Painrace

Why would you consider cheating GM by removing a tune that might have caused damage? Man, rethink what you are saying. Jim and Katech have tuned my cars for years and I have never had an issue with the tune. However, if I did I would not try to get it by GM. I guess the world is just different today and we are all just old idiots but we do still have morals and ethics!

Jim

forg0tmypen

Absolutly. I'm sure there will come a time when I take a step back and reevaluate. I'm not opposed to that. Here's to good health because that's more important

Crash_Z06

Thanks for sharing the info! I hope your health improves, and we can get back on topic!

soulcoaxing

Bravo to you my friend. It takes a strong decent minded person to recognize an error, and especially to take responsibility for it (Very rare these days).

Quick Silver Z

Sorry, I thought this was a relatively simple question for Jim Hall (what would be the point of having the ability to turn back to a stock tune?).

I didn’t realize by asking a question and trying to get the original post back on subject my morals and ethics would be brought into question.

Does this get me drummed out of the scared old white man demographic?

Halltech

I appreciate the forum input. I did get an apology from the lady who posted without all the facts, and apology is accepted.

I am going to try to explain how the fuel trims work during closed loop cycle. Remember, on the Z06, closed loop is under 49% throttle position. On cars like the LS3/LS9 it is under 19% throttle position. It varies from vehicle to vehicle, but here is the best explanation I can come up with.

First of all stoichiometric. This is the theoretically correct burn for different types of fuel. The most common stoichiometric air fuel ratios are E0 (pure gasoline) 14.6:1; E10 (10% ethanol 90% gasoline) 14:1; E85 (85% ethanol/15% gasoline 9.77:1; pure ethanol 9:1

The first number is oxygen by mass, the second is the fuel type by mass.

GM ASSUMES a 14.7:1 air/fuel stoichiometric burn in your ECM. Of course you can see that the correct complete burn is 14:1 for E10, which is the most common fuel now available everywhere. That means that your PCM cannot reconcile stoichiometric when the tables are not correct for your fuel type in any NFF vehicle (non flex fuel)Why GM does not now set stoich at 14:1 is an EPA deal. Your car is always running slightly leaner than 14.7:1 since there is 5% left over oxygen in the combustion chamber no matter what you do, short of tuning that table correctly.

The exception is Flex Fuel Vehicles, which re-calibrate stoich after each fillup. During the first 60 seconds of startup, the PCM looks at the O2 sensor readings and adds or deletes fuel until the long term fuel trims are back to close to zero in each fuel cell.

How the MAF works during closed loop:
The Mass Air Flow sensor reads the mass of oxygen and signals the ECM based on preloaded MAF transfer curves set up by GM. They are based on the MAF read area at the MAF sensor.

If an aftermarket intake like our CTS-V intake is 13% larger at that read area, the MAF will incorrectly under-estimate air by 13% and the long term fuel trims will be approximately +13% both banks assuming the O2 sensors are in perfect condition (they can go bad).

That 13% un-reported air is automatically made up for by the O2 sensors requesting more pulse width from the injectors until they have reset the burn to the stoich table. So can you run lean with an intake that is 13% larger at the read area? Not in closed loop you can't. You will not even see lean codes until +25% under-reported air. This unreported air would require the first type of tuning I referred to in my first post, but not because of closed loop. +13% under-reporting is a definite problem for open loop. I'll discuss this tomorrow.

For now, this parody might make more sense. It's like the host at a restaurant that serves a balanced diet. He is supposed to allow only 100 people in the front door at a time. Someone did not tell him that the door he was monitoring was made larger, and 113 people got in for the meal even though he counted 100, based on his training and experience.

The inside servers named O2bank1 and O2bank2 see the real number of customers based on actual counting, since they have served 113 meals to each customer sitting at their tables.

The 13 extra dinners represent the +13% long term fuel trim averages during closed loop, which is the O2banks correction of the estimated air, based on the O2 sensors real head count. What you get is a constantly perfect burn of 14.7:1 (assuming pure gasoline) provided by the fuel trimming from the O2 sensors. Unfortunately for us, the stoichiometric assumption of 14.7:1 is wrong for our fuel and creates a lean condition all the time.

Here is the example from above.

