I guess my first question is what's lean and what's rich with consideration to the INT and BLM? 128 is ideal so if my numbers are low is that rich or lean and vice versa?? Also, with the O2 reading, is that not a good indication of lean or rich?? Mine jumps around so much that I'm not sure sometimes whether the reading is rich or lean. My assumption is that the O2 reading is only a good A/F ratio measurement at WOT and that reading the INT and BLM is a better inication for idle and part throttle tuning. Am I wrong??

 

BLM lower than 128 means you're rich and the ECM is pulling out fuel. By default, the lowest possible BLM is 108 so if you're there with INT's lower than 128 you've exceeded the ECM's ability to adjust.

BLM greater than 128 means you're lean and the ECM is adding fuel. By default, the highest possible BLM is 160 so if you're there with INT's higher than 128 you've exceeded the ECM's ability to adjust.

O2 sensor readings in closed loop are useless for tuning, the ECM ping-pongs between rich and lean by design so you should see O2 sensor readings bouncing back and forth with 450mV as the median.
Sounds like you have the basic hang of it, O2 sensor is marginally useful at WOT as it's not designed to be super accurate. Better than nothing, though. To do WOT tuning the ****-retentive way you need a wide-band O2 sensor.

 

Thanks again for the help. Exactly what I was looking for.

I was running a 355 with 24# injectors and using the stock 305 chip and had my fuel pressure set to 36psi and my int was right around 110 typically.

I finally got tired of replacing my plugs so often from running rich and decided to get an Ed Wright chip. I installed it and bumped my fuel pressure back up to 45 psi. I was playing around with my idle and I specifically remember at one point seeing my int at 86, can't recall the blm at that point. I've since lowered my pressure to about 42psi and I'm gonna do some more scanning this weekend but my mpg is only about 18mpg right now which sucks. Even running rich with the 305 chip I was still getting 20mpg. I still need to take a couple degrees out of my timing which is probably affecting it some but I still think I may have too much fuel pressure due to my injectors being 24# and I'm sure the constant in the chip is set for 22# injectors.

If you take a look at the following post you can see the data I recorded with my scanner in a run down the road.

https://www.thirdgen.org/techbb2/sho...threadid=85056

What's confusing me is that the data shows higher INTs at lower rpms which to me would indicate running lean but the scanner said rich. I'm assuming this is because my BLMs were below 128 indicating a rich condition even though the INTs at that particular point in time were indicaiting lean???????

Also, after I floored it my BLM/INT was at 128/128 for awhile but once I let off and the car shifted to lower rpms the INT went back to lean again. Is it possible to get a 128/128 condition at both idle and WOT??? It sure seems as if I'm having a problem doing this.

 

At WOT your computer locks the BLM's at 128. It no longer uses the O2 sensors. That is why you see that 128 at WOT. Once you get out of WOT your O2 sensors takes over and the computer uses your BLM's to adjust for the amount of fuel.

 

That's what's confusing me. If the computer uses the BLM to adjust for the amount of fuel then why was my INT at 131 and 141 showing the computer is adding fuel when the BLM is at 110 showing it's already rich. Shouldn't the computer see the 110 and say "hey, the ening is running rich I should take fuel out so it's not running so rich" ... and the lower the INT, not raise it???

 

The reason the BLM and INT jump around so much is that there are 16 BLM cells (0 through 15) based on RPM and airflow in grams/second. You'll typically idle in BLM cell 0, and WOT will usually be in cell 15. The BLM will be based on how accurate the MAF Tables are at each particular amount of airflow (not including other variables), so as you're increasing or decreasing revs and airflow, the BLM and INT will vary some, and you'll be going in and out of various BLM cells. Also, it takes a difference of 5 between the BLM and INT to change the INT, so you can have a BLM of 126 and and INT of 132 and that's OK. A couple reasons why you saw BLM and INT values so far apart may have been that they were in different BLM cells (ie: you did not read them at the same exact time), or you just hit a different BLM cell and the computer hasn't adjusted it yet for your now-lean condition. The BLM is typically updated every 1-1.5 seconds from what I've seen in the $6E-code TPI cars. You can get your BLM close to or at 128 in all of the BLM cells, but it'll take some tweaking of the MAF tables.

