Remapping ECU for lean burn - Fuelly Forums

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Old 03-28-2008, 02:43 PM   #1
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Remapping ECU for lean burn

I have a Honda VX with a D15B JDM full swap. It's Mpg is only about 30 city and 40 hwy. I thought why not chip the ECU, remap the fuel and timing with CROME to provide less power when not needed. Basically lean it out a little. I don't see why this wouldn't work. I can also hook up a switch to be able to switch back to the standard 130hp fuel map on the fly.

When just running around for erands or long boring highway runs, why not be a little leaner? I understand too lean you get predetination if the timing is too advance, but this can be tuned. We all know that the VX D15Z1 can do 20:1. My D15B is a close cousin.

Most people who tune the imports are compensating for turbo's, large injectors, higher compression etc.. So we can go the other way. So what if the car has a little less getty up.
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Old 03-28-2008, 03:32 PM   #2
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I'm sure much more knowledgible people will post after me, but my understanding of the VX VTEC-E engine is that it alters the intake valve timing specifically to promote swirl when in lean-burn mode. My gut tells me you'd need to do that in order to prevent a lean-missfire condition with your D15B.
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Old 03-28-2008, 09:23 PM   #3
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You'll need more control over the ecu than what the typical racer uses.
What sort of things can you control with CROME?
Do you have access to the entire fuel map? ie. high load, low load, at high and low rpm, and everything in between?
Can you change the point where the ecu goes from closed loop to open loop? Or maybe run in open loop all the time?

I have lean burn added to my ecu, my car was not designed with it. I have some experience with figuring out how lean I can run the motor, and when it needs to be less lean.
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Old 03-29-2008, 11:45 AM   #4
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You can control the entire fuel and timing map. Even alter the O2 readings.
I'm thinking you still need a little power to get moving and on WOT. So by using the MAP / RPM / 02 readings to find when the motor is not under heavy load you then program this band to be lean 17:1-18:1.

It's worth a try, I'll have less than $80 in the whole project. Plus I'll have a chipped ECU and a chip burner.
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Old 03-29-2008, 08:28 PM   #5
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I use the same tune for all of my driving. The high throttle, high load section of the fuel and timing maps are set up for max power. It's very rich (about 10:1 A/F ratio) and timing is low (9 to 18 degrees at high rpm)
Light load, light throttle is tuned for max FE. It's very lean (16.5 to 18.0:1) and timing is high (32-37 degrees around 2k rpm).
The areas between max power and max FE are blended together so the fuel and timing values transition gradually. The car seems to run smoother and more predictably when the transitions are smooth, it doesn't like on/off steps.

Edit: The A/F ratio I use is very rich because the engine is turbocharged. Believe it or not, I've leaned out the WOT settings slightly. Factory A/F ratio at WOT was 9.3!
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Old 04-05-2008, 04:27 AM   #6
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OK. I'm off to the races. I have 2 chipped ECU's. A chip programmer and CROME.

I've only had a couple hours so far to play. The first thing I did was to use the low cam number map from a P07 (VX) bin in a modified P08 bin. This seemed to help lean out the idle. But didn't really reduce the power at all. I'm going to lean this thing out until it starts to ping then back it off a little for the 2500-3500 rpm range at part throttle.
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Old 04-05-2008, 07:40 PM   #7
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It might not ping at light throttle if it's leaner than around 16.0:1 A/F ratio. The tendency to knock goes down with A/F ratios leaner than that.
From the stuff I've read and tried on my car, the limit to going too lean is the ammount of power you need since power tapers off with very lean A/F ratios. I've felt the power start to taper off around 16.5:1 A/F ratio during freeway cruising, and it gets worse as you go leaner. I've added a degree or two of timing in the leaner parts of the FE fuel map to keep power at reasonable levels.

If I need more power, I found the A/F ratio likes to be progressively richer. For example, if I'm at 3/4 throttle at mid rpms, the A/F ratio that works best is around 14.0-13.5:1.
HTH and good luck at the track.
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Old 04-06-2008, 03:25 AM   #8
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For some reason, it seems to be "common sense" on this forum that running leaner will save fuel. I have never heard any substantiated proof of this. Could someone please point me to an article somewhere?

The reason I'm so skeptical is because when you run lean, your engine also runs less efficiently. So even though you are lean, in order for the engine to create enough power to keep moving you have to step on the throttle further. On my car (which is 100% tunable on-the-fly with a laptop from the driver's seat), when I try to get leaner than 14.7:1, I might not get pinging right away, but I can feel the engine start to stumble and miss.

Also, if you run lean, you speed up your combustion so instead of a smooth pressure increase you get all the power in a quick "boom" which tends to hammer the heck out of the bearings.

-BC
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Old 04-06-2008, 08:25 AM   #9
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The Honda VX can run in Lean Burn mode at 20:1. During light throttle @ 2000-3000 rpm when cruising it switches to another fuel map to lean out. Thus they can get 50-60MPG on the hwy. Combined average for these cars is typically 45-50mpg.

Not many engines can run this lean. So I can't say you can do this on 5.7L chevy. My Honda D15B is a close cousin to the D15Z1. It has way more power than is needed to cruise 65mph.

I'm getting close to the ECU / Laptop setup you have. I need to get a wide band O2 and data logging next.

My last trip registered about 36mpg. At least it's an improvement. I still have more power than is needed. So I'll narrow down the lean fuel map to the 2500-3500 range @ light throttle. Also I noticed the VX P07 timing map is less advanced than one for the P08. Makes sense. Lean out, retard the timing, loose power when you don't need it.
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Old 04-06-2008, 07:57 PM   #10
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Quote:
Originally Posted by DRW View Post
I use the same tune for all of my driving. The high throttle, high load section of the fuel and timing maps are set up for max power. It's very rich (about 10:1 A/F ratio) and timing is low (9 to 18 degrees at high rpm)
Light load, light throttle is tuned for max FE. It's very lean (16.5 to 18.0:1) and timing is high (32-37 degrees around 2k rpm).
The areas between max power and max FE are blended together so the fuel and timing values transition gradually. The car seems to run smoother and more predictably when the transitions are smooth, it doesn't like on/off steps.
Would you care to enlighten me as to what you have done? I looked at your gas logs. Very impressive. Your car should only be at 26mpg.
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