Any problem running LR3 without cats?

[TroySmith80]

I'm looking at a used lr3 that appears to be in pretty good shape and well-maintained but the catalytic converters are about shot on it and one of the O2 sensors is not happy with the output. Is there any problem on these rigs with all their computers if I just delete the cats or just leave the worn out ones in place, will the computer be unhappy and cause any problems or is it just a matter of the check engine light being on and having to live with that?

The seller said that replacing the cats is north of $3,000 and we're talking about a $9,000 truck here so it's not really exciting to think about replacing them.

I do not have inspection testing for registration where I live.

 

[nwoods]

I would hypothesize that yes, it will be a problem, only in the sense that the engine management computer is looking for signals from the O2 sensors that are downrange of the Cat. I would assume that without a Cat in place, those sensors are either missing or will read values out of the expected range, causing the engine to throw error codes and potentially choke things down.

But I'm totally guessing. honestly, I have no idea. Possibly it will wake the engine up and run like a top fuel dragster. Seriously, my opinion here means nothing and I should probably just deleted this post

 

[Herbie]

Just about any gasoline OBD-II vehicle will throw fits to one degree or another if the cats are fouled or missing - downstream O2 sensor will cause it to complain, at least. Moreover, one of the ways modern ECUs make so much power is by getting the fuel mix just right - the primary (upstream) O2 sensor validates a lot of that intermix chemistry, but the downstream sensor also plays a part. If the cat is bad, I would expect the ECU to radically retard the ignition timing and use a very conservative fuel map - this will both kill the engine's power AND make for poor fuel economy. (That is if the ECU doesn't outright force the vehicle into a limp mode.)

This was a $60,000 truck just 15 years ago - hopefully the example you're looking at was maintained well enough that a set of cats is a worthwhile investment. If not, I'd wager the rest of the truck isn't worth much other investment either.

 

[Shigeta]

Although it will require meaningful research to understand exactly how the O2 sensors and the ECU interact on our particular vehicles, Herbie nailed the general potential cause-and-effects of saying, "screw it!"

You can likely bypass it all by installing things like O2 sensor spacers, etc. but we're back to what Herbie pointed out. Generally, such hacks are designed to skirt the boundaries of a mixture error rather than fine-tune the mixture to be just right. Best case they extinguish the check engine light. Worst case, they exacerbate the problem in a different way. (Remember, the O2 sensors are one of the main ways the ECU validates the air fuel ratio)

Truth be told, if you're considering paying $9k for an LR3 with bad cats, you're about to significantly overpay. For reference, I bought a clean title, California (rust-free), at 140k miles with only minor issues for $6,000 one year ago—and quite frankly, I overpaid a bit.

If you must buy this example of a LR3, you should be able to have properly fitting/functioning aftermarket cats installed. Since you're in an emissions-testing-exempt state, you don't need OEM or C.A.R.B.-approved units. They will cost significantly less and should get the vehicle functioning correctly.

It would behoove you to do your own research & shopping around with exhaust installers.

 

[DaveInDenver]

Beyond the technical advice you've been given that, yes, you'll need a cat for the ECU to be happy I was just poking around Rock Auto (used a 2007 LR3 V8 49-state, not knowing much about them and assuming you're not in CA) and it looks like Davico, Bosal and DEC make catalytic converter downpipes for the LR3 and they're on the order of $300 to $400, so $600 to $800 for both. One of the last things I'd buy from the dealer is exhaust, which is probably what you've been quoted.

 

[Buddha.]

As far as I’m aware the downstream o2 sensor(s) are there for the sole purpose of determining if the cats are operating and effective. If the cats not working if turns on the CEL for emissions reasons only.
I don’t think engine performance is affected by ineffective cats unless they’ve melted down and are a restriction.
People run cat-less exhaust systems without any problem. Assuming you don’t have to get your vehicle inspected all you have to do is plug in a fooler where the downstream o2 would normally go.

 

[DaveInDenver]

You may be able to simulate the downstream and eliminate the cat altogether. You have to retain the forward O2 sensor for the ECU to run in closed loop no matter what.

People have mixed experience with sims, though. Engine designers look for an expected response of the downstream sensors. It may still recognize an incorrect response as a sensor failure and throw a CEL, which if you don't have emissions testing is just an irritating thing.

However, with some trucks this causes secondary issues. Tacomas in some years will disable things like traction control and throw an ABS warning when the downstream O2 issue is recognized, for example. Other year they don't. So it may or may not work with a particular model and year LR3.

 

[TroySmith80]

I appreciate all the responses... They don't lead me to a crystal clear conclusion but they are helpful. I may try to negotiate a price reduction of less than the high replacement quote but more than nothing.

Anybody know who is a real authority guru on the engine/computer systems on these rigs and would know with confidence if/how the downstream 02 sensor affects engine performance?

 

[Carson G]

Some guys in SA have run the v8’s catless I think they used mini cats to fool the o2’s.

 

[TroySmith80]

It may bear mentioning that i think running the catalytic converters is a good idea and i would like to have them if they're not prohibitively expensive, so that i'm not polluting more than necessary. I'd be hard-pressed to spend $3,000 on that, but the $600-800 somebody else mentioned may be in the realm of what i'm willing to do.

 

[Howski]

Get them down enough on price for a full replacement for look for another example

 

[Carson G]

IMO if your going to keep a vehicle long term I wouldn’t cheap out on cats. Since you’re looking at a vehicle to buy I would just find another example. If you already owned the vehicle it would be a different story.
Cats usually don’t just fail something has to kill them so unless you know exactly what caused the cats to fail and know for certain it’s been fixed you would be wasting money on new cats.

 

[Blaise]

It's not $3000, at least not for parts. Find out what the installation cost is, talk them down to cover that plus the cost below. Done.