My STerms are maxing at -35%, my LTerms are at -15%.

I've tweaked my injector constant and that's helped, but is there somewhere else to adjust my closed-loop fuel ratio?

After my LTerms max, then my STerms max, the car bucks and stumbles. Checked for leaks, etc., but none to be found.

 

What about the O2 sensors? In my 94 Formula, I had a bad oxygen sensor and it really made it run FAT and like crap. Not saying it might not be in the tune either, but just something to check.

 

I had a bad B1S2, replaced it, but it's still running rich. Other O2 sensors are flip-flopping (100-900mV) as normal.

 

Might want to mention the specifics of the car.... year, engine, etc.

Did you check fuel pressure? Did you check the calibration of the MAF (if it has one)?

 

1996 Z28/SS - OBDII

Upgrades:
383 c.i. with JE Forged -31cc pistons (9.1:1)
mild CC-304 cam
LT4 Heads and Intake, ASM 54MM TB
P1SC 8# with Twin IC, headers
42# injectors
stock MAF, Stock MAF table settings
M6

--Fuel pressure was set at 43 a couple of months ago, it was off at the time and was reset. Moved again? Unknown at this time.

 

you can scale the MAF table to get your fuel trims in line, basically you look at what cells it is rich in and then adjust the values for those MAF readings. you have to do this correctly though, i.e the curve has to be smooth you can't just change one or two values by a lot

 

I've never adjusted the MAF table. Do you add or subtract? Follow my logic here...

If I add a couple of grams/sec at a given frequency from stock: 10.46@2896 hz to 12.00 @ 2896 what would the result be?

Correspondingly, if I subtract a couple of gm/sec to 8.50 @ 2896 hz, what would the result be?

I can certainly smooth out the curve, but should it be modified in 10% increments, or higher/lesser?

My assumption is that if I ADD value to the MAF table, the PCM assumes there is more air, and running leaner, it will add more fuel??? If I SUBTRACT air from the table, the PCM will assume there is less air, running richer, and subtract fuel to keep 14.7:1. Correct?

Also, how do I determine what cell(s) are affected? With AutoTap I can see the airflow rate (gm/sec) and I assume that's the MAF table presenting the data via the MAF sensor frequency. It's all over the map when driving, so I have to establish a range.

 

Very good questions man, Im doing part throttle tuning as well. But i was told that you want to actually divide the gm/sec by 128 and then scale the maf table by what ever you get. if that makes sense?

 

Basically yes you look at what the afgs is at a certain point and then look at the fuel trims at the same point. If the fuel trim is above 128, then the computer is adding fuel to correct a lean condition, so what you want to do is increase the MAF table value around that afgs entry so the pcm reads more air and adds more fuel. If the value is below 128, decrease the MAF value around that afgs range.

As far as home much to modify it, I've found that a good starting is to note how much percetn away the blm is from 128, then scale the values around there by the same %, then smooth the curve some.

 

Only difficulty in your approach is (I assume) you are referring to OBDI, not OBDII.

 

yes, didn't realize you meant obd2, the logic should be the same though, and since you have the fuel trims in a percentage reading you already have that info.

 

I had same problem (97ss - 383 - D1 obd2 - 72# inj). Closed loop pcm fuel afr way to rich. I dropped the MAF curve 2% with LT1 edit ver_2.2. Also, adjusted the MAP BLM update to trigger @ 60kpa. It really helped afr. Corrected the afr from 10 to 13.5 @ part throttle cruzing. Not ideal, but, runs much better. Also, idles @ 14.5 afr now. I have a wideband dynojet O2 which was very helpfull in the tune. Also adjusted PE vs. rpm @ WOT afr rich problem due to boost ref fuel regulator. Hope this helps. B.

 

Back sensors are only used for detecting the health of the cat. They do NOT contribute to the AF ratio.

Now it makes me wonder about everything you have/ done/ know??????

Why would they still be there in the first place??????

Think you ought to give your PCM to a tuning guru to set it up to your specs. Then you are closer to where you need to be if you have to "tweek" it.