High int, but 128 blm. What does that mean?

[f85gtron]

I have a couple cells that stay 135ish or more int, but blm is steady at 128. What does that mean? Should I bother to correct it (while I'm in there ;) )

[1project2many]

It may mean the calibration you're using is set up to allow wide INT corrections before the BLM changes. We've seen this before as a way for a tuner to make a calibration appear perfect. I would address these cells. The calibration appears fairly lean in those cells.

[f85gtron]

Ok, thanks. I'll keep working on them.

[1project2many]

Did you start with a stock calibration or did you buy one already tuned?

[lionelhutz]

Did you start with a stock calibration or did you buy one already tuned?

Are you wondering what the max allowed BLM value is? Wondering about a tuner that locks it to 128 so the tune looks right.

[1project2many]

Are you wondering what the max allowed BLM value is? Wondering about a tuner that locks it to 128 so the tune looks right.

I am.

[f85gtron]

Did you start with a stock calibration or did you buy one already tuned?

I purchased a mail order tune, based on my mods, and the tuner got close, given he was flying blind. I'm tweaking to make it perfect, now that I'm learning enough to jump into tuning.

[f85gtron]

Are you wondering what the max allowed BLM value is? Wondering about a tuner that locks it to 128 so the tune looks right.

Both the blm and int move. Sometimes, the int will be 135 and blm 119, like they're fighting each other. The int moves super quick while the blm seams delayed at times. I can't get the idle blms right, if i pull too much fuel, the motor will die when i push in the clutch and it returns to the idle table, but not at the normal ve table.

I'm dialing it in and an getting close. With the help of this forum, the car Feels sooo much better and I'm learning tons. You guys rock!

[f85gtron]

Should i skinny up the int and blm ranges?
Here's what I'm looking at:

[lionelhutz]

Double check the min and max allowed BLM scalars. Typically, they are something like 108 and 160 from the factory. Certain mail order tuners have been known to set these closer to 128 so that they can say check your log, the BLM values are close to 128 so my tune must be good.

The BLM and int can be quite different at times. Don't forget, you may be looking at a VE table that uses 200rpm and 5kpa steps for the cells but there will only be something like 9 or 16 BLM cells to cover the whole VE table. So, while inside a single BLM cell you could got to one cell of the VE table and the BLM will change to the correction factor for that cell and then you move to another cell and the BLM has to re-adjust to the correction factor for that cell.

The limited BLM table is why you want to get the VE table decently tuned. A BLM cell has to correct a whole bunch of VE cells and a single correction factor doesn't fully correct all the VE cells. If there was a BLM cell for every VE cell then it wouldn't matter because the BLM could correct each VE cell.

[f85gtron]

Double check the min and max allowed BLM scalars. Typically, they are something like 108 and 160 from the factory. Certain mail order tuners have been known to set these closer to 128 so that they can say check your log, the BLM values are close to 128 so my tune must be good.

I just checked, and they are set at 90 & 160

[1project2many]

Timing affects exhaust O2! Generally, increasing timing produces leaner O2 and higher INT values. If you reduce delivered fuel and it doesn't change or fix the O2 / INT try increasing advance some. And yes, I'd tighten up the INT limits if you want to use a spreadsheet tool based on BLM. I've often disabled BLM completely and used only INT, O2, and well-calibrated SOP (seat of pants) sensor for around town driveability.


Typically, they are something like 108 and 160 from the factory. Certain mail order tuners have been known to set these closer to 128 so that they can say check your log, the BLM values are close to 128 so my tune must be good.


Another trick is to widen the allowed INT before BLM was changed. Easier to catch since INT shows high or low but those errors can be blown off as temporary due to weather or bad fuel.

As mentioned, you get into spots where BLM might be high when running under load, then you back off throttle and suddenly INT swings toward lean while BLM is slowly, slowly reducing fuel. Then BLM drops down to 128 or below and you step on throttle and it's lean... maybe even get a lean pop! How the heck can you tell which cells in the VE are right if you're applying a correction to 5,6,7, 8 or more cells at the same time?? The BLM correction tools work better when there are more BLM cells, less light to light in town type driving, and the BLM responds to INT quicker. It can be a good tool to rough in corrections and to help with cruise conditions but best in town driveability imo is obtained from reading logs and making corrections by hand.

[f85gtron]

I'm actually having the opposite problem in transitions. When i let off the gas (decel), blms drop to 100-ish, wether moving or not. I'd like to lean that out, but am still learning. However, am I correct in thinking I should concentrate on getting a proper ve and idle table before i tale those other items?

[1project2many]

I was just providing an example of how tuning by BLM can be less than perfect.

Correct VE and spark should result in correct BLM's.

I'd work on idle then move to some decel tuning with the vehicle stationary to get an idea of which direction the VE and timing needs to go. Then go out on the road to continue.

[f85gtron]

Ok. Thanks