Mass Airflow Readings

Discussion in 'Performance' started by Hi-psi, Jan 22, 2019.

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  1. Hi-psi

    Hi-psi Full Access Member

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    Anyone out there have any information regarding what kind of mass airflow reading (in g/sec) you should be seeing at WOT? I know that it will be relative to RPM as logically as RPM's increase, so does the air demand of the engine, thus the g/sec being pulled through the MAF sensor should increase in unison.

    Also, while at WOT, with RPM's rising, is it abnormal to see small temporary dips in the reading?

    I'm currently chasing some upper RPM detonation while doing some tweaking of the tune with my Diablo Sport. I'm 99.9% sure it isn't a fueling issue. I know the only "true" way to measure WOT fueling is with a pre-cat wideband, but according to a lot of info and statements out there, on an NA vehicle the equivalence ratio that can be data logged is actually pretty close to the AFR. I'm a still just a tad on the rich side, so it's doesn't appear to be running out of fuel. I've been little by little pulling timing back in the upper RPM's, but that doesn't really seem to be having much impact. So far I'm up to pulling 5 degrees of timing.

    As I've been looking over all the data logs I'm accumulating, I think I may have spotted a trend that right when or just a split second before I'm picking up the detonation at WOT, I'm seeing a momentary dip in the g/sec the MAF is reporting. I'm wondering if that could potentially be the cause. Maybe just an old MAF that for the most part works, but just provides an erratic reading here and there.

    And yes, I've already cleaned the MAF (several times) so that isn't it. A new MAF isn't terribly expensive, but before I just blindly throw parts at it, I was curious if anyone had any knowledge or info specific to the MAF readings.

    Thanks!
     
  2. Doubeleive

    Doubeleive Supporting Member

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    I don't know those technical details but I can share that a screwy maf can cause all kinds of problems.....including transmission shifting, i've chased that dog before, if you have any doubt if it's working properly or not I now consider them to be a maintenance item with a typical lifespan of about 160k.
    @swathdiver may have more information on what kind of readings you should be getting.
     
  3. kbuskill

    kbuskill ***CAUTION*** I do my own stunts!

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    If I'm not mistaken you have the 6.2l so I'm not sure how the numbers will compare to my 5.3l but...

    I did a WOT pull today and recorded it with Torque Pro.

    I have the Diablo I2 and a custom 89 tune from Lew at Diablew tuning.

    My MAF was reading 238.8 g/sec at 5383 rpm.

    As a reference it was reading 7.4 g/sec at idle in gear.

    Don't know if that helps.

    Also I assume you are running premium 93 octane since its a 6.2l... right?

    I know when Lew did my tune he had to cut some timing because of spark knock at WOT. He kept telling me to find better fuel... lol

    ***Side note***

    AFR dropped down from 14.7:1 at idle to about 11.4:1 at WOT.

    Timing advance never went over 19° advance according to the app until after I lifted at 100mph then it jumped up to lile 38° for a sec or two.

    Also zero KR through out the 0-100mph pull according to the app.

    Who knows... maybe I need a new MAF as well... not really sure what these numbers are "supposed" to be... but the Burb runs great!
     
    Last edited: Jan 22, 2019
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  4. Hi-psi

    Hi-psi Full Access Member

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    Yes, 6.2, 93 octane from a top tier station, and the canned 91 Diablo tune that I've started tweaking. Already lined out my fuel trims and injector slope and overall it runs great, I'm just chasing this WOT high rpm detonation.

    5.3 to 6.2 won't really be an apples to apples since obviously a bigger displacement engine will be pulling more air at the same rpm, but at/around 5100 @ WOT I'm seeing 285-290 g/sec, so it's registering high flow fine.

    This is an example of what I was talking about. WOT, rpms are going up, MAF g/sec are going up, then there's a momentary dip in the g/sec, then a split second after the knock shows up, g/sec goes back up, knock fades. And I'm still just a tad rich on the AFR, but that small of an amount rich shouldn't have any impact on the detonation issue. I'd rather for right now be just a little rich. I've got a ton of recent logs I've accumulated while tweaking the tune, and this MAF "dip" is something I just noticed today. I went back and looked at several logs, and it kind of follows a pattern. I'll see the g/sec climbing linearly in line with the RPM's @ WOT, then see a little split second dip, knock, g/sec back up, knock fades.

    I might see if I can round up a friend with a comparable GM vehicle and swap MAFs with them and see if I notice any different behavior.

    upload_2019-1-22_19-21-56.png
     
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  5. kbuskill

    kbuskill ***CAUTION*** I do my own stunts!

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    What are you using to log?

    I am still learning with the Torque Pro app... I am certain there is probably a better way than what I am doing.
     
  6. Hi-psi

    Hi-psi Full Access Member

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    Right now I'm using my Diablo Sport i3 to log, but I've used Torque Pro a lot before as well. Even though logging with the Diablo Sport isn't quite as easy as using my phone & Torque Pro, I've noticed that logging with the i3 gives me a MUCH faster sample rate, so I get more granular data to spot little things like this.

    Unless there's a setting I'm missing somewhere in Torque, or my Bluetooth OBD-II dongle just really sucks, LOL, I only see a sample rate of once a second with Torque Pro, where as with my i3 I'm getting 131 samples per second. Quite a big difference when you're trying to analyze split second changes in things.
     
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  7. kbuskill

    kbuskill ***CAUTION*** I do my own stunts!

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    Ok... so pardon my ignorance but when you log with the Diablo do you have to have special software in order to view the logs?

    I have never really tried to look at any of the logs I've done... I just emailed them to Lew.
     
  8. swathdiver

    swathdiver Full Access Member

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    The above is a run at the track recorded with a Tech-2 and viewed on TIS2000 software. I also looked at several recorded passes made with the AutoCal on EFILive and no drop while the RPMs were climbing, even with KR.
     
  9. Hi-psi

    Hi-psi Full Access Member

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    Yeah, you just download the DataViewer Windows program from Diablo Sports website.

    The handheld tuner saves the data logs in a proprietary format with a .log extension. The DataViewer application can open/access/view those logs and play them back in realtime. You can view a graphical "dashboard" of all the data points/PIDs that you sampled.

    Then under the File menu of the DataViewer application you can export the log file to csv if you like to use Excel to examine the data.

    I'm a bit of an Excel geek, so I feel more at home there using filters, functions, etc to mine the data to spot things. Haha..
     
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  10. Hi-psi

    Hi-psi Full Access Member

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    Screenshot of the DataViewer application playing back one of my Diablo logs.

    upload_2019-1-22_21-25-53.png
     
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