.

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 Post subject:
PostPosted: Sun Mar 19, 2006 10:34 pm 
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I betcha' that piece of crap Pacesetter Header has a lot to do with the loss in power.

Put the car on a real dyno with the conditions it is in right now... then add a quality long tube header, and see what the added benefits are then.

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 Post subject:
PostPosted: Sun Mar 19, 2006 10:47 pm 
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Tjabo wrote:
I suppose that makes sense. If so, then maybe I should try the resistor trick, or plugging the down-stream bung and leaving the sensor out in the air?


Couldn't you just fix it? Correctly?

Tjabo wrote:
I betcha' that piece of crap Pacesetter Header has a lot to do with the loss in power.


Why's that? I had pretty good success with my pacesetter.

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 Post subject:
PostPosted: Sun Mar 19, 2006 11:10 pm 
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MCarp22 wrote:
If the PCM is actively trying to protect the cat due to the feedback in closed loop, it can probably use different open loop tables as well.
Tjabo wrote:
This car has a pacesetter, 12s, ported intake manifold, auto TB, AutoZone turbo muffler, 3.0 tube intake, and a Mopar PCM.
I am assuming that this the Mopar Performance PCM. In that case, dosen't the PCM ignore the downstream O2 entirely? If you just unplug it, no CEL gets thrown and the car runs great all day. I doubt its an issue with the downstream O2.

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PostPosted: Sun Mar 19, 2006 11:12 pm 
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iblue wrote:
I am assuming that this the Mopar Performance PCM. In that case, dosen't the PCM ignore the downstream O2 entirely? If you just unplug it, no CEL gets thrown and the car runs great all day. I doubt its an issue with the downstreak O2.


'95 is the only cat-free year. 96-99 Mopar PCMs still function as stock as far as the catalyst monitor goes. Not sure what the original poster's year is.

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 Post subject:
PostPosted: Sun Mar 19, 2006 11:17 pm 
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MCarp22 wrote:
iblue wrote:
I am assuming that this the Mopar Performance PCM. In that case, dosen't the PCM ignore the downstream O2 entirely? If you just unplug it, no CEL gets thrown and the car runs great all day. I doubt its an issue with the downstreak O2.


'95 is the only cat-free year. 96-99 Mopar PCMs still function as stock as far as the catalyst monitor goes. Not sure what the original poster's year is.

I could have sworn that the ODBII MPP PCM's didnt monitor the downstream O2. Hmm... oh well. This good ol thread definately proves me wrong:
Quote:
1996-1999 MOPAR PERFORMACE PCM DOES NOT IGNORE THE dOWNSTREAM OXYGEN SENSOR; YOU WILL GET A CHECK ENGINE LIGHT IF YOU REMOVE THE DOWNSTREAM OXYGEN SENSOR WITH A MOPAR PERFORMACE PCM.

http://forums.neons.org/viewtopic.php?t=104105

Sorry for cluttering up the thread :oops:

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 Post subject:
PostPosted: Mon Mar 20, 2006 9:13 am 
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At the moment the car in question is a '96 Sport Coupe running a '97-'99 MPP PCM.

Mike,

If by "just fix it" (paraphrasing you) you mean to just put it back how it was, I could do that, and probably will eventually, but I want to learn something first!

super8neon,

I agree with Mike, that my Pacesetter has given me pretty good service, so I'm not inclined to think that the Pacesetter is doing something so goofy that it makes power go away when it has less back pressure behind it. Do you have any thoughts on why that might happen?

The MR Dyno is a pretty straight forward piece of equipment that seems about as repeatable as anything could be that is at the whims of the wind, and undulations in the road. That is why I take 6-8 runs per setup, to get a good handle on what is happening.

In this case, the "butt dyno" matches the MR Dyno pretty perfectly. The car is definitely not as peppy on the low end, but then it never comes roaring back. Clearly, power feels like it has been lost from the whole curve. At the top end, I just have to wait longer for the motor to hit the rev-limiter. It seems pretty obvious.

