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  #1  
Old 08-16-2005, 09:23 AM
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Poor Running 560SL

I could really use some help with this one.

The car is a 1986 560SL with 159K. Decent maintenance most of its life, but a lot of sitting the last 5 years - only 10K miles during that time.

When I bought the car two months ago, it had a miss during warm-up. I cleaned and tested the injectors and re-installed with new seals. Problem went away briefly but returned, worse.

Car also had a surging idle timed to the on/off ratio. I replaced oxygen sensor and re-set mixture. On/off ratio at a fluctuating 45%, right where it is supposed to be. Car ran perfectly for a few days, then the miss returned.

Checked for vacuum leaks and found none.

Cleaned cap, replaced rotor, replaced plugs (Bosh W9D copper). No change. In fact, the miss got worse, happening at all temperatures. I returned home from work last week with car running very poorly. Rough idle and miss under load. Car does not smell “gassy.”

I checked the on/off ratio and it was steady. I tweaked the mixture to see if it would change. As soon as I inserted the hex key and pressed down, the idle smoothed out and the on/off ratio started cycling around 45%.

The car started running perfectly, but two days later, the miss returned, as bad as ever.

Ideas?

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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

Last edited by ctaylor738; 08-16-2005 at 09:31 AM.
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  #2  
Old 08-16-2005, 10:12 AM
MrCjames's Avatar
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Inspect the coil terminal on the distributor cap, a black ring begins to develop where the boot ends. This is carbon buildup, once it accumulates it can/will provide a shorter path to ground causing the electicity to jump to the black plastic insulator. Beyond that the next thought might be the ignition coil. Either of these can be easily tested with a spray bottle filled with water, just give both items a little spritz and watch for any adverse reaction.
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  #3  
Old 08-16-2005, 11:22 AM
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Quote:
Originally Posted by ctaylor738
I checked the on/off ratio and it was steady. I tweaked the mixture to see if it would change. As soon as I inserted the hex key and pressed down, the idle smoothed out and the on/off ratio started cycling around 45%.

The car started running perfectly, but two days later, the miss returned, as bad as ever.

Ideas?
I think you are pretty much narrowing it down to a fuel supply problem, and then further to the fuel distributor. If I were you (yet having no experience with a FD), I would disassemble the fuel distributor and look for clogging, sticky seals, etc. OR, try running some Techron through the system for awhile to see if it dissolves the problem.

Steve
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Old 08-16-2005, 09:08 PM
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Update

Thanks for the suggestions.

Tonight I did check the coil wire, which seemed fine.

I also re-checked the on/off ratio, which looked constant at about 41% but it did move when I tweaked the mixture a little bit. I started it cold, and as it warmed up, the idle did some serious jumping, like up 200 RPM and then back down.

When it was warm, I went around the FD, and cracked each cylinder's line fitting. Each time, the idle got a bit rougher and smoothed when I re-tightened the fitting.

Then I drove it about two miles, running well, and bought and put 2 pints of Techron in the tank. Ran fine on the way home.

So thanks for the suggestions - will report on developments.
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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
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  #5  
Old 08-17-2005, 09:29 AM
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In the morning ...

... ran rough when started, missing at idle and under load. After about 20 minutes, things smoothed out and it ran perfectly. It has done this before.

Also, even when it is running OK, there is a sort of rythmic miss at the tailpipe idling in Park. Goes like "ummmmmm bllub blub ummmmmmm."

Maybe I need to give the Techron more time.
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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
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  #6  
Old 08-17-2005, 10:32 AM
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I found two bottles / tank, followed by a bottle per tank, helped over a 2 wk period. Unless you drive a tank a day, expect at least a couple tanks time to evaluate whether this was successful. I know that can be frustrating if you have to drive 'through' the problems. The only other way is a complete assisted system cleanout. Perhaps some places offer this as a service. Pushing gunk through the system too quickly would risk clogging the injector screens, I suspect, before it has a chance to dissolve.

I know some injector cleaners have been flagged for damaging injector plastic parts if used too frequently (a concern from Ford, if I recall). However, I believe our CIS systems are all metal and rubber, so perhaps much higher concentrations can be used? In other words, would there be harm in soaking the removed components in Techron or other injector cleaner? Anyone know?

Steve
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  #7  
Old 08-17-2005, 12:01 PM
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Just had this and replacing the spark plug wires took care of it. Mine was a slow progression. slowly got worse over 2-3 years. sometimes it was OK and other days it was bad. Dealer looked at it 3 times and did not find a good fix. I was check all those things you checked ( still need to replace the O2 sensor) and found that the wires were old and the spark had to jump a gap in two of the wires.
So New wires, new cap and rotor while your at it. clean and regap all the plugs, or a new set and see how she runs.

For you info you do not need a angled spark plug connector on the 560SL on the right side bank as all the web sites say. the angled connector is required for the W107 that still has the battery in the engine compartment.

Dave
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  #8  
Old 08-17-2005, 10:28 PM
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Update

Tonight on the way home, the rough running developed into what felt like a dead miss. So I pulled the plugs, and 1 - 7 were whitey - tidy, but 8 was clearly fouled. So I dug out a spare 1K ohm wire, installed it, and cleaned the plug. That made an immediate difference. Still have the slightlly rough idle, but no more running problem.

We will see what the morning brings, but looks like a set or wires for sure.

Thanks for all the help.

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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
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