M119 engines have been known to have problems with plugged air injection passages, just like the EGR tubes get plugged with soot / carbon on M104 engines.


On a cold start, take the rubber hose off of the air pump and feel the amount of air volume coming out of the pump, they usually either work or they don't-not much grey area. If you have air flow from the pump, then the air passages in the cylinder head are most likely plugged. This problem is generally more common on high mileage engines.

In M104 engines, when the "hot inlet pipe to the intake manifold" gets plugged up with carbon, you can either replace the pipe or clean it out.

On M119 engines, when the air injection passages get plugged with soot and gunk, the head needs to be removed and cleaned.

Not a happy diagnosis if that is your problem, but I'm sure you'd rather know before you spend money on a pump and still have the same problem. Good luck.

I also had the following passage copied to my computer:

The system uses the o2 sensor to diagnose the air injection system. After the car has warmed up, it will activate the air pump for approx 60 seconds and watches the o2 sensor voltage-as it blows air into the exhaust system it will drop the o2 sensor voltage-it needs to drop below 40mv within 60 seconds or it will trigger the light. When the air injection system is working correctly it will drop below immediately, if there is a minor restriction it may take a while: 15-30 seconds. The same is true of the o2 sensor is getting lazy, then it may take a while for the voltage to drop, it may not drop at all if the o2 sensor is really bad. Good luck.

__________________
Paul S.

2001 E430, Bourdeaux Red, Oyster interior.
79,200 miles.

1973 280SE 4.5, 170,000 miles. 568 Signal Red, Black MB Tex. "The Red Baron".