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Thread: Performance Issue - RPM drop under load.

  1. #1

    Default Performance Issue - RPM drop under load.

    Car/Engine:
    598 BBM Dragster on Methanol
    Tunnel Ram, twin throttle bodies (synced)
    14.5:1 Compression
    284°/294° Duration @ .050"
    .782"/.765" Lift Intake/Exhaust
    MSD Dual Sync Distributor
    MSD 7-AL3, modded by TechWest
    MSD Pro Power HVC Coil
    MSD 8.5mm Wires
    16 Volt Battery

    Car had a simple batch fire Alpha-N EFI previously that ran fine with the above components and Accel 160pph injectors. Simple EFI system wouldn't support Atomizer injectors. Switched over to a Dominator system as we want to run sequential and Atomizer injectors. Attempting to run VE Combo to run the Alpha-N idle and VE main fuel table. I have a borrowed VE fuel table from a 632 dragster that is fundamentally close if I view the PPH in a converted table.

    Completed the install using all Holley components except for CTS and FPS sensors. Engine is grounded at the block with #2 battery cable to a stud on the frame tube. the frame tube stud also has a #2 cable running straight to the battery. No head grounds are on the engine at this time. We used the generic main harness and trimmed everything to length. All unused wires were shortened, ends insulated and "stored" between the seat back and firewall. ECU is mounted on the seat side of the firewall.

    Started with V5.32 and it was unable to send a proper points signal to the MSD after verifying crank & cam signals were proper (System Log). A timing light would flash roughly once a second at 220 cranking RPM. Spark off the coil verified fundamentally 7 missing sparks per cycle. Installed V5.100, selected the Points Output MSD for Ignition Setup and engine fires up immediately. Set timing and rough idle fuel in the Alpha-N idle table and things seemed fine at this point. Installed V5.110 and re-installed same Global File from V5.100 version.

    Got to the track yesterday and adjusted some no load fueling to smooth out things a little. Noted that the engine struggles at 3000 RPM which is 500 RPM above the Alpha-N idle table. Moving fuel in +-10 units in these areas on the VE table got things better but 3000 RPM is still unhappy. Noted that the tach is also jumpy at 3000 RPM. Tach is an Auto Meter dash needle type run by the MSD.

    Got to make a hit and engines fundamentally dies with load just above 3000 RPM. This happens twice in the burnout and several times going down the track, backing off the throttle and getting back in it to allow recovery. Looked at the datalog and it was lean so fuel pressure was turned up 10 psi to remove under fueling as an issue.

    Removed VE Combo and went to VE Based but tach needle is still bouncing. Changed crank trigger from the Dual Sync to an MSD magnetic trigger as it was still mounted to the engine. Reset timing and reference angle after changing Sensor Type to Magnetic and tach needle is now smooth through 3000 RPM. I noticed that when moving the throttle slowly, it had a big flat spot so I enabled injector end angle and set all the cells to +70 as that is when the intake closes at .050" lift. this helps but doesn't cure the flat spot issue. A test "hit" on the transbrake and it hits the chip like a champ.

    The next lap and the engine falters after 6000 RPM and basically lays down, recovers and repeats in the burnout. Leaving off the foot brake is unremarkable followed by the same cycle of gaining RPM and falling down, cycling the gas pedal and repeating. Putting the engine on the transbrake on the return road the engine hits the chip and falls flat on releasing the button. Logs don't show much except for proper fueling as measured by AFR, PW and estimated fuel flow. Looking a a running engine system log shows no clash of Digital Falling cam sensor lining up with Digital Falling crank signal. On "Magnetic" crank sensor, it appears that the digital rising cam signal will align with the falling crank signal, but the falling cam signal never lines up with the falling crank signal. There is a lean spike in the data log in the AFR just after RPM starts to droop with no change in duty cycle and TPS which tells me spark is dropping out. One weird thing is that Vol Comp Ign Dwell starts out at 2.5 msec and falls to 0.7 msec when it falls on its face. The pattern repeats - RPM/load rise, dwell falls. It has really good idle dwell at just over 3.6 msec though. That dwell characteristic just doesn't seem right.

    Who knows what dwell is supposed to do on Points Output Fixed Duty Cycle (MSD) on V5.110 (new feature in V5.100 & .110)? The engine will not run on Points Output Adjustable Duty Cycle, so that isn't an option. Looking for some help as I'm new to this system.
    Attached Files Attached Files
    Last edited by rdkerne; 05-18-2019 at 11:16 AM.

