I always heard that gutting the cats on a car that ran the ODB2 and ODB3 computers would automatically set-off the Check Engine Light...

Will it ?

 

it will,
because it uses the rear O2 sensors to read that the cats are working, which they definitely would see right away.
The 2 o2 sensors read the exhaust gas and the rear ones then would see the cat efficiency, which in this case would mirror the front o2 sensors this is a definite sign of insufficient catalyst.
I know they sell a cheater kit which fools the ECM into thinking they are there and working on Mustangs.

 

From what I can see there are three sensors... (1) at the exhaust manifold passenger side, (2) just after the front cat on the drivers side (3) just after the front cat on the passenger side... The other two rear cats are sensor free...

Lots of 02 sensors... One would think they would sound the alarm if the cats were gutted... Granted it's illegal to remove catalytic converters for a street licensed car... And rumor has it, removing them won't improve HP unless they are clogged and obstructing the exhaust flow... Which is highly unlikely for cars that are only a few years old...

So, the question still stands... And this is a loaded question...

 

If you remove the rears or gut them it won't. I'm pretty sure it will for the front ones because of the poor AF ration being read. But I'm no expert so IDK.

 

OK... So here's the answer... I pulled the OEM exhaust system off the car to do multiple dyno runs as a baseline before we started with headers, extruding, honing, etc. to see if we were barking up the "right tree", or we were wasting money and time...

After doing the first few tests with the current exhaust set-up, I decided to gut the cats to see if that made any measurable difference in the mapping (HP & Torque)... While the pipes were removed, I fired-up the car momentarily and the "Check Engine" light immediately came on... Probably because the 02 sensors were dangling below the car...

We re-installed the pipes with all 4 cats gutted, re-installed the 02 sensors and the Magnaflow still attached... The "Check Engine" light illuminated for appx. 30 seconds then went out... I decided to run the car on the road for about 1/2 hour to see if the light would come back on, but it never did...

We put the DRBIII scan tool on the car to read the error codes... NOTHING !!!

So, the answer to the poll is NO in this case... Granted we will not run the car on the street with gutted cats... However, I always heard that cars equipped with ODB2 & ODB3 would show a "Check Engine" light if the cats are gutted... Not the case that we experienced...

PS: If you plan on doing this for a performance enhancement, DON'T... Not only does the car sound very strange with the cats gutted (like farting into an empty beer can), it's illegal and the exhaust odor is really annoying... AND, I'm not even sure it would do any good for HP increase since we never ran a dyno in that configuration...

If you're going to start messing with the cats... Get some high-flow cats from one of the performance mfgs...

We're hoping to get a header system that will allow us to eliminate the front 2 cats and only run the rears, to make it within DOT compliance...

 

I had this mod done to my previous car, 2000 Contour SVT, and had to get MIL eliminators from Dallas Mustang. I did notice that the R's got up alot quicker and my dyno runs went like this...

-20K w/ gutted precats, true duals, 2 1/4" pipe and Magnaflow resonators and SS race mufflers w/ drop in K&N netted only 159 hp on the dyno.

-32K same above mods and I pulled 167 hp (almost one year to the date, different place for the dyno (same brand) and the weather was almost exactly the same.

-Spring 04' 50K same above mods except I installed a 9" K&N and we used a Mustang Dyno instead of the DynoJet and I pulled 171 hp. The Mustang dyno measures the hp differently and the guy there told us there's about a 10-15% difference between there's and the DynoJet and he said you can take the low amount (10%) and add it to the total. If thats true, I pulled 191 hp out of my 2.5L DOHC V6 w/50K on the clock. The IUM/LIM weren't cleaned and I was runnin' my stock plugs. The kid who bought my car had them cleaned and new plugs/wires added to the car. He dyno'd the car and it put down 186 hp. Speaking of dyno's, is there anywhere we can take the Crossfire to have it dyno'd w/o messing some thing up?

 

I take mine to http://www.buttonwillowraceway.com/ and have it done at the spec miata shop at the track... BTW this is in So. Cal...

I don't know where you are at, but a good dyno run should cost you about $150-$175... And there is nothing to screw-up... It's a dyno that runs the front wheels as well... Not sure of the proper term, but will find out when I'm there in two weeks...

 

...the rear O2 sensor is there just to check cat efficiency. Before committing it to fact that a MIL will not be set by gutting the cat, try this: run it at wide open throttle (WOT) for some period of time after the car had a chance to warm up. A couple of minutes if you can. The A/F will revert to open loop, and there will be some WOT A/F enrichment. Car makers run pig rich at wide open, as that's when more power is needed, more raw fuel is necessary for cooling combustion chambers and the tops of pistons via quenching, and where fuel economy and emissions homologation is never tested and certified. At that condition, there will be more raw hydrocarbons in the exhaust, blowing right through the hollow where the honeycomb used to be. And, my guess is that your rear O2 sensor will kick off a signal voltage which will light a MIL. I would be curious to know what happens when you try this. If it doesn't set off the MIL, then I would conclude that the OBD cal in the ECU is way off. Or, maybe this was somehow manipulated by Upsolute when you had your chip done?

 

WOW!!! This is way too in-depth for my little pea brain...LOL...
And it was PowerChip that did the eprom re-map last year, not Upsolute...

I'll do a "HARD" run at the track on Feb. 4th & 5th... But I'm surprised it didn't initiate the check engine light and I've driven the car since then...

i'll try your experiment tonight and report back...

