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Old 04-09-2003, 06:47 PM
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Join Date: Sep 2002
Location: Kingsport, TN
Posts: 375
Hi Emmy,

there is a speed sensor at the flywheel that tells the computer the engine is running and thus the fuel pump needs to keep running too.

As I said earlier, it is a complicated system and I am not really an expert to give advice on this beyond the simple steps like injector cleaner and idle control valve cleaning, making sure that the parts that deteriorate over time (like plugs, wires, distributor caps etc.) are ok.

I would probably follow bribenz advise and check electrics.

Good luck

Reinhard Kreutzer
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Old 04-10-2003, 09:14 AM
Posts: n/a
Replacing the fuel lines involves jacking up the driver's side of the car or better yet - put the car on a hoist. Getting the fuel line over the rear suspension by the tank , if the car is not on a hoist, can cause a few cuss words and is deserving of a stiff drink after it is accomplished. My main fuel line was so rusted inside that when we took it out - it collapsed and broke in two from it's own weight while it was being removed. Henry took an easier route with his 560sel. He placed an aftermarket in line fuel filter in his gas line near the fuel distributor under the hood. After the lines are changed -there is still crud in the fuel distributor and the screens to each injector must be replaced or carefully removed with a fine screw - cleaned and replaced (that is what I did). Run a tank of gas with fuel cleaner after doing this and if the roughness comes back a little after a while - clean the screens one more time and run a final tank of gas with cleaner in it. I suffered with this aggrevating problem for a long time before I finally got rid of it. My 560 sel now purrs perfectly. Just for the record I did all of the following in an attempt to cure it before tackling the fuel lines:
1) new plugs, wires ,distributor cap, rotor
2) took it to Mercedes for a scope of electrical
3)cleaned and checked idle valve
4) new fuel pump relay, fuel pumps, filter and accumulator
5) checked and replaced vacuum lines as required.
6) replaced defective smog pump on the off chance that circuit was at fault
7)checked engine compression
8)had timing chain and rails replaced
9) checked all emission controls items for proper operation

Remember - the fuel filter on this car is in the REAR - the fuel lines are AFTER the fuel filter-thus rusted lines will cause havoc with the fuel delivery.
HAVE FUN!!!:p :p :p
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Old 04-10-2003, 10:50 AM
Registered User
Join Date: Feb 2002
Location: Orlando, FL
Posts: 788
Can I get the lines from FastLane? Is the R&R pretty straight forward, or do you have to rip apart half the car first in order to do it? How much time should I budget to do this job?

I am guessing then when you replace the lines and filter and clean the little screens and run the fuel cleaner it cleans out the distributor? Should I go ahead and replace the injectors??

If fuel lines are being replaced, do you think it might be a good idea to have the gas tank flushed and cleaned? I have heard there are shops that offer this service.

Sorry for the barrage of questions, but this is going to be my next big project, so I just want to make sure I'm on the right track!
'86 420SE Euro
904 Midnight Blue, Gray Velour
Dad bought it new, now I own it.

"A Mercedes-Benz is like a fine wine, it only gets better with age."
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Old 04-10-2003, 11:32 AM
Posts: n/a
I don't know if FastLane has them - I bought mine from Mercedes - if I remember right it was about $125.00 CDN. Changing them is very straight forward - only problem for me was getting the approximately 8 foot line over the rear suspension as I did not have the clearance from the ground to manouver it over the suspension. If the car was on a hoist it would be no problem. If I had the car on a hoist the whole job would have been 1-2 hours tops instead of the 4-6 hours trying to get the line up top of the suspension without damaging or kinking the new line. Don't replace your injectors. Instead if you are unsure of their spray pattern - have them checked. But I would leave that until the lines are done. Why would you want to clean out your gas tank??? The fuel filter at the rear of the car does the job of filtering the gas from the tank. The suspect fuel lines are AFTER the tank and the rear fuel filter so cleaning the tank would be a waste of money. Oh by the way - the reason the one line was so expensive(ABOUT $95 cdn), if I remember right was because it had a braided section at the end that connects in the rear - otherwise standard fuel grade steel tubing with the proper flared ends can be be bent to fit for the other lines. Unscrewing the support clamps under the car and disconnecting the lines are as hard as it gets. DON'T FORGET TO PLUG THE OUTPUT OF THE FUEL TANK BEFORE YOU START!!!

Last edited by moedip; 04-10-2003 at 11:38 AM.
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Old 04-19-2003, 05:02 PM
Posts: n/a
I had the chance to work on my 91 560SEL yesterday ( on the rough idle)...I cleaned the throotle body and plate with cleaner and removed the plugs. To my surprise, all my plugs were black, and 3 of them had heavy carbon deposits on them..I mean real bad. I could nt imagine my car would run at all with what I have
seen. Since I did not ahve replacement plugs I decided to clean them up with carb cleaner and scrape off the carbon deposits. I installed them back, and the rough idle went away. I have ordered new set of plugs.

I had used the BG 44K fuel system cleaner a few weeks back and I am wokdering whether it might have conributed to the heavy carbon deposits on the plugs?

My car is running fine now. I will observe it it holds up.

One more problem that I need to resolve is it stalls randomly at any speed. I am not sure if this is related to the plugs problem or not. I will open up my fuel pump relay and verify open solder as some other posters have suggested...
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Old 04-19-2003, 05:49 PM
Registered User
Join Date: Oct 2002
Location: Colorado Springs
Posts: 481
sooty and black plugs mean she is running rich, check your lambda duty cycle should be around 50% (high is rich low is lean)
Running to rich is not good for gas mileage or your catalytic converter.
Martin Ingram
Colorado Springs
2005 320 CDI
2006.5 VW Jetta TDI
1991 560SEL (179000 Sold)
1972 280SEL 4.5 ('The Lead Sled' 320000 miles when sold.)
1972 220D (225000 when sold)
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