Okay, so how about this thought:

The MPP PCM leans out the open loop operation to make better power. MAYBE with the cams and such, the extra flow from getting rid of the converter caused it to go over-lean? I really need to get my wideband in there, but I wasn't necessarily sure that was the car I wanted to put it in. . .

Thad

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 Post subject:
PostPosted: Mon Mar 20, 2006 11:03 am 
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Tjabo, try spacing the 02 sensor out of the stream (but leave it active, in the pipe... i used 2 drilled out spark plug spacers on my subaru), and driving the car for a bit to let it adjust to the changes in the airflow maybe?

It does seem strange that you'd lose power, maybe the car just needs to get used to it?

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 Post subject:
PostPosted: Mon Mar 20, 2006 11:09 am 
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Interesting... I just put a new motor in my 96 and had the cat rattling problem too so I just gutted it and put it back on cause I needed the car. I did notice a much louder exhaust note with my Dynomax muffler than before and also thought the new motor felt "flat".. I mean it runs much better than my old 200k mile 96 SOHC did but it just didn't have the "umph" that I expected either. I plan to put a new cat on soon, just haven't had the time.

And I can attest that the 96 Mopar PCM WILL turn on the MIL if you remove the cat or the downstream 02.

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PostPosted: Thu Mar 23, 2006 3:00 pm 
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Matt In Seattle wrote:
Tjabo, try spacing the 02 sensor out of the stream (but leave it active, in the pipe... i used 2 drilled out spark plug spacers on my subaru), and driving the car for a bit to let it adjust to the changes in the airflow maybe?

It does seem strange that you'd lose power, maybe the car just needs to get used to it?

Matt, what effect did you notice from moving the downstream O2 sensor out of the exhaust stream like this?

I'm going to make another set of runs this weekend after driving it all week, before I install some small diameter "testpipe" to see what has happened from letting the computer "learn" (which I expect not to see, since we're talking open loop, but who knows?), and to see whether small diameter will help get back what I've lost, or cause me to lose more.

Ultimately, if for nothing more than sound quality alone, I will undoubtedly be cobbling up something to keep the brick in the converter from rattling, and putting it back on the car.

By the way, my fuel mileage appears to be basically normal without the converter.

Thad

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PostPosted: Thu Mar 23, 2006 6:19 pm 
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What it does is make the upstream and downstream O2 sensors show different readings. Being that you have a mopar PCM, it's expecting to see a difference, accounting for a cat.

My theory is that it's freaking out, thinking that the cat's gone, and dialing some things back on you.

Stack 2 spark plug anti-foulers into each other, and drill out the center big enough for the stock 02 sensor to have like 1/16th of airspace all around it. Throw it back in, and reset the PCM. Make it think that everything's normal would be my theory.

[Edit: does the car still go openloop at WOT if it detects a CEL condition like this?]

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PostPosted: Thu Mar 23, 2006 7:16 pm 
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Hey, here's one problem -- I don't exactly know what a spark plug anti-fouler is! ! ! :lol: I'll head on down to a decent auto parts store, and see if I can find out. I thought you were just referring to stacking a couple of normal spark plug crushable washers in there to move the sensor back a bit.

Wouldn't leaving the downstream sensor in open air accomplish the same thing?

As for the open loop during CEL question, I would submit that if anything, it would never go into closed loop (where it takes feedback and makes adjustments to the cruise and light throttle AFRs). My understanding is that when a problem occurs that bothers the PCM, it always goes directly to open loop to keep it from making some harmful changes based on bad input from a faulty sensor or something.

Aren't bunches of people who have long tube headers running just fine with a downstream O2 sensor CEL? ? ? :?

