SVO Stock Boost Control System

Miscellaneous Ramblings About the Stock Boost Control System


Copyright 1998 Mike Fleming

The part number on the Boost Control Solenoid (E4ZX-9C728-AB) is an engineering part number, not a service part number, that you would order from a parts supplier or dealer. The service part number is E4ZZ-9C728-A for 1984, E5ZZ-9C728-A for 85.5 and up--unfortunately, all of these pieces went obsolete some 10 years ago.

As for the hose that connects the solenoid to the engine parts, if you consult the Ford Parts manuals, the hose is serviced by a standard 7/32 vacuum hose which is more than able to handle the underhood temperatures--which don't reach 200 degrees F. in that area. The compressor (intake) end of the turbo does not get "hot" compared with the exhaust (exhaust) side.

To better clarify the answers to your quest for knowledge on turbocharger management for automotive engines--the type, or composition, of the boost pressure controlling hose will make absolutely no difference on the static or dynamic performance of the system.

Internal diameter and length, perhaps better thought of as hose internal volume may have some minor effect on the transient boost characteristics but I don't think that the variance between 7/32 and 5/16 ID hose would even be measurable by the driver. Same goes for length, although it does make sense that a small diameter hose several feet in length may appear as an additional restriction to the boost bleed function.

The 1984 SVO used a electronic Boost Control Module (one three-wire and one two-wire connector) with a Boost Control Solenoid (one two-wire connector). The control module received a low-level signal from the EEC-IV processor, amplified that signal so it would be strong enough to control a low-impedance solenoid (about 8 ohms if I remember that far back--I have one so I can measure it if anyone really has to know).

The "T" in the compressor outlet has two hose fittings and one threaded end. The threaded end of the "T" has a damping restrictor fitted and the opposite end has a bleed restrictor while the wastegate fitting has a machined sleeve approximately 1.40 mm in inside diameter. Increasing the size of the bleed fitting will result in more airflow through the solenoid when it is powered on. The job of the "T" is to control the pressure getting to the wastegate diaphragm by bypassing some airflow through the solenoid.

(NOTE: It is important to understand that wastegates do not think, they just do what they are told. At least the smart ones do.) The solenoid is controlled electrically in a duty cycle fashion, more on-time percentage equals more airflow bypassed which in turn means more boost pressure.

This is also exactly how the Idle Speed Control (ISC) solenoid works: more on-time means more airflow which means a higher idle speed or load-carrying ability like when the A/C is on.

In the Premium fuel position, two relays are powered on: one relay connects EEC pin 30 to EEC ground; the other relay connects EEC pin 32 to the input of the Boost Control Module. Both of these relays are powered on at the same time. In Regular fuel position, EEC pins 30 and 32 are left floating and the input to the Boost Control Module is connected to EEC power (+12v).

The function of the boost control system is to keep the engine out of the detonation range. The EEC system does not measure boost pressure (there is no manifold pressure sensor as would be found in a speed-density control system). It measures airflow, air temperature and sensed knock (the actual knock can be quite different from what the Knock Sensor hears, especially on the 1984-1985 SVOs).

When knock is sensed, the first action is to retard the ignition timing to reduce detonation, step two is to lower boost pressure (reduce the duty cycle of the boost control solenoid), and step three advance the ignition timing to bring down the combustion temperatures which will reduce the detonation tendencies.

The whole system cycles between timing up/down, boost up/down until the engine is brought into a safe operating range. This all happens very dynamically and is very difficult to measure when the engine is under transient load. This often produces surging (especially in the 1984-85 SVOs) that is very noticeable in the 3000 RPM to redline in third and forth gears under heavy throttle, laws permitting (actually, the EEC-IV processor and the engine are not concerned with the law; they leave that decision up to the driver!).

Obviously a higher octane fuel will help. Not as much of a problem on the 1985.5 and 1986 models until one gets the power way up there. My experience has shown that when the outside air temperature and engine are cold, detonation is hardly noticeable, but when the engine warms up (specifically the piston tops, valves, spark plugs and combustion chamber surfaces), detonation is more pronounced which holds true to theory.

In 1985, Ford used a different driver (transistor) in the EEC-IV processor which could handle the current of the boost control solenoid directly, and used a higher-impedance solenoid (about 24 ohms) therefore eliminating the need for the Boost Control Module used on the 1984 SVO.

All Ford turbo cars (Capri, Mustang, T-Bird, Cougar and Merkur) used the new solenoid in MY (model year) 1985; however, it was not adopted to the SVO until 1985.5 on the 205 HP engine. The solenoids are not interchangeable, although they perform the same function (and use the same 7/32 vacuum hose).

Higher boost has good effects on both power and B.S.F.C (brake specific fuel consumption). One of the prominent reasons is that, in proportion to the rise in boost, charging efficiency increases and provides higher indicated horsepower while the engine's mechanical losses remain almost the same, resulting in an improvement of brake thermal efficiency. That means more power for the same amount of fuel and engine displacement.

Unfortunately the exhaust temperatures can get pretty high when making 150HP/Liter so the engine life may not be good as the heat and coolant flow in the stock cast iron 2.3L OHC cylinder head leaves much to be desired. One short-term solution is to make the air/fuel mixture much richer (when using a liquid fuel) to take advantage of the heat of evaporation by boiling the excess fuel and lowering the combustion and exhaust temperatures. More on that later!