  2. #2
    Join Date
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    Default

    Quote Originally Posted by rdkerne View Post
    Who knows what dwell is supposed to do on Points Output Fixed Duty Cycle (MSD) on V5.110 (new feature in V5.100 and .110)? The engine will not run on Points Output Adjustable Duty Cycle, so that isn't an option.
    Read page 5: https://documents.holley.com/techlib...reoverview.pdf (Specific updates for version V5 Build 110.)

    Fixed Duty Cycle Points Ignition Output
    Custom Ignition Parameters have a new "Output Type" called "Points Output Fixed Duty Cycle (MSD)". The previous "Points Output" has been renamed to "Points Output Adjustable Dwell". It's operation remains the same which is a user programmable fixed dwell used to typically trigger a MSD/CD box. The new type has an output that creates a fixed dwell output of 20-30 crank degrees no matter what the engine speed. This output is intended to trigger a MSD/CD ignition system. This new selection would be the preferred choice to trigger a CD/MSD box. The previous choice works fine, but the new selection is a more ideal method.
    May God's grace bless you in the Lord Jesus Christ.
    '92 Ford Mustang GT: Dominator MPFI & DIS, A/C, Spal dual 12" fans/3-core Frostbite aluminum radiator, Pypes dual 2.5" exhaust/X-pipe/shorty headers, 100HP progressive dry direct-port NOS, 160A 3G alternator, Optima Red battery, LenTech Strip Terminator wide-ratio AOD/2500 RPM converter, 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

    Default

    OK, so that math means the Dwell will be .7 msec at 6000 RPM. Looking for next steps to diagnose this issue. Why does the tach bounce on a Hall-Effect based points signal and not on a magnetic pickup based crank signal? The MSD runs the tach, so what's providing an improper signal to the MSD to send out an improper tach signal and make the engine struggle at the same time? What else would cause the engine to snuff out when it has enough fuel, air & timing to make power?

  4. #4
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    Dec 2009
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    Connecticut
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    Hall-Effect crank & cam sensors? You'll have to analyze a datalog of this occurrence.

    Originally Posted by Danny Cabral
    Quick Datalogger Information:
    Always provide data, not just symptoms. Is the AFR & ignition timing optimized? Overlay the datalog onto your Global File.
    Ensure the Target A/F Ratio table is properly programmed for your engine. Ensure the ECU is "Learning" (Learn Table LINK).
    Scroll through the datalog to the problem area. Then look exactly where this happens on the Base Fuel & Timing Tables. Scrutinize:
    RPM, MAP, MAT, TPS, CTS, IAC, Target AFR, AFR Left, CL Comp, Ignition Timing, Duty Cycle, Fuel Flow, Fuel Pressure & Battery.

    Using the Holley EFI software (LINK), look at where the live cursor moves to during this occurrence, and
    manually tune that area of the Base Fuel Table (enrich or lean) & Base Timing Table (optimize ignition timing).


    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)
    https://forums.holley.com/showthread...s-amp-Datalogs (Datalog & System Log Information - Read "NOTES")
    https://www.youtube.com/watch?v=iqHO...C6FEA0BB99AF17 (How To Record & Email A Datalog)
    https://www.youtube.com/watch?v=q7OZUXLRS1Q (How To Record A System Log & Diagnose A No-Start Condition)
    https://forums.holley.com/showthread...7531#post77531 (Closed Loop Datalog Tuning - Posts #2, #4 & #6)
    May God's grace bless you in the Lord Jesus Christ.
    '92 Ford Mustang GT: Dominator MPFI & DIS, A/C, Spal dual 12" fans/3-core Frostbite aluminum radiator, Pypes dual 2.5" exhaust/X-pipe/shorty headers, 100HP progressive dry direct-port NOS, 160A 3G alternator, Optima Red battery, LenTech Strip Terminator wide-ratio AOD/2500 RPM converter, 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

    Default MSD on V5, who's got one?

    Quote Originally Posted by rdkerne View Post
    Car/Engine:
    598 BBM Dragster on Methanol
    Tunnel Ram, twin throttle bodies (synced)
    14.5:1 Compression
    284°/294° Duration @ .050"
    .782"/.765" Lift Intake/Exhaust
    MSD Dual Sync Distributor
    MSD 7-AL3, modded by TechWest
    MSD Pro Power HVC Coil
    MSD 8.5mm Wires
    16 Volt Battery
    Who has a running example of a Dominator EFI with V5.32, .100 or .110 running a Dual Sync distributor and an MSD box like a 7-AL3 on "Points Output Adjustable Dwell"? Or even just running the MSD the same way with cam & crank triggers? The reason I ask is that I know V4 will run an MSD box with the points signal (the only alternative in the drop down list box) and I'm wondering if I need to back date my software in order to run my engine. I appreciate your responses Danny, but this isn't my first rodeo with aftermarket EFI, been doing this off & on since the late 80s.

