Secondary Air Injection - PeachParts Mercedes-Benz Forum

Da_Boss · #1 10-11-2010, 08:51 PM

1.) What is the factory correct operation of the secondary air injection pump on a 98 S420?
2.) What determines when the pump should run/what inputs does the ECU use to determine when it should run/stop?
3.) How does the air get injected into both cylinder heads?

Thanks for your help!

mbdoc · #2 10-12-2010, 08:23 AM

Believe it OR not....air injection is an emission warm-up system.

When the engine is cold the pump should run from a signal from the ME computer to the air pump relay.

At the same time the computer signals a vacuum switch-over valve to open a vacuum port that opens the diverter valve.

Air is injected thru passages in the cylinder heads. Blockage is possible.

Da_Boss · #3 10-12-2010, 04:25 PM

Here is the issue I'm having. It is much more then your basic everyday secondary air injection fault.
I have had my car for 2 years and have been endlessly chasing this issue on/off for that time. Nobody, not any of the local shops, or the dealer, can figure out what the cause is. It will cause check engine light to come on every other month or so, then it will go off, then back on again.... and the problem will go away for 2-3 weeks, then it will return again and throw the same code. I have replaced the MAF, spark plugs, checked all the air injection lines, checked the sec air pump, replaced the 02 sensors (dealer came back and said replace these, so I did and it did NOTHING). I have replaced the check valves in the sec air injection lines also. Nothing has solved it!! It is driving me cazy!!!!
Here is what happens
My car sits in a garage at night. When I leave for work at around 8am in the morning, I hear the secondary air pump come on for about 60 seconds... I pull out of my street and hit the first red traffic light about .75 to 1 mile down the street. As soon as the car goes to idle, I hear a click behind the dashboard, all the lights in the car dim and the pump turn on for 5 seconds....THE VERY SECOND THE PUMP TURNS OFF... the car stumbles and acts like it wants to stall.... it recovers, and then after another 10-15 seconds I hear the pump come back on again....THE VERY SECOND THE PUMP TURNS OFF... the car stumbles and acts like it wants to stall again. The process is repeated over and over until the car is at and has been at operating temp for some time. The pump was still short cycling after a 7-10 mile drive during one of my tests last week.
When it is stumbling....the idle goes from 600-700 RPM down to 300 RPM, ONLY FOR 5-10 SECONDS....the car lurches forward....it feels like it is going to stall....all the lights dum....the whole car shakes....the tach needle floats up/down wildly......then it rebounds back to 600-700. CEL P0410 will come on after one day.
I can unplug the pump or disconnect the tube over to the valve and it will run fine. CEL will come on.
Friend read o2 sensors from cold start and determined that half the sensors were seeing the injected air and half were not. He suggested that cylinder head ports were blocked with carbon.

Da_Boss · #4 10-13-2010, 08:21 PM

Anyone?

mbdoc · #5 10-14-2010, 11:35 AM

From what you are describing.

Most likely a blockage inside of the engine OR 1 of the front O2 sensors are weak.

Da_Boss · #6 10-14-2010, 08:13 PM

I have already replaced and moved the o2 sensors. Those are not it. What exactly could be clogged and where is it?

mbdoc · #7 10-15-2010, 08:11 AM

Passages inside the cylinder heads directly to the base of the exhaust valveS

BOTH front O2 sensors MUST be in very good condition for the car to pass that test every drive cycle.

mbdoc · #8 10-15-2010, 09:57 AM

Here is the "logic chain" that the computer used to set that code

Da_Boss · #9 10-15-2010, 10:09 PM

None of this explains why engine runs so poorly as soon as the pump turns off. That is the part that I cannot figure out. The running of the pump and/or blocked cylinder head ports should not cause temporary lean (stalling) idle condition.

sogaro · #10 10-16-2010, 12:10 AM

Change you ECU or get it flashed

samiam44 · #11 10-16-2010, 11:06 AM

There are 2 O2 sensors on a 98 M119?

Da_Boss · #12 10-17-2010, 11:04 PM

I'm not replacing the ECU because a pump isn't working correctly. That makes no sense.

Da_Boss · #13 10-18-2010, 08:32 PM

How exactly does the air get from one side of the engine to the other? Where are the air injector ports in the cylinder heads and if they are clogged, how exactly are they cleaned?