Thad

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PostPosted: Thu Mar 23, 2006 7:23 pm 
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AAAH!

okay. An antifouler can be found in the "HELP!" spinner at your parts store. If you call and ask for one, they'll probably give you the same look you gave me, but I've never found a place that doesn't have 'em. :)

Only pics I could find; Click the EvoM link and check out the part numbers. http://images.google.com/images?sourcei ... a=N&tab=wi

See, that's my thought though, if the ECU is in "oh crap what just happened" mode, it's not caring about performance, just about safe running, so of course you stand to lose power based on non-optimal fuel trims.

With it hanging in open air, i'd think it'd see too much of a difference, see you VERY lean by the 2nd one, and change fuel trims accordingly. :)

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PostPosted: Thu Mar 23, 2006 7:32 pm 
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COOL! Thanks, I'll try it!

By the way, just so it's easier for everyone to find in the future, it looks like a good thread on this is:

http://forums.evolutionm.net/showthread.php?t=99137

Thanks Matt!

Thad

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PostPosted: Thu Mar 23, 2006 9:28 pm 
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Yeah, i didn't link the thread because the images in it are dead. :)

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PostPosted: Thu Mar 23, 2006 10:05 pm 
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Slightly OT.

Is this a track car? I didn't think you could pass inspection without a cat in Michigan. :?


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PostPosted: Thu Mar 23, 2006 11:53 pm 
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Of course. This is all for off-road use only. We'd be facing very large fines if we ever did this on street cars. No street cars have been harmed in the making of these parts. </disclaimer>

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PostPosted: Fri Mar 24, 2006 5:36 am 
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No inspection here!

Oh, but other than that, I take the fifth! ! ! :lol:

I'm sure I'll end up with the converter on the car anyway, but this topic has been bugging me for a while now, so I'm just trying to learn something.

Thad

BTW, nice response Matt! You beat me to it!

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PostPosted: Sat Mar 25, 2006 1:24 am 
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Just out of curiosity, has the car ever thrown a CEL because it didn't have a cat, Thad? Is the downstream O2 sensor still installed? If I rememeber correctly I had installed a resistor on the downstream O2 sensor on that car a few years back before I switched to an AFX-Race PCM on it. Unless you changed out the O2 sensor or removed the resistor, the PCM should be fooled into thinking there is still cat there, and should still be running the same WOT maps.

The problem definitely isn't with the Pacesetter header (in case anyone wonders, this is my old car) and the stock 2.25" exhaust tubing shouldn't be a factor either. I did have a Dynomax 2.5" exhaust on the car before I went to a long tube, and with the Pacesetter header, stock cat, and 2.5" exhaust, the car wasn't noticeably faster or slower at the drag strip or SOTP than the stock 2.25" exhaust.

The car was catless for about three years when I had it and definitely didn't lose power then, but that was with a Blackdog long tube header and intake manifold (and 2.5" exhaust). I wonder if the loss of power could be related to a loss of exhaust velocity or some other similar exhaust phenomenon or if it is something in the PCM that is causing the power loss.

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PostPosted: Sat Mar 25, 2006 7:10 am 
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Keith96DOHC wrote:
I had installed a resistor on the downstream O2 sensor on that car a few years back before I switched to an AFX-Race PCM on it. Unless you changed out the O2 sensor or removed the resistor, the PCM should be fooled into thinking there is still cat there, and should still be running the same WOT maps.
-Keith

VERY interesting Keith! ! ! :idea:

I haven't noticed whether an ADDITIONAL CEL has been thrown, but I guess now I'll have to go out and get the codes out of the car and see what's up!

I say no "additional CEL," because I've been running a '97-'99 MPP PCM on it without any provision to run the fan, and there has been a CEL the whole time from that.

So, I did pick up a pair of the spark plug non-foulers to try, but if there is no code from the downstream O2, I can probably move that experiment down the list, and move on directly to fabbing up some smaller diameter down-pipes to see what that does. . .

Thanks!

