Lafngas93z28

iTrader: (1)

Have a 96 Impala with TrickFlow 195 heads, 230/236 .560/.565 @.050 on a 114, longtubes(tri-y) and full Hooker Aerochamber exhaust. Tuned in speed density and runs GREAT, but doesnt start well after warm up. Tried turning MAF back on, starts great but runs like POO! Any help would be greatly appreciated! BTW, I'm using the JET software for tuning....Thanks

96capricemgr

iTrader: (1)

If the MAF is not modified I would not be trying to "tune" it. Sounds like a fuel tuning issue to me and possibly you have an aftermarket TB that needs IAC system attention.

F0x Slaughter

Data log the car if using DataMaster, its AFGS to look at. Check the BLMs, when lean look at the AFGS. Go into TunerCat, go to the MAF tables, find the closest number to it. If its lean you need to add to it, if its rich remove from it.

When scaling 1.xx will increase (richen) .xx will lower (lean out).

WS Sick

I agree with 96capricemgr here. The MAF tables are supposed to be a definite figure, if it is working properly then no need to change MAF tables. What method for SD tuning did you use, Gregrob has a very comprehensive method he has spoke of many times on this forum. Search out his name on the subject.

F0x Slaughter

The MAF needs to be tuned for changing things.

"MAF Sensor Tables

There are four tables for the MAF, which split up its total frequency->airflow grid.

First, find the airflow reading for your idle in your logs. Then, find the closest value(s) in the MAF sensor tables; you will sometimes have to alter two cells to affect one airflow range.

To richen your fuel mixture (BLMs > 128), increase the value(s) you found as mentioned above.

To lean the fuel mixture (BLMs < 128), simply decrease the appropriate MAF cells as mentioned above.

These values are also efficiently modified using percentages (%), or multiplying the values (1.xx to richen, 0.xx to lean). Start with 1% (1.01/0.99) changes for every 2 BLMs off; so, a BLM of 118 would require a 5% decrease (128 - 118 = 10 / 2 = 5), or multiplying the MAF airflow value(s) by 0.95. Again, trial and error will be needed to see if you have overshot a BLM of 128 with your changes."

From Solomon, a well known LT1 tuner.

96capricemgr

iTrader: (1)

I understand lying to the pcm about airflow can be used to modify the AFR. I am saying that IMO it is better to change the commanded fueling for the measured airflow.

Basically don't **** with the sensor readings fix what the pcm does with them.

F0x Slaughter

Then while running the MAF how would you tell it to change the AFR?

Considering in closed loops you use o2 sensors, ECTS, and MAF to adjust the AFR.

WS Sick

VE tables. If you get those nailed the only real place you may have to "trick" the car would be at low airflow levels.

F0x Slaughter

VE is when in Speed Density. For instances if the MAF fails, or when entering PE mode, or in Open Loop. They will not effect AFR when running MAF. The PCM doesn't even look at those tables, it just uses sensor inputs.

gregrob

iTrader: (8)

This is not correct. By that logic you shouldn't change the VE table either or you are "lying" to the PCM. The truth is when you make modifications that affect airflow, even something as simple as a CAI, you need to correct the MAF calibration.

F0x Slaughter

Exactly. Why do you think companies sell a MAF and a CAI Tuned MAF. Most people will install a CAI but not rebuild an engine so to correct the amount of airflow they sell pretuned MAFs for those people. But those of us who will extremely modify an engine know the MAF has to be tuned to be used properly.

If you don't want to change the MAF then delete it, and run Speed Density. You do realize before MAF sensors, cars running fuel injection, cars just ran Speed Density and Speed Density as I stated is only back up for if the MAF system fails?

(Not directed to Gregrob but to the others)

I bet if you looked at your tune, since you two probably didn't tune it yourself, if you are running a MAF it will be different than stock.

2.45
2.88
3.34
3.87
4.45
5.12
5.85
6.64
7.49
8.41
9.40
10.46
11.60
12.82
14.11
15.48
16.98
18.60
20.34
22.22

That is the stock on MAF table 1.

gregrob

iTrader: (8)

Speed density isn't strictly a backup... the car doesn't determine fueling solely on MAF input, although it is the primary source. It uses manifold pressure and predicted airflow (VE) as well.

I do agree though if you want it to run properly MAF calibration is essential
If you're not willing or equipped to do that then delete it and run in SD only.

WS Sick

Thanks for clearing that up. I absolutely understand where you are coming from about the MAF tables, I just like to not touch them until the last resort, on my particular cars I havent had to tweak them except down low.

96capricemgr

iTrader: (1)

I understand MAF tables can need tweaking if their ducting changes because that does affect the reading.

I still argue that using that for the main fueling correction is the wrong way to go.

gregrob

iTrader: (8)

First off are you talking open or closed loop operation?

Let's say you're talking closed loop non PE mode operation. You go through the VE tuning process and have the as close to 0% correction STFT and LTFT as is possible.

Now you reenable the MAF and suddenly your trims are way off. Are you to then go again to the VE tables and force them to predict an inaccurate airflow amount, so the fuel trims come back in line?

I would rather tune the MAF as is the proper way, until closed loop operation both MAF and speed density overlay nearly seamleassly.

The same principle applies for enrichment mode as well. If you are commanding X wot AFR and not attaining it WHEN the VE fueling is correct then you need to work on the MAF calibration until desired matches actual output. NOT provide incorrect numbers to the VE table or PE mode adjustment tables.

WS Sick

You need to write an E-book and sell it.

WS Sick

Fox I tuned my car myself thank you. No need for cendescention.

F0x Slaughter

Then you should know you need to alter the MAF frequencies.

WS Sick

I will as soon as I buy the aftermarket modified MAF........