I have reset the BLM boundaries a couple of times. Current settings:

MAP
RPM 30 60 80
1000 X X X
2000 X X X
3200

The scan tool reports cell numbers that should be different. The X marks are all reported as BLM cell 4.

What gives? Anybody have any ideas.

I use pocket programmer to burn the chip.

thanks

 

I don't believe there is a bug in TC...although the ANHT Hac for MAP setups did have an error in it with regard to BLM cell boundaries.

Have you ever gotten out of cell 4? Cell 4 is an idle cell...some things like VSS are necessary to get things out of that cell.

Also, here is an example of driving around under a bunch of conditions, stop and go as well as steady cruise. Click the pic to make it fullsize. http://forums.corvetteforum.com/zerothread?id=568584

Could probably set up a histogram or something in a spreadsheet program that would do the same thing so you get an idea of which cells you are hitting more than others.

Good luck, Matt

 

Skip,

This confused me at first also. I found my answer on the thirdgen.org message board:

It's what's called the "forced Idle cell" constant. On the 91, fuel cell #4 is called the idle cell (Constant in Tuner Cat: Force BLM idle Cell CCP % D.C. threshold). Even though you are not at the conditions (MAP vs rpm), the computer forces the trims from that area of the fuel table during idle when the CCP duty cycle is below a certain threshold (i.e. 14.8%). I've change mine to 0 %. This deactivates this condition.

This makes tuning more understandable and you will might see cell #8 if your MAP is high enough at idle.

Beth


[Modified by Beth396, 11:29 PM 11/11/2003]

 

Wow- thanks to both of you. Obviously, this is not a new issue.

Exactly. Your other post with the cell counts looks very similar to how mine would look. I will record them when my software arrives. Although I would have more 14s. The other thing that has been bothering me is that I have no cell 15s. Everything less goes to WOT condition, but I haven't seen a cell 15. Although I don't think I've recorded anything above 5000 RPM.

Beth, you are brilliant. This is one of those constants that I suspected was messing things up. I will turn it off with all the other things I seem to be turning off.

I am at the point where I am going to set each table to a single value and start from scratch.

Constantly adjusting the MAP and spark tables is getting silly without adjusting some of the base table values. I made minor changes to the "Injector PW Correction vs Battery Volts" table and the "Low Pulse Width Injector Offset vs. BPW" table. Instantly my rich BLM/INT values went to lean.

In addition, turning off all the EGR values has helped.
-------------

Holy hex code, vettepersons, all these tiny delta adjustments for the original OEM product. This is a bit over kill on the fine tuning. I guess teams of EEs need jobs in Detroit, too.

thanks again, fellow vetters





[Modified by Skippy Stone, 6:36 PM 11/11/2003]

 

Morning Skip,

Brilliant-No, diligent-Yes. That forced idle cell threw me for a loop. I still don't understand the purpose behind it....If the CCP (charcol canister purge) duty cycle is less than 14.8% then use fuel trims from cell 4?? Why? After deactivation of this parameter, I haven't noticed any difference except the data logs make more sense.

I also don't understand the purpose of the BLM boundries. We have a fuel table(s) that is broken up into individual cells and each one has a "fuel trim" which is the correction to the base pulse width (BPW) for that particular rpm and MAP (or MAF).

The volumetric eff. table (fuel table) is a 13X13 matrix with 169 cells. The extended volumetric eff. table is 9X11=99 cells. So if your at a MAP of 55 kPa and at 2000 rpm, the fuel correction will be from that indivdual cell in the extended fuel table (plus overlap interpolation I gather from research). So what if I'm in fuel cell #6, what does it matter except to give a general idea on where you are in the fuel matrix.

Maybe DrJ can give us some ideas. The algorithm probably uses the 0-15 fuel block numbers.

Beth

 

BPW, heh? Well, I am lost on this one. In TunerCat, is this from the crank PW table or calculated from the injector size constant? Maybe I'm going blind, but I don't see a simple base width field or table.

You don't like being called brilliant? Or you are just honest?

 

I read the fuel injector pulse equation post and it appears it uses the injector size constant. I was just confused because TC sometimes use PW tables and other times it doesn't.

Now I'm trying to track down the TRUE resistance of my Ford 30#ers verse what GM used for the 22lbs that were original equipment. The ZR1 injectors were different and examining a zr1 EPROM shows different calculations. Hmm.

 

OK, I see where my name has been taken in vain.

My boat is finally ready for storage, and parts for
my winter car projects aren't in hand yet; so I have
a little free time to read posts here.

Seems like you both have tuning questions - sorting out a new
cam & heads can be rocky the first time you try it.


Here is a little info that may help answer some Q's above:

1. Interpolation for the 3-D VE tables was mentioned.
The best discussion I've seen for the process is here:
http://forums.corvetteforum.com/zerothread?id=547494

How it works is also in the $8D code, but this write up is much
easier to follow.

Tell you the truth though, interpolation is more of an academic
tweak than something critical to basic tuning, IMHO.


2. BLM cells have nothing to do with the VE tables; their actual
use was stated somewhere above. Mainly BLM cells smooth
fuel transients while driving - I've not found them of great
importance in getting the spark & fuel set so an engine runs well.


