Hello.

I have a 560SEL that has a slight rough idle in park. It’s goes away in drive. It’s also running very rich, so much that it’s left a black mark on my shop floor and smokes a gas smelling smoke. I think the 2 are related. I have check the 02 sensor, new wires, cap, plugs & button. I have sprayed enough either in the shop to get high looking for a vacuum leak. It has good vacuum on the gauge. I have checked the cold start injector it’s not spraying when it’s warm. I have tried to adjust it in the TB plate via the hex key but still have the stumble. I have taken the lines off the injectors and cleaned them and sprayed cleaner in the pump ports and injector input ports. Have not taken them out to soak. I can listen with a theta scope after I clean them and they have a nice whoosh and click to them but after a while the make a screaming sound as if fuel was getting forced past them. High fuel pressure? Can there be such on a mechanical system? I have read post here till I was blue in the face about rough idle but I would not call this rough it’s more of a bumping or stumbling. It’s not to bad “Yet” but this and bad gas milage is what it came into my shop about. This car is a tad older than I work on and is somewhat of a mystery. If it’s not EFI or OBD2 I become a non-mechanic. “LOL” any way, any ideas, let me know. It’s not lean, and it’s not a miss, it’s more of a sporadic bumbling at idle in park. No idle speed issue, No lean condition.

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Spookeay Bird.
1985 190
1972 280 SE
1987 190

Have you taken compression readings?

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www.theworkshopmercedesbenz.com
Nahum:1.7

Yes, about 135 on all 8 may be 2% dif. I don’t know if I have a stuck electrohydraulic fuel actuator, I out of lash valve or a vacuum leak perhaps in the intake. I just don’t know where to start and was just picking about here to see if any one has some ideas.

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Spookeay Bird.
1985 190
1972 280 SE
1987 190

on that engine, the most common vacc leak is at the lower portion of the intake (sometimes it takes parts wash or brake kleen to find it) at the r/h side in front. The intake splits in-two, and the seals at the split become hard and suck in air, quite hard to find. Fought this problem before, had to remove intake, reseal it and replace injectors (they all are supposed to have a high pitched noise, if any are dead or low, replace'em).

My two cents.

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www.theworkshopmercedesbenz.com
Nahum:1.7

Have you done the two most basic tests on these engines - checked the on/off ratio and measured system and control pressure? The first will tell you if the mixture is right and the mixture control system is OK, and the second will answer your question about fuel pressure.

How did you check the O2 sensor?

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Chuck Taylor
Falls Church VA
'66 200, '66 230SL, '96 SL500. Sold: '81 380SL, '86 300E, '72 250C, '95 C220, 3 '84 280SL's '90 420SEL, '72 280SE, '73 280C, '78 280SE, '70 280SL, '77 450SL, '85 380SL, '87 560SL, '85 380SL, '72 350SL, '96 S500 Coupe

What should the fule psi be in this car? At idle it's about 9 Bar. it has the dule pumps and one is making a noise. I think this is it becasue the fulctuation from 8.5 to 9 bar is rapid and feels like it's with the stumble. In what I have it says 4 bar is about right but I dont know if that is for the dule pump system. Any ideas? I bet it's going to be the pump but I have put $200 worth of parts it did not need on it. I hate to hit him wiht a $200 pump also. But one is making a bad noise.

__________________
Spookeay Bird.
1985 190
1972 280 SE
1987 190