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Thread: Holley Commander 950 TBI to MPFI question.

  1. #11

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    A - #1 & #3
    C - #6 & #8
    B - #2 & #4
    D - #5 & #7

    I'm probably splitting hairs here but, considering the Chevy firing order is 18436572, the injector timing seems like it should be:

    A - #1 & #3
    C - #4 & #8
    B - #2 & #6
    D - #5 & #7

    This is still bank to bank so I don't get why 6 and 4 are swapped?

  2. #12
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    Since it's not sequential injection, the ECU never knows which cylinder is #1 at startup.
    So it never injects in sequence to the ignition's firing order. That's not the purpose here.
    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. #13

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    Batch fired EFI (bank-to-bank) sprays 4 injectors on one bank, then 180 crankshaft degrees later, the other 4 spray on the opposite bank. The C950 ECU has 4 drivers and each one pulses the ground on 2 injectors (drivers A & C fire together and B & D fire together). On the C950 MPI harness, the injector connectors with the same color ground wires are pulsed together.

    If you want to minimize the 'fuel pressure drop' at the fuel rails/injectors, you can wire the harness to 'batch fire' a pair of injectors on each bank. This is an improved strategy for batch fired (bank-to-bank) EFI so each bank doesn't fire at the same time, which can possibly disrupt the 'fuel pressure stability/distribution' (especially with large injectors and a single fuel feed line).
    In other words, wire the injector harness like this (Chevy):

    A - #1 & #3
    C - #6 & #8
    B - #2 & #4
    D - #5 & #7
    Forgive my ignorance but the above statement says "Batch fired EFI (bank-to-bank) sprays 4 injectors on one bank, then 180 crankshaft degrees later, the other 4 spray on the opposite bank". Does this not imply that there is a sequence where one bank is sprayed and then the other bank is sprayed? That is a description of a sequence that involves two events (instead of 8).

    If an 8 event sequence should be 18436572 then why isn't a 2 event sequence (the injector sprays cylinders 1,8,4 and 3) in the middle of the 1843 ignition and then, 180 crankshaft degrees later, the 6,5,7 and 2 injectors spray? If it truly doesn't make any difference then it does not matter if the injectors are wired randomly and/or if they are sprayed bank to bank, correct?

  4. #14
    Join Date
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    Quote Originally Posted by BBshark View Post
    Forgive my ignorance but the above statement says "Batch fired EFI (bank-to-bank) sprays 4 injectors on one bank, then 180 crankshaft degrees later, the other 4 spray on the opposite bank". Does this not imply that there is a sequence where one bank is sprayed and then the other bank is sprayed? That is a description of a sequence that involves two events (instead of 8).
    My statement is in reference to the ignition firing order.
    Bank-to-bank injection doesn't inject in sequence with the ignition firing order.
    Bank-to-bank injection only knows every two ignition firing events - spray four injectors...
    two more injection events later (180°) - spray the other four injectors. (Four-stroke cycle.)

    If an 8 event sequence should be 18436572 then why isn't a 2 event sequence (the injector sprays cylinders 1,8,4 and 3) in the middle of the 1843 ignition and then, 180 crankshaft degrees later, the 6,5,7 and 2 injectors spray? If it truly doesn't make any difference then it does not matter if the injectors are wired randomly and/or if they are sprayed bank to bank, correct?
    The C950 fuel only knows ignition events; it doesn't know which of these events is cylinder #1, #8, #4, #3, etc.
    Each time you start the engine, bank-to-bank EFI can start injecting on either batch of cylinders, because it can't identify #1 or any others.
    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. #15

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    Quote Originally Posted by Danny Cabral View Post
    The C950 only knows ignition events; it doesn't know which of these events is cylinder #1, #8, #4, #3, etc.
    Each time you start the engine, bank-to-bank EFI can start injecting on either batch of cylinders, because it can't identify #1 or any others.
    Then, I guess, it doesn't matter how the injectors are wired or if they are bank to bank or 3 on one bank or 2 on 1 bank etc.

    Even though you say that it makes no difference, I will wire mine so that the first 4 ignition events are on the same group of 4 injectors and the last 4 igniton events are on the remaining 4 injectors. That makes more sense to me than:

    A - #1 & #3
    C - #6 & #8
    B - #2 & #4
    D - #5 & #7

    With a 18436572 firing order, in this scheme, the phasing is (partially) out on 1 injector per side or 1 injector is phased and the other 3 are out.

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