Well as in many other post the Debate onOpen loop A/F ratio goes on. I am looking for some clairifcation on what tables are used. I have been expairimenting on the Dyno, and don't know if my luck is just by accident or that I used the right tables- anyway hereit goes!! [all tables in discusion are in Tunercat] 3 Tables that I know of that controls open loop A/F ratio(There may be more that I don't know about).

"AFR x 10, Open Loop Vs Coolant Temp. Vs. MAP" Table:, I think this table controls A/F ratio in closed loop NOT AT WOT, maybe for intial start up. But I am preety sure that I am wrong about this.

"% Change To Fuel/Air Ratio Vs. Coolant Temp at WOT" & "Change To Fuel/Air Ratio Vs. RPM at WOT" Tables:These are the tables that I have used to make my corrections, I have had pretty good luck useing them. If I am correct(not sure) than these tables are used to get the WOT A/F Ratio with the Formula [WOT AFR = 14.7 / (1 + %Change vs Cool/100 + %Change vs RPM/100)], so if this formula is use what does the "AFR x 10, Open Loop Vs Coolant Temp. Vs. MAP" table Do?

Any Guru's that know how this works please help!


Thanks !!!

 

Just a guess....
Could it be used for people who run speed density, like I believe the 93 Z did.
Like I said just a guess, maybe I don't understand it period. I'm sure someone will correct me.

I have only really seen people use the last two table to tune for AFR.

 

Kyle,

"AFR x 10, Open Loop Vs Coolant Temp. Vs. MAP" - I believe the table is just what it says in the Tunercat calibration help - this table is used in open loop. Typically only the first few minutes after starting the car when it's cold. A cold engine likes to run a bit richer, so that is why you can set the afr here vs temp.

Once the car goes into closed loop the pcm always shoots for 14.7:1. You never see this value explicitly anywhere - it is hardwired in the code and not editable via tunercat or lt1-edit.

The PE tables only have an effect at WOT, as I'm sure you know.

Joe

 

Joe,

But what happens at High MAP (90-95-100) isn't that the map at WOT. Witch table does it use than.

Witch tables in Tunercat are the PE tables?I think PE is a table in lt1 edit, but what table is that in Tunercat?

Thanks for resonding!!!!

Hopefully we can together figure out how it works. I think the hardest part of tuning is figureing what tables the ECM uses and when it uses them!!

 

Kyle,

In closed loop when the tps goes above the threshold for WOT (there is a table for that) the car applies the power enrichment tables to 14.7. The 2 PE tables in Tunercat are labelled "% Change to Fuel/Air ratio VS Cool (or RPM) at WOT". It doesn't matter what map you are at. But yes WOT corresponds to high map.

Joe

 

I emailed TC@tunercat about this. He emailed back today and this is what he had to say. He said that the "AFR x 10, Open Loop Vs Coolant Temp. Vs. MAP" table is only used during startup. The "% Change To Fuel/Air Ratio Vs. Coolant Temp at WOT" & "Change To Fuel/Air Ratio Vs. RPM at WOT" tables are the only ones used in WOT.

My Question is this- In the "% Change To Fuel/Air Ratio Vs. Coolant Temp at WOT" & "Change To Fuel/Air Ratio Vs. RPM at WOT" tables you target an AFR. But if the O2's are not used in Open Loop, what does it use to try to get the AFR that you put in it?

 

Yeah, that's what I've been saying....
The answer is - it doesn't. The actual AFR may very well be different from the pcm's targeted AFR. In Open Loop, and WOT (which is essentially open loop) the pcm does not and cannot used the O2 sensors for feedback since they are narrowband and completely inaccurate for the richer AFR's that occur under these conditions.

 

But what does it use to do its calculatons? It must get it's info from someware to try to get the targetted AFR. If we knew what info(tables) the computer used, we could make sure those tables were correct. Than the PCM would have a better chance at hitting the targeted AFR.

 

Kyle,

It uses the maf for it's calculations. If 147 grams/sec of air are coming in, then it's going to call for 10 grams of fuel if the target AFR is 14.7:1. If the targetted afr is 10:1, it would call for 14.7 grams of fuel.

Now, when in closed loop, the blm's are then applied. So, say we are calling for 10 grams of fuel and the blm is 140 (about 10% above 128), then the computer is going to call for 11 grams of fuel (original 10 plus 10% of 10). The blm's are the result of the O2 sensor feedback.

Speed density mode, not normally in operation on a maf-based LT1, is a little more complicated. Instead of measuring the mass of air coming into the engine directly, the pcm calculates it using rpm, map, intake air temp, and the ve tables. Then it's pretty much the same as above.

Now that the pcm has a number, it needs to deliver that fuel. That is where the injector constant and injector offsets come in. The injectors constant is a multiplicative factor, and the injector offsets are an additive factor. So they affect the fuel delivery insofar as the pcm assume they are accurate. If they are off, the blms will change to compensate, but there is a limit on how far they can adjust.

So, we already have access to the tables that control fueling.

At WOT: It doesn't really matter what afr the pcm thinks it's seeing. All that matters is what the actual afr is. So stop worrying about the pcm's target (calculated) afr.