Im working on my open loop, speed density tune. I know the VE tables are used.

What about the PE table. Does the car still go into PE mode at WOT. I was also wodering if the open loop coolant temp vs load table is used.

 

PE is not used in Open Loop

 

But the open loop coolant temp vs load is used?

 

From what I can remember Yes it is, but PE no.

 

Something strange is going on, I changed the PE tables to 0 and I noticed the car leaned out a little bit. So I changed them opposite and went to 50 with all the values. The car is deffinatley way rich now WOT.

So it seems to be working with the car in open loop?

 

PE Tables should be referenced all the time, no reason not too. PE fuel is important, if it needs PE fuel once it needs it all the time.

 

ummm thats weird maybe it depends on the flash, Open loop PE never worked for me.

 

Pe works for me in open loop...

 

Same experience here too. PE vrs RPM works in open loop for me.
1996 OBDII PCM.

 

Yes PE does work in open loop. Look at your "%TPS threshold for WOT vs RPM(low cool)" and that will tell you at what TPS% PE mode is enguaged. This is also where you can force the car to use PE mode at idle and tune accordingly if your having troubles in closed loop. Of course if your locked into open loop and tuning for open loop only this is not necessary.

 

Let me preface this by saying I know nothing about reprogramming the stock PCM, because I ditched mine 8 years ago and went to an aftermarket system. I'm not challenging anyone... just trying to learn.

Why would it not be logical for PE mode to be used in either MAF or speed-density operation? If PE is not used in speed-density, how does the PCM set a richer target A/F ratio, when you go WOT?

 

"Why would it not be logical for PE mode to be used in either MAF or speed-density operation?"

Mainly because during normal driving you want to be as close to 14.7 A/F Rat. as possible. This is tuned into the MAF tables and Speed-density mode which uses the VE tables. However to get best performance the car needs to have more fuel thrown at it thus GM has programed another table that is used for PE mode. This mode is engaged only when the %TPS is above what is set in the "%TPS threshold for WOT vs RPM(low cool)" table no matter if it is running in Speed density, MAF, Closed or Open loop operation.

"If PE is not used in speed-density, how does the PCM set a richer target A/F ratio, when you go WOT?"

Exactly. It wouldn't unless you had a WOT table that is used for Power Enrichment(% Change to Fuel/Air Ratio vs. RPM at WOT) or unless you tuned your normal everyday driving tables (VE, MAF, inj. fuel trim)to run a richer A/F ratio all the time which wouldn't neccessarily be feasable for fuel economy. Basically what is being said here is why tap into the power when you aren't requiring it. When you go WOT you do require it so the PCM puts you into a different table for PE.

 

Actually.. the point being missed here is you dont "tap the power" when your not requiring it. If you logged some data you would see you enter PE mode at and above certain MAP parameters vs RPM - much the same as RPM vs TPS. You could "simply" modify these SD MAP tables to give you the correct fueling you need. A quick and easy way is to add or subtract from the SD tables to control WOT fueling is by using the PE vs RPM table. I believe the stock SD tables are generally setup for 14.7 afr across the board. You will never enter for example 95KPA MAP at 5500rpm without being in "PE MODE". If you run out of headroom in the SD tables then you should lower your fuel injector flow rating then compensate by lowering all other related tables. If you dont want this type of accuracy then simply add or subtract using the PE vs RPM tables.

Now, seems from factory everybody builds in "extra" adjustment for whatever happens in the field (like base fuel programming error or adding 5lbs boost).

Same goes for 2-Bar MAP sensor in place of the 1-Bar sensor, you basically burn the MAF, Zero out the PE vs RPM table and run full SD mode to control fuel. No reason to ever use the PE vs RPM tables unless you go beyond 100% VE (which then you should reduce your injector flow rating assuming you have large enough injectors).

Now the real question is why some people run boost with no FMU by simply adding or subtracting the PE vs RPM table and think it's ok.

 

No - I know that's not right. The "MAF table" is a calibration table that translates the MAF sensor output frequency (Hz) to grams/second of MASS air flow. Speed-density uses the RPM, displacement and VE tables to calculate the VOLUMETRIC air flow rate, then converts the VOLUMETRIC flow rate to MASS flow rate by calculating the density of the incoming air from the inlet air temp and the manifiold absolute pressure. At that point, whether you started with the mass flow rate directly from the MAF sensor, or went through the speed-density calculation, you are at the exact same point. Now all the PCM has to do is divide the mass air flow rate by the target A/F ratio, and arrive at the required mass fuel flow rate, which it then converts to the injector pulse width. The target A/F ratio in closed loop operation is hard-coded as 14.7:1. The target A/F ratio is calculated when the PCM goes into PE mode.


You almost got that right, but screwed it up with your last sentence. Open loop, closed loop and PE mode are fueling strategies. MAF and speed-density are two different ways of arriving at the mass air flow rate, one directly measured and one calculated from other sensor data and the VE tables. That's why I asked the question I did.... why would a speed-density based PCM not use a PE mode table to revise the target A/F ratio?

Still looking for an answer to that question.

You might want to review my online scanner guide for some additional insight to A/F management in the LT1.

http://members.aol.com/InjuneerZZ/ScanMast.htm

 

I read your first comment 3 times to try and see where you were saying something different than what I was saying. My statement is a more general statement without going into the detail that you did as to how each table actually relies on each other. MAF is one way to arrive at a certain A/F ratio. Other tables used as kind of a back up so to say but also must factor in to refine the A/F ratio is Speed Density mode that is tuned through the VE tables. Yes, speed density is a "calculated" amount of air going through a given set up and if used during open loop operation can be used to adjust the A/F ratio. The key here being open loop. In closed loop yes the pcm is hard coded and will use several adjustments to get back to stoich such as fuel injector pulse width ect.

I guess on the second question I'm not understanding what your asking. However to my understanding, which I am still learning and by no means an expert here, PE is not used until the WOT table is tapped into. The WOT table is taped into at a set value based upon TPS%.

As there are many ways to arrive at a given A/F ratio through several methods the method I have chosen to use is Speed density mode by disabling the MAF and tuning out the O2 sensors in open loop operation. I use a FJO wide band monitoring MAP/RPM/AirFuel Ratio and tune the VE tables(14.5:1) for normal street driving and the WOT tables for PE mode when I want my A/F to hit 12.8:1. Now based upon some input from some folks on this site I am tuning my idle to hit around 16.0:1. Also based upon other comon sense things my higher load map areas,5000rpm and 60kpa and higher, I am tuning closer to 13.5:1. Maybee that will explain where I'm coming from in my conversation.

I know the maf is a good system but I've spent over $400 trying to fix a problem I'm having with it to no avail so yes I've gotten rid of it.