A point made by Wilson about the BLM locking at 128 at WOT is wrong. If you happen to be in BLM cell 15 and not in Power Enrichment mode (or Highway Fuel mode), the BLM will be updated and this will be reflected in the amount of fuel added once you hit PE mode. The BLM is locked into whatever the last value was in that BLM cell, and the INT is locked at 128 since it's not adjusting the fuel based on that, just based on the BLM adjustment and the PE tables.

 

greg i was reading this post and you have just answered alot of questions for me-thanks for you wisdom. but also raised another question in my head. (BLM will be updated and this will be reflected in the amount of fuel added once you hit PE mode. )
currently im trying to get into burning but have been having a hard time getting some simple answers. but more to my point my car while in cell blk 0 idles very lean (150-160) blm - soo say im at the track-is my car going to run better(theoreticaly) by leaving the line @ 1200 rpm where my blms are (128) as opposed to leaving from an idle where my blms are (150)?
of course all other variables aside,traction,converter flash,ect.

thanks,

 

Nah, it won't make a difference with regard to the BLM since you're in BLM cell 0 at idle and cell 15 at WOT. If you've just started up your engine and haven't gone WOT before launching (except for the burnout), you're BLM will still be at 128 once you hit cell 15.

 

Greg,

I've read other posts where people say that both INT and BLM are locked to nominal at WOT. Leaving BLM where it is/was makes sense from a design standpoint, but that would mean that AFR could only be off by about 4% (5/128) from nominal, based on INT jumping around just before hitting WOT. Could this be peculiar to MAP cars, or is it the same for both MAF and MAP? I know that this is the kind of thing I'll be able to observe for myself in a few weeks, but there's still snow on the ground up here and junk on the roads.

Can you please comment?

thanks

 

The BLM can be much higher or lower than just 5 units away from 128. So can the INT if either the BLM is maxed out or the BLM hasn't updated as fast as the INT is changing. This should be the same from both MAF and MAP from what I've seen.

 

Are you sure that MAF cars use Cell 0 for idle? On the MAP cars I have scanned, idle is Cell 4.

 

I was just wondering that this morning. When I scan, I idle in 4. I cruise in 4 also, for the most part.

350 TPI with the Speed Density system.

 

Well, that was a generalization, since it depends on if the engine is warmed up, what the requested idle speed is, and what the BLM parameters are. As for Synapsis, you might have a VSS issue or problem if all you're seeing is Cell 4, unless it just happens that you idle and cruise in Cell 4 but do "visit" other cells when driving.

 

Nah. I'm usually in 4 or 6 when I'm cruising around.. but I'll go up to 10+ when I'm leaning into it.

Am I supposed to be in cell 0 at idle after warming up?

 

I can understand if the BLM is maxed out one way or the other - what if it's (example) stabilized at 115 and therefore pulling fuel out consistently. When you hit PE mode, doesn't that mean that the BLM has already "tuned" those particular conditions to AFR=14.7 i.e. PE changes are made from that starting point?

 

Again, you may wish to dig into the MAF hacks more and see what happens. Yes, in WOT MAF goes into Cell 15 but it appears to be a "Special Cell" and you are never in Cell 15 except in WOT, so if you are relying on the BLM feature to "self-tune", you are going to be sadly disappointed.

With SD, which has a little more logic than MAF in regards to BLM, WOT and Idle are "Special Cells" and they use Cell 4. There is no learn feature to rely upon. I am still reviewing the actual computer code relating to SD and how it relates to BLM etc and I hope to have more information in the future. Hopefully one of you MAF guys will dig into the code for MAF and report.

But, in my reviewing of various scan data for a buddy of mine that has a MAF car, the only time he is in Cell 15 is in WOT and it appears to be a "special cell".

