Quick question about Long Term Fuel trims

[BRD-PREY]

If Long term trim reads -7.20 then my computer pulled 7.20 % from the fuel.
another words it was running rich. If Commanded AFR was 14.63 or Equiv 1.0, then I was running at 13.57 or .928EQ. Did I interpret the data correctly?
Ed

[WeathermanShawn]

If Long term trim reads -7.20 then my computer pulled 7.20 % from the fuel.
another words it was running rich. If Commanded AFR was 14.63 or Equiv 1.0, then I was running at 13.57 or .928EQ. Did I interpret the data correctly?
Ed

Ed, you have the general premise correct, with one big exception. The PCM has had to decrease the Injector pulse width by an average of 7.20% to remain stoich.

So, in reality your AFR stayed stoich..fuel was just pulled to keep you stoich. Your AFR would not go to 13.57..it would still be ~14.63..

[joecar]

It would have run rich if the trim did not correct it... so like Shawn said it stayed at stoich (it is not rich because the trim prevented it from going rich as soon as it started to go rich).

It means your airmass calculation is 7% too much air.

[mr.prick]

What injectors are you using?

[BRD-PREY]

stock injectors, I'm in the process of recalibrating a 100mm maf for a custom air box. Interesting is the fact the table I got for the MAF guy Bruce at POWRMAF were way under what ended up being close. I'm still tuning but if someone is interested then I will post the custom Ram air box and MAF setup with more specifics.

Thanks for your answers I just miss typed I knew the PCM drove it to Stoich. I just want to make sure which direction and the proportional part. In short I'm going to lower my air flow at the MAF freq that had lower (-) numbers (richer) by the percent of the LTTrim and raise the air flow at the freq that had positive numbers.
PS my B120(?) MAF only rpm normally set at 4000 I have set to 600 rpm so my trim should only be based on maf numbers right?
Ed

[joecar]

Yes, from 600 and above it is using MAF only.

[WeathermanShawn]

I don't use LTFT % (BENS) for the 'upper portion of the MAF Frequency. That won't be accurate.

Its very important to maintain the 'slope' of the entire MAF curve, or your WOT fueling can be way off. For a more advanced discussion, see these Summary Notes: (MAF Tuning): http:///forum.efilive.com/showthread.php?16280-CALC-VET-Summary-Notes (http://forum.efilive.com/showthread.php?16280-CALC-VET-Summary-Notes)

[BRD-PREY]

I have B3647set to what I want for enrichment, B3618: PE Modifier Based on Rpm (EQ): is set to 1.0 . With B0120 set to 600 rpm it will still use table b3647 right?

[WeathermanShawn]

I have B3647set to what I want for enrichment, B3618: PE Modifier Based on Rpm (EQ): is set to 1.0 . With B0120 set to 600 rpm it will still use table b3647 right?

Are you comparing Commanded EQ to Actual via wideband?

[BRD-PREY]

yes, I'm asking if commanded EQ is 1.13 in B3647 for 4400rpm at 80- kPa. Then when my engine is at 4400 rpm 80- kPa even in MAF only mode I still have 1.13 commanded right. Right now all of my PE are set to 1.0. So all of my commanded fueling is a reflection of B3647 if my coolant temp is in range. What I was asking is with VE off by setting b0120 to 600 rpm I'm still driving commanded fuel by B3647 right.
In summary should I ever have anything other than 1.0 in my PE tables?

[WeathermanShawn]

I can not find B3647..:confused:

Is this a COS?

IMO, when MAF is enabled B3618 dictates Commanded Fueling. Your OS, may be different, but personally I would modify your B3618 as your Commanded Fuel.

[BRD-PREY]

This is my table.

[BRD-PREY]

Yes I have COS5 my bad. I should have said something. I'm pretty sure I've got it correct, but you never know.
Ed
Joecar help! Does b3647 function in MAF only. Should I leave PE at 1.0?

[joecar]

I have B3647set to what I want for enrichment, B3618: PE Modifier Based on Rpm (EQ): is set to 1.0 . With B0120 set to 600 rpm it will still use table b3647 right?
Yes, in OL it will use B3647.

