How to hypermile Civic HX?? - Fuelly Forums

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Old 10-18-2008, 04:26 AM   #1
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How to hypermile Civic HX??

OK, I've been hypermiling since late '06. But in a big old Volvo that was EPA 19/24 or thereabouts.

Now I'm driving a '97 Civic HX with 5-speed. EPA 31/39 and most drivers seem to be getting low 40's mpg. Which is what I've been getting.

How to do better?? Tires are at 44/42 front/rear, wheels are HX alloys, no other mods except for silly fog lamps added by first owner, now dead.

Does anybody have any information on how to know or predict when it's in lean burn and when not?? Somewhere I read that outside the USA the HX's had a lean burn indicator but I have no confirmation or additional information. Sure would be nice to know when it's in lean burn mode, or at least to have some idea of when/how it goes into that mode and what kicks it out.

Any information on rebooting the ECU?? I saw a comment on that at the honda-tech.com forum but no detail on that either. The post suggested it's a good idea to do that kinda frequently for an HX but I take it with a grain of salt or ten.
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Currently getting +/- 50 mpg in fall weather. EPA is 31/39 so not too shabby. WAI, fuel cutoff switch, full belly pan, smooth wheel covers.

Now driving '97 Civic HX; tires ~ 50 psi. '89 Volvo 240 = semi-retired.
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Old 10-22-2008, 11:58 AM   #2
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Quote:
Originally Posted by brucepick View Post

Does anybody have any information on how to know or predict when it's in lean burn and when not?? Somewhere I read that outside the USA the HX's had a lean burn indicator but I have no confirmation or additional information. Sure would be nice to know when it's in lean burn mode, or at least to have some idea of when/how it goes into that mode and what kicks it out.
I am curious about this as well. Anyone have some insight?
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Old 10-22-2008, 07:41 PM   #3
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as for the lean burn question i think none of the HX models has a Lean burn monitor or indicator. I owned a 98 HX CA model and has the 5 wire o2 sensor for lean burn. you can feel a slight reduction in power when the car goes in to lean burn. with the help of a scan gauge II i've learned that sometimes when you feel the reduction in power it isnt always in lean burn but very close. its best to be below 70 mph for lean burn but once you're in lean burn you can go past 80mph.

the best way is to have a scan gauge to monitor lean burn.

use the code below to monitor lean burn with the scan gauge II
To Monitor Lean Burn, type in:
TXD 686AF10115
RXF 044105150000
RXD 2808
MTH 000100020000
NAM LBN

and save

If the value for LBN = 0 you are in lean burn.
If the value is higher than zero, you are not in lean burn.
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Old 10-22-2008, 08:04 PM   #4
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Thank you MrChoi!

Hopefully once I get a ScanGauge II I'll understand how to follow that procedure!

Did you use this on your '98 HX? Mine is a '97 so I would expect the engine control computer is the same.

Thanks again!
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Currently getting +/- 50 mpg in fall weather. EPA is 31/39 so not too shabby. WAI, fuel cutoff switch, full belly pan, smooth wheel covers.

Now driving '97 Civic HX; tires ~ 50 psi. '89 Volvo 240 = semi-retired.
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Old 10-23-2008, 06:24 AM   #5
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Resetting the ECU excessively is a bad thing because it takes time for the ECU to re-learn all the offsets it finds for various sensors. In the mean time you are getting less than ideal performance and fuel economy. It also puts the OBD2 ECU into "not-ready" status so you wont pass your smog test. You really only need to reset the ECU when you change the base ignition timing, Idle screw (which you should never touch), replace a sensor, or something drastic of that nature.

The HX doesn't respond well to hypermiling (namely pulse and glide) because it conflicts with lean burn and 12 valve mode. The advantage to buying a lean-burn engine is that you don't have to hypermile.

