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Thread: How to extend AE duration?

  1. #16
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    Hi guys,
    This is just wanted to say thanks for your replies.
    I'll need to take some time to go through what you've posted, I'm sure once I've got my head around things I'll have some questions.
    Thanks again for the help.

  2. #17
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    Hi Dud,
    Just trying to understand your statement "The smaller the number, the longer the pulse time".
    If I'm understanding you correctly then reducing the uSec values as a trend should potential increase the AE duration?
    I had previously assumed that the larger uSec value meant longer pulse time at the injectors.
    I made up and AE vs TPS difference graph to for you to comment on as a visual example of what I think you meant, please let me know if that looks correct?
    Attached Images Attached Images

  3. #18
    Fuel Injected! dud's Avatar
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    Yes. Lower values = longer AE duration.

  4. #19
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    Thanks for confirming that.

    Looks like I've been going the wrong way, increasing AE vs TPS values when I should have been reducing them to increase the AE's duration time.

    It potentially makes sense now, about a year ago I went back to a near stock bin which would have had stock AE vs TPS values and I remember thinking the van felt like it accelerated a little bit better.
    Unfortunately the next day I increased the fuel pressure and tuned for that, at the time I probably thought I'd better increase the AE vs TPS values because stock values must be too low.
    I've put my van away in storage ready for the winter but once I've gone through 84Elky's last post I might need to get the van out of storage and try some things.

    Thanks again.

  5. #20
    Fuel Injected! 84Elky's Avatar
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    Quote Originally Posted by dud View Post
    TPS Difference AE Coefficient vs. Temperature will stretch out the AE pulse time. I had a lean spot that occurred before the engine got heat soaked that I couldn't get rid of until I worked with this. I think it's because of the volume difference between the new vs. old intake manifolds. For me this also made the engine feel more responsive and smoother.

    The smaller the number, the longer the pulse time.

    Beware that you may have to adjust AE vs. TPS Difference accordingly.
    Thought I'd weigh in here. Apologies for the long post.

    First, the table Dud referenced (0x4B5A=TPS Difference AE Coefficient vs. Temperature), applies to AE-TPS only.
    Let's look at exactly how it's used:
    -A coefficient (% change factor), is extracted from the referenced table based on coolant temp
    -That coefficient is later used to lag filter the Current TPS%. Lag Filtering is a technique used to smooth-out values to avoid rapid changes.
    Formula: NewFilteredTPS% = PriorFilteredTPS% + [(CurrentTPS% – PriorFilteredTPS%) * LagFilterCoeff]
    The smaller the coefficient, the closer the new filtered value (NewFilteredTPS%) is to the old value (PriorFilteredTPS%). Plugging values into the formula will prove this.
    -After the NewFilteredTPS% is computed, it's subtracted from CurrentTPS% to obtain a Delta TPS%, and to determine if TPS% is rising
    -If Delta TPS% is not rising, AE-TPS is NOT invoked; or if currently invoked, it's exited
    -If Delta TPS% is rising --AND-- NOT currently in AE-TPS --AND-- the Delta TPS% is > (0x48B9=TPS Difference to Enable AE [Factory = 1.17% .vs. the posted BIN here = 0.78%], AE-TPS will be invoked.
    -Once invoked, an AE-TPS PW is extracted from the table (0x4B45=AE vs. TPS Difference) based on the Delta TPS%

    So why this detail? On-balance, the Delta TPS% will generally (note "generally") be larger with lower lag filter coefficients because TPS% - [lower]NewFliteredTPS% = [larger]Delta TPS%. This means the AE-TPS PW extracted from the 0x4B45=AE vs. TPS Difference Table will be larger (larger Delta TPS% = larger AE-TPS PW). But remember "generally". Delta TPS% is calculated 160 times a second. Due to varying engine conditions (TPS position), it's impossible to know at any point in time exactly what a given Delta TPS% will be.

    IMO, it would be far better to change the PW provided at any given Delta TPS% by changing values in the 0x4B45=AE vs. TPS Difference Table. Now one knows exactly the AE-TPS PW that will be provided at any given Delta TPS%. Don't have to wonder what the Delta TPS% will be. Can't control it anyway. Other than for the coefficient, it's calculated with values we can't control.

    Granted changing the table coefficients "may" work, but here's something that is supported by a multitude of tests over many years: Mildly changing lag filter coefficients (and there are many) rarely results in consistent output. Exact results are indeterminate. And radically changing coefficients can have unexpected results.

    Bottom line, it's best not mess with them. The GM Engineers had significant data to support what they used. As above, there is generally a more concrete way to achieve a desired result than changing filter coefficients.

    FWIW, Elky

  6. #21
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    Hi 84Elky, sorry about the time it's taken to reply. I've had a vintage computer problem to solve and I didn't want to focus on this until I had that sorted out.
    Thanks for taking the time to have a look at the csv. log, I appreciate it.
    I don't normally look at the csv. file because of it's sheer size but I do now realise there is a lot of useful information in there.

    Getting back to your original comments on my csv. log:

    -Yes, the van is heavy and acceleration in high gears is underwhelming, but I guess that’s what I should expect given the RPM and the weight it has to move. I probably should have gone with a 383 for a bit more low RPM torque or a slightly lower diff ratio. I have played with the shift tables in the past and it was better.
    Not sure why the IAC is sitting at 73, even at W.O.T. I just assumed that was normal?
    I'm not sure what parameters control the IAC but I'm guessing it's not looking at throttle position once above a certain speed or in a certain gear?

    -Knocks: thanks for the comments, it’s be a real monkey on my back trying reduce/eliminate knock counts. I’ve spent so much time over the years trying to sort it out and you’re right it’s probably just a rattle somewhere.

    -PE: I reduced the “TPS % for PE” to get PE to come on sooner. So while you mention it not normal, it’s what I wanted to try.
    I when accelerating up an onramp, manifold vacuum would drop to around 8" and at that point I wanted PE AFR’s not Stoich. Changing that value allowed me to at least be able to get PE to come on when I squeezed the throttle a little bit more.
    If it was a heavy vehicle with a carb that's about the point I'd like the power valve to start operating.
    I know early PE is not the best for economy but the van was staying at 14.5-15.0 even when the manifold vacuum was getting down to 5”. It normally cruises in the 10”-16” range at 60.

    -CL idle is actually set to open loop. I’ve found the engine idles a bit smoother at 13.5-1 rather than Stoich so I’ve set it to go open loop when at idle. I run a heated Narrow band O2 sensor as well as a heated Wideband. I could see how it might have looked like the Narrow band O2 sensor wasn’t up to temp though.

    -Yep, you’re right I do need to work more on my VE in the 1100-1500 range.

  7. #22
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    Understand your comments. Explains several things. I wouldn't be concerned about the IAC. Only adj is to properly set it at idle. Stupid as it seems, I would check to see if throttle body is 100% open when pedal is on the floor.

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