Street economy without Cats

In reply to fanfoy:

It checks before the cat warms up. After it warms up, yes it can't provide much meaningful information, other than cross-checking when it sees something wrong. (Hmm, front O2 is reading dead lean, we're adding tons of fuel and it's still lean, but wait the rear O2 on that bank is pegged rich. Maybe it's a failed front O2 and not a lean condition?) Not every manufacturer has this level of complexity, and there's also the time-travel effect of working on cars coming up on 20 years old and the engineers were tickled just to have some sort of functional misfire detection algorithm...

The catalyst cross-checks involve things like rear O2 time spent high, time spent low, time to switch low to high, time to switch high to low, and way more others than I care to think about. Usually by the time it throws a 420/430 code, it's obviously a dead cat and both O2s on that bank are playing follow the leader.

SVreX wrote: I am asking if there is any point in trying to bother replacing it, or just cut the darned thing out.

If it matters any, the cat is the exhaust manifold, so there's no "cutting out". Replacing can be done in chassis, perversely the rear bank is more easily accessible than the front bank.

If it's not rattling (and therefore breaking up) and you don't have smog testing to worry about, I'd just leave it alone. If it's truly dead, then it isn't going to clog up since it isn't getting hot. If it's rattling, then it IS breaking up and probably causing a restriction, if not now then soon.

Regarding noise...

I've driven a lot of cars with cats removed. None of the cars I've driven without cats had significant noise increases based on the cat removal. Remove the muffler, sure. Lots more noise. But the cat is not a muffler.

But I don't have first hand experience with a Honda.

Knurled wrote: If it matters any, the cat is the exhaust manifold, so there's no "cutting out".

Yeah, that could make a difference...

In reply to alfadriver:

If I understand what you are saying, you are using the rear O2 sensor as another correction factor on top of the front O2. But it is still a only a fine tuning to mostly keep the cat at peak efficiency. So its removal from the management process (with an anti-fouler) will have very little effect on the actual running of the engine. I.E. you remove the rear O2, the car through's a code, you remove the front O2, the car won't run.

Also, all the cars I've wrenched on (05 and older) have always had a three-wire front sensor (yeah the rear one is four wire, my bad). I haven't checked my 2012, but are they going to a front heated O2 for emissions reasons? I mean, how long does it really take for the front O2 to warm up?

Sorry, but I've only played with aftermarket injection systems on older engines, so I'm not really current with the latest OEM tech.

fanfoy wrote: I mean, how long does it really take for the front O2 to warm up? Sorry, but I've only played with aftermarket injection systems on older engines, so I'm not really current with the latest OEM tech.

A lot of cars go into closed loop before the end of your driveway.

The vast majority of emissions comes from cold start. Once the engine is in closed loop, emissions drops remarkably, and once the cat lights off, emissions is zero as far as we're concerned. The trick is getting the engine into closed loop ASAP so it can light the cat ASAP. I can't remember the last time I saw an unheated O2 and pretty much everyone is using close-coupled cats now.

The engine in question is kinda interesting in that not only does it have a close-coupled cat, but the "manifold" (in the sense of bringing many pipes into one) is part of the head. There's only one exhaust exit per cylinder head.

Knurled wrote: Replacing can be done in chassis, perversely the rear bank is more easily accessible than the front bank.

I thought the 1st gen Oddy was 4cyl only?

In reply to Knurled:

So the overall strategy hasn't really changed since the beginning of OBDII? Because what you are telling me is what I learned 10 years ago. You are just using more and more precise sensors to acheive the same effect? Does it allow more advanced strategies?

Back in university, we had experimented with a very lean mixture just after cold start to try to bring the temperature up as fast as possible. But we were using a normal three-wire O2 that didn't provide the precision (especially off stoichiometry) to make it work effectively. When we tried a wideband, its reaction time wasn't fast enough. That might have been ECU related, but we couldn't make it work.

Also, what the strategy behind incorporating the manifold into the heads? I can't think of any good reason.

Sorry to the OP to have derailed the thread.

I'm assuming that putting the manifold in the head warms up the engine faster. It's probably deleterious for keeping the manifold hot, but that may not have been the direction they needed to go. Bigger engines take longer to warm up. (I understand this is why Nissan never gave us the RB engines, just way too much mass/displacement for decent cold-start emissions)

fanfoy wrote: In reply to alfadriver: I haven't checked my 2012, but are they going to a front heated O2 for emissions reasons? I mean, how long does it really take for the front O2 to warm up?

The best systems go closed loop in about 8 seconds. Unless you have a really short driveway, not only are you closed loop, but the catalysts are up and working. As Knurled said- most of the emissions are in the cold start- and when your stadard is PZEV, then that part has to be done BOTH really well and quickly- there's not much time where you can run without the catalyst working very well.

One interesting thing- there's work going on to allow the sensors to be working when you key on.