Thad

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PostPosted: Sat Mar 25, 2006 10:50 am 
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Well Keith, you saved me some time with this, thanks! I checked the codes, and all I get is 12, 35, and 55. So basically it doesn't like the fan circuit (#35), and other than that, everything is okay.

So, the next item to try is some small diameter down pipes. That should be interesting!

Thad

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PostPosted: Sun Mar 26, 2006 7:34 pm 
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In case anyone else is as geeky about finding out things like this as I am, here is the report on the last goofy thing I tried:

Following the collector pipe size two sizes bigger than the primary tube size rule of thumb, tonight I fabbed up a down pipe out of 1 7/8" exhaust tubing. The 1 7/8" part is about 13.5" long.

So, I got down into the 5.2s for my 15-59 MPH second gear dyno pulls. I did have a little less gass in the car, but that was accounted for in the vehicle info factors, as were the atmospheric conditions.

When I overlay the three run averages of the middle runs, it shows that I got back most of what I had with the converter, and even eeked ever so slightly ahead at the very top end, but I'm still missing some low end from about 2200-3700 RPMs.

Interestingly, the biggest gain I got from going from 2.25" to 1.875" for the down pipe was at the top end. Who would have guessed! ! ! !

An added benefit is that the exhaust note is much less annoying.

I think what this means is that I have to try 1.75" for the down pipe before I go back to the converter. . .

Thoughts anyone?

Thad

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PostPosted: Mon Mar 27, 2006 7:48 am 
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I'm finding that after I clear the codes that it takes about 2 days for it to return (CEL) and it's the same code everytime (P0420 cat efficiency). I can't believe you guys aren't getting a CEL from removing the cat.?

Is there a resistor mod that I can do or am I stuck with running the Cat?

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PostPosted: Mon Mar 27, 2006 10:31 am 
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Neon Mechanic
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Keith did the resistor mod to my downstream sensor when he owned the car, and it is working. I think you can probably find the necessary information on the Archived Posts board. If not, post back here and someone can probably tell you how to do it right off the top of his or her head.

Thad

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PostPosted: Mon Mar 27, 2006 1:05 pm 
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Searched all that I could and didn't see a thing... this search engine on here seems to never work right for me though :(

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'96 4D Highline
SOHC, MTX, K&N, Mopar ECU
Dynomax Turbo muff, Boogers,
urethane filled FMM, New PT clutch, ATX TB.

2001 SOHC swap complete! Going Honda huntin... :)


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PostPosted: Mon Mar 27, 2006 2:24 pm 
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Here is the information you want (I think). It was in a post on the second page of the archived posts:

IF YOU HAVE A 1996-1999 NEON:
1.) Go to www.casperselectronics.com, and purchase a MIL eliminator. This clever little device plugs into the engine wiring harness, and modifies the oxygen sensor heating circuit, and converts it into a signal tricking the
computer into thinking the downstream oxygen sensor is still in place. A
MIL PLUG IS NOT JUST A RESISTOR! I cannot stress this point enough, many "uneducated" people think this is just a 39-cent resistor, and they are ripping people off. I personally have one of these, and have used it for almost 20k miles, and I have yet to receive one oxygen sensor related code.
2.) You can try the resistor trick. This involves soldering a ¼ watt, 1
megaohm resistor into the black wire of the downstream oxygen sensor. This will effectively fool the computer into thinking there is still a catalytic
converter in place, by changing the output of the downstream oxygen sensor. The resistor trick will only work if you leave the downstream oxygen sensor in the exhaust piping. You cannot remove the downstream oxygen sensor from the exhaust piping, coil it up, and use the resistor trick; it does not work. I have personally (along with about six of my friends) have tried to use the resistor trick without the downstream oxygen sensor in the exhaust pipe, it does not work that way. The downstream oxygen sensor MUST be in the exhaust pipe for the resistor trick to work.


Hope that helps,

Thad

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--'97 M5 look 540i/6spd

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PostPosted: Tue Mar 28, 2006 11:48 am 
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Neon Mechanic
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I see people appear to be looking at this, so I might as well keep posting my observations I guess. . . .

