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I have rebuilt these FD's before and would like to make some comments.
1) The only true way to clean the FD is in a citric acid bath in a sonic cleaner. 2) The system needs to be synchronized when you change or repair the FD. a) the FD piston needs to be set in the proper location in the barrel. The nut that sets the FD piston is recessed .6 mm in the barrel. Don't forget the o ring. b) the FD needs to be set on the AFM ( o ring between FD and AFM) and synchronized -see below. c) 1-2 mm of free play of the AFM plate before FD piston moves.
After doing the above this is how you do the basic start up set up. This is one of the few times it is OK to mess with the 3 mm screw.
Disconnect all the fuel lines at the fuel distributor. Normally, you would only disconnect one fuel line but since you may have some blockage issues I would disconnect all of them. Back off - counter clockwise, the 3 mm screw one full turn. Put a old rag around the FD to suck up any spilled fuel. Jumper the fuel pump. Slowly turn the 3 mm screw clockwise until fuel barely comes out of the FD ports. (Ideally, all the ports should flow evenly) If not flowing equally both halves need to be cleaned as mentioned above. Then a 1/8 counter clockwise turn of the 3 mm screw. Shut off fuel pumps Reattach injector lines.
The car should start assuming , Fuel pressures are in spec, ignition system is 100%, no air leaks after the throttle body.
Ill try to find the write up from a CIS Bosch rebuilder.
Last edited by Dave Kost; Feb 7, 2025 at 05:54 AM.
All eight injectors are brand new Bosch injectors. The old ones were definitely gummed up, I took them to a professional shop for cleaning and they couldn't. get them clean.
I did as you suggested and jumpered the fuel pumps after removing the hard lines from the FD and did a full counter clockwise turn of the 3mm screw. When I started turning the 3mm clockwise I had three ports start to fill up with fuel and nothing from the others. After turning the 3mm a bit more fuel still didn't really fill the remaining five ports. Deflecting the air plate did fill up the remaining ports. My FD must still be clogged. I'd be amazed if there was an issue with the top half of the FD as well as the central "hub" they've been cleaned and scrubbed to within an inch of their lives. I'm betting the issue is in the bottom half of the FD. There's nothing in the FD bottom other than those adjustment screws and no doubt metering pins or other magic, maybe the strainers you mentioned above. I even noticed muddy fuel rising from one of the three "good" ports. What do you think?
I do have an ultrasonic jewelry cleaner that I've used for cleaning carbs in the past. I might need to do half of the FD at a time as the jewelry cleaner is physically not big enough to hold the bottom plate laying flat. Do you have a suggestion for the citric acid cleaner? I did a quick search and there are lots of them. Do you suggest something like the Zep citric acid cleaner/degreaser or something else? Can the eight metering screws be removed for cleaning? I had been told that the world would end if I messed with those screws...
I did as you suggested and jumpered the fuel pumps after removing the hard lines from the FD and did a full counter clockwise turn of the 3mm screw. When I started turning the 3mm clockwise I had three ports start to fill up with fuel and nothing from the others. After turning the 3mm a bit more fuel still didn't really fill the remaining five ports. Deflecting the air plate did fill up the remaining ports. My FD must still be clogged. I'd be amazed if there was an issue with the top half of the FD as well as the central "hub" they've been cleaned and scrubbed to within an inch of their lives. I'm betting the issue is in the bottom half of the FD. There's nothing in the FD bottom other than those adjustment screws and no doubt metering pins or other magic, maybe the strainers you mentioned above. I even noticed muddy fuel rising from one of the three "good" ports. What do you think?
I do have an ultrasonic jewelry cleaner that I've used for cleaning carbs in the past. I might need to do half of the FD at a time as the jewelry cleaner is physically not big enough to hold the bottom plate laying flat. Do you have a suggestion for the citric acid cleaner? I did a quick search and there are lots of them. Do you suggest something like the Zep citric acid cleaner/degreaser or something else? Can the eight metering screws be removed for cleaning? I had been told that the world would end if I messed with those screws...
Thanks!
Just as I figured, some of the ports are clogged. I bought a 2.5 quart Ultra Sonic Cleaner from Harbor Freight . I got the powered citric acid from Amazon and mixed it with water at 15% ,( which I just guessed ). Let it run a few hours. Relatively a lot of gummy brown stuff came out. Do the top too, since you're into the job this far. If you remove the metering screw, measure the position the best you can, so they can be replaced. (you can't screw it up any worse that it is? Right?) Clean the barrel that holds the piston too. As you know it has the tiny metering slits that clog easily.
Are you sure the fuel pressures are in spec.? How about the flow volume? Did you clean the EHA?
The secret sauce is the cleaning and calibrating the flow with that special Bosch flow tool. One of these days I am going to build one.
PS -I am just a hobbyist and have never done a 8 cylinder FD.
I read they should be 6.4 -6.2 bar system pressure. You reported 78 psi -5.37 bar.
