Civic HX Manual trans 1996-2000 Lean burn information

[firehawk618]

Since there seems to be a lack of solid information about the 6th gen HX's lean burn functionality I figured I would start a thread with my experience.

My ecu is from a 97 HX, manual transmission ECU is 37820-P2N-A22 federal version.

**I am running a DX geared transmission.**

I would like to keep this related to the 6th gen Civic *96-00* only.

There already seems to be plenty of information regarding the VX's out there.

In general here's the requirements for me to get into LB.

1. Engine must be running ~3 minutes.

2. TPS must read > 11% and <21.9%

3. Minimum mph ~28

4. Gear must be 3rd, 4th or 5th.

5. > 1800 and <3099 rpms. It seems to really like 2700 rpms to engage.

6. Engine load, I haven't nailed this down yet but definitely must not be >80 so far.

7. IAT's do seem to play a roll. What roll TBD.



When my car is in LB the commanded AFR's from the ECU seems to stay ~20.5.

When not in LB the commanded afr is ~14.6

[firehawk618]

So far I have been able to get into LB generally anywhere above 2100 rpms.

Tonight my IAT's were ~70 degrees and I was NOT able to get LB anywhere below 2400 rpm's. When I would dip below 2400 it would disengage repeatedly. This was tested during a 60 mile drive.

I will pay more attention to what my IAT's are when the car's being nice and letting me get LB at lower rpm's.

I did a tiny amount of data logging. Here's proof of exactly what the ECU is commanding for AFR's. This is directly from the ECU.

https://www.youtube.com/watch?v=vz8RKaXNPv8

[firehawk618]

I wonder to myself, is it better for economy to intentionally keep the rpm's in range to use LB or is it better to shift if you're not in the highest gear and be out of LB rpm range.

Some will say that the vacuum gauge is the best way to tell if you're getting the best MPG possible but I am not completely sold on this.

A scenario is cruising along in 5th gear, flat ground. Let's say my vacuum gauge is sitting right at 15. Now LB kicks in and I now have to give more throttle to maintain my speed. The vacuum gauge will now read 7..... You can see where I am going with that.

I can say that when I am in LB in 3rd or 4th gear the shift up light will be illuminated the entire time and if I shift up a gear I will be out of the RPM window for LB. This would be even worse with HX gearing in the transmission.

Once I get my MPGuino in the mail I should be able to figure this out easily.

I guess I could watch the injector duty cycle and figure it out, but it's kind of hard to get a real good picture watching the scan tool.

I have to think, that in the most simplest terms, the lower your injector duty cycle at any given time the better your economy will be.

Seems like ultimately that's what really matters.

[firehawk618]

I have figured out with the help of MPGuino that LB is hardly what I thought it would be.

I am certain that a VX ratio transmission would return far greater MPG than LB does.

I do now know that I'm much better off selecting the next gear to lower rpm's vs staying in a lower gear to keep in LB.

[Xist]

Some people on here really like lean burn and some people do very well without it. Bruce Pick told me that he burned the same exhaust valve twice and he believed that was from maximizing his time in lean burn. He recommended that I focused on EoC or pulse-and-glide, saying he thought that would actually net better mileage.

Then there are the expensive oxygen sensors.

[firehawk618]

Originally Posted by Xist

Some people on here really like lean burn and some people do very well without it. Bruce Pick told me that he burned the same exhaust valve twice and he believed that was from maximizing his time in lean burn. He recommended that I focused on EoC or pulse-and-glide, saying he thought that would actually net better mileage.

Then there are the expensive oxygen sensors.

I'm pretty sure it's been tested and proving that in LB the cylinder / exhaust temps are actually lower then when running at stoich afr's.

I can see his point though on EoC and P&G being more of a benefit than LB is.

In my case I am really starting to see the benefit to taller gearing *which I do not have yet*

[firehawk618]

On this 18 mile trip I basically accelerated WOT upto posted speed limit then immediately dove into 5th gear. I must say the D16y5 is quite a torquey little guy at very low RPM's vs the y7 and y8.

I didn't try to get LB at all, just let it happen when it was ready. Once in LB I maintained it unless speeds were dropping such as climbing a hill then I would downshift a couple gears and WOT to a touch above the speed limit then back to 5th.

I did lots of EOC as there's a long downhill stretch BUT I also had to climb up this same hill on the same trip.

I will say my fuel injector cut button works great now that I have put the IAC on a different 12v source. No CEL and the LB timer does NOT reset as if you turned the key off and on to kill the engine.

I can tell right now that the MPGuino is going to pay off large for me. I really had no idea how to drive the HX + LB properly.

I have the MPH dialed in perfectly and used the spreadsheet to calculate the values for the injectors. I think it's close as when I was driving normal it was reporting around 38 MPG which is what I had been averaging.

I will fine tune the flow rates as I get a few tanks through it!

Personal best for me.

[Chrysler kid]

Lean burn seems to be hit and miss as far as fuel economy, but I think my tire pressure has affected my current tank.


96 civic hx manual transmission factory shift light, s40 LSD trans. Markings on my chassis indicate my car was one of the first m/t hx's produced in 1996. There are grease pen markings on the underside of my hood for the inspector number and qc checks passed 76/76

Lean burn at 55 mph @ 2300 rpms. Lean burn disengages at 78mph. I find that the up shift light is more of an economy light to keep the car in the correct throttle and power settings

1998 civic hx manual trans no shift light stock trans

Best tank was 38 mpg, car was very sluggish and mediocre at fuel economy. Lean burn was intermittent most of the time the car would not engage lean burn until fully warmed up after 10+ minutes. I can remember the car bogging when shifting at 2100 rpms with the hx trans, really really slow when trying to accelerate onto the freeway from a stop light. I mean really slow, having to floor it to keep up with soccer moms and even big rigs

Best observed economy was 51 mpg highway with my 96 on 86 non ethanol gas. Best tank 44mpg, average tank is 38mpg summer 36 mpg winter

[firehawk618]

I am well on track to hit my first goal of a 45Mpg tank.

My fuel gauge is ~1/4 with 330 miles on it. Normally I am down around the empty mark and any time now my low fuel light would start to flicker.

Today's commute home, didn't have engage LB a single time.

[Chrysler kid]

I'm at 275 sitting on the top side of half of a tank of gas. The needle tends to fall very quickly after half tank and I fill up at a quarter tank. I'm sure I would gain the most economy the less fuel I carry on board however I do not like the added stress and heat on the fuel pump. Im sure if I took out my two 12 inch subwoofers it would make a difference too lol.

I'm also running 10w30 synthetic, again I should switch to a lighter weight once summer hits full swing

Next tank I will try some marvel mystery oil. See if that snake oil does anything