MAF Max?

[schaid]

So on 2 separate vehicles with 2 completely different setups I've now seen this number as the absolute top airflow, 86.69. One being my twin turbo coyote and the other being a kenne bell supercharged boss 302 that I've been working on.

What my question is...is this a max reading issue with scanner or is this the maximum that the coyote maf can register? The cars don't seem to be having any issues and both maf tables are super close on ft, +/- about 2%. Both have values higher than 86.69 in the top uSec they are seeing.

Thanks for any input.

[bbrooks98]

It's just the max the scanner PID can report.

[15PSI]

As far as I know, very few have exceeded the maximum of the OEM MAF. As bbrooks98 noted, the value you received is a limitation of the PID, not the MAF.

[schaid]

It's just the max the scanner PID can report.

So if I'm understanding this, it should be as simple as raise the limit of the pid in scanner. Not that it's critical information just sort of why would they not just set it to something crazy high like 200 instead of 86.69. Math says that's around 870 crank hp if you go off the 10lbs/min per 100hp equation.

[Witt]

Its not an HPTuners issue. Its the limit of the SAE PID. See this for more info. 655.35 g/s is 86.69 lb/min.

[Plimmer]

If you log period you'll see it keeps on reading even though the MAF reading has stopped

[15PSI]

For your viewing pleasure: http://www.lbcc.edu/attc/documents/OBD2.pdf

[schaid]

If you log period you'll see it keeps on reading even though the MAF reading has stopped

This is a joke right?

[bbrooks98]

So if I'm understanding this, it should be as simple as raise the limit of the pid in scanner. Not that it's critical information just sort of why would they not just set it to something crazy high like 200 instead of 86.69. Math says that's around 870 crank hp if you go off the 10lbs/min per 100hp equation.

I'm sure there is some way around making the values max out much higher if someone had the know how and wanted to do it. Mitsubishi guys had a similar issue with their load values maxing out in the logger with standard OBDII PIDs. Those guy ended up writing something with 2Byte vs 1byte along with a custom pid and were able to work around something similar where there was a hard limit. Its too bad we don't have that kinda support like those open source ECMS do were rather than just deciphering the OEM code those guys write a lot of their own patchs.

[jchambers]

This is a joke right?

No, absolutely not. The airflow PID is dimensioned with a clip at 86.69 lb/min. This has been recognized for a long time. The hertz and period PIDs are not clipped so they will continue to report correctly even after the airflow PID has reached the clip. Now this is a datalogging clip, not a hardcoded ECU airflow clip like you might be used to with the old EEC-IV strategies. However, if it bothers someone that much, scale the tune just like you used to have to do with the EEC-IV to keep your max airflow below that 86.69 lb/min limit and you'll be able to log it throughout the flow range.

[15PSI]

MAF Airflow Example.png

An example of higher airflow values from the MAF in my blown Coyote.

[jchambers]

Again, the airflow is NOT clipped. Only the amount reported by this particular PID in the scanner. You can actually flow much more than 89.69 lb/min with the MAF, but the scanner is going to flatline the airflow in lb/min at 86.69 lb/min.

[06300CSRT8]

Isnt there a non-SAE airflow PID that can be logged? Seems like the SAE should be the only one with the SAE scanner limit.

[tbrtuning]

Why do you guys need to see it? Is it not just a value being reported based on what value you have in the MAF table of the tune anyways? I've never given it much thought before because as long as I can still get the data for whatever the MAF axis is using and EQ Error / Fuel trims it isn't really something of much use to me. If you want to see if it flowed more air after a change look at the period / volts.

[bbrooks98]

Why do you guys need to see it? Is it not just a value being reported based on what value you have in the MAF table of the tune anyways? I've never given it much thought before because as long as I can still get the data for whatever the MAF axis is using and EQ Error / Fuel trims it isn't really something of much use to me. If you want to see if it flowed more air after a change look at the period / volts.

You're right its mostly a wish list item and there is no need to know in most cases, but it is nice having accurate data available when needed or even as a quick rough estimation of horsepower. Slightly off topic, but what's the highest air load value anyone has seen?

[murfie]

You can always use the fuel flow rate and actual lambda ratio to get a value of air flow rate.

[tbrtuning]

You can always use the fuel flow rate and actual lambda ratio to get a value of air flow rate.

This is more accurate anyways. If you use MAF Airflow at least scale it by EQ Error / Fuel Trims.