This morning I filled up with my normal gas (all the way up to where it sits in the filler neck so I can get a consistent fill), and checked the mileage I got from having the 2.25" tube on the car in place of the converter.

My expectation was that I would have lost a little bit of gas mileage for the following reasons:

1) I've seen other vehicles apparently lose mileage when the converter was removed.

2) Conventional information on the .org is that you lose mileage (substantially) when you remove the converter.

3) I had done the dyno pulls for the 2.25" pipe (two separate sets on two separate days), and the dyno pulls for the 1.875" tube on this tank. That was basically the only mileage from this tank that I had on the 1.875" pipe.

4) The car was just loud and NASTY UGLY sounding with the 2.25" pipe on, so it is hard to imagine that any efficiency could be occurring. :lol:

On the other hand, I knew the mileage wouldn't be a lot worse, since the mileage on the tankful as the needle came down off of full was right in the normal ball park.

To cut to the chase, the mileage on this tank was up just slightly from the last one with the converter, at 29.05 MPG. I get very consistent mileage figures, and had been in the low to mid 28s for most of the winter with this car.

I'm going to at least see how many miles it takes for the needle to come off of full on this tank with the 1.875" pipe installed before I determine whether have the motivation to try some 1.75" pipe in there. So far, the motor feels very happy with this setup, and my guess (which obviously is likely to be wrong) is that my mileage will improve a bit.

By the way, the car sounds noticeably less annoying with this setup than it did with the 2.25" pipe installed.

Thad

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--'05 Dodge Grand Caravan SXT Dogvan 3.8L

--'97 M5 look 540i/6spd

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PostPosted: Tue Mar 28, 2006 1:14 pm 
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Interesting findings Thad... I can't believe you have the time and patience to keep climbing under the car and changing the exhaust piping! I hate exhaust work!

Right now I still have the gutted cat in there and the car sounds pretty damn good really but it has some serious resonance that annoys me. I think I'll try the resistor in the 02 and see if that keeps my MIL off and if it does then I'll just pull the cat out and weld some straight pipe in place but if the MIL comes back I'm just getting a hi-flow cat for it.

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'96 4D Highline
SOHC, MTX, K&N, Mopar ECU
Dynomax Turbo muff, Boogers,
urethane filled FMM, New PT clutch, ATX TB.

2001 SOHC swap complete! Going Honda huntin... :)


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PostPosted: Tue Mar 28, 2006 1:34 pm 
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Neon Mechanic
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Yeah, curiosity killed the cat! (and I get to weld when I do exhaust work :twisted: )

Thad

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--'05 Dodge Grand Caravan SXT Dogvan 3.8L

--'97 M5 look 540i/6spd

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PostPosted: Wed Mar 29, 2006 9:09 pm 
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super8neon wrote:
I'm not a fan of these electronic dynos... there are way too many factors that can adjust/ change each run.

It will change a little; ie w/i 1.6HP over 3 nights.
I suppose if you were to hook a boat to your car and do a run ...

Theres prolly a handful of people here that can afford unlimited dyno time,
for the rest of us, this is an ideal.

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PostPosted: Thu Mar 30, 2006 7:32 am 
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Just an FYI data point. . . This morning on the way to work with the 1.875" down pipe installed, the gas gauge needle fell off the peg at 75 miles. That isn't a good sign for gas mileage, and basically I will probably be in the same general range (or slightly worse) than normal or the tank with the 2.25" pipe.

Unless something changes over the next couple of days to tell me that I was wrong and that there really is something better about the 1.875" than it looks right now, I'll probably throw the stock converter back on it and have that as my next data point/comparison.

I think I'm about done with this, but it has been a fun little experiment!

Thad

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--'05 Dodge Grand Caravan SXT Dogvan 3.8L

--'97 M5 look 540i/6spd

--'96 Sport Coupe -- Hibernating


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