What does the BLM lock function on a chip do?
- Thread starter rastaz
- Start date
The table of learned BLM's is always used for calculating injector pulsewidth. This is great at part-throttle as changes in fuel pressure are compensated for (within the limits set on the BLM values). However, it means that at WOT as you turn the boost from very low to very high the engine will start out too rich, and then get progressively leaner and leaner. Only at one boost will the air-fuel ratio be optimum (however you want to define that). If you want to run more boost you have to make a new chip which adds in additional fuel at WOT (yes, I'm assuming everything is still on-scale dc-wise), or if you want to use less boost you need a chip which takes out some fuel. One way around this is to "lock" or set the BLM to some fixed value at WOT. Now, no matter what it learned to at part-throttle, at WOT it will always be some constant value so as the fuel pressure is increased or decreased the amount of fuel the engine actually receives will change. That lets you independently vary both boost and fuel without burning new chips. The advantage is that it's great for tuning, but the disadvantage is that now it's your responsibility to do the tuning and make sure the mixture is right. The value usually chosen to lock to is 128, since that's the middle of the BLM range of 0-255, and I published a very short patch to do that several years ago on the gnttype list (go to www.gnttype.org and search the archives). I also published a longer, more flexible patch a couple of years ago if you want more reading 
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