Remember: MAF and OL/CL are independent of each other.

So with B0120 set to 600, PCM does this:
- above 600 rpm PCM reads MAF (and ignores VE) and computes cylinder airmass,
- PCM determines whether it should be in CL mode or OL/PE mode,
- for OL/PE mode, PCM sees B3647 is richer than B3618, so it uses B3647 to command fuel.

[joecar]

yes, I'm asking if commanded EQ is 1.13 in B3647 for 4400rpm at 80- kPa. Then when my engine is at 4400 rpm 80- kPa even in MAF only mode I still have 1.13 commanded right. Right now all of my PE are set to 1.0. So all of my commanded fueling is a reflection of B3647 if my coolant temp is in range. What I was asking is with VE off by setting b0120 to 600 rpm I'm still driving commanded fuel by B3647 right.
In summary should I ever have anything other than 1.0 in my PE tables?Some people set their PE table to look like the last two columns of B3647.

[joecar]

I can not find B3647..:confused:

Is this a COS?

IMO, when MAF is enabled B3618 dictates Commanded Fueling. Your OS, may be different, but personally I would modify your B3618 as your Commanded Fuel.Yes, B3647 is the COS version of B3605.

B3647 is looked up using RPM vs MAP, gives more control over commanded fuel, but requires ECT multiplier table.
B3605 is looked up using ECT vs MAP.

[joecar]

Yes I have COS5 my bad. I should have said something. I'm pretty sure I've got it correct, but you never know.
Ed
Joecar help! Does b3647 function in MAF only. Should I leave PE at 1.0?B3647 functions in VE and MAF modes.

The richer of B3647 or B3618 is used to command fueling...

altho Shawn did make some curious observations with B3618 set to 1.00 while running from the MAF.

Also, be aware that any cell in B3647 that is 1.00 will cause STFT trimming while in OL, this causes wideband BEN to be 1.00... you want to avoid this by avoiding 1.00 (use 0.99 or 1.01) in B3647.

[joecar]

Your MAF table is wrong, Shawn said above that the "slope" of it must be maintained (the "slope" is a 3rd order polynomial curve... look at the GM stock MAF table, your new MAF table must have a similar constantly increasing slope/curve looking like the GM table, except the whole curve shifted up/down/left/right).

[joecar]

...
altho Shawn did make some curious observations with B3618 set to 1.00 while running from the MAF.
...You can test this out... (post some log/tune files)...

set B3618 to 1.00 and do a logging session; then in this log look at GM.EQIVRATIO when PE conditions are met (as in B3616), see which of B3618 or B3647 it follows (using the scantool->tunetool dynamic cursor linking feature)... when PE conditions are met, if EQIVRATIO is 1.00 then it follows B3618 (this is bad, not enough fuel), otherwise it will follow B3647;

Shawn says that EQIVRATIO will stay at 1.00... but do the experiment since there are conditions to this that we are not aware of, such as FUELSYS may not necessarily say OL, but OL-drive... or even CL in which case B3618 is commanding fuel (so it should be set sufficiently rich, i.e. same value as last 2 columns of B3647).

[joecar]

B3647 is the COS open loop commanded fuel table, it functions during OL in both VE and MAF modes.

B3605 functions the same.

[BRD-PREY]

I think I see what you are refering too. I recurved the top. This is a graph with my old factory MAF curve on the right. I left the bottom anomolies in the curve as I felt they were the result of measured data.
ED

[WeathermanShawn]

This forum is lucky to have someone with Joecar's knowledge. One of the ways Joecar probably learned was that he logs almost every day. It would be real easy to do the experiment Joecar was referring to and then see which Table is controlling.

Try making one Table richer and then see. Some OS's may differ (as I found in the 2002 Camaro). Try his experiment. Thats the best way to learn.

Good luck..:)

[joecar]

Thanks for the kind words :cheers:

I don't know that much, but I do log every day, and I read everyday, and I compare other people's observations/experiments with my own... it is an on-going learning experience, I see myself continually doing this until my very last day :)

I've done that experiment in SD (MAF-less) mode, I will repeat it in MAF mode, soon.

