BLM question

[Buick Beginner]

Gentlemen,
Thanks for taking the time to look at this post, I'm using DS right now but something that has always BUGGED me is the information provided with the program. The instructions are helpful in regards to installing the program, etc. But there is virtually no practical use info. for the readings you are getting from the DS program. The example being, BLM's. I can give you the "book definition" of what a block learn mulitplier is, but what's the practical use of it? It's like a doctor coming in and doing an EKG on you, he then says, "you're at 76 - 83 - 95 - 22 and 31". Then he leaves the room, and you're sitting there going, "great, but what does it mean?" Can someone kind of break BLM's down to a Kindergarten level for me? Like, "OK, little boy, when you see this number thats BAD, when you see this number, thats good". Thanks for the help. - BB
(P.S. Does anyone produce a tuning guide for our cars? One that will explain what the readings mean, rather than just give the book definition?)

 

[T-top87GN]

128 is good air/fuel mixture. Higher BLM numbers mean it's getting lean. Lower BLM numbers mean it's getting rich. You can always find the answers to most questions over at http://www.gnttype.org, go to Member Services and use the archive search. HTH.

 

[Buick Beginner]

Thanks

Bandit,
Appreciate the info. I did find that page and it was very informative. Here's the link in case anyone wants to take a look: http://www.gnttype.org/techarea/faq/BLMINT.html Thanks again - BB

 

[ijames]

Umm, I have to disagree some with the INT portion of that page on gnttype. On a cold start the INT is set to 128 and kept there until the coolant reaches a threshold value, a timer says the engine has been running long enough, and the O2 sensor has warmed up and started responding. The ecm then sets the closed loop flag which means that if other conditions are met (not in PE, DE, or DEFCO modes, primarily) the ecm uses the O2 sensor to control the INT. It adds to the INT in small increments until the O2 voltage goes above a threshold so the ecm knows the engine is now rich, then it starts subtracting from the INT until the O2 voltage goes below another threshold and the engine is lean. The ecm keeps cycling the INT, trying to keep the time spent rich equal to the time spent lean so it knows that the average is stoichiometric. If other conditions are met then the learn control flag is set and the ecm keeps a moving average of the INT values. If this average is not 128, it will add or subtract to the current BLM value to move the INT average towards 128. This is done a few times a second, without the INT ever having to get to an extreme value such as 90 or 150, as the gnttype page states. The stock BLM range is 105 to 150, but even if the BLM has reached one of these limits the ecm is still able to keep the engine averaging stoichiometric so long as the INT is not also at a limit. For example, the BLM could be 150 and the INT ranging between 135 and 145.

If you have a scan tool or DirectScan you can watch this process. The ALDL update rate will keep you from seeing all of the INT values but you will still see the long term trends. Start the engine and let it warm up so that learn mode is enabled, then pull the vacuum hose off of the fuel pressure regulator. The fuel pressure will jump up 4-7 psi and the engine will go rich. The INT will drop below 128 and go down until the engine finally goes lean or a limit is reached, and will then go up and down over a range of maybe 10-20 units as the ecm keeps the engine bouncing between rich and lean, and the BLM will start dropping. As it does, the average INT will rise back to 128. Once the INT average is 128 the BLM will stop changing. Put the vacuum hose back on, the fuel pressure will drop, the engine will go lean, and the mirror image of the above will occur. The INT will rise, start bouncing up and down, the BLM will rise, and the INT average will eventually reach 128 and the BLM will stop changing again.

 

[TurboDave]

Carl, the reason there are so many erros in that gnttype explanation page is because (I think) it was taken from a Chevrolet publication. I can't remember where I saw it, but it's chevy stuff. You can also see this by looking at their BLM table. It's a mirror image of ours. Chevy's have their tables like that.
Most of the theory there is correct, if you're driving a chevy

 

[JDEstill]

So why don't one of you experts rewrite it so it's correct? Shouldn't take too long!

BB, the way I think of BLMs is this: the ecm figures up the injector pulsewidth by multiplying a bunch of numbers together. One of those numbers is the BLM. Everything was originally set up so that the BLM would be ~128.

If the BLM is higher than that, then the ecm is multiplying by a bigger number than design, so that means it is adding more fuel. Why it's doing this, could be any number of reasons.

If BLMs are low, the ecm is multiplying by a smaller number, so that means it thinks less fuel is needed - again, for any number of reasons.

I never could keep that rich/lean thing in my head, I find this easier - big BLM, more fuel, low BLM less fuel. Again, that doesn't mean it is the wrong amount, just different, for some reason.

