anondude13

I've done a search on this and it hasn't given me anything right off the bat, and you guys like to post on forums anyways right?

I'm tuning my GTA this weekend starting from a stock vette MAP/6speed bin, gonna do the basic datalogging thing for the low RPM VE table, and do trial and error on the high end and spark tables. I'm wondering if my life would be easier if I just got rid of PE and only worked with values on the high RPM VE table (I'm guessing they would get higher at the top end than normal). If so how do I disable PE. Thanks for the feedback.

justlearning

well yeah im sure it would be easier but that dosent mean its better....now im a total newb but id say to disable pe you can just zero out all the tables for pe correction and use that space for some thing else more useful to u. but i think its all about what the car wants not whats easier to do from what ive been reading. thats just my 2 cents
John

Ronny

iTrader: (1)

my experience when i started tuning was that PE saved me from causing harm to engine. i optimized the underlying VE with multiple datalogs(30?) and then coommanded PE at 12.5/1 and on dyno it ended up 12.0/1. a little unnerving when you have no clue as to what to expect on A/F when car is humming along big time. this is prior to my on board WB.

as a side note i am in OL now for past couple weeks.

i like it.

idle is 13.5/1. the hunting settled down. 0 steps IAC. AE seems better possibly since i am adding AE in the VE tables with no BLM correction occurring. at tip in i fattened up the VE when it runs into higher MAP areas.

so i guess you can do what you are thinking but i would no do without WB at your side. i did zero "some" of main fuel table 2 and just recently fattened up those at 4000 up to 6400 rpms to see if it affects my WOT runs.

anondude13

In theory if you leave the PE tables stock and just tune the VE/spark tables properly, you could get a good tune, right?

Ronny

iTrader: (1)

well "good tune" is hard to define. i was pleased i did not melt a piston on dyno. i believe it was said if VE is in line PE A/F will be real and follow. was in my case. that was phase 1 of mods. phase 2 i am running lean at WOT at 13.5/1 commanded to 12.5/1. as i said i fattened up the MF table 2 to see if that helps. i dont want to up FP if not necessary but prob will have to.

anondude13

Well your second round of mods will be a lot harder to tune to thanks to that cam. I don't see why you would have to up the FP unless your current injectors are just too small.

BMmonteSS

Thats the beauty of TBI, you only get 90 lb/hr injectors. Luckily TBI injectors will take a lot more pressure than what they run from the factory, and it's easy to double the FP when your only running 12 psi to start with.

I wouldn't disable PE permenantly if I were you. Disabling it can be used to tune your higher load and RPM cells in your VE curve. You can use just your VE curve to get the desired AFR, but the stock code is designed around PE, so you may run out of room in the VE curve to get your desired AFR (can't go past 100%). Remember this table is used to calculate 14.7, so in order to get somthing in the 12.8 range you need to richen the table up by ~13%. You could easily break 100% VE with this unless you fudge some things. For what ever reason, the less you lie to your computer the better things work. All PE does is alter the desired AFR for which the ECM aims for. I would just set the PE AFR for what you want and tune your VE curve to match, then all you'll have to do in the future is name the AFR you want.

I'm sure some one else can explain it better.

Ronny

iTrader: (1)

80 lbs @ 17.5 FP @90% duty cycle supports 320 HP.

difficult to run WOT logs where i live(safely). strip is like 45 miles away.

BMmonteSS

Luckily I live near a highway and it's easy to do a quick second gear blast and get a good indicator of what my AFR's are. I'm only over the speed limit for a few seconds, and even then it's only about 80 mph in a 70 zone. Back country roads or city streets would suck.

Ronny

iTrader: (1)

i think monte is right on. i forgot ve only allows max at 100 combined. if 125 was allowed then it might have worked. i guess GM knows what they are doing.

anondude13

Right on, PE stays. I'm seeing that the stock AXCN (my baseline) VE goes from about 31 at idle to about 94 at max load and torque RPM. I know my engine is gonna need more fuel than the stock vette, and I think I run the risk of breaking 100. So I'm planning to lower the injector constant (and thus a majority of the VE table) to give myself a little more room at the top. What is the general rule of thumb for lowest VE value you can have before your idle starts to suck?

Ronny

iTrader: (1)

we need some others to chime in. i was told not to change BPW. just adjust BPW for the change in FP to achieve proper tune. FP is part of the BPW calc.

anondude13

I thought changing FP only made the car seem like it had bigger injectors and you changed the injector constant to change what the ECM views as how big your injectors are. Either way I should have come up with a better thread title to attract more readers

Ronny

iTrader: (1)

not sure if this is reason not to fudge BPW but the AE function i believe is predicated upon knowing what the FP is and the CID is etc. much relates to BPW being "accurrate. MAF cars may be different on BPW. anyway it was said not good to fool computer. again we need an xpert.

BMmonteSS

There really isn't a certain VE% that will cause your idle to go flaky, its a minimum PW time that will cause problem. You don't want to go much lower than 1.8 ms with multi port and .8 ms with TBI. As long as you stay above those numbers you should be good to go.

Rbob, grumpy, care to elaborate or correct?

Z69

Ronny, 8D and TBI handle fuel calcs differently.
If you need more fuel on TPI, you get bigger injectors or raise the FP. Then adjust the IC to match the new size.
Some people adjust the IC to get their BLM's inline instead of the VE table. Not the recommended way to do things.
You can also adjust the PE table for more fuel independent of the VE table. That's how people add fuel at 6k on a stock bin.

1.5ms is what I see put out a lot.
8D has a single fire mode also.
Fires twice as long but every other time compared to dbl fire.
So then when you get into the .8ms range your at the same point. Some tunes get flakey right at the single double swap point. It's adjustable of course. Also some injectors work better at say 1.4 than others. According to Bruce at least.
I've seen open time ratings on different injectors on a few sites. This backs up Bruces' findings.
It takes a finite amount of time to open and close the injector. So if the commanded pw is less than this time you'll have problems. Unless your injectors are oversized for your app you shouldn't have a problem. Boosted engines run into this problem more often.
A turbo motor could use a 24lber at 50 kpa cruise but need a 60 at 200kpa WOT.

anondude13

I figured since my fuel curve is pretty far from stock that a customized VE table was the best answer. Either way, does anyone know offhand how the PW is calculated from VE so I can figure out a conservative minimum for VE?

Ronny

iTrader: (1)

i wanna say the BPW or IC as Z pointed out is calc from a formula. search will show many postings. i have it at home but dont refer to it often unless i change FP. takes into account # of cylinders-CID-inj size-FP. not sure is MAF is same as SD in that calc but may be same?

Z69

Stickies
8D Pw limit fix & p4 doc

anondude13

EDIT: I just read the p4 document, and I'll either do the calculation when I have a lot of free time or just trying to power VE values and see if I get in trouble.

Ronny

iTrader: (1)

https://www.thirdgen.org/techbb2/sho...se+pulse+width

is this applicable to your situation?

Grumpy

First do as much of the low load fuel tuning as possible. ie 40-50-60 K/Pa tuning. Then work on the timing. Then work back and forth between the two getting EVERYTHING you can done, in the lower load areas. When you get that all done, then make short runs into the higher load areas. Stick to 1-2 gear, and get that worked out as much as possible. Depending on how you have your original PE enables set, you should now have 80+% of your VE and Fuel tables set. Then start working on your PE fueling (I just 0 out the PE spark adder). The work back and forth with the fuel and timing for best performance.

I've never found it necessary to fully disable PE to get a good tune. Tuning is in large part about taking notes, and looking for trends. The other part is about letting the engine tell you what makes it happy, and not trying to force the engine to want what you think it needs......