BLM advise needed
Thread Starter
Racer
Joined: Sep 2005
Posts: 449
Likes: 1
From: Victoria
BLM advise needed
Just fitted zz4 cam and bosch 111 injectors,comp rockers etc in my 89.
I have an AFPR fitted and set at 43.5lb what should the BLM be? I have been told 120 others 128.
and will this vary if a custom chip is done?
Waiting to get my tech one back to check
I have an AFPR fitted and set at 43.5lb what should the BLM be? I have been told 120 others 128.
and will this vary if a custom chip is done?
Waiting to get my tech one back to check
Le Mans Master
Joined: Aug 2000
Posts: 8,838
Likes: 31
From: Australia
128 is optimum ( center of fuel range )
Read BLOCK LEARN section at bottom of page
http://carprogrammer.com/Z28/PCM/FAQ...on%20Works.htm
BLM is same as Long term fuel trim
http://www.cartechbooks.com/vstore/s...=3657&CATID=21
Read BLOCK LEARN section at bottom of page
http://carprogrammer.com/Z28/PCM/FAQ...on%20Works.htm
BLM is same as Long term fuel trim
http://www.cartechbooks.com/vstore/s...=3657&CATID=21
Race Director
Joined: Sep 2003
Posts: 16,835
Likes: 337
From: Database Error Indiana
128 is where you want to be. The ECM can compensate + or - 8, but the closer the better. My 87 idled rich when I went with the ZZ4. To take full advantage of the cam, you will need a new chip.
Burning Brakes
Joined: Apr 2004
Posts: 762
Likes: 1
From: Huntington ma
The BLM values are just the ECM telling you what it is doing to correct the fuel table to achieve the target A/F ratio. A BLM value of 128 means that No correction is being applied for that particular load/rpm condition.
A BLM value less than 128 means that the ECM is "removing" fuel, or that the table value is too rich. A value higher than 128 means that the ECM is "adding" fuel, or that the table value is too lean. Rich and lean here are relative terms - keep in mind that the target A/F value itself is a variable.
There is no magic to the number 128, it is simply the mid point of a single 8 bit "word" of 256 possible values (in hexidecimal numbering).
A BLM value less than 128 means that the ECM is "removing" fuel, or that the table value is too rich. A value higher than 128 means that the ECM is "adding" fuel, or that the table value is too lean. Rich and lean here are relative terms - keep in mind that the target A/F value itself is a variable.
There is no magic to the number 128, it is simply the mid point of a single 8 bit "word" of 256 possible values (in hexidecimal numbering).
Safety Car
Joined: Jan 2004
Posts: 3,759
Likes: 8
From what I've read you want the BLM as close to 128 as you can. And that the computer can compensate + or - 10. And if your BLM's go outside of that range, then you actually are running rich or lean that could cause problems.
Race Director
Joined: Sep 2001
Posts: 14,641
Likes: 749
From: NEwhere Ohio
If you are not at 128, you will hear people say either:
1: can't do anything abt it, its entirely a function of what the o2 sensors say (other than make sure no vacuum leaks, o2 sensors are good, etc.)
Or...
2. You can tune your ve table to compensate. Even in closed loop mode the table still has an affect.
Im not sure what the correct answer is.
My blms w. Hotcam went rich. App. 116 at cruise. I datalogged an hour drive, and found a calc program where you input your datalog and it outputs a table( rpm, map) of correction facttors to multiply your ve constants by.
I haven't done this yet I want to collect more data and run the progra, again to see if it gives me the same correction factors
1: can't do anything abt it, its entirely a function of what the o2 sensors say (other than make sure no vacuum leaks, o2 sensors are good, etc.)
Or...
2. You can tune your ve table to compensate. Even in closed loop mode the table still has an affect.
Im not sure what the correct answer is.
My blms w. Hotcam went rich. App. 116 at cruise. I datalogged an hour drive, and found a calc program where you input your datalog and it outputs a table( rpm, map) of correction facttors to multiply your ve constants by.
I haven't done this yet I want to collect more data and run the progra, again to see if it gives me the same correction factors
Safety Car
Joined: Sep 2001
Posts: 4,137
Likes: 531
From: Glenbeulah Wi
The stock 1989 BLM range will be 108 to 160. The idleal BLM number is 128 but if you are close the tune will operate fine.
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