Besides the wideband O2 the HX relies heavily on the CKF sensor to detect misfires so that it's able to run the leanest possible mixture w/out causing driveability problems. The factory calibration is far more advanced than that found in the P07 and that's why HX's didn't have the low reliability reviews that the VX got. It's a great and unique car, easily one of the best among gasoline engines. I would count the Civic GX as a better car except that many parts of the country don't have access to CNG and because of the bloated price ($10,000 for a 1998?!).
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Old 01-01-2009, 03:13 PM   #6
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OK, this is a silly question.....

but does the Octane rating (87, 89, 93) affect the efficiency of a lean burn engine ???
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Old 01-02-2009, 08:30 AM   #7
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Originally Posted by suspendedhatch View Post
The HX doesn't respond well to hypermiling (namely pulse and glide) because it conflicts with lean burn and 12 valve mode. The advantage to buying a lean-burn engine is that you don't have to hypermile.
I don't see how it would respond any worse than an 8-valve non-vtec like mine. It should be at least as capable. Then, it has the EXTRA lean-burn mode to play with in certain conditions.

Bruce: what rpm does it run at 60 mph? I'm at 2750 rpm.
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Old 01-02-2009, 02:25 PM   #8
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...
Bruce: what rpm does it run at 60 mph? I'm at 2750 rpm.
At 60 mph:
2350 using ScanGauge data
2400 using instrument gauges

I got the ScanGauge about 6 weeks ago. It's nearly impossible to get much time in lean burn in New England winter weather. I can see when it's in Lean Burn from the LBN setup in the ScanGauge (X-Gauge setting as by MrChoi above in this thread).
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Currently getting +/- 50 mpg in fall weather. EPA is 31/39 so not too shabby. WAI, fuel cutoff switch, full belly pan, smooth wheel covers.

Now driving '97 Civic HX; tires ~ 50 psi. '89 Volvo 240 = semi-retired.
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Old 01-02-2009, 02:38 PM   #9
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I was thinking the HX has somewhat taller gears for slightly better highway mileage.

Consider a grill block this winter. I find the warmup times are so long, most of my drive is in the bad cold engine mode. A full 100% grill block helps that somewhat. I doubt you get lean-burn until it's warmed up.
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Old 01-03-2009, 04:53 AM   #10
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Yes, the HX has taller gears. I was fortunate to get a copy of the owners' manual with my car and it shows the HX does have higher gears.

Yes, I have a grill block, about 95% or so.
The engine warms up within a few minutes, unless I do a lot of EOC in which case the engine isn't running much so it takes longer. With the gill block, intake air temp (IAT) seems to run about 10-15 degrees above outside ambient air temp, at highway speeds. Idling, it rises higher than that.

When time and weather allow, I plan to run a wire lead from the rad fan to the dash, to let me know when that fan kicks in. This, along with Coolant Temp readout on the ScanGauge, will show me the max allowable temp, at least in terms of how the computer is programmed. So far I only know that with grill block, temps stabilize between 179-190 deg. F. Usually about 179-182

I've paid close attention to various other parameters in an attempt to find out when and why it goes in and out of Lean Burn. I feel pretty confident that I've sorted out a few points, but something is still unknown to me as I haven't found a way to get and keep Lean Burn in cold wet weather.

Engine has to be warmed up.
Roads/weather have to be dry.
TPS (throttle position sensor) has to be below 20 to enter LB.
(minimum is 9, I think maximum is 89)
Must stay below 32 TPS to maintain LB state, once achieved.
Sometimes won't go into LB after an idling coast, but sometimes it will.

I have theories re. wet weather preventing LB state.
One is that the cooling effect of wet/damp air flow over the exhaust system keeps the cat from running at maximum efficiency. There's a post-cat oxy sensor which could detect this. So possibly a belly pan closing off that area could help.

Another theory - damp weather permitting more ignition advance due to the high moisture content damping the combustion speed and reducing knock. Just possibly the computer is programmed to not allow LB when there's lots of advance. This is fairly roundabout logic and I don't put much stock in it but it's conceivable.
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Currently getting +/- 50 mpg in fall weather. EPA is 31/39 so not too shabby. WAI, fuel cutoff switch, full belly pan, smooth wheel covers.

Now driving '97 Civic HX; tires ~ 50 psi. '89 Volvo 240 = semi-retired.
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