The part number on the Boost Control Solenoid (E4ZX-9C728-AB) is an engineering part number, not a service part number, that you would order from a parts supplier or dealer. The service part number is E4ZZ-9C728-A for 1984, E5ZZ-9C728-A for 85.5 and up--unfortunately, all of these pieces went obsolete some 10 years ago.

As for the hose that connects the solenoid to the engine parts, if you consult the Ford Parts manuals, the hose is serviced by a standard 7/32 vacuum hose which is more than able to handle the underhood temperatures--which don't reach 200 degrees F. in that area. The compressor (intake) end of the turbo does not get "hot" compared with the exhaust (exhaust) side.

To better clarify the answers to your quest for knowledge on turbocharger management for automotive engines--the type, or composition, of the boost pressure controlling hose will make absolutely no difference on the static or dynamic performance of the system.

Internal diameter and length, perhaps better thought of as hose internal volume may have some minor effect on the transient boost characteristics but I don't think that the variance between 7/32 and 5/16 ID hose would even be measurable by the driver. Same goes for length, although it does make sense that a small diameter hose several feet in length may appear as an additional restriction to the boost bleed function.

The 1984 SVO used a electronic Boost Control Module (one three-wire and one two-wire connector) with a Boost Control Solenoid (one two-wire connector). The control module received a low-level signal from the EEC-IV processor, amplified that signal so it would be strong enough to control a low-impedance solenoid (about 8 ohms if I remember that far back--I have one so I can measure it if anyone really has to know).

The "T" in the compressor outlet has two hose fittings and one threaded end. The threaded end of the "T" has a damping restrictor fitted and the opposite end has a bleed restrictor while the wastegate fitting has a machined sleeve approximately 1.40 mm in inside diameter. Increasing the size of the bleed fitting will result in more airflow through the solenoid when it is powered on. The job of the "T" is to control the pressure getting to the wastegate diaphragm by bypassing some airflow through the solenoid.

(NOTE: It is important to understand that wastegates do not think, they just do what they are told. At least the smart ones do.) The solenoid is controlled electrically in a duty cycle fashion, more on-time percentage equals more airflow bypassed which in turn means more boost pressure.

This is also exactly how the Idle Speed Control (ISC) solenoid works: more on-time means more airflow which means a higher idle speed or load-carrying ability like when the A/C is on.

In the Premium fuel position, two relays are powered on: one relay connects EEC pin 30 to EEC ground; the other relay connects EEC pin 32 to the input of the Boost Control Module. Both of these relays are powered on at the same time. In Regular fuel position, EEC pins 30 and 32 are left floating and the input to the Boost Control Module is connected to EEC power (+12v).

The function of the boost control system is to keep the engine out of the detonation range. The EEC system does not measure boost pressure (there is no manifold pressure sensor as would be found in a speed-density control system). It measures airflow, air temperature and sensed knock (the actual knock can be quite different from what the Knock Sensor hears, especially on the 1984-1985 SVOs).

When knock is sensed, the first action is to retard the ignition timing to reduce detonation, step two is to lower boost pressure (reduce the duty cycle of the boost control solenoid), and step three advance the ignition timing to bring down the combustion temperatures which will reduce the detonation tendencies.

The whole system cycles between timing up/down, boost up/down until the engine is brought into a safe operating range. This all happens very dynamically and is very difficult to measure when the engine is under transient load. This often produces surging (especially in the 1984-85 SVOs) that is very noticeable in the 3000 RPM to redline in third and forth gears under heavy throttle, laws permitting (actually, the EEC-IV processor and the engine are not concerned with the law; they leave that decision up to the driver!).

Obviously a higher octane fuel will help. Not as much of a problem on the 1985.5 and 1986 models until one gets the power way up there. My experience has shown that when the outside air temperature and engine are cold, detonation is hardly noticeable, but when the engine warms up (specifically the piston tops, valves, spark plugs and combustion chamber surfaces), detonation is more pronounced which holds true to theory.

In 1985, Ford used a different driver (transistor) in the EEC-IV processor which could handle the current of the boost control solenoid directly, and used a higher-impedance solenoid (about 24 ohms) therefore eliminating the need for the Boost Control Module used on the 1984 SVO.

All Ford turbo cars (Capri, Mustang, T-Bird, Cougar and Merkur) used the new solenoid in MY (model year) 1985; however, it was not adopted to the SVO until 1985.5 on the 205 HP engine. The solenoids are not interchangeable, although they perform the same function (and use the same 7/32 vacuum hose).

Higher boost has good effects on both power and B.S.F.C (brake specific fuel consumption). One of the prominent reasons is that, in proportion to the rise in boost, charging efficiency increases and provides higher indicated horsepower while the engine's mechanical losses remain almost the same, resulting in an improvement of brake thermal efficiency. That means more power for the same amount of fuel and engine displacement.

Unfortunately the exhaust temperatures can get pretty high when making 150HP/Liter so the engine life may not be good as the heat and coolant flow in the stock cast iron 2.3L OHC cylinder head leaves much to be desired. One short-term solution is to make the air/fuel mixture much richer (when using a liquid fuel) to take advantage of the heat of evaporation by boiling the excess fuel and lowering the combustion and exhaust temperatures. More on that later!

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