Open loop afr

[Kitch]

So assuming I'm running off the Open Loop AFR table and for example the engine is running in a cell that commands 14.0:1 AFR what happens if that's not the AFR I would would have if I was running as I am now off the VE table? If the VE table isn't accurate what happens?

I was looking at the Open Loop AFR table in respect to inches of vacuum and that's why I highlighted the area between 20" and 0" but it does make sense that it's more a percentage scale of some sort.

[myburb]

I am just off the top remembering when I did the test in open loop. I have my open loop ve quite lean in the low load/rpm area like high 15,s. I then set for open loop afr and set those to high 15's. It started cold and drove fairly well until it warmed up and then went lean and started to miss. I stopped and put my good chip in and came to the feeling that if you're open ve is good that is all you probably need. I am only guessing but think when you set the open loop afr the pcm assumes that your ve is 14.7 and does calc's from that.

[Kitch]

Interesting, my VE table is pretty good at the moment so I might just work from that at this stage. Thanks.

[lionelhutz]

It's likely just 100 - MAP and was done in the XDF setup.

The VE table is not the AFR. It is a table telling the PCM the volume efficiency of the engine at each operating point. The VE table and the engine or cylinder displacement are used in a calculation by the PCM to determine how much air is entering the engine. The VE is used to calculate air, not fuel.

Then, knowing the air entering the engine, the PCM can use an AFR value from somewhere else and calculate the amount of fuel to add to the air.

If the VE table isn't accurate then the air calculation isn't accurate and when the air isn't accurate the fuel calculation based off the air isn't accurate.