L67 VE Tuning

[XtremeRevolution]

Ok, I found some dude's very comprehensive tuning guide on 60degreev6. Forgot what his name was (Gary?), but it seems everyone's using his tutorial.

I want to VE tune. Unless someone can prove to me that it does absolutely nothing, I want that dialed in.

The PCM is a 99 Monte Carlo L36 PCM. This is an L67 swap in a 95 Regal with headers, 3.4 pulley, CAI, autolite 104's, 3" high flow cat, 2.5" exhaust, and 3.29 gearing.

Now here's what happens. I disable PE, and I fail the MAF by unplugging it. The tune instructions show that I should be able to fail the MAF in the tune, but I don't have those options available to me when I go in there in hptuners. Not sure why, as many tabs are completely blank. Anyways, that's where I'm at. When I turn the car on, it takes a long time to crank. Actually, it always takes a long time to crank, with or without the MAF plugged in, typically 3-4 seconds. Once it starts up with the MAF unplugged, the idle is very, very rough and I have to keep my foot on the gas to keep the engine alive. During this time, a very loud howling/suction noise is coming from the engine bay. I've determined this to be the IAC valve being wide open. Here's the problem. If I let it sit for a while and give it some gas, after about 5-10 minutes, eventually that howling noise will go away. I can then sit and rev around a bit, and as the scanner is populating the LTFT cells, that noise comes and goes a bit, but not as loud as in the beginning. I can then get it to the point where if I just sit in idle, I will have a great, steady idle, with the noise completely gone.

However, the moment I start driving around again, that howling noise comes back.

Here's the problem. When that howling noise comes on, it causes my STFT's to run off the scale as extremely lean. At the same time, the O2 sensor is reporting very low numbers (60-80), and there is a very strong and obvious smell of gas out of the exhaust. When that howling noise goes away, the O2 sensor starts reading rich, and the STFT's go in the other direction and also read very rich. All it takes is for me to start driving around again, and the IAC will open up and throw off all of my data.

Here's another thing. I can command a certain RPM using VCM controls in the hptuners scanner. With the MAF plugged in, it will run at the commanded speed. However, in SD mode with the MAF unplugged, if I command 800 RPM, the IAC valve will open wide again and it will idle between 1200 and 1700 despite being commanded at 800.

I have no clue what's going on here. It seems to be working fine with the MAF plugged in, albeit rich with LTFTs between -10 and -16, but that's about it. Any idea what this could be?

[oakleafresin]

What does that tell you, when the car runs perfect with the MAF plugged in but wont run at all without it?

People aren't just saying that VE tuning is worthless just to say it, there's actually CODE inside the OS that specifically tells the PCM to not use the VE table and it sounds like this is what's happening in your case.

Tune your MAF sensor and be done with it imo.

[XtremeRevolution]

What does that tell you, when the car runs perfect with the MAF plugged in but wont run at all without it?

People aren't just saying that VE tuning is worthless just to say it, there's actually CODE inside the OS that specifically tells the PCM to not use the VE table and it sounds like this is what's happening in your case.

Tune your MAF sensor and be done with it imo.

Does this then not apply to 3800's?

Let’s start with VE, and the VE table. Volumetric efficiency for our application can be considered, in the simplest of terms, as the amount of air entering the engine. As far as it is used in the VE table, it is a calculation, rather than and actual measured value. This data is entered into the VE table, which is plotted on a MAP vs. RPM basis. VE values are used by the PCM to set the fueling of the engine, in conjunction with the MAF, or solely if we are in SD mode. These values are of course calculated by GM’s engineers to be correct using the stock components the come with our vehicles.
From the factory, our vehicles (for the most part) come equipped with a MAF, which is a device that measures the actual airmass entering the engine. So, if we have a MAF, why do we have a VE table at all? One thing the VE table does is provide a reference airmass calculation. The PCM uses this reference to compare the measured airmass supplied by the MAF to so it can ensure that the MAF is operating correctly. Also, while the MAF is accurate at measuring airmass that is entering the engine at a constant rate, it is not at all accurate when the airmass is changing, like during throttle transitions during normal driving. At these times, the PCM blends the MAF signal with the airmass calculations derived by the VE table to provide accurate fueling. So, above 4000 RPM, or during steady MAP conditions, fueling is set using the airmass measurement provided by the MAF alone. Under 4000 RPM, during unsteady MAP conditions, fueling is set using the airmass measurement provided by the MAF, modified by the airmass calculation derived from the VE table. Understanding the close interaction between the MAF and VE table, it is easy to see why it is important that they both are correct and working together. Unless of course we remove the MAF from the picture completely. More on this later.

Source:
http://www.ls1tech.com/forums/pcm-di...uel-trims.html

[bilemke]

Funny, I can unplug my maf and the engine runs fine with a tuned ve table.. Jacked up VE table, unplug the maf, engine can barely stay running (if it does)..

Going to see this discussion all over the place for the v6 cars.. But if you are not concerned about the maf ever failing, dont bother with the ve table right now.

[oakleafresin]

There's 3 (or 4) different values the on/off bit can take for the airmass calculation. Many are set to not use anything in the event of a MAF failure, some are set to use the VE table, some are set to use the default air flow table...

Regardless, the VE table seems to only be used in the event of a MAF failure like bilemike said. Set the table to all 0's and see if the car still runs with the maf plugged in. If it does, you're likely wasting your time with it.

[XtremeRevolution]

There's 3 (or 4) different values the on/off bit can take for the airmass calculation. Many are set to not use anything in the event of a MAF failure, some are set to use the VE table, some are set to use the default air flow table...

