"Lean Cruise" ECU Modification Thoughts
 

First, let me say that I can't be the first to think about this but I wanted to run it by the group for comments. I've already got a chip burner for another project I'm currently working on and I've been reading as much as I have time for on the pgmfi site about modifying the stock Honda ECU....it looks very straight forward. Here's what I'm thinking. Setting the ECU up for data logging and gathering some logs for a typical day's drive for me to determine where the engine spends most of it's time rpm and load wise during the drive. Once I have that information, modifying the fuel table(s) to run leaner in that range. I'm betting you could go at least to a 16:1 AFR if not better with no damage. The GM ODB1 ECU I'm currently playing with has a lean cruise option that is configured from the factory to run at 15.4:1. I will need to get a WB O2 sensor and get my other project a little farther along before attempting this.

Any comments/criticism to this idea. Has anyone tried this? If so, what kind of FE results did you experience?

Thanks in advance for your input.

Oh, I have a 94 Civic DX coupe with the D15B7 and manual tranny.

-- Scott

If you want you could buy dan's chipped p06. Anyway, lean cruise it something you'd really need to set up with a wideband, so if you get it, go for it, I say, but it'll be hard to see the benefit. Honda's lean burn is so damn complicated I don't think anything we do can compare, so I've somewhat given up on trying to imitate it.

Thanks for the advice! I'm not trying to imitate the Honda lean burn, just trying to tweak a little more mileage out of the car. Sounds like you've experimented a little, did you use a wideband?

-- Scott

I wish my r18 was lean burn. Honda cant do that, mmm it would get to good a mileage and ruin the Hybrid sales. :)

i did not, that's my issue is not being able to afford one. it's generally thought as helpful among the tuning community if you do it with a wideband, and some say you can go up to 17:1, but some things suggest that the power loss in an engine not designed for it will negate some of the savings once you get past a certain point.

Scott,
with SVOBoy's help, I have experimented with lean burn on the Del Sol. In addition to cutting the ECT and IAT compensation in half, I whacked 10% off of the fuel map at 2500 rpm and below and at 11 in hg and higher. I did notice a slight gain in FE by by cutting the ECT and IAT compensation but nothing really from messing with the fuel map. The car definatley had less power and had a higher tendancy to ping. IMO it's not worth it.

Wanna buy my chipped ECU?

This is about the only thing I would do on a non-VX ECU. I think the ECT trimming would probably net you a good result on shorter trips and the IAT should have the effect of leaning out the engine just slightly.

Thanks for the comments everyone. I'm going to experiment later in the summer after I get a wideband. I'll let you know if I discover anything other than what was discussed here.

krousdb, what do you want for your ECU? It looks like I can chip my own for about $15.

-- Scott

I was hoping for $100 but it sounds like your DIY will be cheaper.

DIY EFI had the leasn cruise working on GM V8's a couple years back. IIRC, they cycled it on/off so as not to get things too hot running too lean too long.