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Thread: Acceleration is sluggish for a GMC Motorhome.

  1. #1

    Default Acceleration is sluggish for a GMC Motorhome.

    I just had a Terminator EFI installed in a 1973 23’ GMC Motorhome, with a new (approx 1000 miles) ‘high performance’ Oldsmobile 455 V8 engine & GM HEI distributor. I also installed the Holley pump kit 526-2, which is supplying fuel at about 43 psi, according to a gauge on the regulator. The motorhome is about 10,000 lbs and has a 3 speed THM-425 transmission.

    Startup, idle and cruise all seem fine. However, acceleration from stop and driving up hills are a huge problem - there doesn’t seem to be any power. The ECU hasn’t finished its learning yet, but I’m hoping I can tweak the acceleration. In section 32.1.2 of the manual, ‘Acceleration Enrichment (load based accel enrich)’ has a default value of 16. The manual suggests that this value may need to be increased based on heavy vehicles.

    What do you recommend I do to increase power for acceleration for stops & hills?

    I hooked up a laptop to the ECU and I’m still trying to get familiar with the software. Here are some parameters from the handheld unit (Link):
    * Software version: ECU 587, Hand-held: V23
    * Acceleration Enrichment - Basic Tuning: 54
    * Acceleration Enrichment - Advanced Tuning: 16
    * Target AFR: Idle: 13.5, Cruise: 14.0, WOT: 12.5

    Thanks!

  2. #2
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    Quote Originally Posted by mrtoadsc View Post
    I hooked up a laptop to the ECU and I’m still trying to get familiar with the software.
    Review a datalog of this occurrence. Is the AFR too rich or too lean? Maybe it needs more ignition timing advance too.
    https://www.holley.com/document/tech...9r10543rev.pdf (Datalogger Instructions)

    Also, what are 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.
    May God's grace bless you in the Lord Jesus Christ.
    '92 Ford Mustang GT: 385" SBF, Dart SHP 8.2 block, TFS TW 11R 205 heads, 11.8:1 comp, TFS R-Series intake, Dominator MPFI & DIS, 36-1 crank trigger/1x cam sync, 160A 3G alternator, Optima Red battery, A/C, 100HP progressive dry direct-port NOS, Spal dual 12" fans/3-core Frostbite aluminum radiator, Pypes dual 2.5" exhaust/off-road X-pipe/shorty headers, 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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    Quote Originally Posted by Danny Cabral View Post
    Review a datalog of this occurrence. Is the AFR too rich or too lean? Maybe it needs more ignition timing advance too.
    Thank you for your quick reply!
    I believe we still need to work on the timing. Full advance should be at around 3000, and right now it's at 2200.
    I'll look at the log tomorrow. I'll have to interpret the table to see if I can recognize if it's too lean or rich.

    Quote Originally Posted by Danny Cabral View Post
    Also, what are 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.
    Right now both of these values are 7. I'll change the AE vs MAP down to 4-5 tomorrow morning and take it for another spin.

  4. #4
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    Quote Originally Posted by mrtoadsc View Post
    I believe we still need to work on the timing. Full advance should be at around 3000, and right now it's at 2200.
    I'll look at the log tomorrow. I'll have to interpret the table to see if I can recognize if it's too lean or rich.
    Read pages 4-10 of this Edelbrock EFI tuning manual, it's very good:
    https://edelbrock-files-v1.s3.amazon...ers-manual.pdf

    http://forums.holley.com/showthread....at-At-High-RPM (Additional Information)

    Here are some parameters from the handheld unit (Link):
    * Software version: ECU 587, Hand-held: V23
    The EFI software version (2.2.0.3) is not the ECU firmware version (0587).

