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Thread: Ram Jet 502 MEFI 4 Crank Position Sensor?

  1. #1
    Super Moderator dave w's Avatar
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    Ram Jet 502 MEFI 4 Crank Position Sensor?

    I'm trying to find information about the Ram Jet 502 MEFI 4 systems that uses the crank position sensor. Does anyone know which MEFI 4 (4, 4a, or 4b) uses the crank position sensor? Does anyone know if the Ram Jet 502 uses the same 4x crank trigger wheel as the 96 - 2000 L29 / Vortec 454?

    Any help is greatly appreciated!

    dave w
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  2. #2
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    Ramjet 502's (502hp/567lb/ft torque)and Ramjet ZL1 454 510hp/493lb/ft don't use CranKshaft position sensors(CKP sensors)
    They do use:
    Ignition Control (IC) module
    Engine Coolant Temperature (ECT) sensor
    Manifold Absolute Pressure (MAP) sensor
    Throttle Position (TP) sensor
    Knock Sensor (KS)

    You are correct about the 1996-2000 rpo L29 Vortec GEN-6 454 using the low resolution 4x reluctor and crab(flat cap) distributer with 9 high tension connection(1 coil to distributer and 8 distributer to spark plug) use the "blackbox" PCM with 4 approx. 30-34 pin connectors and a 257kb calibration file.

    The 1998-2001 Vortec 454 rpo L21 GEN 6 BBC uses the high resolution 24x reluctor wheel to provide the CKP sensor signal, and it uses the same lower portion of the L29 distributer but instead of the flat crab 9 pole distributer cap, it simply has a plastic cap as the distributer isn't used for high tension electrical distribution, the L21 distributor is ONLY used for oil pump drive and the 1x CMP signal. The L21 uses the 512kb 0411 like PCMs, which are the same as the same year LS1 driven Y-body Corvettes. The L21, like the Corvette LS1's use 8 individual Coil Near Plug(CNP) ignition with short high tension plug wires AND an Electronic Throttle Control. The coils are held in place by a specific L29 BBC valve covers. Basically the L21 thinks its an overgrown Corvette LS1.

    The choice of MEFI ECMs is/was either MEFI-3 for the Ramjet 350, 502 and ZL1(only 200 original Ramjet ZL1's built by
    Production Automotive Services (PAS), the same company that was responsible for production of the:
    1989 Pontiac Turbo Trans Am-turbocharged/intercooled 250hp@4400 rpm, 340lb/ft torque@2800 rpm 1555 units built
    1991 GMC Syclone turbocharged Intercooled 4.3 V6 engine rpo LB4-All Wheel Drive(AWD) pickup truck 2995 units built
    1992 GMC Sonoma GT naturally aspirated 4.3 V6 rated at 195hp@4500rpm/260lb/ft torque@3400rpm 806 units made
    1992 GMC Typhoon turbocharged Intercooled 4.3 V6 engine 280hp/360lb/ft torque(AWD) SUV 2,497 units made
    1993 GMC Typhoon same as 1992 2200 units built

    did the ZL1 Ramjet assembly.


    I didn't realize that the Ramjets use the CKP sensor signals. I still think that they may not.


    o therefore wasn't equipped with an O2 sensor or its associated O2 sensor wiring, thus always runs in Open Loop when cruising.
    The MEFI-4 ECM is/was used for the same engines (save for Ramjet ZL1-I'm not 100% sure it was available with both the MEFI-3 and/or the MEFI-4 from GM) you could upgrade any for closed loop operation.

    Its either going to be a MEFI 3 or 4B if its a real Ramjet crate,Ramjet from Chev Performance Parts. It could be a Marine 502 with the Ramjet 502/454 intake. I'm thinking its an actual Marine engine as the OEM marine engines had to pass emissions and run catalytic converters, so in order to allow the cats to live, miss fire monitoring would become mandatory. The CKP sensor signal becomes mandatory to measure crankshaft acceleration variations on a cylinder per cylinder basis to detect misfires. Miss fires allow for unburned hydrocarbons which will kill cats in short order.

    Even the MEFI site doesn't list the Ramjets using CKP sensors.

    I'd be pulling that CKP sensor and with a flashlight looking at the CKP sensor, its either going to be the 4x/24x/58x.
    If its 24x stuff the part numbers are: Reluctor 24x BBC only - 12552480 crank sensor - 10456248

    I also notice that the pictured engine doesn't have the proper Ramjet 402/454 ZL1 throttle control. Which is p/n 12489597 of the Ramjet BBC kits.

