PE Table Question (E38)

[LSx Believer]

Hello all,

I'm a noob tuning with hp tuners. I've done tuning with some stand alone units, but as many would know hp tuners is a different animal, especially the e38.

I've done some searching, but am not able to find the answer I'm looking for.

My question is what role does the PE table play in the big picture. I know it's used for WOT fueling, but is it a multiplier of the VE coefficients tables? Is it affected by any other tables, or when you go WOT does the E38 use only the PE table fueling? I know it's a multiplier but what is it multiplying? I had read that 14.7(stoich) is divided by the pe table #. So 14.7/1.20=12.04 target afr. How does the ecm know what 14.7 is at WOT? Does it take the Cyl. volume and calculate 14.7 then add the PE table # into the equation?

I'm tuning in MAF only. I have the dynamic airflow disable rpm set to 100rpm and the enable rpm set to 0. I noticed that when I go into WOT mode the maF stops showing readings while I'm logging.

I know my question my be a little odd. But I'm the type of guy that likes to know when I'm applying a value to a table and what affects it has on other values/tables, and what effects other values/tables have on the table I'm working on.

Thanks in advance

David.......

[Peteej]

you are correct on how the computer arrives at the desired afr based on the pe modifier. and you are also correct on the computer calculating cylinder air to figure out how much fuel is normally 14.7 to 1. the computer uses the maf calibration table to convert the hz output of the maf to airflow in lb/min. there are several other tables to calculate the grams/cylinder the computer ultimately uses to calculate fueling. hmm...never really seen an e-38 where the maf stops reading during wot, the camaro ive played with showed maf readings all the time, even during wot. as far as the pe table goes, it lowers the afr for wot, and also when the motor is under load. when you richen the mixture it resists spark knock to an extent, so when the motor is under a decent load it activates too. table-wise there are several tables in play before the pe modifier. offhand i cant remember them all but you have your maf calibration, virtual ve table, theres a ve to maf table as well, a stoich afr table, multipliers for barometric, ect, engine run time, iat, and various o2 feedback tables that affect the final number. during wot though forget the o2 feedback. basically the pe table is something you as the programmer decide on, and tune other tables to get the commanded to match the actual afr. normally the e-38 pcm uses the maf, filtered, if available and only uses the ve tables to verify the maf didnt go bad, or as a last resort when the maf fails. i believe the ve tables are also used to calculate dynamic air, such as transients. in the e-38 you probably have whats called virtual ve tables, which use constants thrown into a complex equation to calculate the ve in real time, i cant fully explain them, but chris from hpt has a good writeup on them on here. they are really hard to adjust, and there is a homebrew software program to convert between a table and the coefficients floating around here. search for eq <> ve, latest version i know of is 3.5 and is "tuned by bluecat"

[C6Z_sd]

He poses an outstanding question...might have an answer.

For MAF tuning (WOT) you leave PE enable, but disable VE. Therefore, you're assuming that at some level (X Hz) the MAF is operating in WOT only and you ensure VE is not complicating the situation. As a result, you calibrate the MAF in that range to coincide with the commanded PE ratio as a matter of procedure.

For VE tuning (WOT), you're really only talking about 1-2 columns...and it's the same as MAF WOT tuning.

So...not really much of a mystery here. You command PE, and calibrate VE and MAF to fall in line. Is that OEM design? Dunno, but I'd say it is SOP for basic tuning.

Not to hijack a thread, but my question is: why is an OEM PE line jagged rather than a flat line with ramp functions?

Good luck. Don't know if I helped, but I like this discussion. Thanks for posing the question (hope someone smarter than me chimes in).

[LSx Believer]

Thanks guys for the input......

I'll post up a log file here in a little while. To show that my maf's hz readings go away when I go into WOT. Since I don't usually save my log files I don't have one to upload.