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Thread: Let's Talk Fundamentals Of Injector Pulses/Strategies

  1. #1

    Default Let's Talk Fundamentals Of Injector Pulses/Strategies

    I'm asking general questions, not specific to any one engine, ECU, or injection system.
    I'm by no means even remotely educated in tuning EFI, but I'm always wanting to learn things.
    I know that a carburetor uses an "accelerator pump" to aid in raising the RPM when the throttle is opened.
    I know that TBI ECUs have an "accelerator pump" strategy in them, that modifies the injector pulse in a way that could be compared to how a carburetor's accelerator pump works.
    What I was curious about is do MPFI engines use a similar AP strategy? Does it have anything to do with the fact that many TBI fuel pressure regulators aren't vacuum referenced?
    Or does something about the fact that it is directly injected defeat the need for an accelerator pump strategy?

    What sparked all of this was I was looking at a buddy's Holley Pro-Jection TBI system. The ECU had (5) pots that you could turn to adjust. They were:
    1) "Main"
    2) "Idle"
    3) "Choke"
    4) "Accelerator Pump"
    5) "High RPM"

    After I saw that, I got to wondering, is the accelerator pump strategy there because:
    A) Because it's not direct port injected.
    B) Because that system does not use a vacuum referenced FPR.
    C) Neither, all engines use some type of accelerator pump strategy.
    D) None of the above, there is something else that I'm not thinking of.

  2. #2
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    Quote Originally Posted by B2-BOMBER View Post
    What I was curious about is do MPFI engines use a similar accelerator pump strategy?
    Holley's TBI & MPFI ECUs have the same six Acceleration Enrichment (AE) parameters.

    Does it have anything to do with the fact that many TBI fuel pressure regulators aren't vacuum referenced?
    No. TBI fuel pressure regulators (FPR) aren't vacuum referenced because the injectors aren't subjected to intake manifold vacuum.
    Exception: Terminator TBI fuel injectors are below the throttle blades (intake manifold vacuum), and should use the vacuum reference hose (on FPR).

    What sparked all of this was I was looking at a buddy's Holley Pro-Jection TBI system. The ECU had (5) pots that you could turn to adjust.
    Originally Posted by Danny Cabral
    EFI AE In Carburetion Terms:
    "AE vs TPS Rate of Change" = carburetor accelerator pump
    "AE Correction vs TPS" = carburetor accelerator pump cam (shape)
    "AE vs MAP Rate of Change" = carburetor power valve function
    "MAP AE Time vs Coolant" (Decay) = carburetor shooter size
    "AE TPS vs Coolant Temp" = carburetor choke effect (in terms of AE)
    "MAP AE vs Coolant Temp" = carburetor choke effect (in terms of AE)
    "AE vs TPS RoC Blanking" = carburetor accelerator pump lever adjustment (feeler gauge)
    "AE vs MAP RoC Blanking" = carburetor idle transfer slot/circuit exposure (idle & off idle)

    "Coolant Temperature Enrichment %" & "A/F Ratio Offset" = primary carburetor choke functions
    "Target Idle Speed" & "IAC Parked Position" = carburetor choke fast idle cam & idle kickdown functions

    Additional Notes:
    You may also be interested in the injection strategy info found in this thread:
    http://forums.holley.com/showthread....amp-Paired-EFI (EFI Injection Strategies)

    Originally Posted by Danny Cabral
    The "AE Correction vs TPS" changes the "AE vs TPS Rate of Change" based on throttle position.
    The "AE vs TPS Rate of Change" parameter functions on how slow or fast the throttle is opened.
    The "AE Correction vs TPS" parameter functions on throttle position at any particular moment.
    So it's possible that two similar datalogs or incidents can have very different AE transient fueling.

    The AE vs TPS Rate of Change is the easiest to tune:
    You can plot an Acceleration Enrichment lb/hr curve by watching the "live cursor" and air/fuel ratio at each TPS/MAP "Rate of Change" cell. This requires varying the amount of throttle to reach each consecutive cell for tuning. Increase the lb/hr value at each throttle point if it's too lean, and decrease the lb/hr value if it's too rich. Tune the "AE vs TPS Rate of Change" in neutral and tune the "AE vs MAP Rate of Change" in gear. Remember, the TPS RoC & MAP RoC (as seen on the Data Monitor & Data Logger) is the activity happening after the RoC Blanking value is applied.

    For very slow TPS/MAP off-idle movement, the new "AE vs TPS RoC Blanking" and "AE vs MAP RoC Blanking" parameters need to be adjusted (in Fuel Modifiers/Fuel Control/Accel Enrichment). This is because the first cell value in the AE vs TPS/MAP Rate of Change tables are now always set to zero. These first zero cells are the new "AE vs TPS RoC Blanking" and "AE vs MAP RoC Blanking" parameters. So if you increased these first cell values with the old software/firmware version, you'll need to adjust these Blanking values. The Holley EFI software's "Help ?" function has good AE vs TPS/MAP RoC Blanking tuning information. Ensure there's no TPS/MAP RoC signal activity at idle, due to noise/kPa fluctuation.

