FAQ: How to tune the PCM? (Series II SC)

Theoretically yes, SD/VE tune is a good idea, for LS engines at least. One thing I've heard from 3800 tuners: VE table is back-up and doesn't get used unless the MAF sensor fails. I run stock VE table and never have any issues that I'm aware. Can easily tune with MAFF down to 2500 Hz.

A common question 3800 owners have for the pro tuners: can I tune for SD and lose the MAF? The answer I've read is "no" because our VE table sucks for tuning, it would require lots of work, and MAFF is much simpler to adjust and works great.

So here's my question: if SD requires more work compared to MAFF, when MAFF already works so well, why do people keep assuming SD is the way to go? It can't hurt, and some swear by it, but how is it so many can get by without touching VE values?

I'm curious who wrote that or what their reference was - it's a wiki editable by anybody, but the information seems more specific than anything I've seen before. It mentions more heavily referencing the VE table up to 4000 RPM and light to mid throttle (stoich values). It makes a lot of sense that it won't work on anything beyond stoich (14.7 or 14.2 if you are using E10) without a wideband.

AA wrote:

how is it so many can get by without touching VE values?

This is probably fine for most mild/street tunes. What about some of the more powerful builds? Once you begin to exceed the flow ability of the stock MAF range things can get weird. It gets much harder to make a more powerful engine run nicely on street/cruise levels (think big lift cams very small pulley or turbo, etc). I know a few people who had heavily modified cars that were practically dumping gas out the tailpipe under daily driving until I did VE then MAF tuning for them. I don't know what they had tried before.

My MAF failed on me earlier this summer and I was forced to run on VE table for a couple weeks until I got a new MAF sensor.

In that time, I was able to tune it up pretty well and got my fuel trims 0 to -3

Yesterday, I flashed my PCM with stock VE table to tune and it was just awful!  SUPER rich of course because PCM wants to protect the engine and stalled everywhere at each stop!

It didnt take long to scan and get the info I needed to redo the VE table. I reflashed it with the new one and everything from the idle to driving ability was GREATLY increased. I only stalled once since. I will keep tweaking until it's PERFECT.

When I get home I will see if I can get a screen shot of stock VE and my tuned VE tables so you can compare.

If you dont think your VE table matters, try zeroing it all out and see how your car drives with just MAF.
And as someone who experienced a MAF failure during driving on the highway, knowing that I have a well tuned VE table is quite comforting. Regardless of how it interacts and assists with MAF/daily driving.

The VE table is important, yes. However, the car doesn't run solely off of it. It's merely a base platform for the MAF to make changes from. Is it good to get your STFT to 0? Yes. Is it really going to affect performance if you don't? No. That's what the MAF is for. Adding/subtracting fuel when it's needed based on IAT, TP, MAP, and 02 readings. You can run a window of +/- 10% STFT and not even notice a difference compared to locked in at 0 (which will change from day-to-day). Anything greater than 10% will usually toss a "rich" or "lean" code. There's your sign that you have a problem.

My STFT is locked in at 0 when at WOT. It doesn't even flicker. It does jump up and down a bit when I'm not in PE though. Not enough for me to worry about.

Most of the people that toss a pulley, Intake, Plugs, and Exhaust on they're car really have no need to tune VE at all. This accounts for most of the members on this site. The combo of a good CAI and high-flow exhaust is enough to compensate for the pulley drop without making any major tuning changes if any.  

Building a high HP race engine? Yes tune for VE. The more you change on the engine, especially Cams, high ratio Rockers, things like that, the VE is tossed WAYYYY out of whack and needs to be tuned because you're physically changing the amount of air the engine can ingest and spit out.

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If you dont think your VE table matters, try zeroing it all out and see how your car drives with just MAF.

Well, yeah - if you zero out the VE the MAF tune is built on, sure things will be messed up. That's like if you were to zero out your MAF. No one would ever do that without re-tuning the other table!

My point is, you can adjust MAF to compensate for any issues in VE. And you can make plenty of power doing it. Dyno Brian (dyno tunes for INTENSE) said he prefers tuning with MAF and he tunes some big power cars. I know sensor failure is possible, but not common. Still running original MAF at 278k miles and LTFT is really close to zero.

