84 380SE - busted bolt on fuel inj. vacuum arm contraption - PeachParts Mercedes-Benz Forum

TerryH · #1 03-08-2006, 10:17 PM

Hey guys, I'm new to the MB world. I know the terminology for modern fuel injection, but don't know squat about what words to use for my 84, so please bear with me.

Think about the top part of the engine, just under the air filter stuff; kinda like where a carb would be located.

This part will probably confuse people but here goes...

I broke off the top part of the bolt that holds the vacuum plate (my term) to the fuel inj. arm (my term). The vacuum plate appears to be aluminum about 5" in diameter and is attached to an arm that is attached back towards the round fuel injection distributor/head. The arm/plate combo gets sucked down once the engine is started. I think the downward movement of the arm causes fuel to be squirted into the cylinders.

Anyway, I broke the head off the bolt that holds the "vacuum plate" to the arm. Then I broke an extratror bit off in the bolt and now can't remove the extractor bit. (I got into this predicament because I have a high idle and was trying to understand how everything works, but man, if I had only know what I was getting into! But that's a different story.)

So, I'd like to know how to replace the arm (because I can't remove the extractor bit in order to reattach the vaccum plate).

Does any know how to replace the arm? Or have any suggestions about how to resolve my problem?

I've spent many hours searching this and other web sites for the removal procedure, but couldn't find anything.

Thanks for any help!

SatRoc · #2 03-09-2006, 02:30 PM

Sounds to me like you're referring to the "Mixture-Control Unit", the "Air-flow sensor plate" and the "Air-flow sensor arm". First off, I'd suggest that you purchase the "Bosch Fuel Injection & Engine Management" book from Bentley Publishers. I got my copy from Performance Products (Performance Products4Benz.com) or 1.800.243.1220. The entire unit can be removed from your vehicle for bench repair. I have not had to do this operation yet, but it would appear that you need to disconnect all fuel lines and any electrical connections going to the Mixture-Control Unit, then remove the unit from your vehicle. The above referenced manual is invaluable in working with these units. Good luck!

TerryH · #3 03-09-2006, 08:38 PM

Thanks Roc for the help and the quick reply! I'm going to order the manual. I have one more quick question if you don't mind and can answer without much trouble.

There are 3 screws on top of the mixture control unit. These are very close to where the fuel lines attach to the top of the unit. While I was troubleshooting my problem, I tried to loosen them. I could loosen two of them but the third wouldn't budge.

My question is...do you have to remove these 3 screws to remove the mixture control unit or do you have to remove the numerous bolts around the base of the unit?

I'm thinking and hoping the latter.

Thanks again for the help!

raymr · #4 03-09-2006, 08:47 PM

You really need to stop turning things before you know what they are

Seriously, that area is the most expensive part of the engine, and its not the first place to look to trouble-shoot a problem. Hate to see a fellow W126 owner wind up with a $1500 repair!

SatRoc · #5 03-09-2006, 08:53 PM

As I mentioned earlier, I haven't personally torn one of these units apart. In looking at my 280SL, it appears that you do not have to take the top part apart. I'd suggest that you remove the whole unit and work on it on the bench. There should be an attachment at the base of the unit, which is where I'd start. Good luck!

TerryH · #6 03-09-2006, 08:58 PM

I'm laughing! That is great advice that I wish I had last weekend when I broke the bolt off that air flow sensor plate. I wouldn't be in this predicament if I wasn't tinkering.

And $1500 is pretty hefty. Thanks!

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