Untuned MAF tables with our CTS-V intake:


After MAF recalibration tuning only (check out the LTFTs after the host got retrained to count correctly):

Halltech

Simple. You tune your car for different size wheels, high octane fuel (better timing), better leaner open loop performance, better torque, rev limiter changes for the Autobahn Katech Track Attack next year, or any track event.

You flash your computer at the track; fill up with CAM 2 110 Octane gas at the local Speedway station and you are ready to rock.

Right after dinner (paid for by Katech), you reflash your ECM back to stock so that you are Obama legal for the street (EPA requirement you know)

Hope that explains it. Of course whenever you visit your dealer, you confess that you have run into the rev limiter on the street, and tracked your car, tuned it for the track. This would be the honest thing to do.

If you worry about your warranty, keep your ECM stock. How easy is that?

mirage2991

That's exactly how I tuned my buddy's 2000 SS when he had headers, no cats and CAI. If I recall his LTFT's were in the 12% as well. I don't think I managed to get 0.0 but we were extremly close. I recall shooting for 0 to -3 but no + at all because if I remember right, when the LTF's see + numbers it will add the fuel on the top end too.

What's your take on the new self tuning ECMs? (I believe FAST and now Holley have one) I've read some really good positive reviews on retrofited BBC and SBC. Granted it uses a wide band o2, but, you set your idle ARF, then cruise AFR and WOT AFR and it does the rest. I wonder why the auto industry has not switched to something like it: Imagine, you could do mods and the ECM would self adjust = instant gains.

Knowing the correct E10 AFR makes me want to go plug my HPT Pro the the Z and set it up right... eh I'll have to wait a couple more years until the warranty runs out or I get it off it's DD duties.

40YRW8

You know that we all wish you the best and we all thank you for dedicating a large chunk of your life to helping us enjoy what we love most. Now is the time to let someone else carry the load so that, hopefully, you can get to attacking the old bucket list. My first was my Vette. "CHECK" Last year my brother and I went to Bonneville. "CHECK" Thursday is going to be the Monterrey Historics at Laguna Seca. "CHECK" Did I mention Bonneville? Man, that was way cool. Of course, I don't have to tell you that. Don't forget to hit the forum every now and then just to keep us posted and to say, "Hi!"
Gary Knox
StealthTitanium

40YRW8

Jim,
Something just ocurred to me. Do you think the 14.7 stoiciometric with our E10 running a little lean might be contributing to most of us getting slightly better fuel mileage than the EPA numbers? I know that not too many years ago, if your car actually got the EPA fuel mileage you considered yourself really lucky. It seemed to never happen.
Gary

OOPS! Never mind. I don't think this is the case because I forgot that with E10 you lose about 5% of you mileage. Probably cancel themselves out.

forg0tmypen

Yes it does. Besed on your original question I'd put your age in the 15-25 category.

Quick Silver Z

Thanks Jim, get back to you when it runs out.

glenB

Outside of the 19%/49% or whatever % is used by the particulars, is the PCM now considered in Open Loop and what table does it use for fueling ?

Second, it's been said that the PCM checks it's fueling by referencing the MAF table against the Virtual VE table, is this correct?

JUIC3D

Subbing for potentially one of the most informative threads on the forum.

Halltech is such a pleasure to deal with and I wish you the best Jim

Halltech

The VE table should be correct if you expect to have perfect commanded PE/RPM equivalency ratios when going from your stoichiometric base when transitioning to OL. I do not tune that way, and have always used dual wideband onboard O2 sensors for our vehicles to dial in the OL air fuel ratio. Safer that way. The dyno O2s do a good job as well, but have no interpolation software that I have seen to get E85 a/f ratios correct. Using Lamba tables is a must when converting to E85, or dual onboard Widebands with the FAST E85 hardware. You can set it up to interpolate E85 or Methanol (stoichiometric baselines for Lambda 1.00)

Maybe you could reveal your method of doing that, while I stick with my discussion of open and closed loop. My guess is the folks will enjoy more information and participation here, or even your own thread.

Prime Target

Another Lee Harvey....

I thought I logged on to the Z06 section, not CNN.

Jim Hall, get well brother

My07C6

Why does GM drop out of closed loop so soon? I would have expected closed loop through the majority of the throttle position.

