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Old 04-10-2010, 04:33 PM   #1 (permalink)
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Default Battling Lean Burn Purge Cycles

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?
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Old 04-10-2010, 06:48 PM   #2 (permalink)
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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!

HTH!



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Old 04-10-2010, 08:41 PM   #3 (permalink)
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What determines their interval and duration?
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Old 04-11-2010, 10:09 AM   #4 (permalink)
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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.

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Old 04-11-2010, 10:49 AM   #5 (permalink)
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Originally Posted by Insightful Trekker View Post
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!

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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Old 04-11-2010, 10:50 AM   #6 (permalink)
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What determines their interval and duration?
Yes, I think this is what I want to know as well.
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Old 04-11-2010, 12:42 PM   #7 (permalink)
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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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Old 04-16-2010, 03:03 PM   #8 (permalink)
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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"

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Old 04-16-2010, 06:29 PM   #9 (permalink)
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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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Old 04-16-2010, 09:03 PM   #10 (permalink)
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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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