Abaddon wrote:

My STFT is locked in at 0 when at WOT. It doesn't even flicker.

As it should - anything more than 50-60% throttle and the PCM doesn't do fuel trims anymore - it relies on tables only. The stock O2 sensor can only give stoich reporting. (base desired air fuel ratio, 14.7:1 or 14.2:1 for E10). Yes, you can see richer and leaner values but when the PCM wants 12:1 the O2 reading is just a guess. You need a wideband O2 sensor for an accurate reading non-stoich.

deekster_caddy wrote:

As it should - anything more than 50-60% throttle and the PCM doesn't do fuel trims anymore - it relies on tables only. The stock O2 sensor can only give stoich reporting. (base desired air fuel ratio, 14.7:1 or 14.2:1 for E10). Yes, you can see richer and leaner values but when the PCM wants 12:1 the O2 reading is just a guess. You need a wideband O2 sensor for an accurate reading non-stoich.

Which is where a good MAF tune comes into play?

Abaddon wrote:

Which is where a good MAF tune comes into play?

Yup. Only a Wideband sensor can tell you what your true A/F ratio is at that point. The tailpipe probe used by a dyno has the issue that it's post-cat. If you have no cat, it's fine, but if you have a cat you are getting a secondary burn so it's not giving you a true reading. A good wideband location is about where the stock primary O2 sensor is.

You could even do this with an inexpensive external wideband sensor and gauge setup, as long as the gauge has some form of logging. You can then use the 1/4 mile to make adjustments to the WOT areas.

I'm wondering if I tried to tune the VE table too far, and if that's why I had so much trouble getting my WOT to lean out. My car goes pig-rich at full throttle, and I'm sure it's costing me some power up top. Again, I'm not sure how much the VE table is referenced at WOT.

I wish I had my car back so I could tinker some more!

deekster_caddy wrote:

Abaddon wrote:

Which is where a good MAF tune comes into play?

I'm wondering if I tried to tune the VE table too far, and if that's why I had so much trouble getting my WOT to lean out. My car goes pig-rich at full throttle, and I'm sure it's costing me some power up top. Again, I'm not sure how much the VE table is referenced at WOT.

I wish I had my car back so I could tinker some more!

Sounds like maybe that had to do with your PE tables? I think that's where you would lean out WOT.


Also, why do you think GM gave us stock VE tables that are not smooth at all? Mine was jagged and caused all kinds of hiccups and inconsistencies.

Once I referred to scanned info and smoothed out the table, my fuel trims looked A LOT better, the car idles better, and all in all, runs better.





here's some more info on VE tuning:
http://www.j-body.org/forums/read.php?f=64&i=23783&t=23783

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Volumetric Efficiency (VE Tables)
The VE tables are where the ACTUAL fueling changes are made. These tables are either TPS based (Alpha N) or MAP based (Speed Density). All Idle VE tables will be MAP based. It is important to not have choppy VE tables. It is also important to have smooth transitions between the tables from cell to cell. The bigger the number, the more fuel that will be added. Volumetric efficiency (VE) is typically defined as "the actual amount of air being pumped by the engine as compared to its theoretical maximum." Basically, VE is a measure of how "full" the cylinders are. As most of us will know from basic science, gas will expand to fill its container. Seemingly, that would suggest that the cylinder is always full. And, in the pure volumetric sense, that is correct. A 0.5 Liter cylinder will always have 0.5 liters of air in it. The measure we are looking for here is air density. Now, where is this air density measured? This is one of the points of disagreement. The point at which air density is measured is crucial. Many will claim that you must take the measurement at a standard, such atmospheric density. This, however, can cause many issues with VE measurements. Forced induction cars will have skewed VE values due to the simple fact that they are forcing more air into the manifold. With more air available to the engine, it will receive a larger/more dense amount. This is not a pure measurement of the efficiency of the engine. This is where the VE Offset comes into play. The VE Offset will allow you to achieve values greater than 100.

I just dont understand why the stock VE tables look the way they do.

To say the jagged OEM VE table causes hiccups and inconsistencies - that's your take on it, and maybe due to your mod plan. My experience is different. I have no idle, running, or other issues to speak of. I mean, from the factory the car idles and runs smoothly, so why would I change VE unless some other variables were introduced that caused an issue?

