MAF Sensor Frequency vs GPS Airflow Table

[finishline]

Anyone have a Frequency vs GPS airflow table for a stock 87 GN MAF?

I'm getting ready to tune my GN and I need to know how many GPS of airflow I have per the frequency HZ reading from the MAF Sensor.

Thanks,

Randy

 

[salvageV6]

I only have two data points from the service manual.

32Hz. is 3gm/sec. and 150 Hz. is 150gm/sec.

Hopefully it's linear so you can just connect the dots on a graph.

 

[finishline]

MAF HZ vs GPS

I only have two data points from the service manual.

32Hz. is 3gm/sec. and 150 Hz. is 150gm/sec.

Hopefully it's linear so you can just connect the dots on a graph.

I have run a crude test on my MAF and have learned that actually there is a range that 3 GPS fits into. I came up with 37 for 3 GPS 38.6 for 4 and 43 for 7 GPS. I was hoping a tuner or some of the other anal scientist like myslef on this board had done some simular testing that I could compare my results with. Thanks for your help.

 

[turbopaul]

How are you gonna tune knowing the gps of the MAF? Most people tune by monitoring the O2 sensor (WB or NB type) and by how much knock is picked up. Don't you have a scan tool that displays the gps? Could you explain a little more on what you're doing? Sounds very interesting.....

Paul

 

[finishline]

How are you gonna tune knowing the gps of the MAF? Most people tune by monitoring the O2 sensor (WB or NB type) and by how much knock is picked up. Don't you have a scan tool that displays the gps? Could you explain a little more on what you're doing? Sounds very interesting.....

Paul

I use an Innovate Wide Band with their LMA-3 Aux Box to data log 12.5 frames of data per second. It takes a frequency reading off the MAF but the chip (bin file) is in GPS. So I need to be able to look at my data run see where I go lean and convert that frequency to GPS and adjust the chip accordingly.

ps--scan tools are to slow.

 

[ijames]

ps--scan tools are to slow.

Well, direct scan gives you 18 frames per sec, more than the lm1. I use the lm1 with rpm cable to log rpm, tps, map, and afr, and direct scan to log everything from the ecm, all on one laptop at the same time, then I use the tps and rpm traces to align the two datasets for analysis. I wouldn't want to try syncing with the maf signal, it changes so slowly and you will have to do your own calibration. Besides unless you have an extender the maf will be pegged most of the run anyhow, and all the fuel "curve" tuning is really done with the pe/rpm table, so I think rpm would be a must for you to log.

 

[finishline]

Well, direct scan gives you 18 frames per sec, more than the lm1. I use the lm1 with rpm cable to log rpm, tps, map, and afr, and direct scan to log everything from the ecm, all on one laptop at the same time, then I use the tps and rpm traces to align the two datasets for analysis. I wouldn't want to try syncing with the maf signal, it changes so slowly and you will have to do your own calibration. Besides unless you have an extender the maf will be pegged most of the run anyhow, and all the fuel "curve" tuning is really done with the pe/rpm table, so I think rpm would be a must for you to log.

First my apologies to you about direct scan. I didn't know it was that fast. I try to buy tools that can easily be adapted to many cars. Most of what I tune are Corvettes and Camaros both OBDI and OBDII. I can't justify buying another tool like Direct Scan when what I have now will do the job quite well. I datalog all the same stuff you do except I don't log MAP since I use a MAF sensor. I am datalogging the MAF Frequency which I have found to be very sensative. I tune cars for everything including driveability, cold start, idle, you name it. The dragstrip is not the only thing I tune for so yes I still need the Frequency vs GPS data. I could do it without it since I can tune my GN on the fly but, I'm anal about getting things very close on my first attempt. One thing I also data log that you don't is my fuel pressure. I know you already know how critical that is on our GN's. I sure wish you were using an AUX-BOX instead of that RPM CONVERTER, then you could overlap your scans like you do and give me the data I'm looking for. I appreciate your input and time.

 

[ijames]

Go to http://www.gnttype.org/techarea/chips/chippage.html and click on "printable spreadsheet", and save this. Open it in excel or get the excel viewer from Microsoft. Scroll down to line 1740. The column labeled "data" is airflow in grams/sec. Column G is 1927-(counts of a 65536 Hz clock). The 1927 comes from lines 1727 and 1728 and represents 34.01 Hz, the lowest frequency to be handled. So on line 1740 the airflow is 3.3 g/s and column G is 64 so 1927-64=1863 counts and 65536/1863=35.2 Hz. Clear as mud? The subtraction plus table lookup is a tricky way to form the inverse, and the extra tricky part is that they use six tables to span the full frequency range instead of one big one so they can vary the granularity. That gives them steps of about 1.5 gram/sec down at 3-5 gram/sec and steps of 33 gram/sec up at 140 gram/sec.

If you don't want to wade through this, the frequency range is 34.01 to 149.97 Hz and a few examples are:
3.3 g/s = 35.2 Hz
31.2 g/s = 72.6 Hz
141 g/s = 119 Hz
219 g/s = 135 Hz
254 g/s = 144 Hz and higher

I kept everything at 3 significant figures; I wouldn't expect more out of this scheme. I have NOT verified this with an oscilloscope . If you want more, get the "ecm secrets" file from gnttype and look at the code at about $ED84. Hope this helps.

 

[ijames]

PS It's true that this ecm doesn't read the map but it is nice to log it so you can make sure the boost was behaving, and to not have to try to look at the gauge to see what it is while at wot . While fuel pressure is certainly as critical as anything else I think the boost is useful much more often, while the fp is pretty much something to look at only when the motor isn't running right.

 

[ijames]

Oops, forgot the "rest of the story". The stock maf was pretty temperature sensitive, so much so that buick added the manifold temperature sensor (yes, I know they put it in the air filter and not the manifold but they called it a mat) and only used it for maf correction. In the promdata spreadsheet go down to the next table and look at line 1818. This is a two dimensional table indexed by raw airflow and air temperatue, with the correction in percent and the neutral (no correction) temp 22 C (72 F). Line 1818 says that at zero grams/sec measured and 22 C the correction (data column) is zero percent. Line 1891 says that at 33 C and 80 g/s the correction is +2%. Below 22 C the corrections are negative which means the measured maf (which is what you will be getting with the lm1 and the stuff I posted above) is a little too high, and hotter than 22 C the measured readings will be a little low. Remember that the stock air intake was under the hood just off to the side of the radiator so the inlet air temps could get pretty hot. Oh, and just to make life more tricky they do interpolation between the temps and maybe also between the measured maf's (I'm a little to sleepy to wade through that code this early, sorry).

 

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MAF HZ vs GPS

Carl,

I was out of town until late Sunday night. I finally had a chance to catch up on mail and messages.

Thank you so much for the answer and explanation behind all those numbers. I've never been able to understand all that code. I have already worked up all the numbers for every chart and was amused to find that my testing was very very close to the numbers I came up with after doing the math. Thank you again. I will be studying the rest of the code at a later date.

Randy