Testing Lean Burn on my RX8.

[serialk11r]

Wait, vacuum leak? That shouldn't make your engine run lean, the O2 sensors will detect it and compensate.

You need a wideband O2 and narrowband emulator to trick your engine into running lean, and then redo the fuel map so it's running rich under load so your engine doesn't blow. You probably want to add some extra premix to the fuel to help lubricate the engine.

I would not get too greedy, and try to get it working at something modest like 1.1 lambda. At 17 AFR, my FR-S engine was not running too great, and that thing has 12.5 compression ratio and port + direct injectors. The 22:1 Honda lean burn engines had a lot more tricks up their sleeve to make it work.

I think your idea about the spark plug is interesting though, it had crossed my mind before. Hope you get it working.

[Daox]

What are you using to measure EGTs?

[Harlan]

The Vacuum Leak is causing it to run lean because I reprogrammed the engine and forced it into open loop. I'm using the stock WB 02 sensor for both AFR and EGT. The stock NB sensor is disconnected because it would not let me lean burn the engine.

I can reprogram the engine for lean burn in closed loop, however that is limited by the range of the WB 02 (about 20:1 AFR) and I can't currently change the AFR on the fly.

I think it will have drastically different results when cruising under load.

[serialk11r]

Interesting, the ECU is okay with the NB sensor being disconnected? My car also had WB sensors + a narrowband, and the narrowband would kick in at cruise to correct my lean biased WB, foiling my lean burn attempts.

20 is plenty, don't get greedy. In fact the sensor accuracy at 20:1 is not that good, I wouldn't go over 18. Yea, you don't save as much fuel, but there are rapidly diminishing returns after that point because combustion temp and stability fall.

[Harlan]

I had to silence some CEL codes, but otherwise the ECU doesn't care. At about 16-18:1 the flame front begins to break down leading to worse fuel economy as you push further; however, if you can avoid that fuel economy will continue to increase.

I'm assuming the mechanics of the rotary engine will let me get beyond 20:1 without the flame front breaking down, but it remains to be seen.

[Harlan]

Also you will need to advance timing as you lean the mixture if you want the most gains.

[pgfpro]

Originally Posted by Harlan

The Vacuum Leak is causing it to run lean because I reprogrammed the engine and forced it into open loop. I'm using the stock WB 02 sensor for both AFR and EGT. The stock NB sensor is disconnected because it would not let me lean burn the engine.

I can reprogram the engine for lean burn in closed loop, however that is limited by the range of the WB 02 (about 20:1 AFR) and I can't currently change the AFR on the fly.

I think it will have drastically different results when cruising under load.

Under load is where it gets real. I don't even bother with lean burn tuning at a idle.

[oil pan 4]

I run a lean idle. It just kind of harder to start and keep running for the first minute or so on cold mornings until the hot air can kick in.

[serialk11r]

Idle is where you'll see the biggest improvement % wise if your engine doesn't start stumbling. I saw 10% fuel economy increase from going 10% leaner (MAF reading stayed identical, but AFR was leaner) on my FR-S. The 12.5 compression ratio and stratified charge from the direct injector probably help make that possible.

Turning the air conditioner on in neutral, the MAF reading also barely went up at all, so I was saving another 10% on the marginal fuel usage of the air conditioner.

[pgfpro]

On my car at idle I save only 2% going from 14.7:1 A/F to lean burn 20:1 A/F.
At idle I can't run any leaner do to the lack of turbulence in air flow.

At 55mph I save 29% going from 14.7:1 A/F to 33:1 A/F. Plus the amount of fuel weight used at 55 mph compared to idle is massive.

My best savings at idle is when I shut the engine off. So I turn my engine off a lot instead of having it burn fuel at idle.