bl#s @ questions

[carrddine]

can someone please tell me what your bl#s should read while driving around city and freeway at 65-75 mph? mine seems to be at 130-148 on the freeway which makes me think I have a vac.. leak am I right or wrong.please help..any input at this time is much needed...thanks

 

[BlackMetal]

It it was a vacuum leak I'd think you'd see a high BL all the time, not just at cruise.

 

[carrddine]

I kinda thought the same thing,Im just curious because they say if bl is lower than 128 you start going rich and if it goes the otherway you start going lean, im just not sure on this one.All of my scanmaster #s are where they should be and bl is at 110 at idle...

 

[carrddine]

anyone else?????

 

[pacecarta]

there are 16 BLM cells for adjustment of the idle to the point of WOT fuel table and these cells will change the values depending on your cars specific mechanical tune and driving habits

above 128 indicates a lean condition and fuel is being added
it bases its adjustments on what the o2 reads so if o2 sensor is bad (reading low) then the ecm will add fuel (as seen by a higher BLM # ).
if your o2 is reading air from a leaking exhaust manifold (after the normal combustion) then it will mess up the O2 readings and the ecm will add fuel until the value it sees makes sense (blm goes up) ,this would cause an overly rich mixture
if your injectors are not flowing the anticipated volume due to lower fuel pressure or bad injector or even miss burned chip for the injectors than the ecm is doing what its supposed to do and correcting the mixture , if its not at the limits of correction and INT is close to 128 than there really is no need for concern ,

if you are reading less than 128 than fuel is being pulled . if the blm is at its extreme as well as the INT (lets say it reads 90 or on some chips 105) than its possible to still be rich as the ecm cant correct to make the mixture right ,
generally any blm cell stored to +/- 10 of 128 (with normal driving) you should look into why its off and take steps to correct , above 138 look for vac/air leaks, low fuel pressure, below 118 look for excessive fuel pressure or air entering after the MAF(like from a torn stock inlet hose or loose clamp)
besides a bad o2 a bad maf (or air leaking in after the maf) can also affect BLM as its value that the ecm sees is used to determing fueling so if its off fueling will be too for whats expected

btw a vac leak will have little effect at cruise , to have any effect at cruise it would have to be huge you would have serious issues with the idle

to learn more
http://www.gnttype.org/images/blmint.gif

http://www.gnttype.org/techarea/faq/BLMINT.html

 

[carrddine]

ok I just went on a run and this is what happened bl was at 138-144 but int was at 128 and never seemed to move from that spot what am I missing here???

 

[pacecarta]

if your injectors are not flowing the anticipated volume due to lower fuel pressure or bad injector or even miss burned chip for the injectors than the ecm is doing what its supposed to do and correcting the mixture , if its not at the limits of correction and INT is close to 128 than there really is no need for concern ,


to learn more

http://www.gnttype.org/techarea/faq/BLMINT.html

HTH