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Ok, now that I have your attention, I have a question.
I measured the voltage across a spare B13 DE maf I had in the garage by blowing air past the sensor with a blowgun, and the maximum voltage was 7.70 volts. As most people know, the maximum the ECU will interperet is 5.11v. I have a Techtom CMX-100 on the car, and sure enough, it peaked out at 5.11v.
Now my question is, has anyone ever looked into modifying the maf table so it can deal with more than 5.11v?
Another thought. It's my understanding that a bored B13 maf tops out approximately the same power level as 370's @ 4 bar. What about using S15 480cc side feed injectors with a bored maf, and modding the ECU to read over 5.11 from the maf. That should raise the level of useable safe horspeower on an inexpensive setup.
The VQ map only has 64 blocks. Each block is 0.08Volts. If you wanted a cheaper MAF option you can take the sensor out of the stock maf and place it into a peice of tubing.
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Well I shouldn't say CAN'T, how about can't easily.
If you used a stock MAF setup blow-through you could just take the sensor out and put it into your charg piping, that way you dont have to have any bottle necks.
Well at some horsepower level the 53.5 or 55mm bore would become a major restriction, but I have no idea where that would be. I was just intrigued seeing that the maf could actually produce a 7.7v output and was thinking that was the key to getting some more horsepower out of the stock maf.
Why not change the values in the 64 blocks so it could measure > 5.11v?
C
This is what I can tell you from an electrical engineering standpoint:
The ECU can't interept higher than 5.11V even if you could store larger numbers in the map. The reason? It has a 9 bit analog to digital convertor or A/D.
a little binary number lesson:
1 bits: resolution = 002, range = 0 to 001
2 bits: resolution = 004, range = 0 to 003
3 bits: resolution = 008, range = 0 to 007
4 bits: resolution = 016, range = 0 to 015
5 bits: resolution = 032, range = 0 to 031
6 bits: resolution = 064, range = 0 to 063
7 bits: resolution = 128, range = 0 to 127
8 bits: resolution = 256, range = 0 to 255
9 bits: resolution = 512, range = 0 to 511
Depending on how nissan setup it up the 5.11V reading from your ECU could actually mean 5V. It's just a matter of how they setup the A/D converter. I would suspect the A/D has a maximum reference of 5V and they just divided that up into a range of 0 to 511 because its easy to design and cheaper. It actually doesn't have any effect on tuning because the maps are based on the 0 to 511 range.
Again this is just what I see as the reason for this 5.11V max. I could be wrong but I'd be willing to bet I'm right
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A few ideas on how to use a MAF to read higher airflow:
The maf is little more than a variable resistor dependent the airflow across the filliment. It probably has a buffer at it's output (ex. opamp setup as a voltage follower). Even without a output buffer this would work:
Build a op amp circuit with a high input impedence to scale the MAF voltage (this is what a SAFC does) and retune.
This would work if the output from the MAF is consistant above 5V. It doesnt have to be linear b/c the ECU is tuned using maps aka "look up tables." It just has to be consistant.
This is what I can tell you from an electrical engineering standpoint:
The ECU can't interept higher than 5.11V even if you could store larger numbers in the map. The reason? It has a 9 bit analog to digital convertor or A/D.
No, it has a 6 bit resolution. What Nate said is correct, 0.8V steps, maxes out at 5.08V. It is buffered at both the maf and the ecu of course, and the ecu 'knows' the value of the gain stage applied at the ecu (I'm not sure what the actual A/D refrence voltage is, but its pin 30 if you want to figure it out) hence when you ask the ecu what the maf voltage is (or battery voltage, etc) you get the correct value.
The A/D has a full resolution of 10-bits, but its a successive approxamation type so you can make some trade-offs for resolution versus speed.
No, it has a 6 bit resolution. What Nate said is correct, 0.8V steps, maxes out at 5.08V. It is buffered at both the maf and the ecu of course, and the ecu 'knows' the value of the gain stage applied at the ecu (I'm not sure what the actual A/D refrence voltage is, but its pin 30 if you want to figure it out) hence when you ask the ecu what the maf voltage is (or battery voltage, etc) you get the correct value.
The A/D has a full resolution of 10-bits, but its a successive approxamation type so you can make some trade-offs for resolution versus speed.
So the ECU must use a running average filter to clean up the input from the A/D and round off the least significant bits... but I dont understand the 5.08V max. So if the resolution is 6 bit then the range has to have at least 9 bits (6bit plus 3 LSBs set to zero) to reach 5.08V and even then 5.08V is not possible b/c its between 504 and 511.
The Nissan ECU uses a Hitachi MCU right? Basicly a Motorola 68hc05 clone correct? Or some similar 68xx family chip. Do you have any code that I could look at, not just maps but disassembled code. Is there any commented code flying around If you could provide me with any kind of documentation like datasheets, part numbers, links, code, whatever I would be greatful.
So the ECU must use a running average filter to clean up the input from the A/D and round off the least significant bits... but I dont understand the 5.08V max. So if the resolution is 6 bit then the range has to have at least 9 bits (6bit plus 3 LSBs set to zero) to reach 5.08V and even then 5.08V is not possible b/c its between 504 and 511.
The Nissan ECU uses a Hitachi MCU right? Basicly a Motorola 68hc05 clone correct? Or some similar 68xx family chip. Do you have any code that I could look at, not just maps but disassembled code. Is there any commented code flying around If you could provide me with any kind of documentation like datasheets, part numbers, links, code, whatever I would be greatful.
On the first part, no, its a bit simpler than that.
On the second part, nope again , its a mitsubishi mcu. It has no relation to any motorola part. The older nissan ecus used hitachis (Z31, Z32, early S13, etc), the later ones (B13, S13, and up) used mitsubishi, then the much newer stuff (some R34, etc) dabled in hitachi again. I have no idea what the late model stuff uses now. Hitachi and mitsus mcu lines merged to form a company called Renesas. I've posted datasheets and stuff in this forum before, dig a little.
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If you could provide me with any kind of documentation like datasheets, part numbers, links, code, whatever I would be greatful.
