Ignition box questions

volaredon said

These will refer to factory Mopar style 4 and 5 pin ecu's.
I forgot what's the difference between a 4 pin and a 5 pin box
I remember one can be used in place of the other but not the other way around. Which one works for all and why won't the other do likewise?

I'm seeing some Delco replacement ones on feebay, some 4 pin and some 5 pin versions.
I also hear a lot of talk about people using an actual GM HEI module on mopars especially it seems in a lean burn delete situation.
I've read some of the threads over the years about the "advantages" of HEI vs a factory Mopar ECU, would a Delco branded replacement ECU for a Mopar be wired inside like an HEI or like a stick Mopar ECU? I guess it's possible that Delco doesn't actually make them but buys them elsewhere and reboxes them. Does anybody know this to be the case or did Delco actually MAKE the modules they sold, even those they sold that weren't for a GM application

Like everything else these days that isn't made how it was made 30-40 years ago, I've read about modern replacement ignition parts for older application. So I'm looking at some new parts that were actually made back then. And I can tell by the labels these aren't recently made parts though they are brand new.
(I did buy a new but old niehoff 4 pin ecu and a filko brand voltage regulator last week. Brands no longer even heard of... I'm always looking for stuff like that

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A four pin ECU can be used in a five pin ECU system, but a five pin ECU cannot be used in a four pin ECU system.

The original AC Delco replacement ECUs did not employ a GM HEI module inside. Their original ECUs contained circuitry similar to the Chrysler ECU to perform the same function.

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For more information about the difference in ECUs and systems, refer to the following:

The Chrysler ECU employs timing and driver circuitry internally to switch a power transistor which “turns on and off” to switch the coil primary on and off, similar to the action of contact points, producing the secondary spark. The electrical current primary ignition path is from the battery through the bulkhead connections, through the ignition switch contacts, through the ballast resistor, through the switching transistor, then to ground. The power transistor mounted on the outside of the ECU case with a heat sink can sink more current than contact points. The Darlington pair power transistor can sink up to 10 amps continuously and up to 15 amp peak spikes. The transistor switching performs the same action as the points of the old system. The dwell time of points that was adjusted by setting the point gap is controlled electronically within the ECU timing circuitry. The ECU mounts solidly to a body ground, both mechanically and electrically, and uses a molded five-pin connector to wire into the vehicle electrical system, ignition coil, and distributor. The distributor points and cam lobes of the old system are replaced by a reluctor wheel and magnetic/inductive pickup. The reluctor wheel has high points which vary the magnetic field strength, or reluctance, in the pickup coil generating the signal to the ECU.

A dual ballast resistor was used with the ECU, which had a five pin connection, for the first several years of production. The primary, or compensating, side of the dual resistor used with the ECU is the same type as the earlier point systems with an open back, ceramic housed, wire wound nominal 0.55 ohm resistor initially, but the value changed to 1.25 ohms later. The resistor still performed the same thermal adjusted coil current/voltage stabilization as with the points system. The resistor also limits the current through the power transistor of the ECU, protecting it, similar to the same action with points.

The other side of the ceramic case dual ballast resistor houses an enclosed "non-thermal" auxiliary resistor which measures 4.75 - 5.75 ohms at 70-80 degrees Fahrenheit. This nominal, five ohm resistor is connected to the "fifth pin" of the ECU. Internal to the ECU, the auxiliary resistor connects to the collector lead of the driver transistor for the main power transistor and part of its biasing. It limits overall current from the 12 volt supply. The other four pins of the ECU connect to the dual lead of the distributor pickup coil, the 12 volt Ignition Run primary power, and the lead to the negative side of the coil for the coil switching action, similar to the connecting lead from the distributor points in the old system.

In 1980, Chrysler revised the five pin ECUs to remove the external auxiliary resistor connected to the fifth pin of the ECU. The external resistor function is included internally in the revised internal circuitry. The two terminal ballast resistor is 1.25 ohms ( 1.12-1.38 ohms ) for the primary circuit to the coil.

A four pin ECU can be used in a five pin ECU system with its four terminal ballast resistor. The five ohm resistor half of the dual ballast resistor is not used, nor is the ECU pin connected internally, even if a "dummy" fifth pin is present. However, an early five pin ECU cannot function in a system with a two terminal ballast because there is no circuit to connect to the "real" fifth pin and power the ECU.

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For more information regarding the various production ECUs, refer to the following:

Chrysler’s electronic ignition, which replaced their contact point ignition system, first appeared as a running production change after May 6, 1971 on 1971 models with 340 engine and manual transmission (Ref. Technical Service Bulletins 71-8-8 and D71-8-9), and introduced the four-terminal, dual ballast resistor, part number 3656199 and Electronic Control Unit (ECU), part number 3438850.

