BLM question

[1984 t-type]

So my BLMs were stuck at 142 after changing out to a new FPR, before hand they were right at 128. I did some searching and saw a mention of maybe adding more base fuel pressure and decided to give that a try since I was certain I had no vacuum leaks. So I bumped the pressure from 42lbs line off to almost 50lbs line off and reset the ECM now my BLMs are back at 128. So I’m curious as to what this is telling me since most would put a high BLM issue on a vacuum leak, just trying to learn and get more of an understanding of what’s going on in they system. I want to get my knowledge and understanding of these cars to the point where I’m the one answering questions and not always just asking them.

Oh and by the way I set the fuel pressure to 42 line off just because that’s what I have always read and done but after I switched to E85 the other year I bumped it up to around 50 line off per recommendation of a member here can’t remember who to help with an off idle stumble I was having and it worked.

Thanks

 

[750H.P.V6]

If everything seems to be functioning correctly and you have no vacuum leaks it could be in the chip programing. If the injector constant in the chip which correlates directly to the injector size and fuel being used (E85) is not correct the BLM values can be high or low across the board.

Everyone tells you to shoot for 128 which is the midline value but BLM #'s will move around. 142 is a bit high but the Min / Max on aftermarket chips is typically 90 - 160. Bounce the injector constant question off the person who burned your chip to verify the calibration is correct in his mind.

Neal

 

[Turbo6inKY]

Everyone tells you to shoot for 128 which is the midline value but BLM #'s will move around.

The reason to shoot for 128 is about duty cycle authority. The stock ECM and stock-ish fueling algorithm can add and remove fuel based on O2 sensor input inside a relatively narrow range, and making sure the engine is in good shape so it's normally in the middle of that range gives the most operating margin.

 

[750H.P.V6]

The reason to shoot for 128 is about duty cycle authority. The stock ECM and stock-ish fueling algorithm can add and remove fuel based on O2 sensor input inside a relatively narrow range, and making sure the engine is in good shape so it's normally in the middle of that range gives the most operating margin.

I get that, I used to burn chips. It's best to be in the middle of the range to have adequate room for the ECM to make fueling changes + or - to achieve a stochiemetric A/F ratio across all 15 BLM cells. According to the OP the belief is that the engine is in good condition with no vacuum leaks which is why I floated the theory that the injector constant could be off requiring him to compensate with additional fuel pressure to end up in the middle of the BLM range. It's really pretty common for the injector constant to be off. Back in the day most of Red Armstrongs chips were off and a lot of others too.

Neal

 

[750H.P.V6]

Something else to consider with running E85 is that depending on where you live the ethanol content can change throughout the year. Typically the ethanol content is less in the winter to aid in cold starting. This being said E85 might actually only be E70 during the winter. If the alcohol content of the fuel changes the fuel trims (i.e. block learn values) will too. I don't think that is what is happening here but the scenario came to mid so I thought I'd mention it.

Neal