AutoSpeed on running lean for fuel economy

[tasdrouille]

Generally, it's easy to screw things up when you don't have proper feedback.

You really need to have a wideband sensor to monitor what you're doing. You cannot tune appropriately with a binary sensor.

You should also only lean it out at low loads. 80 mph isn't exactly what I would call a low load on a car with an average CdA.

And finally, if your mileage is crappy, you are probably running too lean.

[chilimac02]

I'm VERY interested in the how's of leaning A/F mixture. I have a scangauge II, will it display A/F mixture? I've been noting when closed loop vs. open loop occurs. My car stays in closed loop up to about 90 Load, unless the throttle position is over about 75%.

The article you mentioned discusses cruising in open loop... My car doesn't do this. Does that mean that I cannot modify the A/F mixture at cruising speeds (55mph)?

[Peter7307]

Hi Julian and Welcome from me as well.
Autospeed is frequently mentioned here and many people benefit from the knowledge posted there.

Cheers , Pete.

[cfg83]

chilimac02 -

Originally Posted by chilimac02

I'm VERY interested in the how's of leaning A/F mixture. I have a scangauge II, will it display A/F mixture? I've been noting when closed loop vs. open loop occurs. My car stays in closed loop up to about 90 Load, unless the throttle position is over about 75%.

The article you mentioned discusses cruising in open loop... My car doesn't do this. Does that mean that I cannot modify the A/F mixture at cruising speeds (55mph)?

You may be able to display the voltage of the 02 sensor using the X-Gauge option, but you will need to know the access code for it. However, I have not seen a specific example of anyone doing this, and the 02 sensors flips back and forth so much that you would need a refresh rate that is faster than the ScanGauge's "4 digital gauge" option. Sooooo, it may not be practical.

CarloSW2

[tasdrouille]

Originally Posted by cfg83

chilimac02 -



You may be able to display the voltage of the 02 sensor using the X-Gauge option, but you will need to know the access code for it. However, I have not seen a specific example of anyone doing this, and the 02 sensors flips back and forth so much that you would need a refresh rate that is faster than the ScanGauge's "4 digital gauge" option. Sooooo, it may not be practical.

CarloSW2

I did it 3 months ago.

[cfg83]

tasdrouille -

Originally Posted by tasdrouille

I did it 3 months ago.

Mea Culpa! I missed that

CarloSW2

[ALS]

The fuel being injected in to the cylinder actually cools the piston and cylinder wall from the last power stroke. That is why people who run too lean will get a damaged piston, burnt valves or say their exhaust manifold is glowing cheery red. Many manufacturers are now install piston oil squirters. These oil squirters spray oil on to the underside of the piston to cool it down.

[tasdrouille]

Originally Posted by ALS

The fuel being injected in to the cylinder actually cools the piston and cylinder wall from the last power stroke. That is why people who run too lean will get a damaged piston, burnt valves or say their exhaust manifold is glowing cheery red. Many manufacturers are now install piston oil squirters. These oil squirters spray oil on to the underside of the piston to cool it down.

Partly true. The fuel indeed helps with cooling the walls, but temperature peaks at a bit leaner than stoich, and tapers on both sides. Running very lean or very rich lowers temperature, running a bit lean leads highest temps.

See the graph in this document.

The nasty stuff happens simply because you're running too hot, not as a direct cause of running too lean. You might say you're running too lean for for the temperature/load. As you said a solution to run cooler is to run richer. But if the engine could run very lean and without detonation, temps would be down. Since most of the time when you need to run cooler you also want to make big power, you go rich as going very lean leads to a reduction in power (and detonation).

Diesel engines run very lean and are cool. As you richer a diesel you'll see the EGT go up. If you would richen it past stoich (similar to a gasser stoich), the EGT would go down again, but it would be hurling out thick black smoke.

[cfg83]

tasdrouille -

Originally Posted by tasdrouille

Partly true. The fuel indeed helps with cooling the walls, but temperature peaks at a bit leaner than stoich, and tapers on both sides. Running very lean or very rich lowers temperature, running a bit lean leads highest temps.

See the graph in this document.

The nasty stuff happens simply because you're running too hot, not as a direct cause of running too lean. As you said solution to run cooler is to run richer. But if the engine could run very lean, temps would be down. Since most of the time when you need to run cooler you also want to make big power, you go rich as going very lean leads to a reduction in power.

This is what I have read, but I am unable to describe it this well.

CarloSW2