1986 560SEL 110k mi.

Just recently I changed the 02 sensor, plugs, and all fluids on my fathers 560SEL. The oil used was winter weight 5w-40 full synthetic oil that my father had used in his other cars and wanted me to try on the Benz. I accepted skeptically. Typically, heavier weight dyno oil was used due to the voluminous oil capacity the car possesses and the cost of syn, but this was an experiment. The syn oil caused a significant leak from the front main that I will soon correct.

Anyway, the car was inspected a week later and given flying colors for everyhting and passed emissions. Not long after, the car developed a noticible missing at idle. Then, it wouldn't start on the first try, you'd have to crank it twice, or hold the key on start for a few seconds. Now, the car misses at all rpm's and at acceleration hot or cold. The symptom does go away sometimes and may start perfectly once in a while, but then recurs. There seems to be no trend that I can discern about when the car will miss and when it won’t.

I found out later, that after the inspection, my father added to a nearly full fuel tank, a can of Valvoline fuel injector cleaner.

Unfortunately, since all these things were done at nearly the same time, I am having difficulty diagnosing what may have happened to cause the missing and difficult cold starting. The problem has been progressively getting worse to the point where the car feels like multiple cylinders are missing over the full range of engine preformance.

I think the following are possible:

1) fuel additive caused some in-line contaminate to break free and clog either injector or fuel distributor (ugh)

2) thinner syn oil is blowing by valve seals (no blue smoke however) due to less viscosity and fouling plugs

3) bad 02 sensor (unlikely sine passed emissions)

4) plug wire(s) may have failed from being "disturbed" from plug changing

5) failed cold start injector

In the immediate future, I first plan to change the fuel filter, pull the plugs to check for evidence of burning or oil. Pull some injector lines and inspect in-line filters if so equipped. Check fuel pressure.

If I have to I will: replace the distributor, wires and (again) the plugs. Replace injectors (if testing shows that the pattern and opening pressure is incorrect) and if need be, try swapping out or rebuilding the fuel distribution unit (ugh).

Does anyone see anything obvious that I might have missed, or have a recommendation for what I should do first.

Many thanks,

ATLD

When missing started suddenly on our 4, symptoms more severe than would be with the 8, of course, but similar problem. I found a broken spark plug boot, signs of carbon in the cap, on the rotor, and the coil. I replaced it all, and plugwires. No change whatsoever.

From a suggestion here, I removed and sniffed each plug after spinning the starter with ignition disabled. Did it several times, as gas smell would dissipate quickly. Still, one cyl consistently no smell, so I replaced that injector with an old one I had. All back to normal after that.

Steve

__________________
'91 MB 190E 2.3
'08 RAV4 Ltd 3.5
'83 Lazy Daze m'home 5.7

Steve, the car your referring to, was that CIS jetronic or pulsed motronic injection? Was your problem intermittent or constant?

Has anyone had this symptom occur intermittently like mine is?

I have a feeling that an injector is either clogged or preforming poorly. I'll pull them out and check their patterns, oppening and closing pressures, and for leakage but I won't get to it till after the new year.

Thanks and have a Happy New Year

ATLD

verify that all eight plugs have been installed properly. I had a similar problem on my 91 560SEL once, and I traced it to a plug that wa not properly screwed-in. It was tight, but was not seated all the way. I had to use a tread chaser to screw it in properly all the way...

That's CIS-E and the problem was constant.

Steve

__________________
'91 MB 190E 2.3
'08 RAV4 Ltd 3.5
'83 Lazy Daze m'home 5.7

You need to ckeck the idle valve and idle control unit. Check the pictures on this link:

http://cgi.ebay.com/ebaymotors/mercedes-126-380-500-idle-valve-and-idle-control-unit_W0QQcmdZViewItemQQcategoryZ33553QQitemZ8026486401QQrdZ1QQsspagenameZWDVW

Attached Thumbnails

 

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Master Computer Engineer, A+, Network+, MCP/MCSA/MCSE 4/2k/2k3 - Messaging, MCTS, MCITP, MCT, Brainbench, ICDL and starting Ph.D

380SE 1984 <------- Totaled by flipping accident
300SE 1988 <------- Sold
Volvo S70 2000 <---- 4 family
Opel Omega 2002 <-- 4 family
560SEC 1989 <------ Sold
560SEL 1990 <------ Sold
560SEL 1991 <------ 4 my mother
560SEL 1989 <------ Sold
600SEL 1992 <------ Current

http://search.ebay.com/_W0QQsassZkhazenzcc

It won't be the idle control valve or unit.

If you are checking the fuel pressure that should tell you if the fuel pumps are okay, the hard starting and missing does sound like a fuel related issue.

Matt.

The plug wires are worth looking at, especially if they are old. I bought an 86 SL 2 years ago with the original set(!), and just removing/installing them(carefully, with the right techniques and tool) to change the plugs+rotor absolutely killed several wires dead.

__________________
86 560SL
With homebrew first gear start!
85 380SL
Daily Driver Project

http://juliepalooza.8m.com/sl/mercedes.htm

Thanks for the replies. Would a bad idle valve and circuit affect the engine at all rpms and loads?

I think the first thing I will do is check the wires and dist cap. Theses look orriginal. Funny thing was that the car ran fine after the plugs were replaced. The problem started about a week later...

Happy New Years!

ATLD

I tend to think that because the problem is transient, the fuel additive/cleaner that my father put in the car might have loosened up some crud in the fuel lines post filter. This crud may have fouled up a few injectors and either clogged them completely, or damaged the spray pattern enough to get poor attomization and incomplete combustion. Only problem with this is the difficulty to test the injectors. Each has to be removed and put onto a injector testing rig and tested for multiple criteria, and all it tells you is whether you can reuse or replace, you cannot fix or clean an injector for CIS as easily as with pulsed.

I'll still do the wires and dist anyway, just because they should be done at this point in the cars life. That will at least eliminate that possibility. I'll leave the injector testing to last.

Happy New Years

ATLD

Check out this deal on eBay for W124 and W126 Injectors with seals and free shipping for $40 a piece ! I bought 8 and they're genuine . I wish I could send private e-mail to every member because everyone complained at one time or another about idle irregularities or start-up issues . eBay item 8031671714 .
Check it out !