Ok, basics...high BLM counts (above 128) mean rich or lean? I wanna say rich but I also want to verify it.

 

The lower the BLM number the richer. (ex 100-110 very rich) :yesnod:

 

High BLM (over 128) means the car is running lean, but the computer is ADDING Fuel

Under 128, mean running rich, the ECM will be removing fuel

:D

 

Thanks guys...glad I asked.

 

If you are *universally* rich, ie through all RPM ranges. You will want to change your injector constant and play with FP. Once you get them close then mess with the fine tuning. For instance when I got my setup running with #24 SVO injectors. I was running 108-112 blm (very rich). I increased the IC up to 30.5 lbs/hr till everything started to get around 128. I got lucky and all RPM ranges fell into the 128 at the same time, usually doesn't happen that easy. I then started attacking the knock that I had. After some major time pulling the knock got better, but because the burn efficiency in the chamber got better with the correct timing I started getting on the lean side, were I once was perfect. This prompted me to then lower the injectors constant to lie to the ECM that I had smaller injectors. This in turn *added* more fuel to correct the lean condition. Again, the BLMs returned to 128 and I started on the timing again. What I am trying to show is it is a balancing act that you need to perform. And remember, give the engine what it wants, not what you think.

 

Yup, rich < 128 < lean ... i have aimed to keep mine between 124 and 130. I'm still figuring out where I need to add a little more fuel in some spots though.

I have my 30# injetors at a 29.5# constant. I originally had them at 32# because of the difference in the pressure levels the Ford SVT's are set to, but i was around 140 BLM's all the time. So I just had to try 30# then 28#, then 29#, then 29.5#.

 

I was playing with fuel pressure, just wanted to make sure I was heading in the right direction with it. Seems to be running a bit better with the right fuel pressure. My Air/Fuel gauge was pegged rich so I kept leaning out the fuel (down to 38psi), but the BLM's were up close to 160. I put the fuel pressure back to 43 and the Air/Fuel gauge shows right where it should. I have not put the computer back on it to see where my BLM's have fallen yet.

 

160 is very lean. The computer is putting a lot of fuel in to compenate for the lean condition. Just aim for between 124 & 130. That's what I did. I set the fuel injector constant to do this instead of the fuel pressure. It's much easier to change one number in the computer programming than buying a AFPR and messing with it.

 

I realize that 128 is the magic number. I was toying with fuel pressure since I have been fiddling fixing other things before doing a modified program. I had an exhaust leak that I had to accomodate before I could do any programming since that will cause split BLM's and it does not allow for good data to analyze.

It is much easier to adjust the fuel pressure than to reprogram in this case.

 

I'm new to this and not positive about *anything* but even though changing the injector constant is the easiest thing to do in some cases, I suspect you'd have to watch the duty cycle of the injector at high revs. I.e. if you lower the injector constant and the computer thinks the injectors are smaller than they actually are it will keep them open longer and at high revs they can actually be open all the time. Obviously this is only a concern if you're universally lean and have to fool the ECM into thinking it's working with smaller injectors.

Also FYI, It's possible to modify a stock, non-adjustable fuel pressure regulator. A guy over on the thirdgen.org forum (Vader ) did this. See link below.
http://www.gmtips.com/3rd-degree/dox/tips/afpr/afpr.htm

 

Ok.....so if your fuel setting are totally stock and you help the car get more air with a larger exaust and intake...the number should go up right?????
Tom

 

Right, if the computer reads that the engine needs more fuel the BLM number will increase.

 

My left injectors are running 142 and my right are running 125 at idle , after it is hot. I have changed the headers from stock exhaust, cats and motor. I havent changed the air pump valves by the headers (those check valves) can these cause this to happen? This was happenign to the left side of the car with the old motor also, then I changed everything, from injectors to heads, motor, headers, cats etc etc. Steve

 

A lot of info went around the LT1 Edit email list a while back about split BLM's and cammed cars. Seems most of the discussion was geared towards the IAC passage and making sure the Idle air was going through the passageways rather than through the throttle body blades.

The first guess with split BLM's is always an exhaust leak, but if you said you had it before, then that would lead me to believe that it was something else.

 

The only thing that has NOT been replaced is the air pump fittings, valves etc. The air pump is turned off, but I havent removed the air fitting going to the headers. That will be today. I will also check the IAC. Thanks, Steve