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I'm wondering if anything can be done to minimize purge cycles. Are they going to happen regardless at the same intervals, basically, or can any activity on the part of the driver minimize them... besides not going into lean burn at all, of course.

I assume they are generated based on the amount of airflow coming from spent exhaust while in lean burn, so that is basically a constant, in relation to distance traveled (assuming same gear), no?

What I don't understand is that it seems that this means there is extra oxygen in the air... so I don't understand why that needs to be filtered out, or do I not understand the difference between normal exhaust gasses and lean-burn exhaust gasses properly?

And... not that I'm planning on doing this... but would there logically be any way to eliminate them altogether by removing emissions equipment? It seems like that can't really be done on these cars, as so much is controlled by the O2 sensors. I'm curious if someone was to make a "Race Insight" if they would end up being stuck with the stock exhaust system, at least as far as the final cat.

Thoughts? :-? :D
 

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More correctly called NOx purge cycles. Its all built into the PCM control logic. Nothing that you can physically remove to prevent it.

If traffic allows you can recover most of the MPG loss (temporary loss of lean burn) by allowing the Insight to slow down a bit more (again temporairly). Basically drive by the MPG meter and let speed be damned! :D

HTH! :)
 

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At some point in the design phase the engine must meed EPA emissions specifications base on actual performance testing (i.e. actual NOx measurements). Since there is no NOx "sensor" on our Insights I more than suspect its mapped into the programming based on extrapolation of the engine's combustion data.

HTH! :)
 

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Discussion Starter #5
If traffic allows you can recover most of the MPG loss (temporary loss of lean burn) by allowing the Insight to slow down a bit more (again temporairly). Basically drive by the MPG meter and let speed be damned! :D

HTH! :)
That's pretty much what I do. Others use the time to Pulse to get ready for their Glide, which seems to make sense too.

BTW, what does HTH stand for... I forget! :-?
 

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BTW, what does HTH stand for... I forget! :-?
It stands for Hope This Helps! ...or Hail The Hybrid if you want to think of that instead.

Usually I find myself needing the boost in speed and use it as a convenient way to accelerate by bringing it to the 40-45MPG mark without needing to go back and try to reengage lean burn, which sometimes can cost 5MPH of speed when the car is being picky and doesn't want to engage right away and does that weird thing where instead of going to 150MPG from 100MPG, it shoots to 80MPG instead and then drops back down a few times before engaging :-?

If I don't need the extra speed, I'll throttle back to 75MPG-100MPG for the purge cycle, it doesn't seem to take any longer to purge at this level so I figure it saves gas as it runs its rich ratio and then I'll make up any speed if I need to when I gets back to lean burn.

My NOx purge only happens once every 3 minutes or so(feels longer to me but I haven't timed it) so I never thought it made too big of a difference in overal MPG because as 10 seconds as a function of time I don't think it can be all that bad for 45MPG or so for that short of a period. You just need to be careful because if you try to gain speed during the purge and push too far into the throttle, you won't know that it has finished the purge and rejected lean-burn, which can be a serious pain because if you aren't paying enough attention, you've gained 10MPH and used a bunch of gas and now need to slow back down again and deal with getting lean-burn back.
 

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I could be mistaken, but I thought that this pulse of extra fuel being passed through the motor was to protect the catalytic converter when in lean burn mode. With the original ECM, the pulse lasted 6 seconds. Then Honda came out with a recall to replace the ECM's due to a rash of catalyitic converter failures. With the new ECM the pulse lasts 8 seconds.

My point in bringing this up is that by backing off when the pulse kicks in to preserve your fuel economy, you might be causing damage (in the longer term) to your catalytic converter. I'd rather burn a tiny bit more fuel than replace my converter.

"shrug"

Bill
 

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BillR, I never thought about that, I thought it just stayed in the purge cycle a little longer, but you are probably right. ...either that or added NOx release with a 'full' NOx catalyst.
 