    Convert from MEFI 3 to MEFI 4
    12499117
    MEFI 4 ECU & Wire Harness Kit, Ram Jet 502 (not shown)
    • Module/harness kit is used to convert a Ram Jet 502 from
    MEFI 3 to the newer MEFI 4 design, which offers improved
    idle and performance through a closed-loop system
    • Includes module P/N 88962718, wire harness P/N 88961968,
    oxygen sensor P/N 19178918, intake air temp sensor P/N
    25036751 and oxygen sensor fitting P/N 15156588


    Use MEFI 4 ECM on MEFI 3 wiring open loop
    88963118
    Jumper Harness, MEFI 3 to MEFI 4 (not shown)
    • Allows an MEFI 4 module to be used with an MEFI 3 wiring
    system (to stay as an open-loop system)
    • Fits both Big-Block and Small-Block engines


    MEFI 4 harness
    88961968
    MEFI 4 ECU Harness, Ram Jet 502 (not shown)
    • Used in the MEFI 4 Ram Jet 502 P/N 12499121 with the
    MEFI 4 closed-loop oxygen sensor-equipped system
    • Use with MEFI 4 ECU P/N 88962718


    There is no mention of CKP sensors on any Ramjet engines GMPP then CPP through 2017.

    The newer MEFI 5/6 use the CKP signal and would be 58x.

    There is this CPP kit that puts the 58x CKP and 4x CMP sensors on the same front timing kit. Easy CNP/COP for the newer 58x ECMs or newer MEFI PCMs.

    peace
    Hog

    

  3. #3
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    As of 2004, only OEM applications had the CKP signal inputs.

    Here is a GM ditty for Model Year (MY) 2004.
    http://web.archive.org/web/200505131...management.pdf


    On the 4th page, there is a listing, the first input on the left side,


    Compatible with 4-, 6-, and 8-cylinder
    engines (EFI can use a cam sensor.


    It is colour coded in BLACK meaning that ONLY EFI has this input and not the MSTS(Microprocessor Spark Timing System.

    This page lists a CKP sensor signal input for the MEFI 4 ECM, both 24x and 58x,
    http://www.mefipro.com/images/CBM%20...%204%20ECU.pdf

    Here are the pinouts for a MEFI 4 ECM. CKP sensor signal input.

    ECM pin assignment number appears to be J2-16

    J2-16 634 LT GRN CRANK SENSOR SIGNAL
    http://www.mefipro.com/images/MEFI/C...INOUT%20ID.pdf

    Some MEFI ECM designations to part numbers
    MEFInumbertotype.png





    peace
    Hog
    Last edited by Hog; 2 Weeks Ago at 08:55 AM.

  4. #4
    Super Moderator dave w's Avatar
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    I'm looking at three options:
    1. What's currently there. Small Cap HEI with 8 pin ignition module. Seems maybe this setup was for Marine applications?
    2. What's supposed to be there. Coil on plug with a 24x crank position sensor. Maybe MEFI 4b?
    3. What I can do instead. Use the original Black Box PCM (4x) or maybe upgrade to the '0411 PCM (24x).

    I'm going to remove the crank position sensor and use a borescope to see what crank trigger is actually there.

    dave w

  5. #5
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    Quote Originally Posted by dave w View Post
    I'm looking at three options:
    1. What's currently there. Small Cap HEI with 8 pin ignition module. Seems maybe this setup was for Marine applications?
    2. What's supposed to be there. Coil on plug with a 24x crank position sensor. Maybe MEFI 4b?
    3. What I can do instead. Use the original Black Box PCM (4x) or maybe upgrade to the '0411 PCM (24x).

    I'm going to remove the crank position sensor and use a borescope to see what crank trigger is actually there.

    dave w
    I just talked to my marine guy and says that only the Marine engines use the CKP sensor, he also says that MEFI 1-5 uses the CKP sensor in marine apps.

    What was throwing me off was the Ramjet 502 letters on the ECM itself. Is that an Arizona Speed and Marine website listed on the PCM? I cant read all of it.

    From all the guys that have done 257kb blackbox PCM to 0411 PCM retrofits, I would have to suggest the 0411 swap with the L21 reluctor.

    Yo u should be able to tell which reluctor is there from the CKP sensor, the 4x are a single wheel reading sensor while the 24x ues a double wheel reading sensor which is over $100. The 4zx sensor is about 1/2 that price. There are EFIConnection reluctors that allow you to run the less expensive 4x sensor.

    Of course if you have the ability to recalibrate the MEFI without paying the $250, that's an option also.

    peace
    Hog

  6. #6
    Super Moderator dave w's Avatar
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    It appears this 502 has the 4x (low resolution) L31 / L29 crank trigger wheel, see attached pic below.

    I'm thinking the "budget" option is to use the original "Black Box" PCM with a custom 502 flash, along with some modifications to the original L29 wiring harness.

    Looks like I need to install a L31 / L29 distributor, coil, ignition module, and MAF.

    I'll need to confirm the CKP pictured below will work with the "Black Box".

    Is there another "budget" option available that can control both the 502 EFI and 4L80E Trans?

    dave w
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  7. #7
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    If it has the l31 crank reluctor why cant you use an 0411? there is a van l31/4l80 file in the repository that is 12212156 o/s I believe.

  8. #8
    Super Moderator dave w's Avatar
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    Quote Originally Posted by mecanicman View Post
    If it has the l31 crank reluctor why cant you use an 0411? there is a van l31/4l80 file in the repository that is 12212156 o/s I believe.
    The '0411 is a good option! For the moment, the plan is to keep to a minimal budget. I'm sure once the "Black Box" has things running OK, upgrading to the '0411 will likely happen.

    dave w

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