[JOHNBOY]

This is my table.

Can you post a picture of how the MAF is installed and the air box mods? My guess is your getting some poor airflow due to placement. If your MAF is close to a sharp edge leading in or right after a 90 degree bend you can get some goofy reading like that. Some times simply rotating the MAF is enough to get it in cleaner air flow. Other time moving the MAF so there is at least 6" of straight tube in front of it helps a ton. That is not always possible. In my 2004 Suburban the is an air lense before straighten out the airflow before it enters the MAF. The MAF is less that 2" form the opening in the air box that is less then friendly to airflow. The Lens straightens out the tumble and allows the MAF to do its job.

[BRD-PREY]

The output of the airbox going into the MAF tube has a honeycomb laminar flow straightner. The Original F-body never had the required straight sections before and after the MAF sensor. That's why they had a screen on their MAF. I totally agree that uneven airflow is the culpret for bumps or anomalies in my maf table. If no anomolies existed you could just use a formula instead of a flow table.
In the big scheme of things why would you want a setup that adds accuracy to a sensor but decreases the amount of air that is availiable for cylinder filling.
A section of straight pipe in front and behind the maf would have to be how big before adding no flow resistance to the air mass that reaches the 92MM throttle body.
Most vehicles where the person adds a bigger intake and throttle body they use close to the same size intake plumbing.
My Airbox has seals that seal it to the hood when closed and the hood has the 2 original ram air scoops and 2 additional ovals on the bottom side. The airbox output is 104.1mm into the 100mm MAF into the 92mm TB. My goal was that the TB actually the TB Blade be the only restriction to airflow.

I'm not sure but I have evidence now thanks to EFI_live that I'm on the right track:
(but only if I read the evidence correctly)
The table for the MAF I purchased for my application states that I will have at:
1500 hz 3.18 g/s
4500 hz 37.62 g/s
My application has:
1500 hz 5.06 g/s
4500 hz 76.39 g/s

Now I realize my motor is still only taking in what in neededs but the MAF tube is the same diameter in both applications.

In fact the table for this MAF Sensor with a 441cuin LSX stroker had very similiar numbers.
1500 hz 5.21 g/s
4500 hz 69.16 g/s

I don't know what type of intake plumbing the other 2 applications had.

I don't have any definitive reasons for the numbers maybe air velocity, maybe airflow while straight because of my laminar flow straightner is not equally distributed.

I don't have all the answers, in fact very few of them so and thoughts or discussions are welcomed and encouraged.
Ed
At least I get good honest discussions here, on LSTech they want to know where I bought the black wrinkle paint!

[joecar]

Hi Ed,

Question: you're only using 4 wires on the MAF connector...?

Your plumbing looks sufficiently straight (i.e. no bends).

You can try an experiment: clock the MAF sensor (i.e. rotate it), see if it reads different when clocked to 45° and 90°.

The Calc.VET tutorial corrects the MAF table, the Calc.MAFT tutorial calculates the MAF table from the corrected VE (each of those uses LTFT/wideband, but the procedure can be modified to use wideband only, if required).


BTW: are the ram air hood grilles aluminum (did you make them...?)...? [ sorry, I had ask :doh2: :hihi: ]

[joecar]

The MAF airflow numbers depend on engines actual VE ability (i.e. cylinder airmass ability), and how well behaved the air is flowing thru the MAF (laminar vs turbulent).

[BRD-PREY]

No all 5, I probably took the picture when I was doing the AUTOSD ve.
I already tried the clock thing, it's now at 1:30.
No they are plastic and broken I just got a set of SS ones in, but my time is split between getting ready for Sunday when I pull the t56 and rebuild it and finishing up the custom rain baffle I'm designing for inside the hood.

[BRD-PREY]

ps I looked good catch, yah the wire was unpluged and folded back while I was doing the SD tune. I don't think its necessary but their was enough people saying it had to be unplugged even if you killed the MAF with fail freq I didn't want to take a change.
Ed
PSS It's hooked back up