Rough Idling 560SL

[flixbiz]

Here's what Silver Star Mercedes Service in Annapolis, MD did to attempt to smooth my rough idle.

• Crankshaft Position Sensor - $450 [still idles rough]
• Spark Plug replacement $200. - I had installed platinums - they said incompatible with car [still idles rough]
• found vacuum hose disconnected [a little smoother now, but still idles rough]
• Suggested Distributor cap and rotor [$600?] What the ****? The parts total under $200 at FastLane!! over 4 hours in labor? In what universe?

Can anybody tell me what to tell these guys to do? I'm tired of paying for their speculation! I didn't mention that it took them three attempts to fix my leaking tranny seals. On the second attempt, they damaged the tranny and had to replace it with a used unit. They had released the car to me claiming that it idled smoothly and no longer leaked. Not so much - both issues still unresolved! They have now had my car since the first week of June!

Why is it so hard to find decent service for these cars?

[Strife]

Originally Posted by flixbiz

Why is it so hard to find decent service for these cars?

It IS possible to find a responsible, methodical, and honest person to repair your car - even if it winds up being YOU!

There are things I can't do because they are more than one-man operations or require serious lifting or tools, but I live in the middle of "nowhere" and I resigned myself to repairing my own car again after a ten-year hiatus.

[Strife]

There have been many comments on this board about platinums NOT being a good idea for this car.

Have you replaced your ignition wires? Do you know when they were last replaced? Looked at your engine running in a darkened garage (look for blue corona or sparking). This was one of the first things I did with my car when I got it and it REALLY needed them. They are expensive, but they last a long time if you take care installing and removing them with spark plug/cap changes. You can change the wires, cap and rotor yourself in a few hours and pocket quite a bit of the $600 - and KNOW that the job was done right.

[Guenter]

Originally Posted by Strife

You can change the wires, cap and rotor yourself in a few hours and pocket quite a bit of the $600 - and KNOW that the job was done right.

any suggestion on how to get the distributor cap off on a 300E?? Seems there is not a lot of clearance between it and the fan.

cheers

[Tom McMenamin]

Wires is a good start but...

Vaccuum lines, vaccuumlines , vaccuum lines!!!!!

I have found these to be the biggest culprit! Replace all of them and eliminate the concern about that part! cheap and usually fixes the majority of the idling issues! Worth a try!

[kbflorida]

"Vaccuum lines, vaccuumlines , vaccuum lines!!!!!

I have found these to be the biggest culprit! Replace all of them..."

Tom-
When you replaced lines, did use the hard MB tubing everywhere except for connecting points? My 76 450sl is a mixture of the orig. MB lines and later replacement softer black tubing, which actually has a larger inside diameter.
Does it matter which is used?
Thanks

[Tom McMenamin]

You have asked me a question I can't answer, but I would offer this: When trying to troubleshoot something, don't mix things up. If you settle on one type of line use it throughout.

What you are trying to do is pinpoint a problem. By making additional changes you might be compounding a problem. Use a methodical replacement method and stick to your decision. That way you eliminate things one item at a time.
Better yet, ask for a knowledgeable opinion here on the "board". Good heads prevail here. Good mechanics with vast experience. Technical questions are best lleft to them. I am a shade tree mechanic. Not a very good one at that. An auto mechanic is the same as a Doctor. They are skilled, knowledgeable and have EXPERIENCE! It's what they do so it stands to reason they know more than I do.

The thing to remember is that a 560SL and moreso for a 450SL is that they are OLD. Old means things wear. Even if a car sits from new, items deteriorate especially rubber hoses and tubing. Pay close attention to things that wear. bushings, washers, any thing that moves frequently. Regardless of the material, with few exceptions, things age. I do, you do, and so do 560 and 450 SL's

[kbflorida]

Tom-
Good point that consistency in the system should be my goal.
I'm going to start a new post with the technical question of
what kind of vacuum lines were in the system originally.

[Kebowers]

Instead of throwing $$$ in the black hole--a good diagnosis is in order. First ensure the engine does not have internal issues--run a compression check.

Leaking seals around the fuel injectors (that prevent air leaks) are quite common and will definitely cause rough idling. The seals are dirt cheap and R&R a set is an hour tops. Easy way to check--dribble a little water (from a hose) on each injector one at a time--when you find a 'leaker' you will hear it and the engine will change. You can use vapor from a handheld propane bottle just don't light the torch. When the vapor gets sucked in, idle will change.

