Sec Air Inject Malfunction - Page 3 - Mercedes-Benz Forum

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post #21 of 26 (permalink) Old 08-11-2010, 02:59 AM
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Well done, and congrats on quickly nailing this problem.

I also like the logical way you went about it - a sign of a true engineering sleuth! I am also a guy with your background and experience with a soldering iron, so I understand the pitted contact situation.

You have made a lot of progress since you learned last week how to open the hood and remove the air filters!

Eric advised you to add a small amount of grease to the air inlet tube. Add some to the air filter clips also, and the cover will come off easier next time. Final tip there. When you pop the plastic filter cover back in place, always give it a hefty thump in the center (I've seen MB techs do that) to ensure that it sits properly down in place. otherwise you can get 'bad mixture' codes setting the CEL light.

Now you can see just how important it is to get some technical documentation for your ML for future fixes.
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post #22 of 26 (permalink) Old 08-11-2010, 04:02 AM Thread Starter
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"jsap" -- you wonder what causes the relays to 'blow'. I have a degree in Electrical Engineering and I am old. When I graduated -- transistors had just been invented. However, relays were widely used for everything. I got a very good baptized experience regarding relays at a young age. Things like coils, motors and magnets all use windings of wire. They are called 'inductive loads'. Without getting too involved --when you take a voltage away from an inductive load --it spits back a very high voltage. This is how the old ignition coils in cars worked. There is a winding of wire around an iron core. When the ignition points opened -- this current --a very high 'spark' was created (7,000 volts or more) This is what fired the sparkplugs. Points would burn out or stick together after a short period of time. That's why they're no longer used. This same condition occurs with the relay that is used to turn on and off this electrical motor for the Air Injection. This motor draws up to 35 amps. When it shuts off --breaking the inductive field of the motor can create thousands of volts. When the two contacts 'open' there is a tremendous voltage surge across them. The surge not only creates heat, it also causes pitting and surface deformations on the contacts. The relay uses a diode that is designed to shunt or 'short' these high voltages and keep them from destroying the contacts. In time --they still get destroyed. Sometimes the contacts are completely eaten away and no longer make contact with each other (as was my problem) or they fuse (stick) together and create a problem that is discussed on this same forum about the Secondary Air Injection blower on someones vehicle continuning to run even after the car is shut off.
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post #23 of 26 (permalink) Old 08-11-2010, 04:09 AM
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^I still remember the days of burnt and pitted points from my apprentice days in the 1960's


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post #24 of 26 (permalink) Old 08-11-2010, 04:29 AM Thread Starter
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"keyhole" and "eric" --- thanks for your responses. As you mention-- I've come a long way in the last week from learning how to open the hood to fixing trouble code "P0410" and I have to thank all of you on this site for your help. I have additional problems with the vehicle --such as the gas gauge seems to not work. I'll address this and other minor problems on new threads. Please tolerate my ignorance of Mercedes Benzes. I'm used to working on big diesel trucks.
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post #25 of 26 (permalink) Old 08-11-2010, 10:30 PM
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Do let us know where your thread is going to be about the gas gauge. It's a common problem that many of us have, and sometimes a PEA containing fuel injector cleaner or an add like MMO or Seafoam seems to make them well again. Would be very interested in seeing how you approach this one, since I'm one of those who simply put a magical potion into the gas tank in search of a solution....

Beware of stealers
(and shill posters who work for stealers)
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post #26 of 26 (permalink) Old 08-12-2010, 09:25 PM Thread Starter
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Will do. It'll be a few weeks before I'll be able to spend time on it. I'm going camping in a few days for several weeks in the Sierra Nevada mountains.
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