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.

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Spookeay Bird.
1985 190
1972 280 SE
1987 190

One other common cause of 'rough' idle at stop/park is worn engine mounts.

Easy and cheap to fix and often overlooked.

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1988 W126 420 SE

beware of fundamentalists!

Agree with engine mount check. If manifold vacuum is high and rock steady--so should be the engine. If th evacuum varies rythmically--its a bent/burned valve rotating on its seat as it should.

The rich fuel mix may be a faultywarm-up compensator --this is what controls the fuel pressure to the fuel distributor. It is electrically heated. High fuel pressure will definitely squirt more fuel through those constant flow sprayers (which should have a high pitched scream, not a low pitched swoosh) The pintle valve in the spray nozzles should open/close to keep the pressure drop across the tip high to get good fuel spray pattern.

ou can take them out and take to a BOSCH shop for cleaning and testing. They DO wear out, but poor fuel quality caused fouling a lot more often that wear-outs. Run a can of BG-44K through the engine to clean the injectors.

The injector to cylinder head seals also develop air leaks. Easy to find by drooling a small water stream on them--starting at back moving forward--if one is leaking, you WILL hear the sucking sound and definitely feel the misfire.

Ok guys, just got done puting the new pump in. I would say it's helped some. It has taken away the vilolent shuttering on the fule presure tester. However, I do still note that when leaning over the fender and I fell the slight shutter from the motor it is displayed on the guage by perhaps 1 or 2 pound shutter. I have isolated the guage from resting on the body and dont think that is what it is. It's also new. just got it off the Mac truck today $400 WOW! but I did need it. Any way, back to the car. I did take some brake cleaner and shot around the injector seals and did get quite a shutter and bog in the engine, But I am not sure if it's overspray going down the throtle or picking up a leak in the intake some here from the fan blowing around in the engine compartment. I like the idea of water and hear a sucking sound on the seals, more controled. May go out and try that after this post. As for the mounts, I don't think so you can feel it in the motor See it on a vacume guage and see the shutter on the fule guage.

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Spookeay Bird.
1985 190
1972 280 SE
1987 190

You should be getting 2-4 bar at pump 1, which I think is the rear one. The manual says to replace pump 2 if it is higher than that.

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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

Ok, I took a pitcher of water and poured it over the injectors, #3 Bit of a stumble likewise 6 & 7 But #5, It like-to have killed the engine. It boged way down and started hunting. Think we may be on to something here. Perhaps the shutter in the fule presure guage is recoil from the regulator and I am barking up the wrong tree. But it did need a pump so I dont feel to guilty. So are these injector seals a common "O" ring type or are they someting OE that I must order? Dont know why starter fluid did not set it off.

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Spookeay Bird.
1985 190
1972 280 SE
1987 190

You need to order them.

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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