    Also, ensure the 2nd cell value on your AE vs TPS Rate of Change scale isn't set too low (interpolation).
    You might be in between a 2nd cell value that's too lean, and a proper AE vs TPS RoC Blanking value.
    If AE tuning isn't taking effect, the Fuel Table may be too lean.
    AE can't be tuned until Learning finishes self-tuning the Fuel Table.

    Perform another TPS Autoset. The idle speed screw may have backed off a little bit (nonexistent TPS based AE).
    If no amount of AE tuning seems to have an effect, the Base Fuel Table may be too lean around the idle area.
    Look at where the live cursor moves to during acceleration, and tune (enrich) that area of the Base Fuel Table.
    http://forums.holley.com/showthread....s-amp-Datalogs (Datalog & System Log Information)
    May God's grace bless you in the Lord Jesus Christ.
    '92 Ford Mustang GT: Dominator MPFI & DIS, 100HP progressive dry direct-port NOS, A/C, Spal dual 12" fans/3-core Frostbite aluminum radiator, Pypes dual 2.5" exhaust/off-road X-pipe/shorty headers, 160A 3G alternator, Optima Red battery, S&W subframe connectors, LenTech Strip Terminator wide-ratio AOD/2800 RPM converter, M4602G aluminum driveshaft, FRPP 3.31 gears, Cobra Trac-Lok differential, Moser 31 spline axles, '04 Cobra 4-disc brakes, '93 Cobra booster & M/C, 5-lug Bullitt wheels & 245/45R17 tires.

  3. #3

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    Just about the most helpful of a response anyone could hope for. Thanks man!

    So if I'm getting this correctly, a TBI ECU functions fundamentally the same way a batch-fire MPFI ECU does.
    But the overall parameters would be different due to engine size, injector size, number of injectors, etc., (and any number of other variables) right?

    On another note: Would the injector strategies change if an engine was using a vacuum referenced FPR versus a non-vacuum referenced FPR?

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    Quote Originally Posted by B2-BOMBER View Post
    So if I am getting this correctly, a TBI ECU functions fundamentally the same way a batch-fire MPFI ECU does.
    But the overall parameters would be different due to engine size, injector size, number of injectors, etc.?
    Correct. The six AE parameters are the same, however, the tuning of those six parameters is vastly different between TBI & MPFI.

    Would the injector strategies change if an engine was using a vacuum referenced FPR versus a non-vacuum referenced FPR?
    No, the injection strategies don't change (in terms of algorithm) due to the type of fuel pressure regulator.
    May God's grace bless you in the Lord Jesus Christ.
    '92 Ford Mustang GT: Dominator MPFI & DIS, 100HP progressive dry direct-port NOS, A/C, Spal dual 12" fans/3-core Frostbite aluminum radiator, Pypes dual 2.5" exhaust/off-road X-pipe/shorty headers, 160A 3G alternator, Optima Red battery, S&W subframe connectors, LenTech Strip Terminator wide-ratio AOD/2800 RPM converter, M4602G aluminum driveshaft, FRPP 3.31 gears, Cobra Trac-Lok differential, Moser 31 spline axles, '04 Cobra 4-disc brakes, '93 Cobra booster & M/C, 5-lug Bullitt wheels & 245/45R17 tires.

  5. #5

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    OK, next question. Overall, how would the AE strategy differ on an engine with a TBI, and MPFI assuming both are batch fired, and both are injecting the same lb/hr of fuel? For example a TBI with (2) 80 lb/hr injectors versus an MPFI with (8) 20lb/hr injectors. Both firing the same injector pulse width, in a batch fire configuration. What would be the general AE strategy differences between them? If you had to guess.
    Last edited by B2-BOMBER; 07-11-2013 at 02:47 PM.

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    Quote Originally Posted by B2-BOMBER View Post
    What would be the general AE strategy differences between them?
    Install (download) the Holley EFI V3 Software, and look at the
    AE tables in the TBI & MPFI base calibrations ("Open Global Folder").
    https://www.holley.com/support/resou...Fuel_Injection (Holley EFI V3 Software)