John

 

[kenmosher]

... and I've asked about a hundred times for someone to help correct that page.

It was based on some good information in a Chevy book, but when I asked for help to correct it all I heard was crickets chirping Or else, "It's wrong"...

I'd love to see Carl or Dave take a few minutes, make corrections to the tables and text and then I'll put it back up on the site (with the author's names in the byline). I'd love to see it corrected!

How 'bout it?

 

[TurboDave]

Carl, you want to do that or would you like me to tackle it??

Ken, can you accept changes in MS Word format?? That way, I can re-draw the BLM table easier.

 

[kenmosher]

Sure!

I'll have to jigger it around anyway to fit it in the tables on the web page.

 

[Buick Beginner]

Thanks

I hope this dosen't cause anyone a bunch of trouble! Thanks for the info. guys. - BB

 

[ijames]

If you want to do it, Dave, go ahead. Personally I think that the 4x4 table of blm's vs rpm and maf should be there but those whole "expanded" tables showing the INT going from 0-255 or 90-150 for each blm should be deleted. If you want to use part or all of what I wrote above, that's great too.

 

[TurboDave]

I'll get started on something. Hope nobody holds their breath

As a technical writer, I often take longer than many would like

BTW, I'll be plagerizing the heck out of all the sources

 

[Zero Tolerance]

Dave and Carl thanks. This is the type of information that we all can refer to in the future, to better understand what the heck we are doing (or seeing) with these motors.

Now that I've printed the Chevy Material, I'll go line the bird cage.
Thanks again.

 

[Donald McMullin]

Relative Air Density vs BLM, & Reading Boost Levels on DS

I have been noticing an interesting correlation between my BLM (at idle) and the relative air density (RAD). When the RAD increases, my BLM increases which appears to be correct because more fuel is required to obtain the same AFR at idle. This is based on the same static fuel pressure.

What I am doing is recording the changes in RAD, BLM at idle, and my AFR at WOT full boost. I am hoping to develope a table which will allow me to set my static fuel pressure in relation to changing RAD so I can obtain a BLM reading at idle and have a correct AFR at WOT full boost. Also, I would have to have different tables for different boost levels.

By the way, I am using a WBO2 to obtain accurate AFR readings to minimize the errors in my comparison.

On a separate subject, using DS in conjuntion with the TurboLink boost harness, have am able to indirectly read my boost levels during a WOT run. To do this I have to calibrate my MAT reading in DS with my boost gauge before a run. I run my boost up to 5 psig and note the MAT reading in DS. Then during my run I lock the boost gauge at the maximum boost level.

After a run I can note the MAT reading at 10 psig because of the volt booster changes my voltage at that boost level and I can note the maximum MAT reading which correlates with the max boost level I read on the boost gauge. I then can calculate the boost level at different MAT readings. I know this is crude, but it is better than nothing.

Any constructive comments or criticism about my post will be appriciated.


Deep Enough
Donald McMullin

 

[TurboDave]

Originally posted by Donald McMullin
Relative Air Density vs BLM, & Reading Boost Levels on DS

I have been noticing an interesting correlation between my BLM (at idle) and the relative air density (RAD). When the RAD increases, my BLM increases which appears to be correct because more fuel is required to obtain the same AFR at idle. This is based on the same static fuel pressure.

What I am doing is recording the changes in RAD, BLM at idle, and my AFR at WOT full boost. I am hoping to develope a table which will allow me to set my static fuel pressure in relation to changing RAD so I can obtain a BLM reading at idle and have a correct AFR at WOT full boost. Also, I would have to have different tables for different boost levels.

(SNIP)

Any constructive comments or criticism about my post will be appriciated.


Deep Enough
Donald McMullin

I guess my only comments would be, why would you want to go to all the trouble to develope a table to change static fuel pressure?? The main reason the BLM table exists in the first place is to make the changes to the required fuel needed in accordance with the changes in load, RAD, etc. etc. without the operater having to mess around with any fuel pressure changes.

As long as the BLM's you're seeing are anywhere in the 100-140 range, you can be rest assured the car is operating where it needs to be.

YOU DO NOT HAVE TO ALWAYS TRY AND MAINTAIN A 128 BLM!!!

That's another reason so many people are switching over to the Trans/Extender system, never having to adjust fuel pressure for any reason. If you don't like your WOT BLM or O2's, just tweak a knob "inside" the car.
Sorry for the blatant advertising, couldn't help it. The system just plain works.

