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Old 12-23-2000, 03:18 PM
450 SLC 5.0
Posts: n/a
Well speaking of needing theoretical & experiential help…

I will cut this as short as possible. 1980 450, M117-985 engine, U.S. (California) specs. First year of Lambda controlled CIS injection. I am having problems with one cylinder (#5) running way too rich. All mechanical & ignition systems are O.K. after thorough & comprehensive checking. Fuel system pressure & control pressures are O.K. The injector itself is not the cause; I mickey-moused a test rig using a fuel pump & pressure gauges – all injectors are within specs for opening pressures, no leakage, and they have a good spray pattern. (I used mineral spirits as the test fluid – I don’t like the idea of flash fires ).

I have concluded (correctly, I hope) that the fuel distributor is failing. Seems odd, as the fuel filter has been changed religiously. Although I know that no one is supposed to touch the insides of these fuel distributors. (No one other than specially trained elves that live deep inside the black forest of Germany, that is ) I removed the center plunger to check for gunk (none present) and I cleaned the plunger & innards of the distributor with carb cleaner. Upon reinstallation, the same exact problem. No better, no worse.

Now for the tricky part… I can’t help but try to rectify the situation, hopefully without burning a valve in the process. From what I can see in the drawings in the “Bosch Fuel Injection & Engine Management” book (Great book, by the way!) underneath screw-on caps adjacent to each outlet port, there are adjustment screws. These screws bear down on the springs within the individual pressure regulators governing the pressure drop for each port. Theoretically, it looks that by backing off the setting, the spring pressure will be reduced, and therefore reduce fuel flow for that particular port. The setting for this regulator is a pressure drop of only 0.1 bar, and I’m sure that it is CRITICALLY important to get it right. I am tempted to try to see if I can lean out that cylinder. Am I playing with fire? I have nothing to lose if it does not work, as I would need to purchase a fuel distributor anyway. My plan of attack is to remove power from the lambda valve, reset the mixture (temporarily) to the highest & best idle. I would then adjust #5 until it stopped missing and reached the highest & best idle (again), then reattach the lambda valve and reset the mixture to specs.

Steve, please tell me your honest opinion on this - Am I TOTALLY insane? Or does this have a snowballs chance in h*** of working? Or better yet, do you know of a precise way to set the pressure drop, where I can reset all the ports to spec?

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