Honda Insight Forum banner

1 - 18 of 18 Posts

·
Super Moderator
Joined
·
7,168 Posts
Discussion Starter #1
I've been told by one source I think knowledgable that FAS'ing and downshifting both cause catalytic purges, in addition of course to the routine purges. I seem to have noticed the penomenon myself, particlularly with downshifting. I do seem to hang on to lean burn in fifth at the tops of hills by simply lightening the load a bit, but if I downshift lean burn is gone and very difficult to recover.

I realize of course that load is involved and I may simply be using too much load after the downshift, but still I've heard the account of purges.

Could some of the folks with vast years of experience and knowledge comment on this.
 

·
Premium Member
Joined
·
1,069 Posts
Jim,

I spend a lot of time driving close to 34 mph, which seems to keep NOx purges to a minimum. I hardly have any at all.

However, when driving on a hillier portion of the drive home, and approaching speeds up to 40 mph, NOx purges seem to happen almost over every hill. I'm exaggerating a little but purges really pickup dramatically.

FASing does not seem to change the amount of purges, but I rarely downshift the motor either. My high preference for slowing down is coasting with the engine off.

So to answer your question, I have not noticed anymore NOx purges from FASing, but I probably drive slower than almost anyone else on this forum, except for maybe DiamondLarry.

Jim.
 

·
Registered
Joined
·
894 Posts
What I really want to know is whether the car would purge with the cats removed, whether it uses pre-programmed mapped coordinates for air and fuel in the computer to determine purge intervals, or if it relies on sensors including the 3 (or 2) oxygen sensors to provide actual feedback of catcon NOx accumulation somehow.
 

·
Super Moderator
Joined
·
7,168 Posts
Discussion Starter #4
What I really want to know is whether the car would purge with the cats removed, whether it uses pre-programmed mapped coordinates for air and fuel in the computer to determine purge intervals, or if it relies on sensors including the 3 (or 2) oxygen sensors to provide actual feedback of catcon NOx accumulation somehow.
The subject of catalytic purges was discussed a few months back on this thread:

http://www.insightcentral.net/forums/modifications-technical-issues/21511-lean-burn-without-purge-cycles.html

I don't recall all the details there, but the emphasis was on finding a way to avoid purges, perhaps with direct fuel injection into the cats. I too need to reread that thread. I don't think it spoke to either of our interests.
 

·
Registered
Joined
·
737 Posts
What I really want to know is whether the car would purge with the cats removed, whether it uses pre-programmed mapped coordinates for air and fuel in the computer to determine purge intervals, or if it relies on sensors including the 3 (or 2) oxygen sensors to provide actual feedback of catcon NOx accumulation somehow.
I have no way to back this up but, I suspect the car uses a pre-programmed table to determine purges as I've never heard of our cars having a NOx sensor. I'm guessing it would use some formula having to do with level of load over time while in lean burn. NOx is produced at higher levels when the load is higher which would explain more purges on the highway than when just tooling around the countryside.
 

·
Premium Member
Joined
·
2,391 Posts
There's no sensors past the NOx cat so there purges are calculated. Seems that on the highway at 60mph or higher that mine will purge around 1.5 miles plus or minus about .1 mile, most of the time. Less load less purges. Mine will still purge though, even if I'm going 30mph and the load is minimal but at 30mph I'm usually doing P&G in 4th gear without lean-burn because I get better gas mileage when the engine is off.
 

·
Super Moderator
Joined
·
7,168 Posts
Discussion Starter #7
There's no sensors past the NOx cat so there purges are calculated. Seems that on the highway at 60mph or higher that mine will purge around 1.5 miles plus or minus about .1 mile, most of the time. Less load less purges. Mine will still purge though, even if I'm going 30mph and the load is minimal but at 30mph I'm usually doing P&G in 4th gear without lean-burn because I get better gas mileage when the engine is off.
OK, I think most of us believe that this general relationship prevails, and that there is no activation by measurement. So, does downshifting cause an immediate purge? I ask because it seems on both my cars that downshifting drops the LB and it takes considerable time to nurse it back.
 

