Just got my car modded and running and went out for some test runs, monitored with Datamaster. At about 8.5 to 11% throttle I'm getting BLM's of about 116. They range at light load between 115 and 120. BLM's go to 128 at about 30% throttle. I guess my question is in the MAF sensor calibration table in Tunercat, how much should I adjust the gm/s in each frequency range.


1995 Z28, SLP ram air hood (functional), SLP mid length headers, Loudmouth exhaust, Hotcam kit, 1.6rr, lt4 knock module, MAF w/screen, MSD 8.5mm Superconductor, AC R44LTS, Edelbrock heads (full P&P), 58mmTB, 3.73.

 

Are you running the stock MAF still?

 

Yes, STOCK remanufactured MAF w/screen.

1995 Z28, SLP ram air hood (functional), SLP mid length headers, Loudmouth exhaust, Hotcam kit, 1.6rr, lt4 knock module, MAF w/screen, MSD 8.5mm Superconductor, AC R44LTS, Edelbrock heads (full P&P), 58mmTB, 3.73.

 

Ok. You won't need to change the MAF frequency values unless you are using a different MAF.

To fix your long term BLMs, you need to tune your VE tables. But, at 116 they are still within the PCM's range of self-correction so it won't make a huge difference unless you are having part throttle driveability problems.

 

I assume since the BLM readings show that the engine is running rich, to correct this I should lower the VE in the respective tables?

1995 Z28, SLP ram air hood (functional), SLP mid length headers, Loudmouth exhaust, Hotcam kit, 1.6rr, lt4 knock module, MAF w/screen, MSD 8.5mm Superconductor, AC R44LTS, Edelbrock heads (full P&P), 58mmTB, 3.73.

 

Yes.

 

Thankyou. I'll give it a whirl.

1995 Z28, SLP ram air hood (functional), SLP mid length headers, Loudmouth exhaust, Hotcam kit, 1.6rr, lt4 knock module, MAF w/screen, MSD 8.5mm Superconductor, AC R44LTS, Edelbrock heads (full P&P), 58mmTB, 3.73.

 

I had always read that the VE tables made no effect for the 94-95 OBD1 PCMs unless SD mode was used? incorrect?

 

I've read conflicting information on this, but my own tuning experiences showed that changing the VE tables changed my fuel trims on my 1994 Impala SS (I'm running a MAF setup). Furthermore, by tuning the VE tables I was able to tune out a stumbling problem I had. So, it would seem the VE tables do have some effect.

Having said all that, I doubt changing the VE tables actually changed my closed-loop AFR unless the VE table was so far off that the PCM was at its limit of being able to compensate (e.g. BLMs bottomed or topped out). It corrected the driveability problem because I was able to smooth out the VE table transition from one BLM cell to another.

 

Actually after adjusting the ve tables with VEMaster no changes were made to my engines BLMs. But adjusting the MAF calibrations down 7% brought up the BLMs from 116ish to 128 left and 122 right. I adjusted the right bank fuel trims down 3% and that evened things out at 128 BLMs through the mid operating range. Getting BLMs of 124 near idle or 0% throttle.

1995 Z28, SLP ram air hood (functional), SLP mid length headers, Loudmouth exhaust, Hotcam kit, 1.6rr, lt4 knock module, MAF w/screen, MSD 8.5mm Superconductor, AC R44LTS, Edelbrock heads (full P&P), 58mmTB, 3.73, Edelbrock torque arm, SLP panhard bar, Bistein suspension. Stock tires. 13.56@100mph. 0-60 in 5.6

 

Very interesting! How much did VEMaster adjust your VE tables? I went back and looked at the changes I made to get my BLMs inline. At 2000 RPM, when my BLMs were rich, the first 5 entires for my VE table were:

53.1 56.3 59.8 60.9 61.7

After spending an afternoon on them, they were:

44.9 45.3 45.7 46.5 47.7

On a percentage scale, the reduction was:

-15% -20% -24% -24% -23%

I made these changes by hand, in response to how quickly the BLMs went away from 128. Looking at my records, I made at least 10 different changes to the VE tables that day. And my recollection was that I had only gotten the BLMs up to the 120-124 range - more tuning would have gotten it closer.

Thanks for sharing your experiences.

 

VEMaster only changed the table in the mid section only about one to three points. I don't have alot of experience with this so I didn't want to tackle the settings on my own. However screwing up the MAF tables seemed to me to be more logical. For instance, from what I understand so far the ECM is going to calculate the amount of fuel to dose based simply on the amount of air flow it senses coming into the intake and maybe the intake pressure (or actually the lack of). I'm assuming that the BLM's are being calculated based on input from the O2 sensors. Now, also assuming that both the MAF sesor and O2 sensor read perfect the ECM should calculate a perfectly stoic mixture. But if one or the other are wrong the mixture will READ anything but. I,m not sure but I do not believe or cannot be made to believe that all MAF sensors were created equal. I can put certain faith in the O2 sensors judging by the previosly blackened condition of my spark plugs, the BLMs of 116, and the bitching my wife makes every time the smell of raw unburnt fuel drifts from the garage into the house. I,m going to do some more work on this, but I now think calibrating the MAF is the best option.

1995 Z28, SLP ram air hood (functional), SLP mid length headers, Loudmouth exhaust, Hotcam kit, 1.6rr, lt4 knock module, MAF w/screen, MSD 8.5mm Superconductor, AC R44LTS, Edelbrock heads (full P&P), 58mmTB, 3.73, Edelbrock torque arm, SLP panhard bar, Bilstein suspension. Stock tires. 13.56@100mph. 0-60 in 5.6

 

The way vgeglia was suggesting you tune was assuming your ECM is operating in Speed-Density mode. In this case, it would be using Throttle Position, RPM, and MAP Sensor inputs to determine the mass of air entering the enginer at any given time. Altering the VE tables here would change the Volumetric Efficiency constants that the ECM uses to make that calculation at various RPMs and loads. The MAF calibration would play no role.

The way you're tuning is assuming that the ECM is operating in MAF mode, where the only input used to calculate (measure, really) air entering the engine is the MAF sensor itself. VE tables being unused, your alteration to them had no effect.

Both use feedback from O2 sensors to adjust A/F ratio by means of long ans short term corrections (BLMs), at non-PE mode conditions anyway.

There's debate and various reali-life evidence showing that different cars operate in different modes, so whichever works for you, works for you. MAF is theoretically more robust, so consider yourself lucky that you can tune that way (until you move up to forced induction )

 

How did you adjust the "right bank fuel trims?"

I've got split BLM's and this would probably help me.