    Software & Firmware Versions:
    Software: click "Help" tab (top toolbar) & "About Holley EFI".
    Firmware: click "Sync With ECU" & "Get ECU Info" (Key-on/USB connected).
    The latest software & firmware can be downloaded here:
    https://www.holley.com/support/resou...Fuel_Injection (Holley EFI Technical Library)
    https://www.holley.com/document/tech...9r10546rev.pdf (HP & Dominator Quick Start Guide)
    https://www.holley.com/document/tech...g_firmware.pdf (How To Update ECU Firmware)
    Before updating firmware, ensure the current Global Folder is saved somewhere, since it will be erased from the ECU.

    Latest V2 EFI Software & ECU Firmware:
    The latest V2 software can be downloaded here: https://www.holley.com/support/resou...Fuel_Injection
    Read the 199R10632rev5 PDF document for a "V2 Software Update Overview" (in "Holley EFI V2 Instructions").
    Be sure to successfully install the new V2 software, before installing the ECU firmware (read "V2 Update Instructions").
    Ensure the Holley EFI software is not open and the ECU is not powered on/connected when installing the new 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.
    https://www.holley.com/document/tech...10555rev16.pdf (Holley EFI Wiring Manual)

    * Acceleration Enrichment - Basic Tuning: 54
    * Acceleration Enrichment - Advanced Tuning: 16
    I've never used the hand-held controller (and never will), so I don't know what this means, or even what the limits are.
    May God's grace bless you in the Lord Jesus Christ.
    '92 Ford Mustang GT: 385" SBF, Dart SHP 8.2 block, TFS TW 11R 205 heads, 11.8:1 comp, TFS R-Series intake, Dominator MPFI & DIS, 36-1 crank trigger/1x cam sync, 160A 3G alternator, Optima Red battery, A/C, 100HP progressive dry direct-port NOS, Spal dual 12" fans/3-core Frostbite aluminum radiator, Pypes dual 2.5" exhaust/off-road X-pipe/shorty headers, 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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    Hi Danny! Thanks for the info. I'm using V2.2.0.3 of the EFI software and I can read/set parameters on the ECU. I changed the AE vs MAP RoC Blanking to 5 and then 4, and it made no difference. I assume these values take immediately when the laptop is connected to the ECU in "Online" mode.

    I noticed that changing these "AE vs MAP/TPS RoC Blanking" has no impact on the "Acceleration Enrichment" graphs. See these images:

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    I pulled a datalog from the ECU from yesterday before all these changes. The graph shows the first 2 minutes or so of driving the RV up a hill in my neighborhood (road winds up & down), and can be an 8-10% grade in some spots. What values should I be looking at to understand how to change the values to get more acceleration response?

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    I have a feeling the tuning the EFI for the GMC Motorhome application may require bringing in an expert.
    Do you know/recommend a Holley EFI tuner on the central coast of California (Monterey Bay Area, SF Bay Area)?

  6. #6
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    Quote Originally Posted by mrtoadsc View Post
    I noticed that changing these "AE vs MAP/TPS RoC Blanking" has no impact on the "Acceleration Enrichment" graphs.
    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.

    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.
    Which is not the same thing as requiring the 2nd AE TPS/MAP RoC cell value be higher than the AE TPS/MAP 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.

    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 data logs 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.

    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 information found in this thread:
    http://forums.holley.com/showthread....amp-Paired-EFI (EFI Injection Strategies)
    May God's grace bless you in the Lord Jesus Christ.
    '92 Ford Mustang GT: 385" SBF, Dart SHP 8.2 block, TFS TW 11R 205 heads, 11.8:1 comp, TFS R-Series intake, Dominator MPFI & DIS, 36-1 crank trigger/1x cam sync, 160A 3G alternator, Optima Red battery, A/C, 100HP progressive dry direct-port NOS, Spal dual 12" fans/3-core Frostbite aluminum radiator, Pypes dual 2.5" exhaust/off-road X-pipe/shorty headers, 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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    Hi Danny. My mechanic & I spent the afternoon playing with some the of the ECU settings. I think we are making progress but it's going slow.

