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  #1  
Old 04-13-2020, 04:00 PM
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Join Date: Apr 2020
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MB CIS Injection

I'm new here and thanks for allowing me to join. My first question is on this '76 450SL that I have. It's been sitting for a couple years. New pump, filter and flushed out the tank. Car will not run. The cold start valve is working. (Start, run, stall) My issue is with the fuel distributor. There's a lot of pressure on the plate. If I relieve the pressure from the pump the plate ease's up and you can move it. Seems like to much resistance to me for engine vacuum to overcome. With all the lines removed and relay jumped I don't get fuel in the ports till I press on the plate. I'm very new to this injection system but I am pretty good otherwise. Can anyone shed any light on what I might have going on? I suspect a bad fuel distributor.

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  #2  
Old 04-13-2020, 04:08 PM
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Location: Modesto CA
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Ec:

Check for fuel flow at the return line fitting of the fuel distributor. In the event that the pressure regulator has become stuck from sitting, there will be minimal or no flow from the return. If there is no return the internal pressure against the metering piston will be too high.
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  #3  
Old 04-13-2020, 05:25 PM
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It is very common with these systems that the Fuel Distributor needs to be rebuilt after sitting for many years. Also a good time to have the WUR checked out. Check out CIS Flowtech.
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  #4  
Old 04-20-2020, 02:01 PM
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Well, like I said. I'm no expert on these old mechanical injection systems but I think I figured it out. The clue in was when I was trying to do a fuel pressure test. The pressures kept building back up after relieving it. The fuel distributor must be bad. I have fuel coming from both ports going to and coming from the warm up regulator. The port on the rear left and from the top. That can't be right.
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  #5  
Old 04-20-2020, 03:42 PM
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Location: Modesto CA
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Quote:
Originally Posted by Frank Reiner View Post
Ec:
Check for fuel flow at the return line fitting of the fuel distributor. In the event that the pressure regulator (FPR) has become stuck from sitting, there will be minimal or no flow from the return. If there is no return the internal pressure against the metering piston will be too high.
Ec:
In addition to the possibility of the FPR being stuck, the return line from the engine to tank may also be clogged.

Quote:
Originally Posted by Eurocoach View Post
Well, like I said. I'm no expert on these old mechanical injection systems but I think I figured it out. The clue in was when I was trying to do a fuel pressure test. The pressures kept building back up after relieving it. The fuel distributor must be bad. I have fuel coming from both ports going to and coming from the warm up regulator. The port on the rear left and from the top. That can't be right.
Ec:
Symptoms of a stuck FPR, or clogged return line.

Remove the cap nut of the FPR (on the FD), pull the regulator pieces out of the FD, clean the parts, replace the o-rings, and blow out the return line.
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  #6  
Old 04-22-2020, 09:55 AM
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Did all that and nothing changed. The issue is in the fuel distributor. It's leaking past something internally. Shouldn't have fuel at both of these ports. That would explain how hard it is to push down on the plate.
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  #7  
Old 04-22-2020, 09:57 AM
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The return flows fine and the line going back is free. The regulator parts in the FD look ok and just cleaned and reinstalled. Nothing changed. I have a reman FD here now to try. Hopefully I'm good to go and can get rid of this thing.
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  #8  
Old 04-22-2020, 09:59 AM
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And thanks to those that replied and offered advice. Very helpful and now know a little more about these systems. If it were just the EFI system.

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