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Discussion Starter #1
I've had my Insight almost 3 years now, and until a couple of weeks ago had never driven it much below my home elevation of 4500 ft. Now I've driven it twice to the Bay Area, which is about sea level, and it seems to be causing problems.

Around home, I've averaged about 73 mpg over the 3 years. On this last trip I went over the Carson Pass (about 8000 ft) through a late snowstorm that put a few inches of slushy snow on the roads - not conducive to best mpg :) After the climb and descent to about 3000 ft, I was at about 75 mpg for the trip. As I got closer to sea level, mpg dropped dramatically, and the car seemed to be running poorly. By the time I'd gotten to San Jose, mpg was down to 66. Driving around locally, I get a lot of bucking & jerking, and assist wants to come on much sooner than at home.

Had much the same thing happen on the previous trip, a couple of weeks earlier. Thought something might have broken, but when I returned home to Reno, it went back to running as well as ever.

Anyone have a clue as to what might be causing this, and what I could do to fix it?
 

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james said:
and the car seemed to be running poorly.

<snip>

Driving around locally, I get a lot of bucking & jerking, and assist wants to come on much sooner than at home.
I'd start with one symptom and a possible cause, and a low cost countermeasure first. ;)

HTH! :)
 

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Discussion Starter #5
Well, I made the trip again. Filled up with premium gas, purchased at sea level on the way home, and it didn't do a bit of good. Didn't have the snowstorm this time, so for the segment from my place to Jackson (starting at 4500', going over an 8000' or so pass on about 100 miles of winding mountain roads, and down to about 2000') I averaged close to 85 mpg. The rest of the way was miserable: mostly flat freeway (a couple of climbs & descents, but it ran well there), not much wind, and I still was having to drive in 3rd at 65-70 mph to keep it out of assist. Wound up with a miserable 70.7 mpg for the trip.

I'm really puzzled over what's happening. The engine does seem to be running a bit smoother with the higher octane, but I don't think that's the problem. The engine doesn't seem to lack for power, it's just that the assist comes on WAY too soon. Could the manifold pressure sensor or something be reacting incorrectly to the higher air pressure?
 

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I think sometimes we need to step back and look at what we are complaining about (I say we because I do it to). You got 70 MPG. I think that is awesome. Yes, less than normal, but still awesome.
 

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And if Assist is behaving as abnormally described MPG will be _higher_ until the inevitable forced charge. Which may happen anyways due to the return elevation climb.

There is also a learning curve. Usually rather short for most cars, but the Insight may be an exception. It may have been clearer if you had upped the octane immediately upon arrival near sea level.

Let's keep chipping away at it shall we :?: (and use this thread)

It's a strange one. ;)

Sincerely,
 

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Discussion Starter #8
>> You got 70 MPG. I think that is awesome.

It's not that I'm complaining about the numbers. It's just that knowing the car and the way I drive it, I would have expected 80-85 mpg, and I would not expect it to use assist at constant speed on a flat road. That makes me wonder what's happening that I don't understand.

"And if Assist is behaving as abnormally described MPG will be _higher_ until the inevitable forced charge..."

Only briefly, as the assist would discharge the battery until the system went into forced charge, thus kicking me out of lean burn and dropping the mpg anyway.
 

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james said:
Only briefly, as the assist would discharge the battery until the system went into forced charge, thus kicking me out of lean burn and dropping the mpg anyway.
Agreed, but your reply dosen't clairlfy if that's what your seeing. If I'm reading between the lines correctly that *IS* what your seeing and is apparently the cause of your lower return MPG (forced charge most of the way).
 

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There is an barometric pressure sensor. It's mounted inside the ECM so you can't really check it. If it or the ECM case is plugged, it could cause your problem. Maybe the ECM firmware is brain dead and only checks the sensor at start. Did you turn off the car during the trip?

I'd also be suspect of the Evaporative Emission system. There's a reason they redesigned it for 2006. Too high or too low pressure in the gas tank could cause your engine to run rough. Next time, Loosen the gas cap and see there is rush of air (Does it suck or blow?).

If everything is working properly, you should see a little worse MPG at sea level vs. Altitude but the engine should be smooth at both places. More assist than normal could be the result of a higher SOC than normal, since you probably did alot of regen going downhill.
 