    I didn't noticed any real difference changing the values of the "AE vs TPS RoC Blanking" & "AE vs MAP RoC Blanking".
    They were 7/7 originally and then I changed them to 7/4 - no difference (that I can tell) and then to 15/10.

    We went from 25% to 50% on "AE vs MAP Rate of Change" and again this didn't seem to increase our power/fuel on acceleration.
    We are getting popping at 100 kPa MAP and it’s backfiring. Is this the right place to make changes? What is the max values we can go?

    Are you aware of anyone else who have put the Terminator EFI on a large vehicle like an RV?

    We are also looking at the timing and are considering a computer controlled distributor.
    Also, the fuel delivery system is going to be re-examined. Not sure if the existing tank(s) setup is delivering the fuel we need.

  8. #8
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    Quote Originally Posted by mrtoadsc View Post
    I didn't noticed any real difference changing the values of the "AE vs TPS RoC Blanking" & "AE vs MAP RoC Blanking".
    I didn't think it would make much of a difference. I just wanted to ensure the RoC Blanking values weren't on 15 & 10.

    They were 7/7 originally and then I changed them to 7/4 - no difference (that I can tell) and then to 15/10.
    7 & 5 should be fine (at least not what's causing your current issue). Don't leave them on 15 & 10.

    We went from 25% to 50% on "AE vs MAP Rate of Change" and again this didn't seem to increase our power/fuel on acceleration.
    We are getting popping at 100 kPa MAP and it’s backfiring. Is this the right place to make changes?
    You may need to look at the Base Fuel Table first (and maybe the Target A/F Ratio Table).
    Acceleration Enrichment can't be tuned until the Base Fuel Table is well tuned. Is it Learning?
    Review the datalog when this popping/backfiring occurs. Is the AFR too rich or too lean?

    Are you aware of anyone else who have put the Terminator EFI on a large vehicle like an RV?
    No.

    We are also looking at the timing and are considering a computer controlled distributor.
    Yes, it's much easier to make ignition timing changes with ECU controlled timing. A CD ignition box is also a good idea.

    Also, the fuel delivery system is going to be re-examined. Not sure if the existing tank(s) setup is delivering the fuel we need.
    Consistent (static) fuel pressure is paramount for proper EFI system operation. It can't drop under load.
    May God's grace bless you in the Lord Jesus Christ.
    '92 Ford Mustang GT: 385" SBF, Dart SHP 8.2 block, TFS TW 11R 205 heads, 11.8:1 comp, TFS R-Series intake, Dominator MPFI & DIS, 36-1 crank trigger/1x cam sync, 160A 3G alternator, Optima Red battery, A/C, 100HP progressive dry direct-port NOS, Spal dual 12" fans/3-core Frostbite aluminum radiator, Pypes dual 2.5" exhaust/off-road X-pipe/shorty headers, 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.

  9. #9

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    Something bothers me about this entire thread...you said "high performance." That is a very "loaded" statement. Is it possible this is the entirely wrong engine for this application? Too high compression ratio? Too large camshaft? Just how big and heavy is this motorhome?

  10. #10

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    Quote Originally Posted by Danny Cabral View Post
    You may need to look at the Base Fuel Table first (and maybe the Target A/F Ratio Table).
    Acceleration Enrichment can't be tuned until the Base Fuel Table is well tuned. Is it Learning?
    Thanks for your help!
    I believe the system is still Learning. How do I know when learning is complete? The Learn Table has a bunch of neatly arranged numbers in increasing values for high MAP/low RPM, and lots of zeros for low MAP & RPM > 4000. The Closed Loop Compensation Limits are 100% and Learned Compensation Limits are 150%.

    On a related note: How do I adjust the "Target A/F Ratio Table" to make it richer under "Load". The online docs seem to be out of date for this screen.

    Quote Originally Posted by Danny Cabral View Post
    Review the datalog when this popping/backfiring occurs. Is the AFR too rich or too lean?
    From what I can determine the AFR may be too lean. My mechanic is convinced this is a fuel starvation problem, so we are going to investigate that.

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