Closed loop time isn't so much about the ability to heat the sensor- there are some massive heaters available. It's more about durability- making sure that a drop of water does not hit a hot piece of ceramic and crack it.

you asked about advanced strategies- the sensors plus creative ideas plus better understanding of how catalysts work have lead to some really cool control ideas. I've been doing this consistently for about 15 years of my carreer, and of that, the fuel control has changed quite a bit- probably 4 major times, and 6 or so additional minor times, not including that ideas have come up that make systems better.

The idea is to get the best emissions with the least amount of catalyst.

In terms of cold start emissions- having seen some data on Honda, this oddesy is probably running at 15 to 15.5:1 until the sensor is alive, and then it goes into a cycle to make the catalyst work well. For the most part, 13-15 seconds is a pretty good time range to start cycling the fuel, as the cats are hot enough to start working.

this is one of those common instances where solid regulation has lead to a whole series of really interesting innovations.

Knurled wrote: I'm assuming that putting the manifold in the head warms up the engine faster. It's probably deleterious for keeping the manifold hot, but that may not have been the direction they needed to go. Bigger engines take longer to warm up. (I understand this is why Nissan never gave us the RB engines, just way too much mass/displacement for decent cold-start emissions)

there are good ways around that- which is why you see cars like the Vette and Aston Martin and Ferraris being able to sell in the US- fully meeing emissions rules. If Nissan isn't doing with GM can do, I'm not sure what that means.... could be that Nissan is too cheap.

SVreX wrote: Regarding noise... I've driven a lot of cars with cats removed. None of the cars I've driven without cats had significant noise increases based on the cat removal. Remove the muffler, sure. Lots more noise. But the cat is not a muffler. But I don't have first hand experience with a Honda.

Maybe not louder, but every car I've done it on has turned it into a buzz bomb.

m4ff3w wrote:

Knurled wrote: Replacing can be done in chassis, perversely the rear bank is more easily accessible than the front bank.

I thought the 1st gen Oddy was 4cyl only?

This is correct. 1st Gen Odysseys are all 4 cylinder.

fanfoy wrote: Sorry to the OP to have derailed the thread.

That's OK.

I said it was a theory question. It's all about learning.

if you run without a cat you are polluting the air and contributing to global warming. Shame !

SVreX wrote:

m4ff3w wrote: I thought the 1st gen Oddy was 4cyl only?

This is correct. 1st Gen Odysseys are all 4 cylinder.

Huh, never mind then. I've never seen a 4-cylinder Odyssey before. When were they made?

First Generation

Also sold as the Isuzu Oasis.

^^Yep^^ What he said.

I've got an Oasis, and 3 Odysseys. They destroy most other mini vans for fuel economy. They are easy to spot- they don't have sliding doors, so the front and rear door handles are not directly next to each other.

SVreX wrote: ^^Yep^^ What he said. I've got an Oasis, and 3 Odysseys. They destroy most other mini vans for fuel economy. They are easy to spot- they don't have sliding doors, so the front and rear door handles are not directly next to each other.

What sort of MPGs you pulling with those bad boys?

27 mpg pretty regularly, mixed driving. When we are careful, we can flirt with 30. No mods at all (other than old age).

If we put ethanol in the tank, it can drop to 23- 24.

I'd be ashamed to admit some of the fuel economy numbers on most minivans. Is 17 mpg really something to brag about??

I don't know about the odyssey, but my old E30 was definitely louder and stinkier without the cat. I was trying to pinpoint a low power issue and temporarily removed the cat for a month or so, and man, some days it would kind of burn your eyes a little if you were in bumper to bumper traffic with a lot of stop lights. Not good.

I've always kindof wanted one of those Oddities to give some standard Honda hop-up treatment to.

It's like a marginally larger EP3 Civic Si, but better.

16vCorey wrote: ... I was trying to pinpoint a low power issue and temporarily removed the cat for a month or so, and man, some days it would kind of burn your eyes a little if you were in bumper to bumper traffic with a lot of stop lights. Not good.

I'm old enough to remember riding in the family car as a kid, going through LA traffic on the way to a summer vacation destination. This was the late 1960s and the air smelled exactly like someone was putting tar on their roof upwind - for about 50 miles... made my eyes sting.

Nowadays, I can smell a classic car on the freeway when I'm about a quarter mile behind it.

alfadriver wrote: there are good ways around that- which is why you see cars like the Vette and Aston Martin and Ferraris being able to sell in the US- fully meeing emissions rules. If Nissan isn't doing with GM can do, I'm not sure what that means.... could be that Nissan is too cheap.

One of my friends was telling me how the JGTC teams were milling 66 kilograms of iron out of the RB engine blocks because they were limited to 400hp and the engine didn't need that much metal for the level of power.

66kg is also almost exactly what a Ford 302 block weighs.

I have no idea what an RB engine actually weighs, but from the sound of it, it's not light at all That's a lotta mass for such little displacement!

In reply to Knurled:

Special ultra dense iron.