Possible Solution for NOx Purges

[3-Wheeler]

My biggest annoyance with the Insight is the NOx purge cycle that happens on the regular basis when cruising at my snail pace. Although it does seem to cycle more slowly when I drive closer to 35 mph or so compared to 38. The difference is quite noticeable.

Imagine. Your "in the zone". You have reached Insight nirvana. You have finally touched and held the throttle at just the perfect amount and getting north of 120 mpg, when it happens.....

The other day I might have stumbled on to a technique that reduces the purge cycle to almost no cycle at all.

Picture yourself driving along at 40 mph or so.
The throttle is roughly at a TPS of 16.
The purge cycle initiates.
Completely back off the throttle for about 1 second.
Reapply the throttle back to a TPS of 16.
Continue driving normally.
Lean kicks in almost immediately.
No apparent NOx cycle.

________________

Has anyone else observed this behavior?

Jim.

[IamIan]

Originally Posted by 3-Wheeler

Has anyone else observed this behavior?

In my experience ... it is more resistant to go back into lean burn without the purge than it is after one ... and that it seems to try to purge more frequently ... although I have not done any detailed logging to quantify the difference.

Although there are time that it just out right refuses to do lean burn ... no mater how light my throttle is or the load is ... have not quantified all those factors either.

[Eli]

I'll try to remember to test this.

How I deal with the purge is this..

If I'm cruising along at 100MPG and it kicks out of lean burn for a purge, I immediately lift my foot until the FCD is at 100MPG again. If you're ontop of things, you can do this without losing any speed or anything. When the purge completes, just move your foot back to where it was prior to the purge.

I don't think the purge necessarily has to significantly affect overall MPG.

[diamondlarry]

Originally Posted by Eli

I'll try to remember to test this.

How I deal with the purge is this..

If I'm cruising along at 100MPG and it kicks out of lean burn for a purge, I immediately lift my foot until the FCD is at 100MPG again. If you're ontop of things, you can do this without losing any speed or anything. When the purge completes, just move your foot back to where it was prior to the purge.

I don't think the purge necessarily has to significantly affect overall MPG.

Dang! I wish I had seen this a week ago for my trip to Columbus, OH and back. I always assumed there was nothing you could do but just wait it out until the purge was over. It was a round trip of 543 miles and I used almost 3/4 of a tank. Does anyone know all of the conditions that cause the need for a purge? What are the best ways to avoid them altogether?

[aisbell]

Purges are a normal function of the emissions control system. Nitrogen oxides are trapped during lean burn mode when their production is high. When the emissions system determines that the trap is nearing capacity, it reverts the engine to normal burn mode which produces the conditions necessary to convert the trapped nitrogen oxides to harmless nitrogen and oxygen <waving hands because he doesn't know exactly what happens>.

Unless a bug in the emissions control system has been discovered, it should not be possible to defeat these purges because doing so would result in high nitrogen oxide emissions.

[diamondlarry]

Originally Posted by aisbell

Unless a bug in the emissions control system has been discovered, it should not be possible to defeat these purges because doing so would result in high nitrogen oxide emissions.

Agreed. I wouldn't want to defeat the system so much as learn what conditions cause the need for a purge and do my best to avoid or lessen those conditions; kind of like doing everything short of sacrificing virgins to the fuel economy gods to stay in lean-burn.

[Eli]

Originally Posted by diamondlarry

Dang! I wish I had seen this a week ago for my trip to Columbus, OH and back. I always assumed there was nothing you could do but just wait it out until the purge was over. It was a round trip of 543 miles and I used almost 3/4 of a tank. Does anyone know all of the conditions that cause the need for a purge? What are the best ways to avoid them altogether?

It works really well for me. You feel the sudden surge of power when it kicks out of lean burn, so you don't really even have to be watching the FCD closely. If you're quick though, the FCD will only drop a couple of blocks before you compensate. It will do the purge, then when lean burn kicks back in you just re-adjust your foot to where it was before, or whatever is appropriate. There's definitely no reason to sit there at 50-60MPG for 30 seconds, unless you want the additional speed.

[3-Wheeler]

Originally Posted by diamondlarry

Dang! I wish I had seen this a week ago for my trip to Columbus, OH and back. I always assumed there was nothing you could do but just wait it out until the purge was over. It was a round trip of 543 miles and I used almost 3/4 of a tank. Does anyone know all of the conditions that cause the need for a purge? What are the best ways to avoid them altogether?

Yes, I can partially answer your question about how to prevent NOx purges altogether.....

I do drive really slowly to get the maximum mpg, and have found that there are no purges at all at 32 mph or below, but I also think that 32 mph might be the lower limit for lean burn as well.

Once the speed is between 34 and 35 mph, the purges occur, but only about 1/2 the frequency of the occurrence of the purges at 38 mph or so and above.

If there are other details, I am not aware of them at this time.

Jim.

[diamondlarry]

Originally Posted by 3-Wheeler

Yes, I can partially answer your question about how to prevent NOx purges altogether.....

I do drive really slowly to get the maximum mpg, and have found that there are no purges at all at 32 mph or below, but I also think that 32 mph might be the lower limit for lean burn as well.

Once the speed is between 34 and 35 mph, the purges occur, but only about 1/2 the frequency of the occurrence of the purges at 38 mph or so and above.

If there are other details, I am not aware of them at this time.

Jim.

I have seen LB at lower than 32 mph...if I go down to 4th gear. In 5th gear on level roads, it will actually go down to 29 mph and stay in LB. If it drops to 28, LB goes away immediately. In 4th gear, I think I have seen it around the 25 mph level. So it seems one of the main issues for purges is engine load levels? Higher loads=higher purge frequencies?

[Eli]

Originally Posted by diamondlarry

I have seen LB at lower than 32 mph...if I go down to 4th gear. In 5th gear on level roads, it will actually go down to 29 mph and stay in LB. If it drops to 28, LB goes away immediately. In 4th gear, I think I have seen it around the 25 mph level. So it seems one of the main issues for purges is engine load levels? Higher loads=higher purge frequencies?

That would make sense. Higher load = hotter combustion temps = more NOx.