I can tell you one thing, the exhaust smells like crap now... Almost like the nitro methane burners I used to gag-on when I was a cameraman for the NHRA... Burns your eyes !!!

 

juddz: Well in response to your query, I had to find out... Late tonight I took the car on one of my favorite 38 mile canyon roads through the mountains of So. Cal. We call it the Malibu Grand Prix and have been driving it since I was 14 years old... Yes, when I used to borrow my fathers car in the middle of the night...

I tore-up the car pulling 4,000 thru 6k for the entire time, probably 45 minutes... NO CHECK ENGINE LIGHT at all...

I don't know if this has anything to do with it, but I replaced the plugs last week with 12 new Denso Iridium and am running Sunoco 100 octane with Klotz Coxoc in a 4/1 ratio. The exhaust stinks like hell and makes my eyes burn... LOL

I gotta dyno this thing ASAP... Either I've destroyed this little 3.2L engine, or found a few extra ponies under the hood. Either way, I'm surprised that I'm not getting the CE light...

I'll be at Buttonwillow Raceway in a few weeks and can get a short dyno run at the shop... I'm interested to find out what the HP and Torque are at now... Especially since I probably cooked the valves... LOL

 

Wow. I'm really surprised that it didn't set the CEL, and now I am trying to think why it wouldn't. Keep us posted over the next few weeks, let us know if it does come on at some point. Meanwhile, the hamster wheel will keep on churnin' in my noggin. If I come up with an explanation, I'll post.

 

The only thing I can think of is that it's a result of the PowerChip. I do remember we had a CEL when the Eprom was initially installed and they had to turn it off with a program command into the DRBIII port. I'm starting to wonder if their command shut it down entirely...

 

...do you remember the fault code that came up when the CEL was set? If you can get me a p-code, I can cross reference it to see if in fact it was a O2 sensor fault.

 

It was quite awhile ago and all I can remember is after they installed the new chip and fired-up the car, it started missing and the tech got all nervous and got his supervisor. Turned out that they had not re-seated the board properly.

The CEL remained on after the incident and they went to the office to download something off the internet and transferred it to a pcm/cia card which was plugged into a multipin connector then plugged into the DRBIII port under the dash board. They fired-up the car again and the CEL went out...

Now that I think about it more, I know they didn't completely disable the CEL, because I had it come on when I ran the car a few nights ago with the 02 sensors removed...

It's one of those things that makes you go HMMM!!!! because I would think this darn thing would be illuminated with all four cats gutted... Oh well !!!

I wish I had an extra $8,000 hanging around to buy a DRBIII scan tool...

 

Hi HDDP
I really wonder how you know the specific sound of farting into an empty beer can *lol*

I read though the posts and must admit that I didn't understand everything, especially some terms. So if I write something you already discussed - sorry.

For what I know the O2 sensors in the exhaust gives the voltage signal (according to O2 flow) to the main chip which regulates the air/fuel ratio by adjusting the injector pulse. When you said you unplugged the sensors, the circuit is open and most chips then ignore signals from these O2 sensors and produce a standard air/fuel ratio information for injection.
So in this case the check engine must not light. Like it doesn't when the sensors are out of operating temperature when the engine and the sensor heating is cold. But the air/fuel ratio in such an open circuit is always the same whether the engine is cold or not, under load or idle. This might be why your exhaust smells. And maybe your mpg will drop.

I'm not an expert. That's what I remember from school and hope I don't repeat something that has been mentioned before...

Greets

 

I'm surprised you haven't heard of our famous quartet ! We make the sweetest music with beer cans LOL...

I only removed the three 02 sensors while I had the entire exhaust system removed from the car, at which time the CEL "Check Engine Light" illuminated. I only had the sensors removed temporarily, while I gutted the four catalytic converters.

Once I re-installed the exhaust system (with gutted cats) and replaced the 02 sensors, the CEL did not illuminate as expected... It has been a common myth that if you remove the contents of a catalytic converter on a car that is equipped with ODB2 or ODB3, the CEL will illuminate. This is not the case on my '04 Crossfire... I think the myth is propagated to deter people from removing the catalytic converter. Understandably so !!!

The increased odor is a testament to the effectiveness of the catalytic converter and how well it scrubs the hydrocarbons from the exhaust. It now smells like really noxious exhaust fumes. kinda like an old '65 V8 that is running rich !!!

 

Hey HDDP, what did you dyno and was it stock when you did so?

 

I dyno'd the car about a year ago at Buttonwillow Raceway... They have a spec. miata shop there with a dyno... I'm going back to the track on Feb. 4th & 5th and going to TRY to get another run while I'm there. It's just the matter of whether I want to spend another $160 and cut into my track time...

The guys from Extrude Hone want a before and after dyno but are waiting for me to do it myself... NO LOVE !!! LOL

 

They should at least knock the cost of the dyno off of your price! I worked for an accounting firm that was there accountants, all I'll say without breaking my oath is they can afford it!

 

Ah well, everyone deserves to make a buck... $160 is cheap compared to some of the other places... I think DC should be paying for it... HELLO!!! DAIMLER CHRYSLER>>> I'M RUNNING THE CAR ON THE TRACK EVERY COUPLE OF WEEKS... GIMME A BREAK, PARTS, AND SOME SPONSORSHIP!!!