I was looking over some recorded data and Im trying to figure out the relationship between BLM cell and the MAF rate so I can fine tune better. Before I was just looking at the BLM info as it compared to that particular MAF rate but it seems if I could gain some insight on the BLM cell relationship it could make tuning easier.

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355 10:1 , AFR 190 heads, LT4 HOT cam w/ 1.6 roller rockers, complete Superram intake, 58mm BBK TB, 24# injectors, screens out of MAF, MAT relocated, March underdrive pulleys, Streetdampner, Crane HI-6 ignition, 160 thermostat, K&Ns, TES headers(Jet hot coated), Mufflex 4' cat back, B&M shift Kit, 2500 converter, and 3.27s. Chip is custom(doing it myself) Just got a 2 1/2 Harwood and soon to be painted.

 

The 16 BLM cells are divided into a table defined by RPM and grams/second of airflow. The boundaries are 700, 1200, and 2000 rpm, and 12, 22, and 34 grams/second. Using this, you can figure out what amount of airflow at a certain engine rpm would put you into which BLM cell.

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Greg Westphal
'87 IROC 305TPI/A4

 

This is similar to the SD BLM table except where the MAF BLM uses gm/sec, the SD uses Kpa.

I have found that you can adjust those thresholds to have certain engine operations "grouped" better and to utilize more of the cells of the BLM table.

If you have adjusted your idle and it is set just at or above 700 rpm, you may wish to increase the minimum value. Also, I increased the second and third threshold to 1,400 and 2,100 rpm respectively to keep the "slow city" and "highway cruise" more logically together.

I cannot comment on the gm/sec flow for MAF but I found this too could be improved upon for the SD's MAP thresholds. I am sure that you may find there are improvements to be had in adjusting the MAF's BLM gm/sec thresholds too to again group it more logically and to use as much of the BLM cells as possible.

 

I would like to do this. With A/C on, mine idles above 700. I don't see the values in the Tuner Cat software I have. Are these examples of values that we "shouldn't be messing with"? Should I contact TC to get a new TDF with access to those values?



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'87 IROC 5.7l TPI - original owner!

 

On a related note...

I had been having alot of trouble with my Auto X-Ray scan tool. I've been going round-n-round with them about it and have finally gotten one that seems to work properly. However, my new unit tells me that instead of cell 15, I am now in cell 10 when cruising on the highway. What little fuel tuning I have done thus far was based on the old scanner's data. Does it sound likely that it was reporting the cells incorrectly?! I don't see how, but that's what it looks like. With the old scanner, I did move around in the cells, and it looked like everything was OK, but now I'm not so sure. I did find it strange that I was in cell 15 while cruising. That's the entire top end of the operating range of the engine. That's a huge window to try to tune. I feel much better focusing on one cell that's defined on all four sides.

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'87 IROC 5.7l TPI - original owner!