In 1972, electronic ignition was extended to the following applications:

• Standard on 1972 A-bodies, B-bodies, and E-bodies with high performance engines.
• Standard on 1972 Imperials
• Standard on 1972 California C-bodies with 360 two barrel, 400 two barrel, and 440 four barrel engines.
• Optional on 1972 non-California C-bodies with 360 two barrel, 400 two barrel, and 440 four barrel engines.
• Optional on 1972 Dodge light trucks and compact vans, starting in January 1972.
• Standard on 1972 motor home 318-3 and 413-1 engines starting in June 1972.

Different versions and part numbers of the ECU were used in 1972 from 1971, including some with an engine speed limiter which was denoted by heat sink color. The non-limited 3438850 has a gold heat sink. The red heat sink unit, part number 3656127 limits RPM to 5000-5200 and was used on 400 and 440 high performance manual transmission applications. The blue heat sink unit, part number 3656128 limits RPM to 5300-5500 and was used on 340 manual transmission applications.

In 1973, electronic ignition became standard on all domestic Chrysler vehicles. The speed limited ECUs were dropped from production. ECU part number 3656900, with gold heat sink and a white paint dot, replaced earlier ECUs as Chrysler improved the circuitry for better cold starting in low temperature conditions. As a running change in 1973 production, a radio noise suppression capacitor was added to the external wiring, connected to the green wire with red tracer.

In early 1974, ECU part number 3755550, with a gold heat sink, which now included the radio noise suppression capacitor internally, was released. Later in 1974, part number 3874020, with added voltage spike protection and a gold heat sink, replaced earlier ECUs. 3874020 was used through 1979.

In later 1975 production, Chrysler adjusted the primary resistance in the dual ballast resistors to 1.25 - 1.5 ohms and also encased the resistor reducing the thermal action as part number 3874767. The effect of current limiting based on engine speed and temperature variation was lessened to a shorter effective range. Although the actual resistance specification changed, much of the literature specification did not.

The 1.5 ohm dual ballast resistor used in 1975-1979 ECU applications should not normally be used in place of the 0.5 ohm dual ballast resistor used in 1971-1975 ECU applications. The later dual ballast resistor will function okay in place of the earlier dual ballast, but depending on the ECU, optimal coil energy will be reduced.

In 1976, Chrysler introduced Electronic Lean Burn (ELB) which replaced the ECU in many applications, although the ECU function was integrated into the ELB Spark Control Computer (SCC) as the internal Ignition Control Module (ICM) in conjunction with the Program Schedule Module. ELB initially used a dual ballast resistor with the five ohm side connected to the SCC and the 0.5 ohm side still connected as ballast resistor for the coil. The conventional ECU with dual ballast resistor continued to be used in non-ELB applications.

In 1979, ELB was revised with digital control in the Program Module and the extreme lean condition of ELB was dropped. The revised SCC was called Electronic Spark Advance (ESA) or Electronic Spark Control (ESC). The conventional ECU with ballast resistor continued to be used in non-ESA/ESC applications. The ECU and ballast resistor was unchanged but the coil, part number 4167126, 4176009, et.al. was revised. The secondary wire connection was changed to an internal male lock terminal.

In 1979 and 1980, the Dodge Omni and Plymouth Horizon cars, used an ECU with the same body mounting pattern, but different connector and heat sink arrangement, part number 5206390. This ECU is not the same as other Chrysler ECUs of this period. It performs a similar switching action, but the Omni and Horizon cars used a Hall effect pickup module in the distributor, so signalling differs. The same ECU was also used in related European Talbot cars. The Talbot part number is 52209060.

In 1980, Chrysler revised the non-ESA/ESC five pin ECUs to remove the external auxiliary resistor connected to the fifth pin of the ECU. The external resistor function is included internally in the revised internal circuitry. This new unit for 1980 is the "four pin" ECU, part number 4111850, which was used through the 1980s. The new two terminal ballast resistor (part number 4106140, 5206436, et.al.) is 1.25 ohms ( 1.12-1.38 ohms ) for the primary circuit to the coil. The new ballast resistor eliminated the metal bracket and had a mount molded into the ceramic housing.

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Summary of Chrysler Production ECUs​

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Chrysler’s performance parts programs, Direct Connection and Mopar Performance, released higher performance and ECUs. These ECUs typically specify a primary ballast resistance from 0.25 ohms to 0.8 ohms depending on the ECU version and the coil. Early ECUs had five pins and required dual ballast resistors, and later ECUs had four pins and used single ballast resistors, following the similar changes in production ECUs. Following is a listing of the Direct Connection/Mopar Performance ECUs:

Summary of Chrysler High Performance ECUs​

See the Direct Connection or Mopar Performance manuals for more information about ignition modules and required ballast resistances and coils for details.

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