I have an 86 corvette. I am using a bin that was given to me from a company I had do a tune. I am using the 32.xdf definition.

The LM-1 is recording af ratios of 11 or so during wide open throttle runs. So what I have done is record with the LM-1 and with datamaster. With the tach wire hooked up, I can approximate when certain things occur between the two logs. I know it isn't perfect but it is all I have got for now.

So I figure I am about 12% richer than I would like to be at this point. ((11-12.5)/12.5). So I have been reading the stickies for a long while now. From what I read, is it possible to go in and lower the fuel PW vs. load table values by said amount? Like I have read, it is crazy how the fueling is identical at all rpm's for a given load. I guess it works though. I have an approximation of what values I can change based on the LM-1 and datamaster.

My next question lies in the PE A/F % Chg vs RPM table. Should I even mess with the above mentioned table if the rich condition is only at WOT? I do have some questions about this table also. If the numbers stored are negative, does this mean we are richening the mixture?

Well thanks in advance for any responses, I am going to research some more.

Craig

 

PE is where you should aim. It works out pretty well. If I were you, I'd find the PE vs Coolant table, and subtract all the warm engine PE from the whole table, i.e. if 200F is 20%, subtract 20 from the whole table. Then, in the PE vs RPM, set all values to 17 to 18%. Instant 12.5:1 commanded when warm. Then make sure your BLMs are ok at medium high load. Then floor it... If commanded isn't 12.5 when warm (i.e. if it shows 13.6 instead) - look at the conversion equation for the PE vs RPM table, and post it here, as it would be a bug in the conversion equation (I've seen that in some xdf's). Also, keep an eye on the wideband.

The PWs being the same for all rpms at a load is not at all strange. MAF based load (LV8) is truly engine air per cycle. So, the same air should get the same fuel, without regard to how often. The only fudge factors would be needed for any inaccuracy of the MAF or nonlinearity of the injectors. Extreme overscavenging on a batch fire system may also disproportionately pull more fuel out the exhuast than air; just had to mention, but not likely going to apply to anyone with a '165 ECU and single MAF.

 

Thanks for the insight on that. What I am looking at now is a PE table vs. RPM that has all negative percentages in it. I am not sure if there is a bug in the xdf like you say or if this is actually how the tune was made to be.

What will the negative numbers in this table do? As the table states if you were to add a percentage to the a/f ratio that would be lean, and if you were to subtract a percentage from the a/f ratio that would be rich.

Am I thinking about that correctly? RednGold, you say to shoot for 17 to 18 % , is that added from 14.7 or what the commanded is?

 

The PE vs Coolant and PE vs RPM will add together, so negatives will subtract as well. In a nutshell - you want a total of 17-18%; how you get there is by combining the values of those two tables, I typically choose the way I mentioned because I have converted the % in my xdf to show AFR instead, which makes it easy to say what AFR at what RPM should be.

AFR = 14.7/(1.00+.18) = 12.46, where obviously the .18 is the 18% enrichment.

PE vs Temp conversion should be: 0.390625*X
PE AFR vs RPM (displays AFR, not % enrichment) conversion should be:
1470/((0.390625*X-50)+100)

and by the way, open loop enrichment is not added to PE, as far as I know, and the Open Loop % Change vs Coolant Temp conversion should be:
X/2.56-13.67
I know many xdf's have that one wrong

 

Okay, I think I am starting to understand. What I am still not understanding is why when I look at my tune it contains negative percentages for PE % chg vs. RPM. Which from your equation would be leaning my mixture way out.

I am going to start like you said at 17 or so % and see how exactly the car responds, and what the LM1 is telling me.

 

The PE vs Coolant Temp and the PE vs RPM ADDDDD together, so a negative value, such as -6 (vs RPM) and +22 (vs Coolant) = 16

Read my first reply again, and 0 out the warm PE fuel vs Coolant temp, and then set the PE enrichment vs RPM to 17% (or 12.5 if you are using the equations I provided).

 

Ok, I see now, not sure why I didn't see that before. I will correct these tables and log and see what happens.

My next question, and I am sure this has been answered before. When wot condition occurs, what does the ECM look at to base fueling? I thought it would be just the PW tables, but obviously it must also look at the PE tables as well. So not saying this is the correct way, but for my thinking, could the PW table be changed just the same as the PE tables to reach the same goal?

 

IF you were full time Open loop (i.e. NOT using the O2 sensor for fuel control adjustments), you could use the PW table. Fuel economy might get a little worse, though, and sometimes it's nice to have the O2 correct for the day to day variations that affect A/F, like humidity, fuel, etc...

If you have closed loop INT and BLM enabled, then you're pretty much stuck having to use PE fuel and spark.

The choice typically is due to the camshaft specs. Overlap and IVC is the area of most concern. Too much overlap or too late IVC will reduce the idle vacuum and engine combustion stability, and closed loop gets sketchy with the misfires.

 

Thanks for your help in this matter. I am going to do exactly as you told me to see where I stand.

Where can the commanded a/f ratio be seen? I think I remember seeing it in datamaster somewhere maybe??