·
Premium Member
Joined
·
634 Posts
It's not the downshifting that drops you out of leanburn but the clutch signal when you depress the clutch, if you have installed the Calpod switch just flip the switch without shifting and you will notice it will take you out of leanburn.
 

·
Super Moderator
Joined
·
7,168 Posts
Discussion Starter #9
It's not the downshifting that drops you out of leanburn but the clutch signal when you depress the clutch, if you have installed the Calpod switch just flip the switch without shifting and you will notice it will take you out of leanburn.
Of course, why didn't I think of that:(

Kinda makes one want to experiment with an "Inverse Calpod" switch to see if LB can be maintained through a low load shift.
 

·
Premium Member
Joined
·
2,391 Posts
The movement of the throttle and load change needed with upshifting and downshifting will always pull you out of lean-burn, it's not the purge cycle. It's the same as if you release the throttle completely or push too much throttle while in lean-burn, it drops out of lean-burn. Lean-burn requires a fairly specific range of throttle(lower than around 32ish, less throttle at high RPM as you approach 78mph), load(below high 80's), gear(3rd and above), and temperature(over 155f or so and above about 20f ambient) to operate, if you leave those factors you aren't going to go into lean-burn.

If you drop out of lean-burn due to throttle or gear change, you need to wait a little bit but if it's being picky just hold the throttle at around 60mpg for about 5 seconds, then drop the throttle to 100mpg and it will drop right back in, if it doesn't add throttle to 50-75mpg again for a little while and retry. It gets tough when its freezing out and the first few times it goes into lean-burn during a warm up cycle. Both of my cars are consistent with their lean-burn behavior.
 

·
Registered
Joined
·
737 Posts
Through these last few posts, I think I may have come up with a way to to lessen the mpg sting of a purge. Since it's pretty much a given that a purge is a calculated thing and it's not a direct measurement of NOx, and that the clutch signal temporarily (very briefly actually) drops you out of lean burn, I tried something on my trip home from work this afternoon. I have a purge in a most annoying spot; an uphill stretch that's a tad bit over 1/4 mile in length. Since I'm under 75-80% load going up the hill, the car will not go back into lean burn until I crest the hill. There is a very short flat space just before the hill starts so I quickly cycled my clutch switch and dropped out of lean burn and back in before the hill started and managed to stay in lean burn all the way up the hill. It was much better climbing at closer to 80 mpg than the usual 50ish mpg. I noticed that blipping the clutch switch keeps you out of lean burn for much less time than a purge does. I'm going to try this strategy again tomorrow evening and if it works again, I'll try this on the next road trip.
 

·
Premium Member
Joined
·
1,069 Posts
Through these last few posts, I think I may have come up with a way to to lessen the mpg sting of a purge. Since it's pretty much a given that a purge is a calculated thing and it's not a direct measurement of NOx, and that the clutch signal temporarily (very briefly actually) drops you out of lean burn, I tried something on my trip home from work this afternoon. I have a purge in a most annoying spot; an uphill stretch that's a tad bit over 1/4 mile in length. Since I'm under 75-80% load going up the hill, the car will not go back into lean burn until I crest the hill. There is a very short flat space just before the hill starts so I quickly cycled my clutch switch and dropped out of lean burn and back in before the hill started and managed to stay in lean burn all the way up the hill. It was much better climbing at closer to 80 mpg than the usual 50ish mpg. I noticed that blipping the clutch switch keeps you out of lean burn for much less time than a purge does. I'm going to try this strategy again tomorrow evening and if it works again, I'll try this on the next road trip.
Larry,

Try backing off the throttle as well, just for a second, and report back how that works as well.

I use that technique with very high success rate.

Jim.
 

·
Registered
Joined
·
737 Posts
Larry,

Try backing off the throttle as well, just for a second, and report back how that works as well.

I use that technique with very high success rate.

Jim.
I do that when I'm on a road trip and it does work pretty well however, it seems that the clutch method takes even less time to get lean burn back. My standard routine is to accelerate at about 90% (with the clutch switch deactivating assist) load up to 35 mph at which time I shift into 5th and back off. I notice I go into lean burn almost immediately. I then turn assist back on and there is a period of about 3 seconds or less where lean burn goes away then comes back again.
 

