IntroductionAre you experiencing engine starting and running problems ? But you don't have any clue and don't know where to start looking ? This mini tour may give you some guidance.
Consider it as a starting point ! Use the excellent searchfunction from the forum ,there is so much knowledge available .
NOTE : I am not a mechanic or specialist but collected most of my knowledge from this invaluable forum ,the BBB, Haynes,Youtube .
Most mentioned problems and solutions will also apply to the other SL type's, however I am only sharing my 230SL experience .
Help yourself for additional info for your specific type and configuration !
Finally my car is running as it should be , so it's time to bundle most common problems and share links to essential topics and tips.
General :
TIP 1 : As a Guest reader , get a full membership, an absolute no-brainer !
Think your problem is unique ? After 50 years of existence of these SL's ? : Most unlikely
Investing thousends of $$ /€€ in your car but saving a few bucks on membership ? Pennywise and pound-foolish.
Consider this : a full year membership fee will cost you less than 1 hour laborcost of a mechanic, doing a simple job that you can easily do yourself !
TIP 2: My adagium : READ FIRST (ALL you can on your problem) and POST QUESTIONS LATER ! This to avoid starting another a new topic on i.e. " difficult hot starts" when all info is already available for years on this forum .People might get wary to respond...and you 're still in the woods....
TIP 3 : Work systematically, ,step by step ,one item at a time.
TIP 4 : Don't "assume" or "think" that something is (done) right either by yourself ,the PO or a mechanic. Better check , re-check and keep track! . Keep safety in mind,be critical and persistent..
My favorite additional tools:
- Stroboscopic timing light ,preferably with advance function, for setting ignition
-
TIP 5 (Gunson) 14mm Colortune ,my favorite, see photo.for easy troubleshooting ignition and combustion problems. Very helpful for checking/adjusting mixture ,should be in every SL owners toolbox
- Pressure gauge for measuring fuel pressure, a 2,5 bar full scale deflection works nice
- Poptester (homemade) for cleaning/testing injectors
- A simple notebook for keeping track of all your adjustments/settings and writing down various handy data ( where have I seen it before? ) for quick reference like (OEM) partnumbers, torquesettings,threadsizes,o-ring sizes ,suppliers etc.
Here we go:
For a good running engine you need basically 5 things :
1.compression
2.ignition
3. correct linkage setup
4.air
5.fuel
A failure or fault in either one will prevent a proper running engine.
WARNING! : DO NOT START WORKING ON YOUR FIP BEFORE YOU ACHIEVE THE BASIC SETUP FOR YOUR ENGINE : CORRECT VALVE CLEARANCE
AND IGNITION TIMING
AND LINKAGE SETUP !! THIS CANNOT BE STRESSED ENOUGH , OTHERWISE YOU ARE TRYING TO SOLVE ONE PROBLEM BY CREATING ANOTHER ,WHICH WILL DRIVE YOU CRAZY IN THE END ! !.
STEP 1 : COMPRESSION :
Self explainatory : a worn engine (i.e. pistons,rings valveseats),unadjusted tappet clearance ,leaking or burnt valves will cause running troubles.
First important step : do the valve adjustment tour
https://www.sl113.org/wiki/Restricted/ValveAdjustmentTourTIP 6 : More kind of a warning ! When adjusting the tappet clearance the ball stud is sometimes very stubborn to "break free" and start moving .
Check that the ball stud holder ( the 24mm hex part between ball stud and cylinderhead surface) does not come loose.It happened to me and I discovered it just in time.
Since the friction between holder and cyl. head is lower than between holder and ball stud ,you might end up,when unnoticed, with a "runaway" tappetclearance after some driving
To prevent possible problems use an additional 24 mm spanner when turning your ball stud !
Only after adjusting your valves you should do a compression check if in doubt of your engine's mechanical condition.Enough said.
STEP 2 : IGNITION :
https://www.sl113.org/wiki/Electrical/IgnitionSystem * Distributor:
On my 230SL I had a rebuilt 051 distributor which worked OK ,but replaced it years ago anyway with a standard 123 electronic distributor /Bosch blue coil combination,and bypassing the ballast resistor.
This to rule out mechanical failures and ease of maintenance.
Works perfect. I set it up 17 degr. BTDC @1500rpm with vacuum disconnected, gave me 30+ degr. at 3000rpm. Idle timing is less critical.
Back to the mechanical dizzy's.
Over the years there are several types/part nbrs. of mechanical distributors used by MB (i.e.vacuum advance or -retard each with matching throttle body).
Some common dizzy problem causes are:
- Start first with checking if your dizzy matches your throttle body (position of vacuumport !) ,which is absolutely essential.
https://www.sl113.org/wiki/Fuel/Throttle#Body - Dizzy installed with notches 180 degrees wrong.
