CRG Research Report
1967-69 Camaro Emission Systems
© 2005-2016, Camaro Research Group
Primary Author -
Reviewed by the CRG
Last Edit: 18-Nov-2015
Previous Edits: 23-Jan-2015, 12-Mar-2012, 07-Sep-2008, 17-Feb-2008, 27-Oct-2005
Original Release: 25-Oct-2005
All images by the author unless otherwise noted.
This article describes the original emission sytems for
1967-1969 Camaros. These systems reduced exhaust
and crankcase emissions to meet California
and federal air pollution emission standards.
Three emission control systems are found on 1967 through 1969 Camaros:
- The Air Injector Reactor (AIR) system pumped air into
the exhaust manifold(s) to help complete the combustion
process. The AIR system consisted of the air injection pump
(aka smog pump), a fuel mixture control valve (1967) or an air
diverter valve (1968-9), check valves, air manifold assembly
(aka smog tubes), and air injection tubes (one per cylinder).
- The Controlled Combustion System (CCS) was introduced in 1968
and was used on cars that did not receive the AIR system. CCS improved combustion
efficiency via recalibrated carburetor and distributor settings and
higher operating temperatures (compared to 1967). The higher operating
temperatures were accomplished by using a 195°F coolant
thermostat (instead of 180°F) and the use of a
thermostatically controlled air cleaner (ThermAC). The
ThermAC system was designed to warm intake air to 100°F when
underhood temperatures were less than 100°F. It consisted of
a damper door mounted on the snorkel of the air cleaner
which directed warm air from a heat stove on the exhaust
manifold into the air cleaner.
- The Positive Crankcase Ventilation (PCV) system
utilized manifold vacuum to draw crankcase vapors into the
engine to be burned. Filtered air was drawn through the
engine, through the PCV valve, and into the intake manifold.
In 1967 (as in 1966), emissions equipment was required only on cars sold
in California. The California cars were fitted with an AIR
system (Regular Production Option (RPO) K19), and the PCV
system (RPO K24). All engines equipped with K19 had unique
engine codes due to the required holes in the exhaust
manifold(s). Also, the L26 (230 ci L6) engines with K19 used
a different distributor and the L30 (327 / 275hp) engines
with K19 had a different initial timing. Note that smog
equipment was not required on cars built in California but
intended for sale in other states.
1967 AIR Systems
In 1968 and 1969, the California and federal emissions
requirements were the same and all cars were built to the
same 50-state standard. The AIR system was installed on all
L6 cars with manual transmissions, all small blocks with
manual transmissions, and all Camaros with big blocks.
(Chevelles and full-size cars with the 396/325hp engine and
TH400 transmission were the only 68-69 Chevrolet big block cars that
did not have smog pumps.) Only the automatic L6 and automatic small
block Camaros did not have smog pumps, instead they had the
simpler Controlled Combustion System. Generally speaking, an
automatic car required less aggressive emission control than
a manual transmission car because the engine load (and
carburetor fuel metering consistency) was more stable and
In 1968, vehicles exported to Canada and other countries did
not require the AIR system. RPO KD1 was used to delete the
system (if it would have been so equipped otherwise) and
1/4"-18 NPSF straight pipe thread plugs were installed in
the manifolds. It is unknown if a credit was issued on the
Canadian window stickers for this delete. The Controlled
Combustion System was still installed on the exported L6 automatic
and small block automatic cars.
In 1969, Canadian cars used the same emission controls as
PCV became standard on all Chevrolets in 1968 and is still
used today on all cars.
1968 AIR Systems
1969 AIR Systems
System Design Changes
To prevent backfiring when there was a rapid increase in
manifold vacuum (for instance under a decel condition), the
1966-67 AIR system fuel mixture control valve supplied the intake
with extra air to lean out the air-fuel mixture. The approach was
not very successful - it resulted in excessive popping noise through
In 1968, the system was redesigned to reduce backfiring (technically called
after-firing because it was in the exhaust system) and to make it less complex.
When there was a rapid increase in manifold vacuum, the diverter valve,
used on 1968 and later systems, momentarily stopped air
from being injected into the exhaust ports, thus preventing
ignition of the richer exhaust gases.
The 1966-67 AIR pump used filtered air from the air cleaner.
The 1966-67 AIR equipped cars had unique air cleaners to provide
this filtered air. The 1968-and-later air pump had an integral
filter via the centrifugal smog pump fan. The air cleaners for 68-69
AIR equipped cars were different from the Controlled Combustion System
air cleaners due to the ThermAC system on the CSS air cleaners.