Regardless, the VE table seems to only be used in the event of a MAF failure like bilemike said. Set the table to all 0's and see if the car still runs with the maf plugged in. If it does, you're likely wasting your time with it.

That has been the consensus among other boards as well. I've decided to ignore the VE table. I tuned the MAF table and the LTFTs are within 1% on all corresponding MAF frequencies.

Anyone have any suggestions on the slow starting? It really does take 3-4 seconds to start the car in the morning. Its almost as though its not getting enough gas to start up. I really don't know. Its generally fine when its warm though.

[oakleafresin]

Change the fuel filter and then check the pressure. Could be a failing regulator

[murphinator]

Anyone have any suggestions on the slow starting? It really does take 3-4 seconds to start the car in the morning. Its almost as though its not getting enough gas to start up. I really don't know. Its generally fine when its warm though.

incorrect/incomplete injector data ?

[passingpower]

Perform a leakdown test:
http://www.fastfieros.com/tech/fuel_pressure_L67.htm

[darkdragon]

My 98 uses the VE table under full acceleration. I can control the AFR at WOT by simply changing my VE values. It took me a long time trying to tune the MAF and getting inconsistent results at WOT until I figured out it was using VE. I don't want to spark a debate here, just saying what worked for me.

[Bill@HPTuners]

My 98 uses the VE table under full acceleration. I can control the AFR at WOT by simply changing my VE values. It took me a long time trying to tune the MAF and getting inconsistent results at WOT until I figured out it was using VE. I don't want to spark a debate here, just saying what worked for me.

It varies from operating system to operating system, currently we support about 800 v6 operating systems so there are bound to be a few that do and a few that don't.

[XtremeRevolution]

Fuel pressure is what it should be, I've already tested it. Fuel filter is new. Injector mappings are stock. My car doesn't use the VE. I can set them all to 0 or all to 100 an it won't make a single difference. I guess that's just my particular OS.

Anything else I can look at?

[oakleafresin]

Hmm well there's crank fuel settings that you can't get to with HPT but stock is usually fine...

How's your ignition system? New plugs/wires? What's the spark gap at right nao?

[XtremeRevolution]

Hmm well there's crank fuel settings that you can't get to with HPT but stock is usually fine...

How's your ignition system? New plugs/wires? What's the spark gap at right nao?

I'll ohm the plug wires when I get home to see what the resistance is. Those should be fairly new.

The spark plugs are new Autolite 104's gapped at 0.55.

the crank fuel settings weren't stock, so I copied all of the settings from the 2005 GTP tune over to mine just now so I guess we'll see how things work out. I just need to get the long start issue resolved as I have a remote start and it doesn't like having to crank for a long time to start the car, and its getting pretty cold out in the mornings here in northern Illinois.

[oakleafresin]

Just to make sure we're talking about the same thing... there's warmup afr correction and crank fuel correction.

[Mobile Chassis Dyno]

I want to VE tune. Unless someone can prove to me that it does absolutely nothing, I want that dialed in.

Set your V/E to all zeros and flash the car with the maf plugged in and you will not see a change in fuel trims.

Tune your MAF sensor and be done with it imo.

Best advice in this thread.



I can not see tuning the V/E table when it is only good for 140 kpa. Last time I check it meant that a speed density tune is only good for 5.8 psi of boost.


I have been tuning these cars now for at least 4 years and there is no reason other then a maf failing to tune the V/E table. Using the STFT vs Maf histograms you be able to dial in your maf and get your LTFTs no more then a couple percent. Use the Wideband to tune the part of the maf where you are in P/E. (Had one car where the highest LTFT was .8 and that was driving around for an hour.)

Save speed density tuning for the LSX cars and trucks.

[Mobile Chassis Dyno]

My 98 uses the VE table under full acceleration. I can control the AFR at WOT by simply changing my VE values. It took me a long time trying to tune the MAF and getting inconsistent results at WOT until I figured out it was using VE. I don't want to spark a debate here, just saying what worked for me.

That must be some pretty high numbers in terms of V/E% when running in the 140 kpa column.

Tim King's 900 rwhp 3800 Firebird was a maf tune with repeatable results at 30+ pounds of boost with a stock V/E table and 98 GTP OS.

I would be very interested in scans of your car while tuning the V/E table.

[GeforceXtreme]

Unless you car is enabled to reference the VE tables in your 3800, then there is no point in tuning the VE table in these cars. Now the LS V8 motors do use the VE table and those guys have to tune VE as well as the MAF table. However from what I have learned the VE table is only used when the car is cruising.

For some reason in 3800 PCM's this VE table is either enabled or disabled. Every 3800 I have come across in person has the VE table disabled to use it.

I spent HOURS tuning the VE table in my car and never saw any difference. Then one day I set my entire VE table to 1's, 0's, then some crazy stuff.. Started the car and saw no difference in my scans.

The only time I would notice how the car ran is when my MAF was disconnected. The VE table appears to only be in use IF and ONLY your maf is disconnected or fails.

Being my maf doesn't fail everyday.. i see no point in spending anymore time dealing with it. I just kept my VE table stock and actually my car runs ok enough so if my maf was to fail, I could get home.

Focus your time on tuning the MAF and forget about the VE table.

As long as you have the correct histograms made, tuning the maf can be very simple process.

[bilemke]

It is not as simple as being on or off. It is can be used fro a couple different things. Most bins only have it setup to be used if/when the MAF table fails..

It can be used while the car is running with a working MAF as well. On top of that, VE also is not the only option for when the MAF fails..