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#1
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What's an Air Injection Pump designed for?
Dear friends,
It seems that some Mercedes cars have an AIR INJECTION PUMP while others don't. Could someone tell me what an air injection pump is used for? I thought that the vacuum created by an intake stroke is enough to suck air (through the air filter) in a normally-aspirated gas engine. Thank you very much. Eric |
#2
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On the cars 1981 & later MB's the air pump is used as a "warm-up" device. Causes the catalytic converter to come on-line more quickly. So that the O2 sensor & computer can take charge of the amount of emissions produced.
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MERCEDES Benz Master Guild Technician (6 TIMES) ASE Master Technician Mercedes Benz Star Technician (2 times) 44 years foreign automotive repair 27 Years M.B. Shop foreman (dealer) MB technical information Specialist (15 years) 190E 2.3 16V ITS SCCA race car (sold) 1986 190E 2.3 16V 2.5 (sold) Retired Moderator |
#3
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During warmup, the engine is runs in a preset rich condition which results in a lot of unburned hydrocarbons exiting the cylinders. The air pump provides the additional oxygen needed by the converter to convert the hydrocarbons to harmless carbon dioxide and water.
Once the car is warmed up the O2 sensor comes on-line and determines how the mixture is regulated. At this point the mixture is considerably leaner and pretty much optimized for combustion and converter efficiency by the O2 sensor, and the additional oxygen from the air pump is not needed.
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95 E320 Cabriolet, 159K |
#4
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I believe that in some parts of Europe, the emissions inspection process requires the "sniffer" test to be performed within 60 seconds of starting the engine.
The air pump is there to accelerate the warmup process to accommodate this requirement. For all practical purposes, US spec cars could probably do away with the air injection pump altogether...
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2009 ML350 (106K) - Family vehicle 2001 CLK430 Cabriolet (80K) - Wife's car 2005 BMW 645CI (138K) - My daily driver 2016 Mustang (32K) - Daughter's car |
#5
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Actually, a well designed engine, with dual-wall exhaust manifolds and close-coupled catalytic converters doesn't need an airpump.
All of these items improve coldstart emissions i.e. converter warm-up enough, to eliminate the need for it.
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2007 C 230 Sport. |
#6
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Thank you very much for all your precious information.
Best regards, Eric |
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