Interesting to me is DHP's old 1.5 BIN, which was derived from their research and supplied to customers as a base tune, kept the stock VE table.

I know the table "looks" wrong, but apparently GM and DHP thought it to be fine, at least for mild mod levels. I recently found this thread on tuning VE vs. MAF. Interesting reading:

http://www.grandprixforums.net/threads/88485-MAF-vs-VE-Tune-Efficacy

AA wrote:

To say the jagged OEM VE table causes hiccups and inconsistencies - that's your take on it, and maybe due to your mod plan. My experience is different. I have no idle, running, or other issues to speak of. I mean, from the factory the car idles and runs smoothly, so why would I change VE unless some other variables were introduced that caused an issue?

Interesting to me is DHP's old 1.5 BIN, which was derived from their research and supplied to customers as a base tune, kept the stock VE table.

I know the table "looks" wrong, but apparently GM and DHP thought it to be fine, at least for mild mod levels. I recently found this thread on tuning VE vs. MAF. Interesting reading:

http://www.grandprixforums.net/threads/88485-MAF-vs-VE-Tune-Efficacy

AA, unplug your MAF so you are defaulted to VE table. Then tell me what you think!

I've done that before. Great for troubleshooting - easy way to test MAF sensor. Also easy to know when to clean it.

Disconnect your brake lines and tell me what you think!

AA wrote:

Disconnect your brake lines and tell me what you think!

  
  

Just a thought, if it were up to me, I wouldnt want the car to run normally if the MAF sensor died on me. Without symptoms, how do you know something is wrong with your car? I would bet it is intentional that the car "seems" like the VE is poorly tuned from the factory when its really not hurting anything on a stock car when the MAF is working properly.

^^^ Hey, now there's a thought! But those GM engineers couldn't be that smart, right?

I have no idea how you are relating this to brake lines......

My point was, how does your car run with MAF unplugged?

If it runs rough, stalls, whatever, it means you could prrrrrobably use a VE tune.

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AA wrote:
To say the jagged OEM VE table causes hiccups and inconsistencies - that's your take on it, and maybe due to your mod plan. My experience is different. I have no idle, running, or other issues to speak of. I mean, from the factory the car idles and runs smoothly, so why would I change VE unless some other variables were introduced that caused an issue?

You say you have no idle, running, or other issues. But is this with MAF plugged in or not? What I am talking about is with MAF unplugged and running on VE table. With my MAF plugged in, she runs fine too. With MAF unplugged, is was a rough run with new build and before this engine rebuild, until I tuned VE.

After tuneup, and on VE table, car idles and runs fine. I bet you couldnt even tell if it was on MAF or not!

If your Riv runs fine with MAF unplugged on STOCK VE table, i would be surprised. I would be willing to bet you will experience hiccups at idle and a funky tach in low RPMS.

th3fr4nchi5e wrote:

Just a thought, if it were up to me, I wouldnt want the car to run normally if the MAF sensor died on me. Without symptoms, how do you know something is wrong with your car? I would bet it is intentional that the car "seems" like the VE is poorly tuned from the factory when its really not hurting anything on a stock car when the MAF is working properly.

Stalling out and losing power steering mid turn sounds rrrrrrrrrrrrrrrrrreaaaaaalllll safe to me!!!!

dude, this is what SES light is for

You guys can stick your heads and stock VE tables back in the sand.

My VE table will lock my FTs in tight with smooth idle and 0 KR. See ya at the track, noobs.

Charlie, relax. I don't know about your Riv, but mine is designed to run with a MAF sensor. I'm certainly not going to downgrade to a Speed Density system. Why would I (we)?   

This is a great discussion. Let's continue. Why would you call SD a downgrade? I see them as 2 sides to the same coin.

Alot of sources I am reading say the PCM references both the MAF and the VE for fueling.

Thus, a properly tuned VE table is mandatory for optimal fueling/power

http://forum.camarov6.com/archive/index.php/t-96528.html
http://www.thechicagogarage.com/forum/midwest3800s/34216-ve-sd-tune-3800-a.html
most recent tabs opened

also, EVEN if it doesnt affect driving and its totally useless with MAF (! I dont believe this at this point in time and space!) but IF IT WAS...

