Cold weather Lean Burn in Civic HX

Discussion in 'Honda' started by brucepick, Mar 10, 2009.

  1. brucepick

    brucepick Well-Known Member

    Driving a '97 HX for FE in New England can be largely an exercise in getting it into Lean Burn mode and keeping it there. At intake air temp (IAT) below 40 it doesn't stay in Lean Burn much. Wet or snowy conditions seem to also take it right out of LB mode.

    There's no instrumentation to help with that in the car but a ScanGauge will tell you what you need to know. It will read out throttle position, IAT, and will tell you when you're in and out of lean burn mode. And of course it gives you mpg data.

    The OEM air intake port is over near the passenger side fender. Even with substantial grill blocking the warmest I could get in highway driving was about 10 degrees F above ambient air temp.

    By cutting openings in the air filter box I'm able to get the [IAT] about 30 degrees above ambient air. It pulls air which has just come through the radiator. This temp increase means that I should be able to run in lean burn even with outside temps around 15-20 deg F or so. My original plan was to route a pipe to the exhaust manifold to pick up warm air there, but the car's configuration really works against this approach. The air box cuts seem to be doing a fine job. Today in 35-40 deg F temps with rain and snow, I was able to run in lean burn consistently, for the first time ever in such conditions.

    Note: doing this mod will produce a loud, deep moaning sound when you step on the gas more than about 1/3 travel. However, duct tape will cover your openings if you decide you don't like them for whatever reason.

    Here's a photo of the modified air box. I widened the gap at the notched attachment tab to make it easier to remove and reinstall.

  2. PaleMelanesian

    PaleMelanesian Beat the System Staff Member

    I think Wayne programmed a Lean Burn indicator for someone's scangauge recently. MNFocus, maybe? His is the same generation HX as yours.
  3. MnFocus

    MnFocus hanging member :)

    :) yes he did . I'll heartily agree getting into LBN is a pain in this bitin cold we're having now (if I can even get INto the car!). The LBN is working and when it's cold shows a reading over 120. After the engine warms up the number drops below 100 and typically ranges quite a bit without due attention to technique. Near idle speed and very little load its in the 3-9 range. "0" is obviously lean burn. I've been managing to keep the read in the 50-80 range in traffic - I *need* practice for sure. I haven't put a lot of miles on but it seems as though with my city driving the dfco is a much better tool to use out of the tool chest.
  4. brucepick

    brucepick Well-Known Member

    I wouldn't expect to see LB in city driving. I've only seen it on the open road. In town, other techniques certainly are more helpful.

    Yes - Wayne also programmed my SG to indicate Lean Burn (LB). Here's the procedure:

    To Monitor Lean Burn, type in:
    TXD 686AF10115
    RXF 044105150000
    RXD 2808
    MTH 000100020000
    then save. If the value for LBN = 0 you are in lean burn.

    Here's what I have on achieving + maintaining LB:

    I monitor TPS, LBN, ºFIA (Intake Air), and ºFWT (Water Temp)

    To achieve LB:
    Engine temp should be 180 ºF or better.
    TPS below 20 (throttle postition)
    ºFIA (intake air temp) certainly over 40 ºF. 60-80 or more is nice. I haven't yet found the precise needed IAT.

    It seems to require some distance or time of steady driving and maybe a heatup of the cat converter by brief use of a heavier throttle. In other words, merely achieving the three items above will not generally pop you into LB. But a minute or two at steady highway speed and then some fuel will help - when followed by throttling back to below 20 TPS.

    Maintaining LB:
    Stay under 32 TPS (throttle)
    Keep engine temps about 175 ºF or higher

    Wider throttle to get up a hill will kick you out of LB - however generally, it will go back to LB quickly when TPS goes back below 20.

    Hope this helps someone here.
  5. cackalak

    cackalak Member

    I don't know if I missed it, but will this have any affect during those hot summer days? Or do you plan to cover up the holes for the summer time?
  6. SilentLou

    SilentLou Well-Known Member

    I have a similar setup, partial grill block (for summer) and dryer hose connecting to the air intake, setup so it will get to 100F max. on hot days. You definitely need to change the setup between summer and winter. I'd love to have an automatic system.

    Bruce, what fe are you getting on your hx?
  7. brucepick

    brucepick Well-Known Member

    Lately I've been getting between 44-48 mpg on E10 "summer" fuel.

    I made a few changes during spring and early summer weather.

    I find I need to have all grills blocked except for the four large 'segments' in the lower portion on the radiator side (passenger side). That is, lower center and drivers side are fully blocked, and the upper grill is fully blocked. At least in my car, any air blowing on the cat converter is bad for LB. On several occasions when I thought conditions were perfect for LB, I could not achieve LB - and found one or more of those grill blocks had fallen out. Replacing them usually brought back Lean Burn - though I admit, not always.

    I closed off all the hot air intake holes when it got to about 75ºF outside. Intake air temp was up around 120 or so and LB wasn't happening. I opened up about one or two square inches of hot air hole the other day when it was cool and I left it that way. Hopefully I can leave that area open through the summer to help with cool mornings etc.
  8. brucepick

    brucepick Well-Known Member

    Follow up -
    Please see my other thread here, HX Lean Burn Requirement: 2400+ RPM.

    I'm still using the holes cut in air box for a 30-40ºF increase in IAT during winter. The regular intake port is blocked except for a dime-sized hole in center of the cover, which reduces the moaning sound somewhat, which otherwise is a bit obnoxious at wide throttle. Last summer I covered up the holes cut in intake box, theorizing that intake temps well over 100º are outside the car's design parameters.

    With various other improvements, I'm now getting nearly 50 mpg in winter conditions.

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