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My point in bringing this up is that by backing off when the pulse kicks in to preserve your fuel economy, you might be causing damage (in the longer term) to your catalytic converter.
Sorry, no. It NOT there to "protect" the CAT. As I corrected in my first reply is a NOx purge cycle. And NO you cannot "damage" the CAT by trying to avoid the MPG hit (or not) because of NOx purge cycle. The Insight stays in NOx purge (and does that job) reguardless of what your doing with the gas pedal at that time. Its just that slower (within limits) = higher MPG so you can minimize its MPG impact.

CATs are damaged from non reactive impurities in the fuel (mainly Sulfur) the common "smother" failure. Or excessive unburned HC's i.e. "raw" fuel that can super heat the converter and fracture or melt its ceramic substrate. OK, also if you hit one hard enough too. But that would still only count as "fracture" damage. ;)

HTH! :)
 

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So it's on a timer, eh? It sounds like (if care about CO2 but not NOx emissions) you should shift to neutral to minimize fuel consumption during the purge cycle. Failing that, you should at least back off the throttle, not press harder.
 

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So it's on a timer, eh?

That's the assumption. But I doubt its avoidable by the idle technique. And if you just happen to be on a long downhill where such a method could apply its also very easy to "miss" the purge happening (no loss of MPG signaled).

There's probably at least a couple of engine operating parameters that must be met before a successful purge is counted. No, I don't have access to Hondas propritary PCM programming so its all observation, advanced automotive knowledge and a bit of guesswork on my part.

HTH! :)
 

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Lets assume you could disable the purge, what would be the effect?

Unlimited lean burn and no ill effects apart from raised emmisions?

I decrease throttle every time as soon as the purge starts to maintain my choosen high mpg and I maintain speed with extra IMA power if reqd during these periods.

To be honest I think the difference they (the purges) make to mpg is marginally (1-2mpg) especially at high mpg with a hypermiler driving style.
 

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Lets assume you could disable the purge, what would be the effect?

Unlimited lean burn and no ill effects apart from raised emmisions?
Not sure what point your trying to make here Peter. :?

Lean burn would still NOT be "unlimited". There are still limits of physics and the chemistry of combustion that limits its availablity to a narrow range of speed and load.

And IMHO we are all guilty of being too casual with emissions.

NOx is _the_ primary cause of Acid rain. Its no longer theory and I've seen the changes locally. Acid etched rain spots in the paint of automobiles for one. Foliage damage, and when such foliage is a food crop a reduction in yield. Such effects directly reach into _all_ our pockets.
 

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That's the assumption. But I doubt its avoidable by the idle technique. And if you just happen to be on a long downhill where such a method could apply its also very easy to "miss" the purge happening (no loss of MPG signaled).
Wait, lean burn doesn't disable itself when you go to idle? It seems like mine does but maybe I'm not paying enough attention, I've always kept my MPG right at the '1 bar from 150MPG' point when trying to coast to avoid throttle-off regen and to leave lean-burn available during slight downslopes where I don't want to really slow down or speed up.
 

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Wait, lean burn doesn't disable itself when you go to idle?
There's probably at least a couple of engine operating parameters that must be met before a successful purge is counted.
As I stated im my post eariler (as quoted above). And I'd agree there probably isn't NOx purge at idle reguardless of speed (i.e. coasting in neutral).
 

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You were talking about an idling technique going on a long downhill and you said you'd miss the purge with that method, that's where I got curious because I thought there was no lean-burn at idle, so no lean-burn would be no purge anyway. Which is where my question came from.

I think I understand now though.
 

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Agreed.

With such a technical topic even "academic" discussion needs carefully qualified remarks. My eariler statements were overly broad and easily misunderstood.

But you did bring to the top probably the most significant factor: If'n it ain't lean burn'n then there's gonna be no NOx purge'n. :D

IIRC NOx doesn't accumulate in the NOx CAT at a rate that requires a purge except after a sufficiently long duration lean burn run. And the "solution" of a purge is to drop out of lean burn for a time.

HTH! :)
 
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