 

Yeah, I guess that I came to the same realization that I'll have to get into the hacks to understand more. How were the hacks generated? Did someone have to figure out where the code was located in the PCM, download, then disassemble? I understand disassembling, but how in the world did anyone figure out where the code was located?! :hail:

 

Pretty Simple actually. Read the entire Motorola 64K address space. Look for random data, and disassemble it and try to find instructions. Probably a day to months work.
The VERY difficult part is figuring out the algorithms and how they relate to the data sections and I/O. This could take forever. Actually, so far it is taking forever..............that is what one of the things this board is about (I think??).
There is one guy that figured A LOT of this stuff out in the 90's and released it. Smartest ECM person I have ever heard off. Since then, no one even comes close as far as I can see.
Cheers,
J

 

So there's no learning at idle on SD cars? Is idle determined by the park/neutral switch by the ECM?

How much of a 730 bin has been "disassembled" completely? Where can I get this info? I'd be interested in helping figure out the code if I can get some info on the right Motorola opcodes. Is there a post somewhere that tells the processor type...etc?

 

Nope, it's a normal Cell just like the others. I hit Cell 15 on the highway at higher speeds (>70 mph) with a little bit of throttle but still not in PE. It all depends on what the BLM parameters are; mine are >35 grams/second and >2000 rpm (actually 2100 rpm due to the 100 rpm hysteresis). I also hit it in lower gears quite easily w/out going into PE, and have seen the BLM updated.

 

Interesting. Thanks.

 

Yes, the ECM "learns" at idle. Primarily the IAC, which most people forget about.

 

I had a few questions about this I thought could be answered by the tables, but evidently can't. In the blm cell bounderies there are only 3 rpm values, and in the load portion also only 3. How do you get 16 cells out of this and what are the locations, boundaries of these cells? Also how big of a step (%A/F) is there in a delta blm value of 1 (example how large of a difference is there between 128 and 129). Thanks

 

Okay, but do you realize the you have 15 BLM cells available from 0-35 gm/sec of air flow and 600-2,100 rpm. Yet from 35-255 gm/sec of air flow and 2,100- redline you only have 1 cell.

What do you think the likelihood of the "correction factor" the BLM calculated at 35 gm/sec @ 2,100 rpm being correct for 200+ gm/sec at 4,500+ rpm? I will tell you that it isn't very close and you shouldn't rely or expect it to be close to giving the proper correcting when you are in WOT.

 

Think of the RPM values and Air Flow (MAF) or Load (MAP) as the "boundary lines".

Now draw 3 horizontal lines on a piece a paper and then draw 3 veritcal lines that intersect the 3 horizontal lines. You should have 16 cells.

With "tic-tac-toe" you only have 2 horizontal and 2 vertical and you get 9 cells. The BLM is like a "tic-tac-toe" grid but with 3 boundary lines for RPM and 3 boundary lines for AirFlow (MAF) or Load (MAP).

 

To better visualize the blm cells, goto http://www.diy-efi.org/gmecm/papers/anht_hac.pdf and search for "cell". It will take you to a visual representation.

 

Absolutely! I recorded a ton of data from over a dozen different days and plotted the RPM and airflow values on a graph (using Excel) to see how often I was in each BLM cell. I adjusted the middle cell boundaries since I was in some cells a lot more than the others. I am rarely in Cell 15 unless I'm accelerating from a stop or getting close to Power Enrichment. The stock airflow boundary was a little lower, although I may be re-adjusting the top RPM boundary a little to keep me out of Cell 15 unless the revs are higher.

Doesn't matter since I'll be in PE at that point. How do you know that it isn't close at higher airflows and rpms? I do know that my O2 values are quite linear (value doesn't vary up/down much) going up the revs while WOT, so I know that my PE vs. RPM chart is pretty accurate. I have adjusted my MAF tables up to ~80 gps, but anything beyond that is in PE mode for me.

 

If you re-read my original posts, this is the entire point of my post...that correction values for Cell 15 are useless for PE/WOT and people relying on the BLM learning for WOT are in for a disappointment.

 

Ahhh, I see now. You're definitely right about that, although one thing I've noticed is that if the BLM isn't 128 for Cell 15, it'll throw off the O2 values that I typically see when WOT. I ran into that the other week when I had a BLM of 138? for Cell 15 (don't remember why since all the others are always +/-4 from 128) and the O2's were a lot richer at WOT than they normally are. Re-tested the next day with a BLM of 128 in Cell 15 and they were back to normal. Still, it's all a crap-shoot in the end.