I have read a number of posts referring to BLM's. If I understand it, a reading is taken from the ECM (how?) and that gives a number (meaning what?) to tell if you are running rich or lean (and what can you do about it?)
Please KISS as this electronic stuff sometimes give me a real big headache!
Thanks

Subman

 

I'm interested in this also, and from what I've read in some corvette fuel injection books, and tried to understand, is the BLM reading is related to air/fuel mixture reaching atmospheric pressure (14.7 lbs/inch). I obviously don't know much about what the numbers mean or how the ECM obtains the info (through MAT or MAP or both possibly?). I'm sure someone will enlighten us. :seeya

 

Block Learn Values also called Block Learn Mode(?)


See page 2 of this article titled "Fuel Injection Tips (for Corvette)":
http://www.corvettemagazine.com/1999...ion/fuelp1.asp

:cheers:


[Modified by Lone Ranger, 9:03 AM 9/5/2003]

 

Thanks Lone Ranger! That article says it all!! I had some concerns about the 24# injectors I installed in my '85, but I can lay them to rest based on my other mods! :seeya

 

This is a good time to say what i know about this kinda stuff. A few yrs ago i put in some 36lb injectors in a stock 89.:) wrong! Man had a lot to learn. Now i burn my own chips. Heres where you Start for injector sizing... (MAX HP/2)/#cyl= injector rate. for example.
400HP/2=200. 200/8=25. So you'd need a 25lb injector at 42PSI at probly 100% duty cyle to make that power. So go up one notch. go for 28lb or 30lbs and that way you'll have room for improvements and won't run them close to 100% duty cylce. 80% is a general rule for max duty cyle. I'm running 24lbs at stock PSI in my 89. for the TPI guys, just get some 24lb injectors and REPROGRAM the ECM chip. Also, those "off the shelf chips" suck. they are ment to work with stock injectors etc. You need to find someone you can send your PROM to and they can program it for you application. usually ends up cheaper, and more HP, and better overall. Also, scanning while driving is good too. I also reccomend a 3 or 4 wire O2 sensor. I'm running a 3 wire now, but probly will switch over to a 4 wire soon. Those things make the world of difference in closed loop mode. Also, if your ECM is programmed to run in closed loop at a lower temp than stock, say 165F vs the stock 200F pretty sure, it alows you to run your car at 180/185F all day long and get much better performance:) SO one mod i'd have to say is a must for the DOG early C4's is a a custom Chip and cooling mods, along with the 4 wire o2 sensor.

 

Good read :yesnod:

 

the article is good, in simple terms the BL runs from 0 to a high of 255, the middle range of 128 ( air ful ratio of 14.7 to 1) as noted is no correction taking place, numbers between 0 and 128 means fuel is being taken away to lean it out, 128-255 fuel is being added to richen the mixture.. there are 16 differnet cells or blocks each has an operating range containg a range of fuel delivery....

 

Read the article and it was pretty informative. However, I would need to buy the program and a laptop to read the BLM's, correct? If that were to happen and I ended up with a reading of over 128, I would need to have the PROM changed to adjust, also correct? From what I gathered in the article and the responses, the readings come from the O2 sensors. My 91 has only 1 O2 sensor (on the left bank) How would this affect the readings? I realize there are alot of questions but having changed my injectors (Ford 21# from fiveOmotorsports) and installing a AFPR about 2 months ago, I'm not sure that I'm running at maximum efficiency. Thanks for the help!

 

There are several programs that, with the right harness to a laptop, will allow you to read BLM's and other engine parameters. Another option is the TECH-II's which are used by auto shops. The TECH-II is much more expensive.

Not really. I doubt many cars have a 128 BLM in all cells on the dot. There are many things that can affect the mixture, including variations in fuel injector performance, intake flow, and also sensor accuracy. The BLM's are there to "learn" the slight differences in these performance characteristics between different vehicles, and compensate the fuel pulse width to take it into account.

I would only worry if the BLM's are way off from 128. But when this happens (at least on my LT1) I would expect other malfunction codes to set off.

Yes, one O2 sensor will affect BLM's. The only difference between a one-sensor and a two sensor setup is that a two sensor setup on a V-engine is measuring each bank and adjusts the fuel on each bank independently. Either setup will still affect BLM's. I can't quite recall if a two sensor setup (perhaps a four sensor setup in recent vehicles - pre-cat and post-cat) has two BLM arrays, one for each bank.

The only way, IMO, to really find out if your mixture is optimal, is to hop on a chassis dyno with an external O2 measuring device stuck up the tailpipe(s). The vehicle's O2 sensor is only good for figuring out if the A/F ratio has crossed the rich/lean threshold.

Since I usually don't have the cash for casual dyno runs, I usually just check spark plug color to check the mixture.

Hope this helps! :cheers: