Sorry I had to ask this simple question, but I have gotten a few data scans saved up, and want to figure out my mixture status. The integrator seems to avg around 128, but does bounce around that number. The BLMs seem to start at 128 and go down as the scan goes on. They bounce up a bit when the load changes, but mostly run around 110 to 115. Is that showing a rich condition? Both numbers are locked at 128 when learn control is off, which is normal.

From my O2 readings, it looks like the mixture is more on the rich side. My flow rate constants are still at the stock 23.0, and STOI. AFR is set to 14.7. I was think of increasing the flow rate to 24.0, but a friend at work said I should lower the AFR to about 12, to make the car run leaner. My fuel pressure is set at 49psi, haven't messed with that in a while.

What is the overall goal for fuel mixture, to have both the BLM and integrator at 128?

Any advice from some fellow tuners?

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Best ET 14.413 @95.57 without
pulling valve covers or manifolds.
Also with stock 2.77 rear end!!!

 

BLMs lower than 128 indicate a rich condition and your ECM is adjusting the pulse width in order to lean it out.

Bumping the AFR to 12 is stupid. This will cause your car to run RICH (not lean as your friend suggested). The lower the AFR the more fuel.

I would suggest getting an idea of your entire curve. You said that most of the time that they are around 110 to 115 ... but that sometimes they bounce up above 128. That means that you are rich at some points and lean at other points. Changing the injector constant will do the same thing as adjusting the fuel pressure -- this is a GLOBAL change that will affect everything. So, if you increase the injector constant in order to lean out the mixture then you are also leaning out those already lean spots (BLMs greater than 128). I would recommend working with the MAF scalars until you get everything at 128.

Tim

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TRAXION's 1990 IROC-Z
Best Time = 12.244 @ 112.51mph (1.778 60' / 7.819@88.32mph in the 1/8)
All Natural. No Force. No Drugs. Stock Bottom End. Stock Body Panels.
Gunning for NA 11's with bigger cam, bigger stall, and bigger exhaust.
-=ICON Motorsports=-
Moderator: PROM board at thirdgen.org

 

I agree completely with Tim; you are running too lean yet some others are okay.

If you found ALL (or most) of your BLMs where either under or over 128, you could use the Injector constant to do a global change to get you close to 128 and then fine tune the MAF Scalar table. But, as Tim pointed out, when you have basically a 50/50 situation, you are better off just tune the MAF Scalar table as this is the ultimate place to change things.

If it makes you feel better, what you have experienced is normal for most basically stock engines. GM tended to make their eproms (especially WOT) too rich (along with not enough spark IMO).

 

Thanks fellas. After I made this post last night, I did some major searching on this board, and read up on this topic. I somewhat understand WHAT to do, just don't really know HOW to make changes, to get the 128 numbers we all crave.

Glen, I think you meant to say too rich in your post??

Thanks for the info on the AFR, that is what I wanted to hear. I am leaving it alone!! As far as the BLM's, I can fairly say they are mostly below 128. They bounce up to 128 but not really above it. They basically stay around the 110-115 number I mentioned. The integrator seems to avg around 128. Maybe I should lower my FP a bit, but I still may increase the injector constant to 24.0

Tonight, I did about a 10 minute idle test and scan in my garage. I definitely had closed loop, and learn control was on. I didn't touch the gas pedal. The BLM was rock solid at 108, and the INT was solid at 128 or 129. I watched the O2 readings closely, and they avg about .50-.60, kind of a straight line, but moving a little bit. I beleive that is on the rich side.

Was this a good test? Can (or should) I adjust things to get my idle numbers better?

Now on the MAF tables. From previous posts, it seems that these are the tables I need to adjust to affect my fuel curve. Compares to the VE tables for SD cars. Here is my take on these tables.

The MAF sensor is a calibrated sensor that measures incoming airflow to the motor. The tables take the number of counts, from the MAF, and convert them to air flow. The ECM uses this info to calcuate load and injector pulse width. You would hope the sensor and tables are acurate. But if you change the table values, aren't you lying to the ECM? IE, telling the ECM you have XX airflow, when you really have YY airflow? Maybe I am looking at this all wrong, but I want the MAF to measure the real airflow into the engine.

Here is the catch. I have taken the screens out of the MAF, and also the splash guards in the air intake. I also drilled 6x1/2" holes in the bottom of the air intakes. I have done some TB and plenum/runner work, but that is after the MAF.

Also, the tables that I am using right now, are the exact tables in the ARAP bin. These are different than the stock 88 GM tables, as well as the values from my ADS chip. Maybe I need to graph those tables and see how they look. But, where would I start to get the BLMs to move where I want?

Thanks for you help. This board is full of great people!!!

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Best ET 14.413 @95.57 without
pulling valve covers or manifolds.
Also with stock 2.77 rear end!!!

 

For the block learn numbers you're reporting, you should definitely lower your fuel pressure, check them again, then adjust your injector constant to make the global change. Once they're all pretty close, you can adjust the MAF tables to hone in on certain block learn cells.

The test you did only covered 1 BL cell, so you need to drive around and hit as many of the cells (16 total) as you can to see how it looks overall. Yes, you're running quite rich in this cell, and it also looks like your O2 sensor is getting old as it wasn't very responsive. Mine jumps around quite a bit while idling and driving around.

Your take on the MAF tables is pretty accurate, although you wouldn't be lying to the ECM in changing the values since it's not reporting the correct amount of airflow. What you'd be doing is calibrating the tables to match the flow curve of your MAF sensor. Changing things like the intake ducting, removing the screens and/or fins, and sometimes even stuff after the MAF sensor throws off the calibration, so you need to correct it for your set-up. I would start with your stock tables, then change them to hone things in. If you're reading rich or lean at a certain airflow reading and block learn cell, you'd change the airflow value in the table (and maybe the values on each side of that airflow) to tell the ECM what the MAF is actually reading. I'm sure I covered this in a previous thread on MAF's, so maybe do a search for MAF in the text and see what comes up.

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Greg Westphal
'87 IROC 305TPI/A4

 

Mike, yes, I meant rich. I am busy with a lot of work right now and I was just blasting off an answer.

 

Thanks for your reply, Greg. I did do a search last night on the boards, and kind of figured out how to make the changes, just as you mentioned. I like your take on the MAF sensor, just needed someone here on the boards to spell it out to me!!

I have been doing road test scans, and I am finding the BLMs to be low throughout the testing, at different loads. I don't think my 02 sensor is gone yet, car has only 57k on it, and it does transition from 0 to 900+mV, during normal "learn" modes.

Tonight I did lower my fuel pressure, was about 49-50, so I backed it down to 48, just to try it. I had my scan tool running, and the BLM was reading 114-116, in closed loop just at idle. Airflow was also 6.5gm/sec.

I may burn a chip soon, changing the injector flow constant, from 23.0 to 24.0, then do some scans to see where I stand. From the looks of things, it could take several dozen chip burns, to get those MAF tables to come in!!! The fun is just beginnning!

 

Glad my explanation worked. How fast is your O2 sensor switching back and forth? You might want to put a new one in just for improved accuracy. Since your BLMs are low everywhere, I'd reduce the fuel pressure some more (low to mid 40's with the vacuum line to the AFPR disconnected) and see how much that helps. If you can't get it low enough, then start raising the injector constant, maybe .2 or .5 at a time.

Your idle airflow reading is right where mine's at. The more you get into burning chips, the more you'll enjoy it. I love the looks on guy's faces when I tell them I burn my own chips and how many things I can change.

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Greg Westphal
'87 IROC 305TPI/A4

 

I checked some scans for the rate that the O2 is changing. Here are some numbers; 247 transitions in 15 sec, 248 in 10.1 sec, 251 in 28.9sec, 249 in 19.7sec. These were about the quickest it moved. It also transitioned slower than this, I just picked some areas of the scan where the crosscounts picked up fast.

Are these reasonable transition rates? What rate would a new sensor flip at? I swapped out the sensor in my truck at 124k miles, didn't really notice any difference. It may run a little bit smoother. I don't think the O2 moves any faster, but I don't have any hard data to prove otherwise.

I consider the O2 sensor a critical part of the engine. Should be changed as part of normal maintenance. My mechanic told me that they could still work fine, but be slow to react. Hard call to make changing it out now, car has only 57k on it.

 

From the numbers you gave, it seems your O2 sensor is still working fine. Burn on!

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Greg Westphal
'87 IROC 305TPI/A4

 

If you are getting mostly low BLM values, then increase the Injector Flow Constant to globally lower the amount of fuel you are getting. I prefer higher fuel pressure which has it's greatest effect at high load (low vacuum) and least effect at low load (high vacuum).

I think if you were to adjust the Injector Flow Constant and then fine tune the specific MAF scalar table to correspond to specific flow values that are off, you'll will get your eprom tuned faster and more accurately. I also prefer fuel pressure in the mid-high 40 PSI range.

 

Glen, that is exactly what I am doing now. My fuel pressure is at 48, and last weekend I burned a chip with the flow constant changed to 24.0, which is up from 23.0. I will do a scan tomorrow on my way to work, and check the BLM numbers.

As far as the MAF tables, I am using the values from the ARAP bin. I put those values, and numbers from 2 other bins into a spreadsheet, so I could look at them close and graph them. I am thinking about going back to using my stock '88 values, since they are generally lower than the other 2 bins that I have. I think this is the direction I am headed towards anyways.

Thanks for all you help, keep it coming!!!

------------------
Best ET 14.413 @95.57 without
pulling valve covers or manifolds.
Also with stock 2.77 rear end!!!