·
Super Moderator
Joined
·
7,168 Posts
Discussion Starter #14
Through these last few posts, I think I may have come up with a way to to lessen the mpg sting of a purge. Since it's pretty much a given that a purge is a calculated thing and it's not a direct measurement of NOx, and that the clutch signal temporarily (very briefly actually) drops you out of lean burn, I tried something on my trip home from work this afternoon. I have a purge in a most annoying spot; an uphill stretch that's a tad bit over 1/4 mile in length. Since I'm under 75-80% load going up the hill, the car will not go back into lean burn until I crest the hill. There is a very short flat space just before the hill starts so I quickly cycled my clutch switch and dropped out of lean burn and back in before the hill started and managed to stay in lean burn all the way up the hill. It was much better climbing at closer to 80 mpg than the usual 50ish mpg. I noticed that blipping the clutch switch keeps you out of lean burn for much less time than a purge does. I'm going to try this strategy again tomorrow evening and if it works again, I'll try this on the next road trip.
I really envy you guys who have a standard commute that you do day after day. You can learn a lot from doing something over and over again. I might even have to forgo retirement so I can have such a daily commute - nah:D
 

·
Registered
Joined
·
737 Posts
I payed a little more attention while cycling my clutch switch yesterday and found that the time out of lean burn is more like 1 second as opposed to the 3 seconds I had estimated. It's been awhile since I've been on a highway trip but it seems like a purge lasts for closer to 10 seconds? Once again my strategy worked and I was able to climb the entire hill in lean burn at 80-100 mpg as opposed to 50ish out of lean burn.
 

·
Premium Member
Joined
·
1,069 Posts
....My standard routine is to accelerate at about 90% (with the clutch switch deactivating assist) load up to 35 mph at which time I shift into 5th and back off. I notice I go into lean burn almost immediately. I then turn assist back on and there is a period of about 3 seconds or less where lean burn goes away then comes back again.
Larry,

Can you describe in a little more detail about your "accelerate at about 90%"?

When you are accelerating up to 35 mph, are you doing most of the accelerating in 2nd gear, and at what TPS throttle setting for example?

Jim.
 

·
Registered
Joined
·
737 Posts
Larry,

Can you describe in a little more detail about your "accelerate at about 90%"?

When you are accelerating up to 35 mph, are you doing most of the accelerating in 2nd gear, and at what TPS throttle setting for example?

Jim.
I should note that my "target" is a 90% load but it kind of varies above and below. I start in 1st and go to 12-15 mph, shift into 2nd and go to 23-25, then shift to 3rd and go to 33-35 mph and shift into 5th and level off on the throttle. If I remember correctly, TPS is around 30-40 but not entirely sure since I'm paying more attention to the load number on the OBDII C&C than TPS. Because of the layout of stop signs and turns on my commute, on the way to work (starting around 4:00am and running to about 4:30am) I usually don't go much more than 1/4 before I start an engine off glide. On the way home (varies from 1:30, 2:30, or 3:30pm depending on production requirements), there is a stretch of terrain that is situated just right that I have to cruise for about 4 miles where speed goes as high as 37 mph and as low as 30 mph.
 

·
Super Moderator
Joined
·
7,168 Posts
Discussion Starter #18
I payed a little more attention while cycling my clutch switch yesterday and found that the time out of lean burn is more like 1 second as opposed to the 3 seconds I had estimated. It's been awhile since I've been on a highway trip but it seems like a purge lasts for closer to 10 seconds? Once again my strategy worked and I was able to climb the entire hill in lean burn at 80-100 mpg as opposed to 50ish out of lean burn.
I think I verified this morning that this technique works for me also. I took a drive westward from Richmond on I65, which is just one gentle hill after another. I found that pulsing the Calpod switch just before the bottom of a hill, LB would restore in about 1 second, with no throttle movement, and the mid hill purge was almost always avoided. Very interesting how the drop-out algorithm must be designed. Obviously it looks at many variables, but recent shifts is one on the variables.

After pulsing I found that I could pull loads of up to 80% with no assist and no LB drop-out. Climbing at 75MPG certainly beats climbing at 50MPG;)

Thanks Larry for the tip.
 
1 - 18 of 18 Posts
Top