I would still want a properly tuned VE table just incase MAF ever fails. It happened to me once and it's not fun!

There is no way the VE table exists ONLY for MAF failure. I just dont believe it. It's great data that the engine can use to reference in all sorts of situations.

It's a great discussion that's old. I've seen the same sources as all of you. Some say it uses the VE table for reference, some say don't bother.

I've given up on trying to convince anyone it's worth doing. But I will continue to do it on my own tunes. However, from now on I won't bother touching anything in VE tables above 50% throttle unless I can put a wideband in.

If your MAF is broken, you shouldn't be using full throttle anyway. (unless you've done an entire SD tune in the first place, in which case you have an entirely different setup that outflows most MAFs)

I can "lock in" FT's with a MAF tune, and have a smooth idle without touching the VE table.
Are you planning on driving your Riv in the winter? Unplug your MAF sensor and tell us how it runs on your VE tune.....just sayin.

The MAF is the fine tuning point, which is why vehicles have them now. More power, more efficiency. The PCM will ignore VE if the MAF tells it to do so. Which is why the car will run like BALLS with it unplugged. And, as AA said, then you know you have a problem! Nobody here is planning on unplugging their MAF and going drag racing.

And, calling anybody here a noob? You just started tuning dude....seriously. You're getting upset about something you yourself are just learning.

deekster_caddy wrote:

It's a great discussion that's old. I've seen the same sources as all of you. Some say it uses the VE table for reference, some say don't bother.

I've given up on trying to convince anyone it's worth doing. But I will continue to do it on my own tunes. However, from now on I won't bother touching anything in VE tables above 50% throttle unless I can put a wideband in.

If your MAF is broken, you shouldn't be using full throttle anyway. (unless you've done an entire SD tune in the first place, in which case you have an entirely different setup that outflows most MAFs)

Agreed on the wideband and about 50% throttle.

But, if your MAF is broke, it's not just about WOT. It's about idling too. Starting your car after it stalls at each stop light gets old, reeal fast

Abaddon wrote:

I can "lock in" FT's with a MAF tune, and have a smooth idle without touching the VE table.

An interesting note - something I noticed on my car after it was modded - after I did my VE and timing tables to near-perfect, the MAF table was very very close and required only tiny changes down low. So yes, the MAF takes primary role, but I'm sure the other tables are referenced too.

What's that worth in the long run? (again, the old part of the discussion) who knows for sure...

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I have no idea how you are relating this to brake lines......

The relation is that no one would ever unplug their MAF, nor would they disconnect the brakes. The results are obviously bad.

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My point was, how does your car run with MAF unplugged?

If it runs rough, stalls, whatever, it means you could prrrrrobably use a VE tune.

No. It would mean there's a MAF problem that needs addressed.

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You say you have no idle, running, or other issues. But is this with MAF plugged in or not? What I am talking about is with MAF unplugged and running on VE table. With my MAF plugged in, she runs fine too. With MAF unplugged, is was a rough run with new build and before this engine rebuild, until I tuned VE.

The bigger question is, why do you care how the engine runs with disconnected MAF? Just to say your VE is perfect? Of course it runs rough that way. You are disabling a critical sensor!

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Thus, a properly tuned VE table is mandatory for optimal fueling/power

No. It's an option, not mandatory. I have optimal fueling and power. My car was dyno-tuned by a 3800 pro, MAF tables only.

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I would still want a properly tuned VE table just incase MAF ever fails. It happened to me once and it's not fun!

It's not "fun" if MAF fails, but it lets you know something's up without damaging the engine. Your experience is a sampling of 1. It is not the norm. If MAF failure occurred on a regular basis, that would make a better case for perfect VE. I think a good point a few of us are making is, if/when MAF fails, there is some good in knowing something is wrong, rather than assuming everything is fine and running on VE only.

AA, from your comments above, ^^^, would you say that the only use for the VE table is in the case of MAF failure?

I would say if it ain't broke...

EDIT: curiosity is all good. I like to tinker, too. That's how we learn. If you want a perfect VE table, that's cool. I will probably do mine at some point. But, I wouldn't go as far as saying it's wrong to keep the stock VE table if it works for a lot of us. This is one of those age-old debated topics, like engine break-in, oil change intervals, etc. Even the pros don't agree 100%.