    EFI Software Help Information/Instructions:
    ‒ On the top Toolbar, click "Help" & "Contents". This opens all Help topics.
    ‒ When navigating the software, click "Help ?", drag it to any parameter and click again.
    ..This automatically opens the definitions for that specific parameter.
    ‒ Tuning information can be read by clicking the F1 key, when you're viewing any screen.
    http://documents.holley.com/techlibrary_199r10544.pdf (Holley EFI Help/Instructions Overview)
    http://documents.holley.com/techlibr...r10546rev1.pdf (Holley EFI Quick Start Guide)
    http://documents.holley.com/techlibr...10555rev17.pdf (Holley EFI Wiring Manual & Diagrams)
    http://forums.holley.com/showthread....ents-Read-This (Initial Checks & Adjustments - Read Steps #1-#6!)
    Open the Holley EFI software "Help" Contents ("Help" drop down menu), and read "Step-By-Step Beginners Tuning".
    Ensure the EFI software is set to run as an "Administrator" (right click for Properties/Advanced). Set it and forget it.
    May God's grace bless you in the Lord Jesus Christ.
    '92 Ford Mustang GT: Dominator MPFI & DIS, 100HP progressive dry direct-port NOS, A/C, Spal dual 12" fans/3-core Frostbite aluminum radiator, Pypes dual 2.5" exhaust/off-road X-pipe/shorty headers, 160A 3G alternator, Optima Red battery, S&W subframe connectors, LenTech Strip Terminator wide-ratio AOD/2800 RPM converter, M4602G aluminum driveshaft, FRPP 3.31 gears, Cobra Trac-Lok differential, Moser 31 spline axles, '04 Cobra 4-disc brakes, '93 Cobra booster & M/C, 5-lug Bullitt wheels & 245/45R17 tires.

  7. #7

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    Again, about as helpful of a response as I could hope for. Thanks again!

  8. #8

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    Quote Originally Posted by Danny Cabral View Post
    The AE vs TPS Rate of Change is the easiest to tune:
    You can plot an Acceleration Enrichment lb/hr curve by watching the "live cursor" and air/fuel ratio at each TPS/MAP "Rate of Change" cell. This requires varying the amount of throttle to reach each consecutive cell for tuning. Increase the lb/hr value at each throttle point if it's too lean, and decrease the lb/hr value if it's too rich. Tune the "AE vs TPS Rate of Change" in neutral and tune the "AE vs MAP Rate of Change" in gear. Remember, the TPS RoC & MAP RoC (as seen on the Data Monitor & Data Logger) is the activity happening after the RoC Blanking value is applied.
    Danny, can you clarify what to look for in the datalog when assessing AE vs TPS RoC, AE vs MAP RoC, & AE Correction vs TPS? I.E. How much each of those is contributing and whether they should be adjusted? Thank you!

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    Quote Originally Posted by xyzrbs View Post
    Danny, can you clarify what to look for in the datalog when assessing AE vs TPS RoC, AE vs MAP RoC, & AE Correction vs TPS?
    In the datalog, look at the TPS RoC, MAP RoC and the AFR channels. Overlay the datalog on your Global
    File, and adjust the AE vs TPS & MAP Rate of Change if they're causing an excessively lean or rich A/F Ratio.

    I find the most helpful datalog function, is overlaying the datalog on your Global File.
    I'm in the habit of using the datalog Overlay feature every time I review a datalog.
    Click on "Datalog" (on the top Toolbar), "Activate Overlay", then "Open Data Log".
    You can literally "playback" a recorded event, and watch it as it happened on any screen.
    Minimize (shrink) the datalog window, and move it to the bottom of any Global File screen.
    Then click & scroll anywhere on the datalog, and watch it playback on your Global File (EFI software).
    http://documents.holley.com/techlibr...9r10543rev.pdf (Holley EFI Datalogger Instructions)
    http://forums.holley.com/showthread....s-amp-Datalogs (Datalog & System Log Information)

    Acceleration Enrichment can't be tuned until the Base Fuel Table is well tuned.
    If you have a momentary lean spike, on light throttle acceleration, check
    your AE vs TPS/MAP RoC Blanking values (in Fuel Modifiers/Fuel Control):
    If they're 15 & 7, those are the old values from the V1 firmware.
    Change the AE vs TPS RoC Blanking value to 4-6.
    Change the AE vs MAP RoC Blanking value to 5-7.
    Some users reported the need for an even lower TPS RoC Blanking value.
    Ensure there's no TPS/MAP RoC signal activity at idle, due to noise/kPa fluctuation.
    http://forums.holley.com/showthread....7531#post77531 (Closed Loop Datalog Tuning - Posts #2, #4 & #6)
    http://forums.holley.com/showthread....7925#post47925 (Additional AE Tuning Info For Stubborn Engines)
    May God's grace bless you in the Lord Jesus Christ.
    '92 Ford Mustang GT: Dominator MPFI & DIS, 100HP progressive dry direct-port NOS, A/C, Spal dual 12" fans/3-core Frostbite aluminum radiator, Pypes dual 2.5" exhaust/off-road X-pipe/shorty headers, 160A 3G alternator, Optima Red battery, S&W subframe connectors, LenTech Strip Terminator wide-ratio AOD/2800 RPM converter, M4602G aluminum driveshaft, FRPP 3.31 gears, Cobra Trac-Lok differential, Moser 31 spline axles, '04 Cobra 4-disc brakes, '93 Cobra booster & M/C, 5-lug Bullitt wheels & 245/45R17 tires.

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