68-69 AIR Diagrams
(Click on either photo to expand it.)
|68-69 AIR System Diagram
||Diverter Valve Diagram
The 67 smog pumps were a serviceable 3-vane design and the
pulley attached with 4 bolts. The redesigned 68 AIR system
used a non-serviceable 2-vane design with 3 bolts attaching
the pulley to the pump. The 68 and 69 smog pump design was used through
the mid-70's. The pump housing was die-cast aluminum. The end section,
casting # 7801149, is cast iron that was painted semi-gloss black. This
casting was widely used, not only on Chevrolet vehicles, but other GM cars
too. The machining was different for the other GM makes and will not fit
The 68 pumps used on Z28's and big blocks had a pressure relief
valve installed on the side of the pump.
The Z28 relief valve has a green plastic plug and the 396
relief valve has a black plastic plug The 68 pumps for L6, 327, and
350 engines and all 69-and-later pumps did not have the pressure relief
valve on the pump; it was incorporated into the diverter valve.
67 and 68 V8 pumps were either mounted high on the engine, in front of the
intake manifold / carburetor (see 68 diagram), or
mounted on the passenger side of the engine. In 1969, as part of the V8 engine
layout standardization, the pump was moved to the passenger side, below the
The date code is stamped on a pad on the side of the pump. The date code format
is DDDY#P, where DDD = the Julian day, Y = the calendar year, # = 1 or 2, and P
= is the configuration code of the pump.
The meaning of # code is thought to be a shift code. 67 pumps were coded 1
or 2 and all 68 and later pumps were coded 1.
The last digit is the configuration code of the pump. The 67 pumps are coded A and C.
(67 Corvette pumps are coded P and are unique to that application.)
The 68 pumps with a pressure relief valve installed in the pump were coded Y.
Non-pressure relief valve 68 pumps were coded Z. 69 and later pumps (without a
pressure relief valve) were coded S.
|1967 Smog Pump
||1968-69 Smog Pump
Smog pump date code
30681S = 306th day of (6)8, built without a pressure relief valve.
A white smog pump fan was used on smog pumps from 68 to
mid-72. Later pumps and service parts used a black fan
(though the 68 and 69 service manuals show a black fan!). The
pulleys used on the pumps are listed at
CRG Pulley Usage.
White Smog Pump Fan
|Front and Side View
Fuel mixture control valve / Diverter valve
The fuel mixture control valve on 1967 small block engines was located between
the distributor and the valve cover. It was mounted on a bracket which in turn
was welded to the crankcase vent tube coming out of the lifter valley area at
the rear of the block. The mixture valve on big block engines were mounted to a
bracket on the RH valve cover.
Diverter valves were mounted in multiple ways in 68 (directly to the AIR
pump or via an elbow and hose - see the 68 Assembly Instruction Manual (AIM)).
The various 69 Camaro V8 diverter
valves were externally the same, but had internal calibration
differences and hence different part numbers. (Note: Other diverter valves
(e.g., 69 truck) may look very similar to 69 Camaro V8 valves, but
may have a different output housing or output housing orientation.) As part
of the engine layout standardization, 69-and-later Chevrolet V8 cars
used a 3942533 extension to connect the diverter to the pump.
Most diverter valves in 68 had a detachable muffler (via a removable clip),
though a few have been observed with the muffler crimped on.
69-and-later mufflers were crimped on. The mufflers were plated with
|1967 Fuel Mixture Control Valve
||1967 Fuel Mixture Control Valve
Installed on a small block
|69 Diverter Valve and Extension
||Close-up of part number, 29295
The last five digits of the diverter valve part number were
stamped on the diverter valve mounting flange
(as shown in the picture above). The broadcast code was
ink-stamped on the diverter valve; the codes are shown
Note that the 67 Assembly Instruction Manual shows the incorrect part #
for the 67 Z28 fuel mixture control valve - the correct number is
listed below. The 68 AIM also lists different part numbers than other 68
supporting documentation. The 68 AIM part numbers are believed to be correct.
Fuel mixture control valve (67) and
Diverter valve (68-69) Usage Table
|LF7 and 307
|L30 and 350
|| DH *
|396 and 427
|* CT on early vehicles |
Check valves / air manifolds
In 67, the smog pump was connected to the backfire check
valves. The left check valve is part # 5354987, while the
right check valve is a Y shaped valve (part # 5354988) which
also was connected to the fuel mixture control valve.
In 68-and-later cars, the output of the smog pump went
through the diverter valve first, then to a backfire valve
mounted on each air manifold. The 68-and-later backfire
check valves are part # 5361992 and are gold cadmium plated.
The air injection tubes were short pipe extensions (2-13/16
inch long) that were installed before the air manifold was installed.
The air manifolds have a greenish/blackish coloration. On the L6 engines,
the air manifold installed in the L6 head. On the V8 engines, they were
installed into the exhaust manifolds. The threads in the exhaust manifolds
for the air manifolds were 1/4"-18 NPSF straight pipe thread.