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