Engine Compartment and Mechanical




All USA and Canadian SM's were carbureted. No fuel injected cars were officially imported to North America.



All USA and Canadian SM’s were equipped with an emission control system called secondary air injection. Secondary air injection used a belt-driven pump to inject air into exhaust, just downstream of the exhaust valves, with the intent to oxidize (burn) any remaining unburned fuel that would otherwise go out the tailpipe. Per the parts books, Swedish and German cars received a similar system on later SM's.


The main component of this system was a belt-driven air pump that was mounted on the forward accessory tray next to the air conditioning compressor, with sheet metal bracketry that looks a bit Rube Goldberg. 

Secondary air injection also utilized something called a gulp valve which was there to prevent backfiring when the throttle was abruptly closed. The gulp valve was mounted on a metal pipe that straddled the accessory driveshaft. Check valves were installed on each exhaust manifold to prevent exhaust from backing-up into the air injection system. 


Typical USA/Canadian engine compartment showing smog pump and gulp valve

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Typical USA/Canadian engine compartment showing smog pump installation

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Close-up of the gulp valve

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Close-up of an air injection check valve and it's tubing


Unique exhaust manifolds and header pipes were used on USA/Canadian cars since the manifolds needed ports for the air injection. This caused the entire front half of the exhaust system to be substantially different than on Euro cars. These unique exhaust components caused the heat shields above the front exhaust elements to be shaped differently (items 7 and 8 from the part book snippet below). Rear exhaust components were the same as Euro cars. 

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Euro headers on left, USA/Canadian smoked headers on right

Smogged exhaust manifold as found on all US and Canadian SM's (right shown, left opposite)

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USA and Canadian cars had drip trays under each cam cover. They were held in place with two metal tabs that were rubberized to prevent rattles and chafing on the cam covers. We cannot find these drip trays in the parts book, but we believe that all USA/Canadian cars were originally equipped with them. Many however have been removed at this point. 

There is a story floating around that the USA exhaust manifolds ran so hot that they caused the cam covers to leak and drip oil onto the hot manifolds. If true, the drip trays would have had a dual function; to act as a heat shield and to divert leaked oil away from the hot manifolds. 

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Drip tray for leaky cam cover seals



US and Canadian cars had two additional metal / asbestos heat shields in the aft, lower left corner of the engine bay. 


  • One was located just below the steering column and provided heat shielding for brake system hydraulic tubing (part number 5420083). This shield is illustrated in the parts book (see item 20 from the parts book snippet above).


  • The second heat shield (part number 5423374) was apparently designed to protect the steering column itself. This part is listed in the parts book but with no illustration. 


Heat shielding in aft, lower left corner of engine bay - unique to North American SM's


Heat shield for steering column - P/N 5423374


The intake manifold on USA/Canadian cars had a unique part number – they had a threaded port for the smog system on each of the six manifold branches. There was a U-shaped metal pipe that connected these ports (see photos). 

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Un-drilled ports in Euro intake manifold

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Drilled and threaded ports for exhaust emission system in the intake manifold for USA/Canadian cars (the ports were capped off by this car’s owner) 

U-shaped metal tube on intake manifold for the emission system

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Evaporative loss systems to capture fuel tank vapors became mandated in the USA in 1971. The main component of an evaporative loss system is a charcoal canister. The charcoal canister's job was to absorb fuel vapor that would otherwise vent out to the atmosphere. The vapors trapped by the charcoal are then released back into the engine’s intake and burned. 


All US and Canadian SM’s were equipped with a charcoal canister and associated equipment. 


The cylindrical charcoal canister was mounted in the front left fender, adjacent to the hydraulic reservoir (the charcoal canister was the same part number that was used on the DS).  The rubber intake hose between the air filter and the black plastic air distribution plenum was different on USA/Canadian cars due to the addition of a hose spigot for the charcoal canister. The evaporative loss system also had a plastic vapor recovery tank mounted in the aft area of the car, near the fuel tank. A plastic tube ran the the length of the car and connected the recovery tank to the charcoal canister. 

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Euro air intake hose without charcoal canister hose spigot

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USA/CAN air intake hose with port for charcoal canister hose

Charcoal canister in front left fender of an SM. This is the same charcoal canister that was used on the DS.

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Parts book snippet of the evaporative loss system components



USA/Canadian cars received distributors with unique part numbers; one part number was for 2.7 liter engines, one for 3.0 liter engines. They apparently had different advance curves than Euro cars, as part of the exhaust emission compliance. 


USA/Canadian cars had different spark plug heat ranges.



All USA/CAN SM’s had a data plate riveted on the tray at the bottom of the windshield near the left wiper blade. This data plate certified that the car conformed to the applicable emission standards for that model year (1971, 1972, or 1973). 


This data plate was orange on 1972 cars with the 2.7 liter engine, and green on 1973 cars with the 3.0 liter engine. It is unclear what color the plate was on the very few 1971’s that were imported to North America. 

Emission data plate - Orange for 1972 with the 2.7 liter engine

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Emission data plate - Green for 1973 cars with the 3 liter engine

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All USA DS models had a data plate that contained the model year (for example, a 1971 car would have a plate that said, “AC 71”). This plate was installed under one of the screws (or rivets) that held the serial number plate onto the frame, in the engine compartment. 


USA or Canadian SM’s only sporadically have this AC plate. An example of a USA SM that has this plate is shown in the photo. It is not clear why some SM’s do not have this plate. 

Euro SM's never received this plate. 



The parts books show that some SM’s had plastic (nylon) fuel tanks and some had metal fuel tanks. Fuel tank usage was as follows:


  • All carbureted Euro cars received the nylon fuel tank

  • All Fuel-injected Euro cars received the metal fuel tank

  • All USA/Canadian cars (which were all carbureted) received the metal fuel tank (same part number that was used on fuel-injected Euro cars). 


The fuel level sending unit, and other related hardware, were different to match the above tank usage. 


All SM’s have shielding in the trunk to protect fuel system parts from damage due to shifting cargo in the trunk. Cars with the nylon tank had a small shield, but cars with the metal tank had a much larger shield that completely enclosed the fuel filler tube. Since all USA/Canadian cars had the metal fuel tank, they all had the more extensive shielding in the trunk. 

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Fuel filler area on a Euro car with a nylon fuel tank

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Fuel filler area on all USA/Canadian cars (metal fuel tank)



When Citroën changed hydraulic fluid on North American DS’s from LHS2 (brake fluid) to LHM in the middle of model year 1969, it caused quite a bit of confusion. Owners and repair shops were inadvertently putting the wrong fluid in the LHM reservoir, such as using brake fluid or antifreeze (noting that the color of antifreeze is almost identical to LHM green). 


To help combat these serious mistakes, Citroën went to great lengths on the DS to warn owners and mechanics of the correct hydraulic fluids. These included warnings added to the owner’s manuals and various stickers and plates on the fluid reservoir itself. 


A few of these made their way onto SM's for the US/Canadian market including a metal plate on the reservoir cap advising of the correct fluid. 

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Metal plate on reservoir cap to remind users of the correct hydraulic fluid



An extremely low mileage and original SM in Seattle has this cardboard tag taped onto the air distribution plenum. It is our understanding that all USA cars originally had a tag such as this attached to the engine, however nearly all have been lost by now.