Lower chamber pressure- .4 bar lower than system pressure with EHA unplugged
Fuel volume test - 1 liter in 40 seconds after the fuel pressure regulator ( return line)
An ultrasonics cleaner and some citric acid ordered. I understand about the hobbyist comment, I am as well. If you look at the top of this post you'll see that I have my reasons for doing this kind of work. I do enjoy the discovery.
I'll post as soon as I can get the FD in it's bath.
From the last video …RCIS FLOWTECH in Alabama rebuilds Fuel distribution heads. If the rebuild is too much for you give these guys a call. http://cisflowtech.com
Have you read all the test and help sections on K-jets site?
“
Hard to start when warm is often a sign that the system has lost fuel pressure. This could be from the following problems.
1. The one way valve on the fuel pump is not holding pressure and so fuel leaks back into the fuel tank.
2. The system pressure valve in the Fuel Distributor (FD) is leaking allowing fuel to run out into the return line.
3. the diaphragm in the accumulator has a hole and fuel is leaking back to the tank.
4. The Warm-Up regulator is not holding pressure.
5. Injectors dribbling. Can be due to worn injectors or the mixture is set too rich and so fuel is still going to the injectors even though the engine is off. Normally this isn't a problem as the injectors shouldn't open until 3 bar pressure is reached. But, if the injectors are not holding pressure and dribbling they will loose fuel into the cylinders. The system looses pressure and the car is hard to start because the engine is 'flooded' with fuel and the injector lines are empty.
To test these symptoms you really need to have a fuel pressure gauge in the centre of the Fuel Distributor in the Warm-Up regulator system (see attached picture).
1. Start the engine or bridge the fuel pump relay to get fuel pressure up. Switch off engine/pump.
How quickly does the fuel pressure drop? It should hold pressure for at least 30 minutes. If it looses pressure too quickly...
Run the fuel pump to get pressure up again, then, as soon as you switch off the pump put a clamp on the fuel return hose to stop fuel returning to the fuel tank. If it holds pressure, the system pressure valve in the fuel distributor is leaking, replace the seals. If the pressure still drops too quickly...
Run the fuel pump to get pressure up again, then, as soon as you switch off the pump put a clamp on the fuel supply inlet hose. If it holds pressure, the one way valve in the fuel pump is faulty. On some pumps you can replace the valve, on other pumps it is in the pump and the pump has to be replaced. If the pressure still drops too quickly...
Run the fuel pump to get pressure up again, then loosen the fuel injector pipes at the fuel distributor. Is fuel coming out? If yes, then the mixture screw is set too rich and needs to be turned anticlockwise to lean the mixture out. No fuel should flow to the injectors when the engine is not running.
Pull the injectors out but leave them connected to their fuel lines. Run the fuel pump to get pressure up again, then, as soon as you switch off the pump watch the injectors. Do they dribble fuel out of the nozzle? If they dribble, either the injectors are faulty or the CO Allen key is too rich. Try cleaning the injectors in an ultrasonic bath. If they still dribble, turn the Allen key mixture screw anti-clockwise 90degrees (1/4 turn). If the injectors still
dribble, replace them. If the dribbling stops now you
had the CO too rich and you will need to reset the
mixture when hot.”
K-Jet Specialists www.k-jet.biz
Ok I took the time to reread all the post.. sorry for getting lost again.
1. If you completely rebuilt the FD you had to have checked the internal filters..
2. Take a few minutes and go thru this document and look on page 16 to see the filters
OK GOOD LUCK https://cis-jetronic.com/public_doc/07.3-0997-06.pdf
vesiadog, wow thank you taking the time to do all of the posts and research! I've honestly seen the videos on the rebuild and have done exactly as they state. The only thing I haven't done is removed the eight metering pins from the base, because we've been told not to do that from most of the videos and descriptions of a FD rebuild. I think I'm going to bite the bullet and do very careful measurements of the pins and remove them and use my newly purchased ultrasonic cleaner and see what happens.
I need to finish another project first, so I'm not going to be able to do much for another week or so, but I'm definitely motivated.
Thank you again for all your posts and good ideas!
vesiadog, wow thank you taking the time to do all of the posts and research! I've honestly seen the videos on the rebuild and have done exactly as they state. The only thing I haven't done is removed the eight metering pins from the base, because we've been told not to do that from most of the videos and descriptions of a FD rebuild. I think I'm going to bite the bullet and do very careful measurements of the pins and remove them and use my newly purchased ultrasonic cleaner and see what happens.
I need to finish another project first, so I'm not going to be able to do much for another week or so, but I'm definitely motivated.
Thank you again for all your posts and good ideas!
As you can tell I have taken a strong interest in your case . My son has a large R129 store front on ebay “thebenzgarage” . He has dismantled many R129’s .. we rebuild many parts .. have not tackled an FD. We keep lots of PDF’s on how to rebuild etc to help out my son’s customers .
Keep us posted and you will get this done !!!
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