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Engine guides and mods

Secondary Air Injection Pump

Modification Details




It is becoming more and more common for people to report a terrible noise for about 90 seconds on start up.

This is due to the secondary air pump. People with no actual clue often call this an EGR pump.
This secondary air injection pump can be found on 700cc fortwos and Roadsters only.

It is located in the engine bay, over to the right, next to the oil filler cap.



The first thing to try is to remove the end bolt.



Drip some 3 in 1 oil in there and replace the bolt. If the noise stops, the bearing was probably dry or dirty.



Full Strip Down

Remove the Torx45 bolts from the frame rail bracket.



Disconnect the pipe...



...and lift it from the car.



The pump is held to the bracket with rubber suspension bushes.



These can be found broken or can break easily if you try to remove the nut.



So, make sure you hold the back with a 19mm spanner whilst removing the 10mm nut.



Remove the fan filter shell using a Torx30 bit.



Pull it off of the main unit. The part you removed is an air filter to keep the fan clean.
It shouldn't be blocked but you never know. Try blowing through it to check.



In the other side, you can see the fan. Check to make sure it looks clean and not damaged.



Remove the rubber suspension brackets with a Torx30 driver.



Then remove the 4x 8mm bolts holding the motor cover in place.



The motor cover can be pulled away. Check for water ingress, corrosion, free spinning motor spindle
and whilst you are there, look to see if the motor brushes are ok and the commutator isn't burnt.



Give the end bearing a spin and listen/feel how smooth it is. It's a Koyo 626ZL of you need a replacement.
You'll need a puller to remove the old bearing and a press to fit the replacement.



If you really want, you can pop all of the clips off around the fan shroud...



...to see the centrifugal fan design.



EGR or Secondary Air Injection?

EGR is an exhaust gas recirculator. These are fitted to diesel smarts. There is no pump.

An EGR valve opens and closes to regulate a certain amount of exhaust gas back into the engine.
This reduces oxygen, increases NOx output and increased output temperatures.

This helps to heat up the engine and the catalytic convertor or DPF (diesel particulae filter).

Secondary air injection injects air into the upstream flow of the exhaust. The car deliberately runs the car
rich (too much fuel), which reacts with the air to create a lot of heat. This is used to bring the catalytic
convertor up to temperature as it only works correctly and efficiently when over a certain temperature.

The 700cc fortwo (450) and 700cc Roadster (452) have a secondary air injection no matter what other sites say.
The big give away is that everything is clean and exhaust gas is dirty.


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