i changed my VE table by 50% to help startup and idle now it seems that i have a slight hesitation at a rev or pulling out with little acceleration! any help please!

 

Most people only reduce it to 60 to 80%.

 

Only change it up to 1200rpm! Not the whole table.

 

Why would you change the VE table?

 

When you try to start a hot engine the PCM is running in open loop mode off the VE table and injects too much fuel for an aftermarket cam.

 

I thought when the engine is hot, it is in closed-loop?

What does the VE table do exactly?

 

When you first start the car even with a hot engine, the O2s are not hot enough to work, so the engine can't run in closed loop, since the feedback comes from the O2s. The O2s have to be at several hundred degrees in order to function.

 

The VE table (or volumetric efficiency table) is used in both open loop operation and closed loop operation. In open loop operation, the VE table is used to determine how much air is actually entering the engine. In closed loop operation the VE table functions to determine how much of the ingested air measured by the MAF is going to contribute to combustion. Not all of the air that enters an engine contributes directly to combustion.

Multiplying your ENTIRE VE table by 50% is going to cause your engine to add less fuel. The MAF will take a reading of the air that is entering the engine, but your VE table is now telling the PCM that 50% less of the air is going to contribute to combustion. As a result your car is going to add less fuel. The lack of fuel when you get on the gas is what is causing the hesitation.

You need to return your VE table to normal. Then, to take care of the hotstart problem just multiply lower RPM (up to 1200 rpm) by 60-70%. This should take care of the hot start problem.

Just my opinion.

-Kevin

 

The cats have nothing to do with it, if the engine is less then 122 degrees that would be the trip point of PCM deciding to go to open loop to assure O2s get heated up and AIR kicked on until they are.

VE is supposted to be only for cranking engine since PCM uses MAP and not MAF at that point and as soon as engine is running it switches back to MAF and VE then is no longer used so should not effect idle itself over the timeframe engine is running since the startup.

VE then is only used as a backup mode so that if MAF fails while engine is running then would defaut back to MAP and it then uses VE tables.

I see plenty of PCM scans where as soon as engine is started it is in closed loop as long as the 122 degrees has been met.

 

That is what I keep seeing. When my engine warms up, it goes from open to closed. Then the only time I see it go open is WOT.

So if you modify the VE table between 400-1200, that will only affect cold starts?

 

Whoops, I screwed up . . . everywhere I said "cats" I meant to say "o2s." I'll go back and edit the post so no one gets the wrong idea. Obviously the PCM can't read feedback information off the cats.

 

If you re-read the other posts above, not just mine, you will see we are trying to tell you the VE table is used for cranking the engine, hot or cold, so yes it will help the hot start problem. That's the main reason people adjust this table.

 

Hey NoGo!! - Kevin, I thought you had deserted us.Haven't seen any posts in awhile. Welcome back!
Thanks for another great explanation!
joel(Bink)

 

Got it thanks!!

 

thanks guys for all the help. so just to get this straight, i turned my ve table back to the stock settings. so i should multiply 400-1200 by 60-80% and this should help my cold and warm starts. what does this affect as far as if the maf does die and now the ve table is changed. how will it affect performance and does this hurt wot or anything else? thanx
jamie

 

Hey Bink. Thanks for the welcome back.

Z28 Man: Shifting your VE table for the lower RPM is only going to effect your cranking fueling and ignition. This change won't effect the rest of your driving, and won't effect your WOT fueling or timing. If your MAF dies, the car will still run fine.

Good Luck,
Kevin

 

I have to agree with Team ZR-1 on this - the VE table is only used during cranking or then the MAF is not working (SD mode).


There seems to be a confusion here between open loop/closed loop and SD/MAF operation. Open loop/closed loop operation refers to a feedback system from the O2's - if they are active then you have a "closed loop" feedback system - if not, then you have open loop (no feedback). This has nothing to do with MAF/SD (speed density) operation - infact it works the same in either mode.

Fueling itself can be MAF or SD based (in this case). VE tables are *not* needed in MAF operation. The airflow from the MAF is what is injested by the engine - if it isn't it sits in the intake manifold - so additional air doesn't flow in, so the MAF meters less, etc. - if the air isn't used, it doesn't "flow" - so there is no need for a correction factor for the maf.

Infact the SD fueling questions calculate the same parameter the maf measures directly - essentially you assume an ideal engine operating at whatever rpm and displacement you are at. The VE value is then applied as a factor that indicates what percentage of actual airflow you are getting (100% being perfect theoretical). Temperature, baro, etc. are then taken into account to calculate the density and thus mass for a given volume - and thus you end up with a massflow rate.

Presumably at low rpms not enough air is moving in to get reliable MAF readings, hence VE operation. Otherwise when the MAF is being used the VE tables are irrelevant.

 

just to clarify i should mult. the 400-1200 ve table by 70% or %80% or is it 170% or 180%

 

Multiply it by 60% - 80%

 

Chris,

This may be one of those "agree to disagree" things. I am very familiar with closed loop open loop, VE and the such, but I still stand by my original claim that the VE table is not completely ignored while the car is in closed loop.

There is an easy test for this. Mulitply your VE table by 300% and let me know how the car runs.....after you get it to start.

-Kevin