BravoPuma6

i understand the purpose of pe.... hell its almost self explanatory. but i dont understand ve's relationship to pe and how ve affects the outcome of the a/f. i can hardly put what i want to learn n ask u all into words! anyone have anyscreen shots of a bad ve table vs a good one with an explanation as to why one is worse then the other etc?

thanks!

edit: 1 more thing i forgot to ask, if the number is lower or higher what exact impact will it have on the car? richer for higher, leaner for lower?

BravoPuma6

? anyone

pjk91

are you talking about afr? air fuel ratio? higher numbers are leaner, lower numbers are richer (for air fuel ratio)

raptors_67

A correct VE table helps the engine decide how much fuel to deliver to reach an AFR of stoich. When PE mode is entered the current PE cell value is inversely multiplied upon a value of 14.7 (stoich) to achieve the desired PE AFR. So a PE cell of 1.200 would achieve an AFR of ~ 12.25 if the corresponding VE cells are correct. You can even think of it as taking the value in the corresponding VE cell and multiplying it by 1.200 if that makes it simpler to understand. The reason a correct VE is important is to achieve a correct baseline in which the computer can compute proper AFR's. If your VE is consistently out to the rich side of AFRs (meaning the computer thinks the engine is more efficient than it really is) during part throttle than entering PE mode will only amplify this rich condition to provide a PE mode AFR lower than desired.

Witt

Ok, I'll try this one....

I take it from the question that you know what PE is and why its there.

VE is a measure of the amount air an engine ingests. A VE table is a calibration that indciates the amount of fuel needed to match the amount of air being ingested using engine speed (RPM) and manifold pressure (MAP) as variables.

VE is one of 4 ways the PCM can determine proper fueling. The other 3 are MAF, which is the primary and most important calibration on these PCMs, TPS1 (throttle position sensor number 1) which is only used as an electronic throttle check to make sure its working correctly, and SCIP or supercharger inlet pressure (the sensor on top of the supercharger on the inlet side) which like TPS1 is only used to ensure the electronic throttle isn't malfunctioning.

A VE table should be a smooth accurate table when finished. When dialing your VE in, you may have some erratic cells that will smooth out the more data that you log for them. When tuning VE I usually highlight and smooth the entire table more than once.

Don't worry too awful much about VE imho. Its only used as a backup in case of MAF failure. Its primary function is to compare the VE table with your MAF calibration and also with the SCIP and TPS to ensure the electronic throttle isn't malufunctioning. When you fail this test the car will trigger "limp home mode" and will severly limit the amount the throttle will open. The more accurate your VE is, the less of a chance you will have limp home mode triggered.

Bottom line, get VE as close as you can but make sure you dial that MAF in accurate afterwards. MAF is used 100% of the time on an LSJ. Once your MAF is accurate your PE will fall right into place wherever you command it.

06blackg85ss

iTrader: (1)

hmm so I guess I should put my scip back in then. Car never goes into limp mode though (I do have it disabled) with the new intake mani though, I'll be putting it back in. I guess that could help explain my weird AFR's, well I should say my random afr's cause the car never does the same thing on each pull.

Witt

Umm, maybe. Heh

Its just used for ETC checks as far as I can tell. It will throw a DTC for being above atmospheric. Weird thing is that its a 2 bar sensor iirc. HPTuners doesn't have the calibration for SCIP unlocked so in your case you're prolly best leaving it out and disabling the DTC for it.

BravoPuma6

thanks 4 the write up witt. and everyone else. i just had a tough time understanding its relationship to pe. lately ive just been adjusting pe.... and not anything else. as u can imagine my pe is all over the place lol. later on i plan on adjusting my maf and re adjusting pe.

Kennyspec

Another question relating to PE and VE. I was running my car in SD mode (the maf fail freq at 0) so that i could tune the VE table and the car was runing in open loop. How come i had so much burst knock doing light throttle transitions like 10% to 25% throtle?? But once the MAf was enabled all this burst knock instantly went away??? then only thing i could think of was that the Ve table wasnt smoothe enough? Hey Witt can we see a pic of your VE table?

BlackSS/SC

My car did the same thing when in SD mode. No matter how close I got it, and I got it pretty damn close.

About the SCIP sensor, I have the same SC delete plate that TAG made. It's got a port on the piping to run a vacuum line from there to the SCIP and relocate it. When going turbo do you think it's better to run the line to it or just block off the port and disable it in HPT?

06blackg85ss

iTrader: (1)

yeah that;s what I did

Witt

I have a feeling when the MAF fails, theres more to the story that we don't see other than just the PCM using the VE table which is why the knock sensor is a bit more sensitive.

I have to pull it off my laptop, I'll post a screenshot in a few.



Thats my current VE. I have aftermarket cams and have merged the additional fuel flow from 650cc injectors into it so yours might not look similar.

I haven't failed p0068 yet with that so I'm stickin to it.

Kennyspec

Hey Witt do you bother tuning WOT when in SD mode?? Or just keep it out of PE and tune the rest of the cells?

Witt

I try to bring it to the 215kpa limit. Anything over that will just show an excess amount of fuel since you would smooth that into the nearby cells.

For those who don't know, the VE table is limited to 215kpa (about 16.5 psi). If you let it run up to 17psi+ it will stay in the 215kpa cell but require more fuel. When you exceed the limit of any table it uses the last known value (215kpa in this case). When you actually hit the 215kpa mark while driving and you tuned that cell at a higher pressure, you will show a rich area and possibly hit p0068.

Oh, I tune with PE enabled, open loop and compare commanded afr to actual using an AEM wideband. I also richen up PE quite a bit in case I have VE cells that are really lean to start. Some people richen the entire VE table by a certain percent but I found that really screws up the works for cells you can't hit and it gets worse when you smooth the table.

Kennyspec

thats exactly what i do too. Good to talk to other people and see that i am on the right track. Hopefully i think that tuning the VE table when i am turbo will be easier as im gonna have a boost controller and once the wastegate opens it should stay in the same MAP cell and just move down through the rpm range. Then just up the boost a bit till it hits the next MAP cell and start all over again.