Also, the 'standard' heat range spark plug is too cold for slow speed driving and tends to 'carbon foul'. Pull one out and see if it is black (fouled) or white/light tan.(normal)

All the ignition wire connections and spark-plug insulators MUST be coated with dielectric silicone grease to prevent electrical leakage. Also, the internal insulators in the 1950's vintage plug wire ends will fail from age and the spark will jump to ground. Change the wires.

ALL the vacuum hoses on the engine are prime candidates for air leakage. Change any flexible hose or fitting that has hardened (probably all of them German rubber is CRAP compared to US and Japanese stuff)

The fuel injectors and fuel distributor may be dirty or damaged. It only takes a little water to damage the fuel distributor beyond serviceability. Try running a can or two of BG44 fuel injector cleaner through the system to ensure the injectors are clean--or remove the injectors and have your friendly Bosch shop clean them real good--they will get crud in them that will mess up the spray pattern.

[aharley1]

I went thru the same thing with rough idiling when hot & hard starts. I finally went to a different shop & they diagnosed it right off...leaking intake seals. It took $1800 worth of labor to get the injection system straight from what the first guy had done but it runs F-I-N-E now.

"Da Stable is full"
99 Harley Heritage Softail
88 20 Ft Wellcraft
94 30' Sun Sport Motorhome
98 Dodge ram
40 Chrysler convertible
88 560SL

[230/8]

kbflorida:

re: your question on what type of vacuum hose was used, plastic or fat rubber, the answer is both were used. The hard plastic is available in colors so MB used it to make some of the hook-ups a bit easier to keep straight. The soft fat rubber hose was/is used at the ends of the plastic line where connections are made to a fitting and/or sharp bends are needed which could crack the plastic tubing.

My old 72 SL is filled with this mixture. I replaced all the soft hoses, had the fuel injectors re-sealed and now the car runs fine. I also run Techron through the fuel system all the time. It's cheap at Costco, so I am adding a can with each fill-up for the next few thousand miles to see whether it cleans the injectors. If it does not then I may send them off the this place...

http://www.cruzinperformance.com/

for a good cleaning. I understand some folks have used this service with good results. His prices seem fair.

230/8

[ctaylor738]

The 560's have semi-modern electronic engine controls, but no modern diagnostics. There were some proprietary tools from Merecedes, but most of these probably quit working a long time ago. And the mechanics who were trained on these cars are retired or retiring. And no tech is at a dealership is interested in fixing a cranky 560 because he/she won't make any money on a repair that involves a lot of diagnosis. And they will probably get it wrong and have the owner yelling at them the next day. So the dealers throw parts at it and hope for the best because they really don't have any other answers.

We are really running out of talent to work on these cars.

Forget about the dealer techs knowing more than you do. Educate yourself, and insist that the techs work there way up from the basics like plugs, wires, coil, cap, rotor, vacuum leaks, temp sensor, EHA, air flow sensor, and only then look at the exoensive stuff like fuel distributor and engine control module. I think all this stuff is 'way beyond its design life expectancy.

All IMHO - I am currently wrestling with a rough idle during warm-up on a 560SL.

[kbflorida]

[QUOTE=230/8] The soft fat rubber hose was/is used at the ends of the plastic line where connections are made to a fitting and/or sharp bends are needed which could crack the plastic tubing."

Thanks 230/8. That answers my question. Over the years my SL not only had the soft fat rubber at the ends of the lines - but sometimes slapped in the middle of a hard plastic section.

I see the previous point about the diameter change probably not making a difference, but all the repairs to my vacuum lines over the years had the effect of adding many more places for leaks/loose connections - not a good idea.

[balsa]

Vacum lines!!!!! Everyone is saying it is good to replace all the vacum houses in the engine compartment due to age and to smoother the rough idle.

I have a 1986 MB 560sl.

Somone please advice the VACUM LINES part numbers and quantities needed to do the right job once and for all. Lets keep this list of parts/quantities for anyone in need of doing this job (most of us need it desperately due to age).

Thanking in advance a helpfull and experienced donor!!!!

Balsa Martinovic

[Strife]

There would be money to be made if a supplier sourced the proper, color coded vacuum line material, connectors, etc (enough to do the entire engine compartment). Assuming that no one has futzed with them, it shouldn't be too difficult to replace them one at a time.