But as I said, any thing you can do to NOT have to always adjust fueling for changing conditions is a good thing. (The BLM does that for you)

 

[BoostKillsStres]

Donald,
Also keep in mind while using the boost harness with DS that the temp vs. boost level isn't linear because of the way the electronics in the cable function. Ken has software calculations which make it pretty accurate with Turbolink so you need a pump to build you a lookup table as once you pass about 15 psi readings start to change. I believe before I built my lookup table I was running about 17 psi and DS was showing about 22 using a linera plot so it doesn't work too good. After rereading I now see your locking your boost reading so that works good for the peak.

Also, I'm curious as to how your logging your wideband? I'm actually using DS to log mine with the option to log boost or actual intake air temp as I relocated my IAT sensor to the upper plenum. Too bad I can't log them all at the same time into DS along with EGT

cya

 

[Donald McMullin]

TURBODAVE, thank you for the input.

The chips I have been testing lock the BLM at 128 at WOT so I have to adjust fuel pressure for changing RAD conditions. If BLM (at idle) shows that ECM is adding more fuel with increasing RAD then if I do not change fuel pressure the locked BLM will result in a lean condition.

No, I am not trying to maintain a BLM of 128, but when my BLM goes from 140 to 150 (at idle) when the RAD increases (without changing fuel pressure) I am assuming that when BLM is locked (WOT) at 128 the AFR will increase (go lean).

I do not think I am incorrect in my understanding of the interaction between a locked BLM and changing RAD, but I could be wrong, it does happen once in a while.

I am hoping the Trans + (used) I received yesterday will allow me to better establish correct AFR at BASE and WOT.

Deep Enough
Donald McMullin

 

[Donald McMullin]

BoostKillsStres, I have some questions about some of your comments:

"Ken has software calculations which make it" [MAT readings]"pretty accurate with Turbolink" [boost harness].

Do you have Ken's software calculations or do I need to get them from him??

"I'm actually using DS to log mine with the option to log boost or actual intake air temp as I relocated my IAT sensor to the upper plenum. Too bad I can't log them all at the same time into DS along with EGT"

How are you logging WB on DS?? I have logged my WBO2 on a separate program then used the computer time stamp to compare with DS. I know this is crude, but if you have any other ideas please let me know.

It would be nice to log boost, EGT and other millivolt signals with DS, this is a good subject of another post. Think of the possibilities if you could log; boost out the compressor, boost at the TB, exhaust pressure at the header, exhaust pressure down stream of the turbine, air temp out of the compressor, air temp at the TB, along with EGT. As a minimum I would like to compare boost at the TB and exhaust pressure at the header.

Maybe if enough interest is shown, Ken will upgrade the hardware and software to do this.

Deep Enough
Donald McMullin









"Ken has software calculations which make it" [MAT readings]"pretty accurate with Turbolink" [boost harness].

 

[TurboDave]

Originally posted by Donald McMullin


(SNIP)

I am hoping the Trans + (used) I received yesterday will allow me to better establish correct AFR at BASE and WOT.

Deep Enough
Donald McMullin

It will help with the BASE AFR, and cruising, closed loop, etc. But not WOT unless you also choose to run the Extender chip, because on any other chip, once your MAF tops out at 255, you're at the mercy of whatever the chip programmer plugged into the P/E tables. (You'll still be playing with fuel pressure to get the WOT fuel corrected).

 

[BoostKillsStres]

Donald,
I asked Ken about how Turbolink gets the boost right and he told me it had a calculated result and that was that, I don't think he'll be giving that info to anyone.

If your wideband controller is putting out a signal in the 0-4v range then you can wire it into the boost harness and you'll then have A/F reported as temp just as boost is now, just make sure to unplug the map. With some help, I determined that there were enough electronics in the boost harness, mat circuit and ecm voltage divider that I probably wouldn't smoke anything by hooking it up this way and so far things are peachy. I built temp to voltage to A/F conversion table and have a quickie lookup chart on the side of my laptop screen so I can easily convert. As far as I know I was the first one to attempt this --pat on the back-- and its very nice as I can now plot WB A/F vs. any other data that DS can log you just have to account for a slight amount of reading lag time since my WB sensor is in the test pipe but its not much at WOT and other than that its killer for chip tuning. I'm still working to get my WOT fuel curve where I want it then off to the track to make minor fuel changes and see what returns the best mph and go from there.

I think Kent would like to add a bunch of neat options to DS as we've talked about a few. I believe its just a matter of time and him having enough time to put a product together. Just like anything else R&D takes a lot of work.

Enjoy...