"Giving a car what it wants, not what you think it wants".

At first brush I'm sure that practically everyone agrees with this statement but how many abide by it? My first time playing with the Romulator and Mark's TunerPro RT this afternoon was quite an eye-opener as to what this statement really means.

After starting with a fresh bin and entering all the standard Injector constant, base timing, fan on/off temps, etc. I got to playing around with the MAF Table 1 to really see this "instant gratification" contraption in action.

So I started tweaking the values and watching the BLMs and INT do their thing. At first I was looking to give the car the 128 idle, then as I was messing with the values, I noticed a drastic improvement in idle quality and throttle response at 135 BLMs. Seemed odd, so I adjusted the values once again to a 129 BLM and the qaulity significantly diminished. So I plugged it back to the 135 BLM where it seemed to be so happy.

I always got so caught up in the "gotta have 128 BLMs everywhere" mentality based on everything I've read, I fear I may have failed to remember this very important principle. I wonder if I might be misinterpreting so I'd like to invite any feedback...

-Brian P

 

I'd be curious as to what a Wideband O2 would read with both settings. Depending on your cam, it may need extra fuel to idle nicely. May also play with the timing with the BLM's around the 128 area and the 135 to see if that makes a difference. Seems that idle would be pretty sensitive to both fueling and timing, and may need to play around a bit to find the best combination.

Basically what I'm trying to say is, you may be able to get it to run better with less fuel at idle by playing with the timing.

Seeing how inaccurate a NB O2 sensor is (especially after reading some of the threads about it) I'm not surprised that the BLM's may be off when thing's are right. 128 BLM's are NOT "Giving the engine what it wants!"

 

Well I suppose that we should also take into consideration that 14.7 is good for the converter, not the engine.

 

Exactly.

At least it's not necessarily what the engine wants, in a perfect world it would be, as 14.7:1 is theoretically ideal, but we all know different...

 

That's also why I don't have to worry about 14.7:1

 

Even better would be to get your idle right AND have the BLM at 128. This may require putting your BLM at 128 and adjusting spark or other parameters, or even mechanical adjustments.

The reason is that if you can get 128 or close to 128 in all cells, you don't have to worry about "jumping" around between trims. I've personally experienced a hopping idle, for instance, because the car was running between cells, one of which was at, say, 118 and the other was at, say 124. It would bounce between these cells and the RPM would jump up and down roughly 50 RPM. Not only that, but some ECMs re-learn the fuel trim after each start-up. Getting them close 128 means the ECM doesn't have to move as far to get set up.

That said, setting it where the car runs best, regardless of how from from 0 (or 128 in this case), isn't bad either! Just a different philosophy.

Either way, sounds like you're having fun, and thats cool!

 

That does make sense for getting as close to 128 as possible.

I was thinking about the fact that some ECM's reset BLM's at startup the other day. I was actually trying to think of all the stuff that is retained when the IGN is shut off. I was having fit's with a truck with a 7747 that ran really bad until it had been driven a couple days, and had been started cold and driven under most every possible condition. BLM's were pretty close to 128, bone stock application and bin, just repairing, not DIY-PROM'ing it.

 

Changing the MAF scalar tables also causes the LV8 variable to change. This in turn affects many other areas of the code/calibration.

RBob.

 

I think this only applies in an open loop vs closed loop situation. You shouldn't notice any difference between 135 and 128 BLM in a closed loop mode, because the ECM is trimming the fuel to produce a "14.7" AFR with either of these BLMs- the engine sees exactly the same amount of fuel in both cases.

AIUI, the difference in idle quality comes when you run in an open loop mode that doesn't apply the BLM correction.

John

 

Even the best of tuners can get into forgetting that. It's a very difficult thought process to maintain. You have to be really forget your ego, and ego attachment to old ideas, and what you've been told to be open to new ideas, and really looking at the trends your tuning notes are showing you. Sometimes, you have to do a 180 to what you'd expect, and then later figure out the logic of what / how something really works or what it means.

For the guy just starting out, getting to 128s is universally a good thing to do. As you progress from there then tweaking can come into play. The code is more complex then some folks think so changes in one area can effect others, as RBob mentioned.

Phase two is, the code is only simple enough, when it's complex enough to do exactly what you want. There's alot of excess code, for the average hotrod in GM code, and some items missing, that's what the 60 Source Code Project is about.

 

Sometimes though, when it doesn't like what you think it needs, by a large margin, there could be a problem with the car, or a problem with what your thoughts were based on - and this is a perfect example - changing the MAF scalar changes more than just the BLF!!! Just making the car run well with a mismatch of numbers does you no good when it comes time to do another car, or trying to troubleshoot a problem. You learn much more about the system if you and your engine and your engine management don't agree at first but in the end all agree. Usually the engine is right (but not always - injector problem, pressure problem, ignition problem, vacuum leak, etc) and the engine management is usually pretty close to right, but it has to be used correctly. Learning as much as possible about both is priceless.

