Backup VE table

[hpcubed]

If the computer reverts to the backup VE table when in speed density mode(for certain operating systems), then why is it logging data in all map values as in the main VE table? Does it use the backup VE table for calculations, but sets the fuel trims as in the main VE table?

[Dirk Diggler]

set up a map that mimicks the secondary table and you will be good to go.

[Steve Bryant]

hpcubed,
I'll try to answer your question in steps.

For 2000 and before PCM's, the operating systems were structured to have both Main and Backup VE tables. If the MAF frequency monitoring by the PCM determines that the MAF has failed, the PCM automatically switches to the Backup VE table and it will also switch to the Low Octane Spark Advance Table, thus retarding the timing. In this case, the PCM operates in the Speed Density Mode. As you've probably noticed, the Backup VE increments in 10 kPa columns rather than the 5 kPa increments of the Main VE Table. It's really the structure of these earlier operating systems that limit the finesse with which the PCM is able to control the engine in Speed Density Mode, not the MAP sensor or anything else.

Then beginning with the 2001 Operating Systems that were flashed into the same PCM's (same part numbers, etc.) GM Powertrain Engineers had eliminated the Backup VE table. With these Operating Systems fail, the higher fidelity 5 kPa incremented VE Table is used period and the spark doesn't revert to the low octane table either. This more refined means of controlling mixture in the Speed Density Mode has caused some folks who want to remove any and all restrictions to air flow to remove the MAF entirely. This is also the reason that some folks would want to upgrade from the Personal Version to the Commercial Version of FlashScan as it can do a full re-flash of the PCM which includes the operating system. This allows earlier PCM's to have the single Main VE Table with its higher fidelity for speed density MAFless operation. The Workshop Version can do this too. Note, the actual software for the Commercial and Workshop versions allowing full re-flash has not been released yet, but should be "just around the corner."

The Short and Long Term Fuel Trim Values are set based upon the Primary (pre cat) Narrow Band Oxygen Sensors (NBO2). These trim values are constantly being adjusted as long as the PCM is in Closed Loop operation. STFT and LTFT modify the commanded AFR or EQ Ratio determined by the open loop determination of mixture whether that is a blend of speed density and MAF data or speed density alone.

The bottom line is that the PCM logs LTFT data and automatically modifies the LTFT tables for the right and left banks of cylinders. However, the PCM is not logging or changing anything in the main or backup VE tables ever. Not in normal operation, not in MAFless operation.

If this doesn't make complete sense, I can tell you that it is pretty complicated and will take a while (several months) to all soak in if you learn at the same speed that I do which is slow to medium.

Hopefully, this explanation lends some insight. I'll try to answer any follow on questions to the best of my ability.

All my best,

Steve

[hpcubed]

set up a map that mimicks the secondary table and you will be good to go.

We are on the same page here got one setup but thanks.

[hpcubed]

hpcubed,
I'll try to answer your question in steps.

For 2000 and before PCM's, the operating systems were structured to have both Main and Backup VE tables. If the MAF frequency monitoring by the PCM determines that the MAF has failed, the PCM automatically switches to the Backup VE table and it will also switch to the Low Octane Spark Advance Table, thus retarding the timing. In this case, the PCM operates in the Speed Density Mode. As you've probably noticed, the Backup VE increments in 10 kPa columns rather than the 5 kPa increments of the Main VE Table. It's really the structure of these earlier operating systems that limit the finesse with which the PCM is able to control the engine in Speed Density Mode, not the MAP sensor or anything else.

Then beginning with the 2001 Operating Systems that were flashed into the same PCM's (same part numbers, etc.) GM Powertrain Engineers had eliminated the Backup VE table. With these Operating Systems fail, the higher fidelity 5 kPa incremented VE Table is used period and the spark doesn't revert to the low octane table either. This more refined means of controlling mixture in the Speed Density Mode has caused some folks who want to remove any and all restrictions to air flow to remove the MAF entirely. This is also the reason that some folks would want to upgrade from the Personal Version to the Commercial Version of FlashScan as it can do a full re-flash of the PCM which includes the operating system. This allows earlier PCM's to have the single Main VE Table with its higher fidelity for speed density MAFless operation. The Workshop Version can do this too. Note, the actual software for the Commercial and Workshop versions allowing full re-flash has not been released yet, but should be "just around the corner."

The Short and Long Term Fuel Trim Values are set based upon the Primary (pre cat) Narrow Band Oxygen Sensors (NBO2). These trim values are constantly being adjusted as long as the PCM is in Closed Loop operation. STFT and LTFT modify the commanded AFR or EQ Ratio determined by the open loop determination of mixture whether that is a blend of speed density and MAF data or speed density alone.

The bottom line is that the PCM logs LTFT data and automatically modifies the LTFT tables for the right and left banks of cylinders. However, the PCM is not logging or changing anything in the main or backup VE tables ever. Not in normal operation, not in MAFless operation.

If this doesn't make complete sense, I can tell you that it is pretty complicated and will take a while (several months) to all soak in if you learn at the same speed that I do which is slow to medium.

Hopefully, this explanation lends some insight. I'll try to answer any follow on questions to the best of my ability.

All my best,

Steve

Good info for the forum. My question was more about the operation of the VE tables with respect to the fuel trims. I guess it is just the way the operating system works. . So yeh, upgrade to the newer operating system. I think a reflash at the dealer is $100 if they will do it. I would like to get a 2 bar map and the maf going symultaneously. So if we can get our hands in that operating system, it might be worth another $300.

[wait4me]

Good info for the forum. My question was more about the operation of the VE tables with respect to the fuel trims. I guess it is just the way the operating system works. The backup VE provides a safe way to limp home with the check engine light on. I say this because the stock backup VE table is more rich than the main..... So yeh, upgrade to the newer operating system. I think a reflash at the dealer is $100 if they will do it. I would like to get a 2 bar map and the maf going symultaneously. So if we can get our hands in that operating system it might be worth another $300.

Um guys.. I program everyones computers to the latest sps cal or to what ever operating system they want for free, They just have the return shipping of coarse, Which is 7.70 for two day priority anywhere in the us :) Or if the operating system you have is not supported yet by efi i will set it up for a supported operating system.. :) just email me at jessebubb@yahoo.com And ill get you guys taken care of. $100 dollars to reflash the computer at a dealer is wayy too much.. Thats why i do it all for free. jes

[Steve Bryant]

HPCubed,
I probably misunderstood your question. Sorry about that.

So do you want to know about setting up the VE Table by using LTFT?

Wait for Me,
Do you work at a dealership or have access to a Tech II and the Factory Cals?

Steve

[wait4me]

:) i have my own tech 2 and sps.

[Steve Bryant]

Cool! 8) 8) 8)

Steve