Adjusted - Fuel Bypass Spring
 

I pulled the fuel check banjo on the IP yesterday, and found it at ~20.5 mm; stretched to ~27 mm and reinstalled.

https://i.imgur.com/UeD0nzf.jpg

how are the results?

I don't know yet, I still have to get it timed!

Good to hear! Its one of the first steps to achieving a smooth idle..

If you alter 2 things at the same time and you get an improvment you will not know which one caused the improvement.

Hey Diesel 911, I hear that, only I had no problem before; just couldn't get even a puff of initial power building smoke, and since I had the Injection Pump out to inspect the intermediate bearing/bushing, I figured I'd replace the primer pump, old cracking lines (w/tygon), and adjust the fuel bypass spring to spec. (I mostly noticed the lack of resistance in hand bleeding the fuel lines, and things just went from there!)

(I certainly know not to manipulate multiple variables and expect to get any kind of evidence of causative effect; unless, of course, I run a matrix of all of the variables! :P)

(P.S. Intermediate shaft turned out good by the way, with not even .05mm axial play.)

I took a look at the fuel bypass spring on the '83 617. It was at 20 mm. I stretched it out to 27mm and reinstalled. As I pumped the hand fuel pump to bleed the air it seemed to pressurize a lot more than before after a few strokes.

Test drove the car at 45 mph, then 60-65. It seemed to have only slightly more power.

It was easy enough to do, just have 14mm and 17mm wrenches to do the 15 min job.

I drove the car some more today and noticed one significant change. It idles smoothly when stopped in gear now.

Before this minor fix, I would usually move the gear selector from D to N at stop lights because it was not idling smoothly. Now it has the proper idle when in gear with the brakes on.

Thank you for this easy tip to improve the ride!

No worries, I'm glad I stumbled across it and the fix on here (Thanks WHunter!); it just seemed my system wouldn't build much pressure when bleeding. I got the motor fired up, and I have yet to take it for a spin, but I am really happy with the idle, as well as the smooth but quick return to idle.

(I also felt a lot of "seat-of-the-thumb difference" when pumping the system up! Dollars to Doughnuts this would effect folks' drip timing!)

May I ask where is it located on the IP?

It is on the side of the IP near the engine block, near the middle of the IP. There is a fuel line attached by the bolt. The line comes from the fuel filter.

The bolt has two hex-heads, a 17mm with a 14mm on top.

Take the bolt out of the IP and unscrew the top hex to remove the spring. Be careful not to loose the steel ball inside the bolt, under the spring.

Is my memory correct that this item is only there on turbo diesel cars, or do the N/A injection pumps have this same "adjustable" spring as it were?

All mercedes w123 diesels have them and others too....here is where it is located

http://www.peachparts.com/shopforum/...t-img_2826.jpg

Great. Thanks. I'll plan to check both of mine.

Good News they all have one; Bad News some cannot be taken apart becaue they have a Ball Bearing pressed into them insted of a Screw that can be removed.

Finally remembered to check mine, and apparently it is the turbo charged engines that can't be adjusted. Was hoping that this might correct the rough idle and poor fuel economy.

Is there a part number? All I found was this: 1985 Mercedes-Benz 300TD Base Wagon - Fuel Injection - Page 1

Thank you all in advance! :D

Not exactly.

Thank you for the reply! :D

It doesn't have a 14mm nut in the 17mm banjo, so is it adjusted by shimming?

If you have one with the pressed in Ball Baearing that holds the Spring in in theory you can remove the Ball Bearing and stretch the Spring.

The bugger is getting the Ball Bearing out intact.

I know what would work to get the Ball Bering out but a Tool Wolud need to be made and that is too much trouble.

Do an internet search for an Interial Bullet Puller and you what would work.

Mine is a hollow plastic Hammer that has an opening in the end that holds the loaded Cartridge you insert the Cartridge and lock it in and swing the Hammer. When the Hammer strike the Brass Case is trapped but inertia pulls the Bullet out of the Brass Case.

Easier to go to the Junk Yard and get one you can take apart.

Thank you so very much for the help! :D

Opa had a cartridge station he made and finally checked: only has the tool for the cap. I rather just buy new than spend time I don't have. Also, there are no junk yards with older Mercedes.

However, the bypass is no longer available! :(

So is there any other alternatives?

No, I was not suggesting it was worth the trouble to make a Tool to remove the Ball Bearing.

Where I used to work the Cummins PT Fuel Injection Pumps had a Ball Pressed into the Throttle Shaft to prevent somwone from chaniging the Shims inside.

There we heated the Ball bearing end with a Propane Torch and that softened it enough for the Ball to be drilled out. That is the most available way to get the Ball Bearing out.
But, where I worked We had a supply of replacement Ball Bearings to press back in and there is none easily available for the Fuel Pressure Relief Valve.
I can't think of any place where you can buy only one Ball Bearing.


One of our Members modified the Fuel Pressure Relief Valve so it could be adjusted to what ever pressure you wanted but I think not many People were interested in Buying one from Him.

Update:
 

Yesterday I replaced the spring inside the Fuel Bypass Valve with this puppy:

http://i1133.photobucket.com/albums/...doe1/photo.png

Ace Compression spring #144
1" x 15/64" x 0.028"


It seems to work great fuel delivery-wise; but my only concern is idle fuel flow through the bypass is severely diminished, and I know the IP uses the fuel for cooling...

It has been discussed many times, that the spring is a certain type and sadly we have all been down the road of searching the bulk parts bin for a replacement spring. Good for an emergency but I would stick with the OEM one.