Thermactor Exhaust Emission Control System
| 31 August 2004
This month the Pony Tricks column comes from an old Ford Shop Tips bulletin, specifically the November 1965 issue. The article discusses something called Ford’s New Thermactor Exhaust Emission Control System. This system is, of course, centered on the hated air pump that was first installed in California beginning with the 1966 model year.
Description & Operation—The Thermactor Exhaust Emission Control system is mandatory on ALL 1966
Ford cars and F-100 trucks sold in the state of California. Used in conjunction with the closed-type crankcase emission system, it controls the amount of unburned hydrocarbon and carbon monoxide gases which are emitted from internal combustion engines, which under certain conditions may contaminate the air.
The Thermactor system reduces contamination by injecting fresh air under pressure into the manifold at the exhaust valve of each cylinder. The oxygen in the air, plus the heat of the exhaust gases cause combustion during the exhaust stroke of the piston. The undesirable gases are burned in the exhaust manifold and then flow out the exhaust system.
Components—The Thermactor system (Figures 1 & 2) consists of the following components: air supply pump; air manifold for each cylinder head; backfire-suppressor valve; air filter for the air pump; check valve on each air manifold; air nozzle for the exhaust port of each cylinder; air supply hoses and vacuum sensing line.
Air Supply Pump—A vane-type air pump, belt driven by the engine supplies all the air under pressure for the system. The vanes rotate past three chambers in the housing—intake, compression and exhaust. Each vane completes a pumping cycle in every revolution of the pump.
Air is drawn through a filter and into the intake chamber. A vane moves the air into the smaller compression chamber. The now pressurized air is moved into the exhaust chamber. Hoses and air manifolds for each cylinder route the pressurized air into nozzles that terminate just under the exhaust valve heads.
A spring loaded relief valve (Figure 3) is located in the exhaust chamber and relieves exhaust air flow if the pressure exceeds a preset value.
Exhaust Check Valve—Located in the air inlet side of each air supply manifold, is an exhaust check valve (Figures 1 & 2). It prevents a backflow of exhaust gases into the air supply pump in the event exhaust pressure is greater than air pump delivery pressure.
Backfire-Suppressor Valves—Two types of backfire suppressor valves are used; an air gulp-type for large displacement engines, and an air by-pass-type for small and medium displacement engines.
Air Gulp-Type Valve—The air gulp-type valve has one air inlet and one air outlet (Figure 4). It is mounted on the engine and operates only during periods of sudden decrease in intake manifold pressure, such as occurs immediately following the closing of the throttle, after a period of acceleration. A rich fuel mixture results due to the momentary continuation of fuel flow from the carburetor.
The overly rich mixture isn't completely burned by the air being injected into the exhaust ports. Upon the next
firing of the cylinder, the flame traveling out the exhaust port may ignite the overly rich mixture and cause an explosion or backfire in the exhaust system. To prevent this condition and insure complete burning of the gases, the backfire-suppressor valve allows additional air to enter the induction system whenever the intake manifold pressure decreases.
Air By-pass-Type Valve—The air by-pass-type valve has two air outlets and one air inlet as shown in Figure 4 and operates essentially the same as the air gulp-type valve, except for the following three main differences:
1. All the air to the air manifold passes through the backfire-suppressor valve.
2. No Thermactor air is directed to the intake manifold.
3. During deceleration, Thermactor air delivery to the exhaust system is cut off and the air is diverted to the carburetor air cleaner for silencing purposes only.
Service and Diagnosis—The design of the Thermactor system is such that certain carburetor and distributor recalibrations are necessary for best performance. In addition, before perfoming any diagnosis involving the Thermactor system, it must be determined that other engine components are functioning properly. To do this, the backfire-suppressor valve vacuum sensing hose and air supply hose MUST be disconnected at the intake manifold.
For best results and most efficient operation, the emission control system hoses, tubes, oil separator screen, fittings, and carburetor spacer should be cleaned; and the emission control valve replaced every 12,000 miles. Also the air pump filter element must be replaced every 12,000 miles.
If engine components not part of the Thermactor system are functioning properly, use the following diagnosis guide to isolate Thermactor malfunctions.
Excessive Backfiring in Exhaust System—Damaged, plugged, disconnected or leaking backfire-suppressor valve or vacuum sensing hose.
Defective or malfunctioning backfire-suppressor valve resulting in insufficient air delivery to the intake manifold or air delivery not timed to engine requirement.
Excessive Hesitation on Acceleration after Sudden Throttle Plate Closure (Above 20 MPH)—Intake vacuum leak at backfire-suppressor valve, vacuum hose or air outlet hose (to intake manifold). Defective or malfunctioning backfire-suppressor valve.
Air Supply Hose(s) Baked or Burned— Defective exhaust; check valve.
Engine Surges at all Speeds—Backfire-suppressor valve defective or stuck open; improper carburetor adjustment-idle speed, idle speed mixture, automatic choke, etc.
Noisy Air Pump Drive Belt—Drive belt improperly adjusted. Seized or failing air pump. Misaligned or defective pulleys.
Rough Engine Idle—Improper carburetor adjustment-idle speed, idle fuel mixture, automatic choke, etc. Improper initial ignition timing. Intake vacuum leak at the backfire-suppressor valve vacuum hose or air inlet hose. Backfire-suppressor valve defective or stuck open.