Remapping ECU for lean burn

[maxxgraphix]

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.

[samandw]

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.

[maxxgraphix]

Originally Posted by samandw

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.

The VTEC-E is just a VTEC. Works the same as any other VTEC. The difference is that the pistons are dished and the head's combustion chamber is small. Also the ECU has an alternate FUEL /Timing map for LEAN Burn Mode.

[GasSavers_topher]

Originally Posted by maxxgraphix

The VTEC-E is just a VTEC. Works the same as any other VTEC. The difference is that the pistons are dished and the head's combustion chamber is small. Also the ECU has an alternate FUEL /Timing map for LEAN Burn Mode.

I think you have some things confused here

I'm not sure which "vtec-e you were saying is the same but vtec-e is similar but, still very different from regular vtec(y8/z6)

y8,y5 heads have the same casting=same head. The difference is the rocker arm assembly.

Vtec-e is in theory a 12-16 valve operation(secondary opens only enough so gas doens't pool). vtec-e uses "pins" in the rocker arm that slide over to lock the intake arms together to keep VE in par with rpm's.

Hope that helped,
Chris

[suspendedhatch]

Originally Posted by maxxgraphix

The VTEC-E is just a VTEC. Works the same as any other VTEC. The difference is that the pistons are dished and the head's combustion chamber is small. Also the ECU has an alternate FUEL /Timing map for LEAN Burn Mode.

This is partially true and partially false.

You are correct that the physical switching mechanism and electrical wiring for both VTEC and VTEC-E are the same parts.

You are also correct about the VX pistons and combustion chamber. But this is not true of the HX, VTi or Vi (Japan).

You are correct about the ECU map.

Where you are incorrect is that you're suggesting that VTEC-E and VTEC are the same because in fact they are absolutely and completely different.

On a SOHC, VTEC switches both intake valves on each cylinder to a "wild" cam lobe with more lift, duration (resulting in more valve overlap with the exhaust), and it opens the intake valves earlier. This occurs approximately around 5000 RPM.

On a VTEC-E engine, one intake valve per cylinder is almost completely closed (open only enough to allow fuel to pass through) until load, throttle, and RPM conditions are met and then both valves lock together so that they open the same. The lift, duration, overlap, and timing are not changed at all on the other intake valve. This occurs between 1500-3200 depending on throttle and load.

The theory behind them are completely different. The purpose behind them are completely different. The operation behind them are completely different. The only similarity is that you can interchange a spool valve from a D15Z1 onto any 92-95 D-series SOHC VTEC motor and vice versa, or between the Y5 and Y8.

I have a feeling that you know this already but you gave the wrong impression with your wording.

[DRW]

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.

[maxxgraphix]

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.

[DRW]

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!

[maxxgraphix]

Originally Posted by DRW

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.

[DRW]

Originally Posted by maxxgraphix

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.

That's a big question. Aside from the mechanical mods listed in my profile and driving techniques, there are many ecu mods. I'm lucky to have access to a commented disassembly of the factory ecu in my car, otherwise I wouldn't have found as many sections to change. The ecu mods are focused on reducing fuel usage at all times, such as:
leaned out startup enrichment
shortened the ammount of time that startup enrichment is active
leaned out cold ect enrichment
lowered idle at all engine temps (idles low when cold)
lowered rolling fuel cutoff threshold at all temps
lowered temp threshold where ecu switches from cold enrichment to warm enrichment
leaned out various O2 sensor switchpoints and targets
tweaked the timing and fuel maps so I can lug the motor with less harsh vibration
load based knock sensor management to control how much timing is pulled when the engine knocks, how long the timing is pulled, and when to ignore knock
added lean burn code with triggers for vehicle speed, throttle position, and airflow
adjustments to the EGR map
changed the code to match the bigger fuel injectors and upgraded MAF so they work like stock parts.
There may be more that I'm forgetting, but those are the major changes that made a difference.