  6. #6
    Join Date
    Dec 2009
    Location
    Connecticut
    Posts
    21,430

    Default

    Quote Originally Posted by rdkerne View Post
    I appreciate your responses Danny, but this isn't my first rodeo with aftermarket EFI, been doing this off and on since the late 80s.
    I understand, and I hope you resolve this. However, I'd still like the answer to my question in post #4.
    May God's grace bless you in the Lord Jesus Christ.
    '92 Ford Mustang GT: Dominator MPFI & DIS, A/C, Spal dual 12" fans/3-core Frostbite aluminum radiator, Pypes dual 2.5" exhaust/X-pipe/shorty headers, 100HP progressive dry direct-port NOS, 160A 3G alternator, Optima Red battery, LenTech Strip Terminator wide-ratio AOD/2500 RPM converter, 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

    Default

    The Dual Sync distributor has Hall-Effect crank & cam sensors from what the literature states. This setup, when set on Points Output Fixed Duty Cycle (MSD) runs under load to just over 3000 RPM and drops off hard. The Auto Meter tach connected to the MSD also has a bouncing needle at 3000 RPM accompanied by the sound and feel of a struggling engine. Taking home run swings at the fuel map improves running quality below 3000 and above 3000, but is not able eliminate the struggling at 3K RPM.

    Next we bypassed the crank sensor in the dual sync and connected an MSD magnetic crank trigger, reset timing and tested. Engine will load over 3000 RPM, but now falls hard after 6000 RPM. It'll go on the 2-Step fine and snuff out after letting go of the transbrake requiring a restart. Fuel is present, FP is steady, IPW is proper, PPH is within fuel map expectations, duty cycle is well within expected values for WOT @ 6000 RPM. This is leading me towards spark related issues, either points signal quality to the MSD or the MSD itself. Both my main and spare MSD boxes were used late last season and worked fine. I'm also getting the MSD 89981 to verify the boxes again.

    Since changing EFI software versions goes from a no-start to start & running, something doesn't feel right. The ECU should drive the MSD just fine no matter what EFI software version is present, one would assume. So I'm looking for clues why my configuration won't run on Points Output Adjustable Dwell using a dual sync or dual sync cam trigger with a magnetic crank trigger. This is also assuming the no-start issue and the performance issues are related, so fixing one will eliminate the other. Thanks.

  8. #8
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    Dec 2009
    Location
    Connecticut
    Posts
    21,430

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    When you tried the "Points Output Adjustable Dwell" (Output Setup), what Dwell Time (Disabled Dwell Table) did you use?
    May God's grace bless you in the Lord Jesus Christ.
    '92 Ford Mustang GT: Dominator MPFI & DIS, A/C, Spal dual 12" fans/3-core Frostbite aluminum radiator, Pypes dual 2.5" exhaust/X-pipe/shorty headers, 100HP progressive dry direct-port NOS, 160A 3G alternator, Optima Red battery, LenTech Strip Terminator wide-ratio AOD/2500 RPM converter, 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

    Default

    2.0 msec & 2.5 msec.

  10. #10
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    Location
    Connecticut
    Posts
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    Quote Originally Posted by rdkerne View Post
    Since changing EFI software versions goes from a no-start to start & running, something doesn't feel right. The ECU should drive the MSD just fine no matter what EFI software version is present, one would assume. So I'm looking for clues why my configuration won't run on Points Output Adjustable Dwell using a dual sync or dual sync cam trigger with a magnetic crank trigger.
    I suggest two things.
    1) Try using the Comparison/Copy Feature in the EFI software:
    https://documents.holley.com/techlib...reoverview.pdf (Specific updates for version V5 Build 110 - See page 3.)
    2) Read the Holley EFI V5 Revision Log for clues as to how the Global Files may be programmed differently in those software versions:
    https://documents.holley.com/techlib...evisionlog.pdf (Holley EFI V5 Software/Firmware Revision Log)
    May God's grace bless you in the Lord Jesus Christ.
    '92 Ford Mustang GT: Dominator MPFI & DIS, A/C, Spal dual 12" fans/3-core Frostbite aluminum radiator, Pypes dual 2.5" exhaust/X-pipe/shorty headers, 100HP progressive dry direct-port NOS, 160A 3G alternator, Optima Red battery, LenTech Strip Terminator wide-ratio AOD/2500 RPM converter, 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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