I searched - really I did!!
 

Hey all!

Relatively new owner (2 mos) of a 1986 560sl with 165k on the clock. Have been lurking and searching and learning for several months here prior to that. I have read virtually every thread related to vacuum leaks (which I believe I have). I was hoping in my search to find a vacuum diagram for the 560, but to no avail. Nor have I found "exactly" what I have for symptoms but some have been close. Here's the skinny on what's already been done...
1. brand new plugs, wires, rotor, cap - all the right stuff based on info gleaned here.
2. Soon after that, took it to an indy/dealer tech (works at an MB dealer/techs on the side out of his house for the older mb's) for a quick once over to give me a heads-up on what it needs and to plan for any "larger" expenditures that he may have found (like needing a rear main seal - which will be done after driving season). He took off the air cleaner, attached some device to the engine and turned a screw around the (what I assume was the) EFI to "adjust the mixture". Ran great for a while after that.

Now here's the problem, recently the economy gauge is generally pegged to the right (although sometimes when I step on the brake, it moves to the left). Sometimes it will move to the left, stay there during idle or coast but as soon as you step on the gas, it slams back all the way to the right. It sometimes runs a bit rough at idle but not overly so and appears/feels to run fine under load.

I truly believe vacuum is the culprit (per the myriad of posts regarding same) but, being a relative neophyte in auto mechanics (but not afraid to get my hands dirty), I have no idea on how to chase down a vacuum leak - especially without a functional and readable (to me) schematic. There was a great one for a 450sl in one of the posts I read but I'd bet that it's not the same for the 560. Any help and/or suggestions about the problem I'm having and/or a diagram would be greatly appreciated! And thanks for the education you all have already given my with your great posts on any number of topics. This place is a wealth of info and I need it!!:)

Stix

i had similar issue om my 560 sel, it was a loose vacuum connection, rubber was not fitting securely on the valve causing leaks, i would check all under hood connections and verify they were tight

I'd second that advice. Try spraying some 'quick start' (volatile, but safe if there is no open flame or red-hot metal) around the vacuum lines/connections at idle. A leak will bring the idle up as the stuff enriches the mixture in the incoming air-stream. There is a large rubber plenum under the air cleaner which is prone to cracking. I fixed mine with silicone, for now, and plan a tear-down to replace it next winter. You need to get a paper copy of the 117 or 116 engine manual, or the CD, and read up. Most of the vacuum diagrams won't help to find leaks anyway, but will aid in understanding functionality. Welcome to the forum too...

vacuum leak
 

I agree that your problems are vacuum related. If your "economy" gauge is pegged to the right much of the time the leak is massive.

The most overlooked vacuum fitting because it is hard to see is one at the back (firewall) end of the engine. It is located on the intake manifold near the center. The rubber connector for the vac line often deteriorates because it lives in a heat and oil-rich environment. If you look at the multiple vacuum lines that enter the firewall on the driver's side and trace the line that feeds them across the top of the firewall. it enters the intake manifold through that connector. You can use a piece of plastic tubing as a temporary fix until you get the proper connector. You need tiny hands and a lot of patience to reach in there. While you are under the hood, inspect all the other rubber connectors you can find also. The hard plastic lines seldom fail but the connectors do.

This fixed most of the driveability problems on my '88 560SL. Good Hunting!

Is this plenum under the air cleaner common to all 117's or just the SLs?

While I'm far from knowledgable I might suggest that you find a shop in your area that has a "smoke machine". That is the only way I found my vacuum leak(s) after weeks of searching. The test was $100.00 and I wish I had done it weeks before!

http://www.peachparts.com/shopforum/mercedes-benz-sl-discussion-forum/221171-380sl-hard-start-poor-mileage-post1920679.html#post1920679

Agree completely on the "smoke machine". But here's some new info that might help nail it down.

Changed the gas cap. Now, when I start the car, the economy needle stays to the left and moves when I rev the engine (like it's supposed to). When I put it in reverse, it works okay too. When I put it into drive and step on the gas, the needle pegs to the right and stays there although occasionally, if I put it in reverse, the needle will move to the right with pressure on the gas pedal and then return to peg/right. Is there a vacuum line to the tranny that could be causing this? Gonna have to find a garage with the smoke machine! Anyone know what it is actually called? Thanks again for all your help!

Stix

There are several manufacturers of the smoke machines. The brand that the shop used on my car was by REDLINE Smoke Pro. Hope this helps!