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Discussion Starter #1
I recently noticed the FCD dropping about 25mpg, a slight increase in power (only enough to push me 1-2MPH faster), and no visible change in RPM for about 8-10 seconds at a time. This doesn't seem to be the same violent bucking or missing that other people have described so that's why I started a new thread.

It would happen maybe once or twice (that I noticed) during a normal day of driving and only when I was doing higher MPG lean-burn driving. It didn't have me too worried untill I took a trip down to LA last week and for a 20 mile stretch it happened every half mile. It was seriously freaking me out since I could watch the trip counter hit ###.5 and .0 and the FCD would drop from about 75 to about 50 MPG then at ###.7 and .2 it would go back up to what it was previously. It eventually stopped doing it on the .5 and .0 but would still last for about .2 miles or 8-10 seconds when it happened.

When I first started noticing it I thought I just had a lazy foot that was pressing the gas, but if I let off the gas a little it would only go up maybe 5-10MPG. Then after 8-10 seconds it would pop back up to above what it had originaly dropped from. It also doesn't have as much power as if I had pressed the gas to drop it from 75-50MPG, like I say it only goes another 1-2MPH faster.

I was thinking it might have been purging the NOx catalyst but it doesn't sound like that should happen every half mile.

The car might have been doing this earlier than when I started noticing it, but it wasn't untill just a few weeks ago that it trained me on how to drive more efficiently (78.9MPG from SF to LA via 101 :) was up to 85 at times but then it got cold and foggy and I was running a bit late)

It's going into the dealer tomorrow so I can take a tech on a drive and try to recreate what's happening, I'll post what they have say about it.
 

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Re: Brief 25MPG drops/slight increase in power during lean-b

dazey said:
I was thinking it might have been purging the NOx catalyst but it doesn't sound like that should happen every half mile.
Dazey,

what you describe certainly sounds perfectly like the NOx purge.

I'd agree that once every half mile is a little much, but it's never been very predicatble for me either. The frequency and length of purges varies widely. Sometimes it's hard to get out of rich-burn at all.

Ignore it if it doesn't happen too often...
 

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Discussion Starter #4
Having it happen once or twice during a day doesn't bother me and I hardly notice them. But that trip to LA got me somewhat worried and I might as well have it checked out.

I'm not sure what the tech will do when I drive them around unless they hook up a laptop or other device to the OBD-II connector. I don't get any lights or indicators other than the MPG drop. Probably just confirming that it's not something I am causing by applying more gas or whatever.
 

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Dazey, you were somewhere between SF and LA? Where, exactly, when this happened? Some parts of that drive can seem quite flat but have little hills in them.

I agree with others, it sure sounds to me like an NOx purge... but I too have never had it happen so frequently.
 

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Discussion Starter #6
I forget exactly where it was happening so frequently but there weren't many hills, just the occasional over/under pass on the otherwise flat farm lands. I wasn't far enough south to catch those darn long low grades, those suckers killed my mileage, especially since the other side of them doesn't have enough of a drop to do much good.

Around here I notice them more on the flat areas, probably just because it is not often in lean-burn going up the bigger hills and is getting too high of a MPG to notice going down hills.
 

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Discussion Starter #7
Just got back from the service appointment, and of course when I was driving the tech on the freeway it only happened once and he asked if I gave it more gas. He does tend to agree that it is the NOx purge but doesn't think it's a problem so he will ask Honda Tech Line on Tuesday to see if they have any suggestions.
 

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Discussion Starter #8
Just talked to the service manager. Techline told them that if I was going up a slight incline and the assist was on then stopped it could explain the surge. I again told them that there is no change in the instruments (other than MPG and sometimes MPH) and the assist wasn't on when it was happening every 1/2 mile. Anyways, they are telling me there is nothing wrong, I hope they are correct and it was just a fluke. I may be taking a long trip in the next few weeks and if I drive I can check it out again.
 

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My 01 does the same thing on occasion. It is definately a NOX purge issue. Mine will begin a purge which is interupted for whatever reason, slight acceleration/braking etc. Shortly, thereafter, it resumes the purge. Under certain highway speed conditions (long periods of lean burn) it will purge once then again within a few miles. Sounds normal to me.
 
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