3. If you are stuck in Cell 4, I'd hypothesize (lacking any real data
to go by) that you are probably running under the 'Closed TPS'
spark and fuel parameters.

The permissives to get out of the idle cell are in the
TC constants table - generally you need to show a few
% open on the TPS AND a few mph on the VSS to get
out of idle control.

Are you by any chance using some oversized aftermarket throttle-
body? If so, you may not be showing enough TPS opening
to get out of the idle cell until you have built up quite a few
RPMs. The engine probably isn't going to like that much.


4. I put a few of my own Tuning notes on the page here:
http://www.corvetteforum.net/c4/doctorj/cartest.htm

You may find something helpful there, maybe not.

If you are interested in further reading, here is some additional
unsolicited advice :):

I recommend rigorously reading the 'Part Throttle Tuning' posts
referenced on the 3rd Gen site. Until you have the spark & fuel
curves under control at idle & low RPM, there is no point in worrying
the high RPM areas. Making mistakes at low RPM is expensive enough.

URLs to the 3rd Gen site, AKM, free scanners, and many
others are found in the FAQ for this forum.


5. Someone mentioned using the injector 'low batt voltage pw offset' tables to
lean out fuel. THIS IS A VERY BAD THING TO DO, unless you greatly
enjoy spending time with auto parts dealers and their spawn.

Also, inj ohms have little to do with their opening (latency) time unless
you somehow got hold of some low-impedance inj's (3-4 ohm). If you
bought 30# SVO's they are just going to be difficult to control at idle - at
least on a 350 with a large cam. 24# usually are easier to tune, especially
with high efficiency heads.


I really don't spend a lot of time on CF - if you have further Qs feel free
to drop me an e-mail. I'll try to answer if/when I can.

YMMV.

Have fun.
DrJ


PS

Oops - one thing I forgot to post - there was a mention above of the
'VE tables modifying the bpw'. The useage there is not quite 100%
accurate (using my diplomatic voice) to the way the system works.
While the correct usage is only slightly different, it is critical to
how the ECM operates; understanding its operation is in turn critical to
successful ECM tuning. The difference is this:

The VE table is the bpw. That is to say, there is a different bpw
(base injector pulse) necessary for every rpm, MAP, and temp at which
the engine operates, per GM's programming syntax. The 3-D VE table
is simply a manifestation of what the fuel load looks like; injector pulses
are the realization of fuel load in terms of physical (flow) control.

In other words, bpw is a variable - in fact, it's THE variable on
which the fuel injection system depends for its operation. It is on that
bpw variable that modifiers like BLMs, AE, PE, DFCO, cold start, flood
clear, etc operate - to result in the commanded injector pulse (ie fuel load).

I made a longish post recently that spoke to how the bpw is calculated -
it's around here somewhere :). Forgive me if the writing was not clear,
assembly code is not my native tongue. Fuel load is essentially
proportional to Air Flow via the Air/Fuel ratio. Since they are
proportional, the VE graph represents BOTH AIR AND FUEL loads in
pictorial fashion.

Hope that helps.

edit: add random lines of emphasis & addendum for author brain-fade


[Modified by DOCTOR J, 1:26 PM 11/14/2003]

 

I usually do better searches. I'm suprised I didn't see this post before. A couple things jumped right out at me:

A. In the assembled code the order that values are pushed on the stack appears to bias tables to KPA and not to RPM. I have been assuming the opposite.

B. -400 RPM from the table biases the ratios.

C. There appears to be a rounding bias becasue of subtracting Max value then using that absolute value in the following stack push.


I suspect I did the opposite of what I should have and raised these values.

My new engine set-up is extremely efficient. Pumps tons of air for a 350ci. First short highway sets indicate over 35mpg. Normal street driving - the throttle never gets to 20%. 65mph in 5th is 4% throttle.

Good info. I hope it doesn't make me buy a bunch of test equipment.

 

quote:
________________________________________ _______________________

The VE table is the bpw. That is to say, there is a different bpw
(base injector pulse) necessary for every rpm, MAP, and temp at which
the engine operates, per GM's programming syntax. The 3-D VE table
is simply a manifestation of what the fuel load looks like; injector pulses
are the realization of fuel load in terms of physical (flow) control.

In other words, bpw is a variable - in fact, it's THE variable on
which the fuel injection system depends for its operation. It is on that
bpw variable that modifiers like BLMs, AE, PE, DFCO, cold start, flood
clear, etc operate - to result in the commanded injector pulse (ie fuel load).

________________________________________ _______________________

I agree, I didn't mean to confuse you, Skip, I've been away from the tuning "thing" for awhile. Ideally, if nothing changed except RPM and MAP and if the VE table values need no adjusting (fuel trim) to get to AFR=14.7 then the value in the table is used in the BPW calculation.

Ideally (but not realisticallty) your fuel trim adjustment is zero....or close to it. That is what your doing when you monitor long or short term fuel trims and then make a modification to the VE table based on your logged data.

Please feel free to correct anything I post here.

Beth