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Discussion Starter #11
"If I'm reading between the lines correctly that *IS* what your seeing and is apparently the cause of your lower return MPG (forced charge most of the way)."

Not exactly. The cause is that I have to spend a lot of time driving in 3rd to keep it out of assist, so that it doesn't drain the battery to the point of forcing recharge, and thus getting even worse mpg.

I did stop for gas during the trip (in Stockton, which is real close to sea level). No noticable difference before & after the stop.
 

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james said:
Not exactly. The cause is that I have to spend a lot of time driving in 3rd to keep it out of assist, so that it doesn't drain the battery to the point of forcing recharge, and thus getting even worse mpg.1
Then get out a map or your GPS and look for an elevation increase. Can't see that its not a significant factor. Or wire-up Calpods IMA inhibit mod (part of his FAS mod) that enables you to manually turn off IMA assist and see what happens. ;)

HTH! :)
 

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Air density does have an effect on aerodynamic drag. It would take a bit of calculating, but it's significant--several percent at least. Drag depends linearly on density.
 

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Discussion Starter #14
"Then get out a map or your GPS and look for an elevation increase."

Not really an option :) I have to go from my place over the Sierra Nevada, and down to sea level. There are only 3 really practical routes. The way I go (88 over Carson Pass) is the shortest. I80 is maybe 50 miles longer, and horribly rough (I've driven on smoother
dirt roads), US 50 goes through a lot of urban areas and traffic.
 

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Discussion Starter #16
OK, I understand now :)

But you know, it's not really the elevation change that does it, at least as far as I can tell. For instance, I did the trip again last night. There's about a 30-40 mile stretch starting from my house that is comparatively flat (a few hills, but little net elevation change) before the serious climb begins. I was at 79.9 mpg for that stretch. Climb over the pass, and down the other side to about my 4500 ft starting elevation, and I'm still at 75 mpg. On the couple of thousand foot drop to Jackson, I pick up another 8-10 mpg.

But starting from there, on nearly flat roads (and the first 50 miles or so with a 55 mph limit, too), the mpg just keeps dropping, and I end up with 70.5 in the driveway here :-( It just puzzles the heck out of me.
 

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Hey James,

I live in Floriston and commute along 80 to reno daily. I've done the trip to the bay area a couple times, but haven't noticed your problems. What I do know though is I drive a 1200 foot elevation change daily, with fluctuating mileage all year. If the weather is warm and sunny in reno, I get 73mpg easily, but once it gets cooler and windy, my milage drops to 66 and it seems like the car needs to use the assist almost all the time. Is it possible that your mileage problems are weather related? This has been a stormy, cold spring so far.
 

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Discussion Starter #18
I don't think it could be weather, because I don't get the mpg drop until I get down close to sea level. It can be chilly once I get in the Bay Area itself, but the worst part is the 88/I5/I205 across the valley, where it's warmer than in Reno. I usually start down about 7 pm, so it's started to cool off (plus I'm often fighting some headwind component down 395), yet I still do a good 80 mpg on the stretch from home to where I start to climb. Though of course that drops climbing the pass, I get most of it back by the time I'm at the same elevation on the other side.

I've begun thinking it might be EGR-related, because I see a lot more of the bucking & jerking at low RPM down here.
 

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I'm having this exact problem. Drove to Astoria, OR (sea level) from Missoula, MT (3,200 feet). Roundabout the time I got to the Columbia river (400 feet altitude) I noticed it; lack of power, bucking when in lean burn, and it seems to 'stick' in lean burn when I try to give it more gas to get back to stoic (and it kicks in the electric assist when it finally goes back to stoic; I can back off a little to get the electric to go away, which means an added step).

When I got back up to 1,400 feet altitude, problem was gone.

The moderate MPG drop I could live with; the problem is it's very undriveable. The bucking can get quite severe and I can't just ease it back out of lean burn once it drops into it, and having to drive in 3rd on the highway is inherently stressful. So I'm frustrated the entire time.

(for reference, mine is a 2000 MT with about 115,000 miles on it)
 

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Long term fuel trim?
 
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