How do these BLM's look....

Getting ready to do some of my own programming and have been doing a lot of reading on the PCM stuff and trying to figure out what a lot of the stuff means. I was reading some on BLM's and unbalanced BLM's on cam'ed cars. So out of curiousity, I hooked the scanner up to my car and after I was in closed loop, I made a WOT run. I was seeing 135 on the left and 142 on the right. TPS was at 100% and I was running at about 5500 rpm. My O2's were reading 884mv on the left and 915mv on the right and I was running 42* spark advance. No knock detected either. You guys have any input on how this data looks? Should I be looking for improvement when I start programming or is this pretty good data. Just curious and still learning. Thanks in advance for the help.

Ken R. 95Z

Anybody??

Let me see if I understand.

You are looking at your BLM's at WOT? This seems to be the case since you said your TPS was 100%.

If this is, your readings are irrelevant. What the BLM's are for is for non-PE mode. They are modifiers that the computer uses to determine injector pulsewidth. Through the readings from the O2's, the computer is trying to keep the O2 readings at 450mV in non-PE closed loop.

When the car goes to PE mode, it "ignores" what the 02's are saying and goes to 128 on the BLM's unless you were running lean (I think 132 or so on the BLM's) at the moment before going into PE. If lean, then the computer uses the last BLM indicated.

This will help you start on your analysis of what is going on. Just keep posting with more data/questions and do mega searches on the net. I swear I have found mounds of information for the LT1 especially.

Ben

What Ben said is correct, and I would like to emphasize that the blm's do affect WOT fueling. If the blm's are over 128 in the cell where you activate PE (WOT) mode, usually cell 15, then the pcm will use 128 if the blm's in that cell were at or below 130. If they are 130 or higher, it will use the actual blm. So, if you have some kind of exhaust leak where extra O2 is getting into your exhaust, your car thinks it's running lean and the blms rise, causing fuel to be added.

So in your case, you were adding about 5.5% and 10.9% more fuel over the factory tune at wot.

The stock O2 readings are worthless at WOT.

Besides exhaust leaks, another common cause of high blm's is vacuum leaks. The system needs to be sealed as good as possible. Are you running a ported or aftermarket maf? That could do it too.

Joe

So I didn't mention that I already have a custom tune in the computer now, which I didn't do myself. So it's not running a stock program. Basically, the mod scoop is Heads, cam, headers, larger TB, Headers, and all the other little goddies. Would the custom program account for the increased fuel at WOT instead of an exhaust or vacuum leak? I'm assuming it is. My MAF is ported though. Also, been reading on the board here about BLM's that are unbalanced. How bad of an unbalancing constitutes an issue? At idle, or when i'm crusing, I noticed that there is usually a difference of 8 to 10 between left and right. Should they be closer? Just poking around for info. Still learning lots and I appreciate the help. Thanks

Ken R. 95Z

Don't get confused between more power and more fuel. It's the ratio of air to fuel that's important, and that should be taken car of. Too bad your maf is ported, that is why your blm's will be high. Basically your maf is now reporting less air than is going by it. So you would need to scale the maf tables up to get your blm's in check.

The only power increase a ported maf gives is because it is under-reporting the air into the engine, causes it to run leaner at wot where there is not correction. But if your blm's are over 132 at wot, you know the computer is at least adding some of the lost fuel back.

FWIW I ran a stock program after I did all my mods and my blm's were right around 128 with no tuning. Basically the engine is an air pump - it is now flowing more air according to the maf than it was stock, and thus adding the appropriate fuel. The factory tune is conservatively rich, so I had that until I hit the WB O2 at the dyno.....

Usually split blm's at idle are due to aftermarket TB's not properly implementing the IAC port. I would do a search on that - there's plenty of info out there.

Joe

Joe, so are you saying that I would be better off with a non ported MAF, or should I just correct the table when I get the tuner software going? Basically, is a non ported MAF with it's original table the same as a ported MAF with a modified table, or is one better then the other? Thanks for the info and help Joe. It's appreciated.

Ken R. 95Z

Ported/nonported it does not matter as long as you adjust your tables.

I descreened mine and adjusted my tables. I am right on with my BLM's so its all good.

Ben