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

**1project2many** · 08-09-2015

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** · 08-09-2015

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** · 08-10-2015

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.