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  #1  
Old 06-01-2001, 09:47 PM
we300b
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Should the fuel injection pump timing and pump main rack require adjustment as part of a tune up on a 1969 280SL? I'm getting conflicting advice on this: my regular mechanic says it should not be touched, and will be difficult to correct once changed. Another mechanic wants to adjust the fuel injection as part of a tune up.

So my question - should the fuel injection pump timing / pump main rack ever be adjusted on these cars? Is specialized equipment required to do this, or can any mechanic do the adjustment? What equipment should the mechanic have on hand to do the job properly?

Thanks in advance for any insight.

Steve
1969 280SL
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  #2  
Old 06-01-2001, 10:53 PM
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The most important thing to remember is not to adjust any throttle linkage 'stops', the ones with the set screws and locking nuts. The proper way is to asjust the air bypass screw, the one with the spring. (I looked in my old MB ,anual, but it's position escapes me at the moment.) The injection pump is adjusted by the knurled knob on the end of the injection pump with the engine OFF! Do not engage with the engine running or the injection pump will be damaged.

Stay tuned for more, I have an old Chiltons manual I can use. Reply off list to me and I can scan some pages and e-mail them to you.
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  #3  
Old 06-02-2001, 12:50 AM
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There is a idle adjustment and a high speed adjustment and a four or five gas analizer should be used.Does'nt have to but should. We don't touch these during regular maintenance unless a problem is noted by the customer or on a test drive. These adjusters are VERY touchy and it take a fair amount of time to get them just right. If the car is running ok and the plugs look good ,I'd leave it. My two cents worth. Brian
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Old 06-02-2001, 04:32 PM
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I wouldn't touch a thing here, unless your car is running poorly. The knurled knob that wbain refered to (on the back of the injection pump) is the idle mixture screw. It shouldn't be touched unless you have reason to believe that it has been tampered with. Like the fellow said, do NOT adjust that screw unless the motor is OFF. If you do move that screw with the engine on you run the risk of stripping out the interior of that setscrew. The other big screw on top is the air inlet screw and is used to adjust engine idle speed. There is a way to determine if your rack is stuck. At the very front of your injection pump there is a rubber/vinyl cap that covers a metal disc. This is about the size of a quarter. Once this rubber grommet is removed you can stick a small probe into the hole and with a small push you can move the regulating lever (rack). It should move fairly easily, if it doesn't you can squirt lubricant in there to see if you can loosen it up. However, if your car is running well then don't touch any of the controls on your injection pump. Just run a can of good injection cleaner through the fuel system and that should do it. Cheers.
Thom
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Old 06-02-2001, 07:57 PM
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Thanks for the really good advice. Bosch mechanical FI owners are rare and expertise is even more rare. I'm glad to see you still have one. Good driving to you.
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Old 06-03-2001, 04:06 AM
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I've been thinking about your question this evening and it dawned on me that there IS something you can do with your injection pump if you want it operate at maximum efficiency. Change the pump thermostat. I'm not sure what kind of half-life they have but after discussions with friends who've owned and maintained this particular vintage it's probably cheap insurance and will pay for itself in fuel savings. I had to do it on my 280 SEL when I repaired the plunger underneath the thermostat. My MB mechanic friend said that he was getting crappy mileage, around 14 mpg when he changed his and his fuel economy shot back up to 20 mpg. The thermostat bulb sits in the thermostat housing and pushes down on a plunger that determines air-fuel mixture. The further it pushes down, the leaner the mixture. Problem is, when the thermo/bulb gets old it can't push down as far resulting in richer fuel mixtures and poorer mileage. The thermostat is located toward the rear of the injection pump and has two small cooling hoses attached to it. It is held on with two screws and comes off easily. Inside this housing you will find the thermo/bulb thingy. Do NOT remove the steel pin on the bulb or you will render it useless. A new bulb will cost you about $40.00 or so from your friendly MB dealer. Replacing it is pretty cut and dried, just the reversal of removal. Make sure you mop up coolant that leaks down on any of the pump innards. With this little bit of maintenance you can make sure your 280 is getting all the bang for its buck. Byeee.
Thom
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Old 06-04-2001, 01:58 PM
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This is the thermo/bulb that I was refering to in my last post. It resides in the thermostat housing, the one with the two small cooling hoses attached to it.



[Edited by Thom Pintello on 06-04-2001 at 01:14 PM]
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Old 06-05-2001, 03:48 AM
BB BB is offline
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re image does not show

Hey there Tom it's steve in Australia, spoke to you before,
the image it does not come up on the post. maybe repost or put on a link to where the picture is.
Is this the thermostat on the water pump housing? Yes?
This should be a 87 degree switch im told also going to put one in my 280 motor just hard to get to with ride leveler.
Keep you posted on fuel economy improvements later.
BB w123 wagon
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W116 280 se sold
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  #9  
Old 06-05-2001, 12:45 PM
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Hi Steve,
Good to hear from you again. Did you get your tuning problem taken care of? Here's the link to my site which will show you the photo that I refered to in my previous post. And no, this is NOT the thermostat which controls the water temperature. This is the thermostat for the fuel injection pump. A very different creature. http://www.geocities.com/thompintello/MercedesProject.html
The photo is on the second page of the site. Hope you're well. Cheers.
Thom
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Old 06-05-2001, 11:28 PM
BB BB is offline
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Hey there Tom

Just had a look at your web site your project looks like its comming along real nice.
Looking at the motor in your car it is quite different to mine.
Is your motor electronicaly fuel injected Closed loop?
I have heard earlier benzes were and they are able to be tuned very well for both HP and economy!
No I have not had time to go into my problem yet will try this week if I get the time I dont have a garage so if it rains NO Work etc. Its winter here now in down under land.
Catch you around tom and keep you posted.
Regards
BB steve w123 wagon
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W123 280Te 1982 Modified & still going
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W116 280 se sold
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  #11  
Old 06-06-2001, 12:30 AM
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Steve,
No, my particular car is mechanically fuel injected. It's one of the early Bosch CIS units. I'm told that they run for a zillion miles unless they get gummed up and start sticking. Good luck with the weather!
Thom
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