 

You'll also want to consider what changed here (if anything). If you really were in closed loop in both cases, the engine should have been "seeing" the same fueling. Whether the BLM was at 135, 128 or 255 doesn't matter. (ASSuming you weren't at a calibratable limit of the BLM value.) This really shouldn't have made any noticeable difference in steady state idle operation by itself. A value of 128 just means that the closed loop system doesn't have to work as hard to maintain what it thinks is ~14.7. A value of 135 means the closed loop system had to move things around to get to the same ~14.7 spot. However, since some masks will add BLM to the open loop fueling, there may have been a real difference in throttle response.

I agree with Grumpy's statement. But, I also believe we have to judiciously apply a knowledge of the control system and system being controlled to make sure things are OK. Blindly changing things without knowledge of the effects (if any) of the change isn't good, either. So, from the above, we should ask ourselves : Does it make "sense" that the engine behavior changed with two different BLM values? Could the difference in engine behavior be caused by the "tweaks" that changed the BLM? Were the blinders on such that something I wasn't paying close attention to (i.e. spark, MAP, canister purge, etc) had some effect? BLM depends on the O2 sensor. Is there any reason to question the sensor (i.e. age, bad connector)?

Grumpy, I wonder why the rest of your quote is often forgotten... (The part about "Be patient" and "Take good notes".....)

 

Qualify *seeing*. While the math is the same, things do change. ie increasing the BPC by 10%, and decreasing the VE tables 10%, does produce a slight change. In some engines you might not detect it, and in others it might make a noticeable difference.

In this world of instant gratification, the last two often draw blank stares. The *happy engine* is catchy enough to stick with most everyone.

 

An appreciable amount and quality of responses this one has received.

To try and summarize a few of the inquiries.

1) car was in Closed Loop
2) this is a new Bosch 13077 sensor
3) the change was only made to the MAF table 1 at the .55 and .73 volts gram/sec values (not the MAF scalar table 1)

Mechanically, I would say that all is well but I could probably stand to inspect/clean the spark plugs.
Again, I started with a fresh ARAP bin and only changed the injector constant, base timing, fan on/off temps and the cold,warm,hot closed loop timers.

At BLM 128 the car was choppy at idle, lower the gm/sec at .55/.73 and at BLM 135 it was a nice clean idle. AIUI, the BLM/INT is only indicative of how much effort the ECM is exerting too maintain a 14.7:1 AFR so it shouldn't matter, but for some reason it is a material difference.

The ARAP bin has an inherent BLM 145 idle issue from just about everyone I've heard. I was unawares that changing the gm/sec value at the MAF volts you idle at will fudge the LV8 elsewhere in the code--that certainly is not what I want to do. If this is the case, then does everyone just accept the 145 at idle and work to get 128's everywhere else? Or am I missing something like ramping out some of the low load timing to get the idle to come back inline?

Thanks,

-Brian P
89 IROC-Z LT1 intake

 

Read the timing in both situations (BLF at 128 vs 145), and figure it out for yourself. I haven't done this so I can't say for sure one way or another.
Post your results for sure.
If the timing doesn't change, I'd be surprised. But if it doesn't, try changing the MAF scalar for an experiment for the rest of us to see the results.
Enjoy!

 

Don't forget timing can effect the BL numbers.
Not to mention mechanical ills.


From the MAF scaler playing I've done it just changes the allowable *error*. I did a few chips with the smaller tables with the scaler set at 128s, and it just made for a poor running calibration. Using the smaller entries allows for smaller "jumps" in PW from one entry level to the next. *Often* having a scaler value that allows a finally entry of something in the range of 230+ has seemed best for what I've done.

While the only MAF work I've done for a long time is for GNs, with in TGO world having huge injectors, ie 55 PPH and larger this is what I've found.

Taking a make believe engine, and calibration tables, to illistrate my point:

Say table on has to support up to 20gm/sec indicated airflow. You can have either something like Table A or B.

Table A Scaler of 40
Table Entries of:
32, 32, 32, 48, 64, 96, 128

or

Table B Scaler of 20
Table Entries of:
64, ,64, 64, 96, 128, 192, 255

If you want you could even do a table C, like this:
Table C scaler of 80
Table entries of:
16, 16, 16, 24, 32, 48, 64

FWIW, I've done the above up to and including using a 255 scaler in table one to, see for myself how different cars behave. Like I said earlier, this has been with dem lil v6 motors with large injectors so how universal these findings are, I don't know.

In every case I've found the car would be *best* with table B.

It takes the same work as having the BPC/BPW correct in MAP world, for the VE tables.

Again, this boils down to what I've been repeating forever, about not lieing to the ecm to just get the car right in one area by lieing about something, ie using the injector constant to try and fudge the MAF tables into line.

Now if your going to get this deep into it, you might also need to adjust the LV8 scaler, and see what that does for you. But be advised that can really ramp up how fast the timing moves on the LV8 axis of the timing table.

Best answer, for really getting into this is using an ECM bench to see what your dong before you attempt it on a car. Personally, I wouldn't think of getting in too deep with anything without running it on the bench first.