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Old 01-31-2008, 05:17 AM   #1 (permalink)
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Vehicle: Mercedes Benz 280E 12/1979 110 Engine CSI
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280 Running Excessively Rich, Copious Black Smoke

This 1979 (12th Month) 280E Sedan (W123.033.22.062873), 110 Engine, CSI Injection. Runs so RICH it is ridiculous. When the car was aquired, it ran very poorly. Contaminated fuel, worn injectors, fuel & air filter were all attended to. Engine would start & run reasonably, but could not be idled down. The aftermarket injector seals were incapable of being sealed by the retaining plate and thus leaked air. If one applied pressure to an injecter, the engine would immediately run EXTREMELY RICH and stall (I considered it to be too rich beforehand). The car would not restart and one would normally have to wait till the following day. It would eventually start from stone cold but quickly get too rich and, once again stall. Replacement of all injector related seals was done using genuine parts. This, as one could guess, further enrichened the black mess. All basic, common sense engine checks have been performed and it appears to be in reasonably good order, and yes, the plugs are new. A couple of Mercedes repairers have suggested that it would most probably be the Fuel Pressure Regulator. The Fuel Distributor has been checked and seems okay as per the Workshop Manual. With all due respect to the publishers, the Haynes Shop Manual for this model may as well have been written in Dalek. I've read a few shop manuals in my time, and have been employed in the automotive industry, but this one takes the cake. Parts seem to be renamed, depending on which page you are on. Without the resources to aquire a spare Regulator, living in a rural area (Australia) and having no cash. This trade for a slab of Jim Beam has caused no end of drama. Any thoughs out there PLEASE!!!
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Old 01-31-2008, 05:58 AM   #2 (permalink)
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The control pressure is too low. Perhaps the return line has a restriction.Also check the voltage at the WUR (at least 11.5V)
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Old 01-31-2008, 07:25 AM   #3 (permalink)
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Vehicle: 1978 280ce euro found dead on Ebay
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NUTZ saves the day again

EUREKA EUREKA EUREKA,
Thank you for your post and thanks Nutz for your reply. As you know I am bring alive my cheap euro. I am having the same problems as noted below. I start car and if fires up even at 15 degrees outside no problem. But it runs Super rich. I mean there are black soot spots in my driveway. I pulled plugs and they were BLACK with carbon. I tired to feed as much air as possible backing out the 3mm hex screwing out CCW and raising idle. Still ran rich.
Now here's the BIGGY I know I have a restricton on my return. When I changed tanks the return line was completely clogged from the rust from old tank. I ran a coat hanger through end of it and got to damp part where old fuel was still in line so maybe I have an 1/8 in dia meter return or maybe my retun is still clogged. I figured that the return pressure would push out the crudge from return line but it was pretty bad. I assume it did since engine ran.
Here's my plan, Nutz let me know what you think. Disconnect the return line at fuel distributor (FD). Attach a fuel hose from FD to 5 gallon gas tank this will do two things drain my fuel tank and unrestrict the return line. I should be able to adjust the fuel mixture with return running to gas can (correct ?).
When gas tank is empty I can pull off return line and cut hard metal return line further back (more forward in car) behind the resriction and connect a longer flexible fuel line to tank this should unrestrict the return and correct the rich problem.
Poleaxed did you change or clean or flush your gas tank? My 280CE tank was toast I am thinking you might have the same restiction I have. Does your car leave black spot's on driveway does it run that rich?
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Old 01-31-2008, 07:37 PM   #4 (permalink)
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Sounds like someone cranked the mixture control screw way down to compensate for vacuum leaks initially. Have you since readjusted the mixture after repairing the leaks? It's impossible to determine the condition of the metering head or WUR, let alone the system overall, unless you know what the control and return pressures are, or the overall mixture. Since the condition exists at all times (apparently?) it's doubtful the warmup regulator is the ultimate culprit, but checking the power supply is a critical step as Nutz mentioned. With good power, it should time out within a couple minutes at the most to allow full return, as the engine requires significantly less fuel once warm. Beyond that, and I'll say this every time CIS comes up, you've got to get a pressure guage on it before doing anything. Otherwise you're just guessing.
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Old 02-01-2008, 01:40 AM   #5 (permalink)
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Could also be that the control plunger is jammed up at top of fuel distributor,exposing all the slits to maximum delivery to the injectors at all times.

Also,are you sure that you used the correct o-rings for the injectors?
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Old 02-01-2008, 04:45 PM   #6 (permalink)
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Once the K-jetronic works that's all the bugs are ironed out. Pretty much nothing goes wrong but the fuel pump and filter right?
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Old 02-01-2008, 05:16 PM   #7 (permalink)
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Yeah, and the thermo-time switch.
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Old 02-02-2008, 01:07 AM   #8 (permalink)
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Check that the cold starter valve is not stuck open. Yes the k-jetronic is very reliable and lasts at least twice as long as a carburettor. fuel consumption should be the same as in the drivers manual.
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Old 02-08-2008, 07:47 AM   #9 (permalink)
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Many thanks for the sound advice. We've checked the return line, it did have a fair bit of junk which has been dealt with. As far as checking the WUR goes, I'm guessing you mean at the plug to the unit. Unplugged it and attached volt meter with ignition on. Result, virtually zero. I will check through the electrical sytem. Another helper noticed that quite a bit of emissions equipment has been tampered witth, and the vacuum fittings on one of the thermo control valves that bolt into the cylinder head have broken fittings. We're attempting to put all this gear in order and rectify any vacuum leaks. Trouble is, the diagrams on hand are very vague. If one goes by the diagrams, this car appears to have a mix of equipment between CSI and carburettor models. How do I get hold of a decent Australian spec diagram? Oh yes, have to scrounge up a decent battery too. Whilst we have power, there's little cranking capacity. I'll be better off when I have a new one, but will have to save up. Once again, many thanks and I'm enjoying reading the posts in this Forum, very informative.
P.S. whoops, missed a couple of posts. No, haven't cleaned out fuel tank but that's doable. Yes, I have correct o rings for injectors. I need adapters for my fuel sytetem tester. Haven't fully checked the cold start valve. Also what voltage is required there?

Last edited by Poleaxed; 02-08-2008 at 07:53 AM. Reason: Update
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Old 02-09-2008, 07:50 PM   #10 (permalink)
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Yes the vakuum diagram in the haynes manual is a mess, ask the dealer to mail/fax you the correct one. If you go to a junkyard for parts you should get a fuel pump, fuel pump relay, and an electronic ignition control unit to keep for spares.. The 110 engine itselves is indestructible, it will only die if the oil isnt changed and the valve gear fills up with dirt. Some below standard camshafts can wear out, but can be changed without removing the head. Allso the ignition with cap, rotor and ht-leads must be in good condition to keep the mpg right, the engine starts easy even if the ignition parts isnt 100%
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