Leaning out AFR's for cruise.

Sassimac · Post by **Sassimac** » October 17th, 2011, 7:01 pm

Hi there...

Is it worthwhile to lean out the AFR's in the 1500-2500 RPM range with the view of slightly increased economy? I am thinking Lambda 1.05.

Considering that this is the RPM range the car sits in for most cruising speeds, I figured that there would be little performance impact.

Thanks...!!!

October 17th, 2011, 7:31 pm

Makes for high EGTs and high NOx emissions. You won't see as big of an improvement in hot weather as it will heat up the engine and increase the tendency to knock.

Sassimac · Post by **Sassimac** » February 2nd, 2012, 8:12 pm

Steve...

A couple of questions.....

1: Is there any indication in the code of a maximum permissible lean Lambda value?

2: Any idea on what the narrow band O2 range is in terms of Lambda?

3: Does VT have a way to reset fuel trims besides flashing a new tune?

Many Thanks.

Sassimac · Post by **Sassimac** » February 3rd, 2012, 1:42 am

Hello All...

Just a further to my previous question about maximum permissible lean Lambda value.

Is there any code relating to forcing the AFR to be no higher than Lambda 1.00? I tend to notice (via Dashhawk) that the AFR will eventually target Lambda 1, even though the CL table is pushing for 1.015.

February 3rd, 2012, 8:16 am

I'll have to check.

Sassimac · Post by **Sassimac** » February 3rd, 2012, 8:32 am

Hi There...

I have tried (briefly) a file with zero change to the CL fueling table. Straight away, the idle afr returned rock solid to 14.81:1. So as a test I have flashed the same file with a low load/rpm target of 1.02 Lambda.

Let's see what happens.

Sassimac · Post by **Sassimac** » February 3rd, 2012, 11:51 pm

Steve...

I have attached a log and VT file for this current test.

The drive is targetting cruise speeds, and is all low load. The target AFR for this low load and RPM range is 1.02 Lambda.The way I read it, is that the whole run should have been leaner. However, looking at the log, the ECU never targets this leaner AFR. It looks like the ECU is very reluctant to target more than 1.004.

I am beginning to wonder if there is something in the ECU that prevents a leaner condition than Lambda 1.00. Or maybe the O2 sensor is not capable of reading much past Lambda 1, and the ECU is programmed to recognise that.

Anyway..... It's interesting...!!!

February 4th, 2012, 1:45 am

The WB02 reads to ~2.000 lambda You see that when you get fuel cut. I'll dig into it after I finish the project I'm working on now.

Sassimac · Post by **Sassimac** » February 5th, 2012, 8:33 pm

Hi All...

I have returned the CL AFR Target table to stock, and fueling returns rock solid to 14.81:1 for idle and general driving.

It kind of makes you wonder what the ECU is doing.

Sassimac · Post by **Sassimac** » February 6th, 2012, 5:46 pm

Hi All...

Flashed on a file that leaned out the CL AFR Target table to 1.01 Lambda.

Initially the AFR's targeted perfectly, but after about 10km idle and cruise AFR's crept to just under 14.81:1. The odd thing is that fuel economy is terrific with a slightly leaned out target in the low load area of the CL Target table.