Catalytic converter theft: still drivable?

[MillCreek]

The local news just did another story about catalytic converter theft. This causes me to wonder: will you damage your car by driving it without a converter?

[Nick1911]

I can't see how it would damage your car, unless something was dragging underneath.

The O2 sensors will likely be unhappy, and throw a check engine light.

Also... it's gonna be loud.

[Bogie]

Your fuel economy will drop. A little.
 
Sleeve in a piece of exhaust pipe, and that will quiet things until you can get it fixed. I hope they didn't get the front one.

[zxcvbob]

I can't see how it would damage your car, unless something was dragging underneath.

The O2 sensors will likely be unhappy, and throw a check engine light.

Also... it's gonna be loud.

I test drove a couple of Dodge Ram trucks last summer, and someone had stolen the cats off of them in the dealer lot the night before.  The late 90's truck ran just fine (but it was loud.)  The early-mid 2000's truck ran like *expletive deleted*it.  It accelerated okay, but when trying to maintain 50 to 55 mph, it sounded and felt like it was running on 2 cylinders (and not a balanced 2 cylinders, lol.)  He said they both ran fine the week before.  They handled the missing O2 sensor differently?  That's all I can figure.  They both had approximately the same size engine (about 350 cid) but the newer truck was a next generation engine.  They were both 3/4 tons, so they had the minimum emissions control systems.

You can buy something called a "test pipe" to temporarily replace the converter.  That's what I would probably do, and if it ran okay it might be a "temporary" for a long time.

[HankB]

. . . You can buy something called a "test pipe" to temporarily replace the converter.  That's what I would probably do, and if it ran okay it might be a "temporary" for a long time.

Some years back, "test pipes" were a very popular way to improve both mileage and performance with converter equipped cars. Wouldn't surprise me if newer cars didn't respond the same as older ones.

[Hawkmoon]

It depends.

Older vehicles have one O2 sensor. It's ahead of the catalytic converter, so it doesn't know or care if there's a cat or a test pipe back there. Then somewhere in the late 90s (maybe when OBD2 came along) they added a second O2 sensor, downstream of the cat. The system compares the values from the two sensors, and if the second sensor doesn't read "cleaner" than the first, it throws a code.

[Jim147]

It really sucks when they grab the converter then pop a hole in the fuel tank to steal the gas.

[French G.]

Depends on how smart your car is. How the computer is programmed to deal with out of bounds values from a sensor. Like my car is really dumb. Had cat codes for years, no problem. It senses fuel pressure in one place, at the pump. So with the fuel filter clogged it proceeded to tune the car to where it absolutely would not run and the pipe in front of the cat was glowing. All the while never giving codes that really directly addressed the problem.

[Bogie]

If your cat is just zorched, but not clogged, you can buy offset things you can screw the O2 sensors into to get them out of the main stream - this will spoof them somewhat. The OBDII check will read clean, but if the inspector sees them, it won't pass.

[dogmush]

If you are thinking of running without cats long term, they make, or you can build, what is called a MIL eliminator.  Basically you splice a resistor in the signal return wire, and a small cap across the signal wires on each rear O2 sensor. That will simulate the proper O2 level in the downstream exhaust and allow your computer to run with no issues. Lots of folks eliminate the cats on their daily drivers, and just spoof emissions inspections.

The presence or absence of cats won't effect the fuel trim as the car's computer calculates that from the upstream O2 sensors anyway. 


If you mean can you drive it home, or to a shop to get it repaired,  yeah, it'll be fine, but loud.

[Brad Johnson]

If the pop just the cat, you'll probably get a downstream O2 code but the vehicle will still run. As others have said, there will be no question the converter is missing. You, your neighbors, and pretty much everyone in town will hear it.

If, however, they snag enough pipe to cut, damage, or remove the upstream converter, your vehicle may throw a fit. Depending on manufacturer, some vehicles will simply revert to base fuel/air maps, set a Check Engine light, and keep going. Others will run like poop, or refuse to run at all. There is the remote possibility of damaging the 02 sensor wires in such a way that they zorch the ECM. Not common, but it can happen.

Brad

[Ron]

Drive without cat converters? Why do you hate the earth? 

[Ben]

Why do you guys want to convert cats anyway? Leave the cats alone.

[HeroHog]

At one time, the Ford round cats with the conical ends flowed the best and gave the best performance. If you want to go cat-less, pop out the cat and gouge all the guts out of it, do the above wiring mod, and no one's the wiser, until they stick an exhaust gas analyzer on it. Fortunately, my state doesn't do that.

[Bogie]

Or... an inspector sees the mod. You gotta be stealthy...
 
One of the kids at work, who thinks he is all fast and furious, cored his cats, etc... and then had problems...