I'm not a tuner, but have been programming industrial controls for 25+ years. I do plan on buying HPTuners pro sometime in the near future and learn the ecm programming just for my own cars.

Thanks for the education.

MTIRC6Z

What an awesome and intelligent policy with regard to locking ECMs.

As opposed to the jackass mentality that causes a tuner to lock your ECM, then 4 years later when you've made some minor adjustments to your car and thus wish to make some minor adjustments to your tune, the tuner says: "Sure we'll help you out, just remove your ECM, send it back to us and we'll make the adjustments you want.". Of course the time and expense of all this is stupid, not to mention, what if the adjustments don't accomplish exactly what you want, now you're gunna have to go through the whole process again! Thanks, but no thanks you paranoid *********, who's car is this anyway???

So what's a guy to do when his ECM is locked and the tuner has essentially told you to f-off and not bother them if you don't want to keep giving them money? That's when Shawn David comes to the rescue...he's the man, not to mention an awesome tuner.

Moral of story, asked your tuner (before you give him your money) what his policy is on locking tunes and if it's a policy similar to my original tuner (I'll leave who that tuner is to your imagination) walk away and don't ever consider doing business with such an organization.

Cheers, Paul.

PS. Thanks for letting me vent, I've been waiting a while for an appropriate opportunity to do this.

Halltech

Actually, running your car in closed loop to 1/2 throttle makes little sense, except to the headmaster at GM. That means your are driving at nearly 15:1 air fuel ratio all the time. Makes for great EPA mileage numbers, but that's it.

Having the transition to OL at 16 to 20% makes new found throttle response and worse mileage on the downside, because you find going into fuel enrichment a torque paradise.

The PE/RPM static open loop table is the table that effectively provides an equivalency ratio for each rpm. In the case of the LS7, every 250 rpm there is a ratio for that rpm and OL. For instance, at peak HP, or around 6500 rpm the table commands a 1.27 EQ. So if your stoichiometric value is 14.7:1 you divide 14.7 by 1.27= 11.57:1 air fuel ratio. That is very rich and will not make best power. This is what GM gives you.

At 6000 rpm the EQ is 1.31. 14.7/1.31=11.22:1 commanded air fuel ratio.

Commanded assumes stock volumetric efficiency and MAF transfer curve accuracy. If your intake is made with a +13.3% larger MAF read area, that 13.3% will be under-reported in OL as well as CL, but OL has no communication with CL or the O2 sensors, so it is on its own, depending on the MAF sensor readings. The result is around 13.1:1 air fuel ratio due to the under-reported airflow.

Generally speaking it is better to recalibrate the MAF transfer curve to get the LTFTs closer to zero both banks.

The 13.1:1 air fuel ratio might make plenty of power on the road with maximum cooling/Beehive to keep IATs ambient, but put that car on the dyno and you would likely see poor power. Why? GM's safety protocol is much more likely to kick in with that much new air in OL. AT 1616F degrees at the cats, the cat overtemp protection equivalency ratio kicks in and adds as much a three levels of fuel. That last level for 1700F plus degrees is 1.205. Down you go into the 10:1 air fuel ratio and whatever power you made, is masked by super fuel enrichment.

Timing is pulled when knock sensors see pinging, and if too much knock is recorded, you drop into Low Octane timing, which is around 10 degrees less timing that High Octane. Yes, the ECM has a knock count protocol. You sit in Low Octane until you refill the tank. 91 Octane state Corvettes run Low Octane tables most of the time, especially when it is really hot.

Power tuning is a balancing act, which done wrong is not good for motor longevity. There are many many factors to consider when deciding on tuning or not to tune. For most, leaving your car alone with an intake that does not require recalibrating the MAF tables, and headers is the hot ticket.

Jim Hall

My07C6

So you are saying even if the ecm was running at the correct sticometric ratio you gain more power by going OL and richer but not as rich as the original GM programming.

I find it really interesting that adding more fuel when the cats are going into overtemp actually cools them instead of going into thermal runaway.

Also you say when the ecm goes into low octane mode it stays there until the next refill. Does it know the next refill by the fuel guage going over a certain percentage or by any fuel level increase?

One more question, I bought my 2010 Z06 in CA but live in KC, does GM use the same tune in all the Z's or do they have different tunes based on the original shipping location or elevations?

Thanks again, this is very educational.