- Worn wobbeling shaft/cam ,causing erratic dwell angle and thus uneven running
- Burnt /pitted/sticking or bad quality breakerpoints
- Faulty or wrong condensor
- isolation failed or damaged on passthrough in dizzy housing between points and condensor causing shortcut to electrical ground
- vacuum hose leaking or clogged
- vacuum opening in venturi (bore) clogged
- incorrect operation(range) of vacuum unit
- loose electrical connection
- mechanical distributor failure ( i.e. worn shaft,cam ,sticking centrifugal advance weights ,weak or broken springs or loose or sticking contact breaker plate,etc. )
- rotor finger worn /failure ( electrical resistance should be 5k Ohms)
- Distributor cap /central carbon contact worn,cracked or damaged ( look for black traces/hairline cracks on the inside) or oxidation on metal parts causing a weak spark.
- Sparkplug wires in wrong sequence
https://www.sl113.org/wiki/Electrical/Distributor *sparkplug wires, connectors or wire ends :
- wire ends at distibutor cap should have no more resistance than about 1 k Ohm
- sparkplug wires should be solid copper core type with max. 1 k Ohm resistance . Check wires for cuts ,,chafing, damage or aging cracks Never use carbon core type wire's !
- sparkplug caps should have no more than 5 k Ohms ( 1k Ohms could be the better choice, stronger spark)
- Using an Ohmmeter measure continuity and total resistance between distributor cap and sparkplug caps ,They should be more or less equal.
-run your engine in a pitchdark envirionment ,check for sparking around high voltage components
* Ignition coil :
Several coil types with corresponding ballast resistors were used by MB , black, red or blue
- check if your coil and ballast resistor match (
https://www.sl113.org/wiki/Electrical/IgnitionCoil)
- Check your ballast resistor in cold (and hot !) condition with an Ohmmeter
- coils can ( and do) fail with age causing failing to start ,misfiring,poor acceleration , power loss. They may fail intermittent when getting hot during driving,harder to detect as troublesource.
- if your coil gets very hot after driving it might be an indication for failing
- check for positive voltage at terminal 15 with the starterswitch in "run" , if not available: check,battery voltage , wiring harness or starter switch ( bad or oxidized contacts?)
-Note that there is no fuse incorporated in the ignition system.It is hot-wired via the starter switch
- check for visual damage ,cracks , leaks, loose terminals or swollen housing
- remove all wiring from the coil and check internal primary resistance between terminal 15 and 1 . It should read somewhere between 0.2 an 3 Ohms . The internal secundary resitance between teminal 1 and 4 (high
voltage terminal) should read between 5 -20 k Ohm. These are very general numbers and depending on type , but give you an indication what to look for. So low Ohms primary and high Ohms secundary
* Sparkplugs:
Use ONLY non-resistor sparkplugs indicated by the absence of the "R" in the partnumber. . Some brands label them with "R0" Use a slightly hotter type than factory standard. They have a better self-cleaning ability .
NGK BP5ES or Bosch W8DC are widespread used in the community with good results
If you think you are having problems with your spark plugs you should "read" them, meaning their color and appearance tell you a lot about how your engine is doing !
https://ngksparkplugs.com/en/resources/read-spark-plug https://ngksparkplugs.com/en/resources/spark-plug-basics https://ngksparkplugs.com/en/resources/understanding-spark-plug-heat-range https://www.boschsparkplugs.net/heat-range-conversion-chart-2* Ignition trouble shooting :
Most problems are limited to a single cylinder if all above mentioned checked OK . You are probably aware of finding the the troubled sparkplug and/or cylinder by pulling the sparkplug caps on a running engine one at a time and observing a slight drop in rpm (or change in running) of the "good" cylinder an no observed change with the "bad" cylinder .
But is it really an ignition sytem problem or is bad ignition caused by something else ?
Here comes my favorite (Gunson) Colortune into play ! This simple but clever kind of transparent sparkplug makes it possible to peer inside your cylinder with a running engine .Now you can actually see what is happening in there .
This is how it works : Remove the sparkplug of your suspected cylinder. Screw in the Colortune and connect it to its sparkplug cap ,Now run your engine and observe if you have a good bright spark and judge the color of your combustion proces. The color will tell you if you are running rich or lean . Using the Colortune I found the culprit of a bad running engine( stumbling,misfiring,backfiring) : suspected an ignition problem but it was a leaking injector instead .Colortune is a maybe the better alternative for the split linkage test to judge your AFR for each cylinder at any rpm. Back to troubleshooting .
1.If you observe a bright ignition spark and see regular pulsating "bunsen blue" flashes in the Colortune it tells you that you ignitionsystem (and AF mixture) for that particular cylinder is OK. Just your sparkplug may have failed. Replace it.
2. Observing a weak spark accompanied by irregular blue flashes or no spark at all indicates an ignition problem. . Check if a weak spark is limited to one or all cylinders to narrow your search.Just one cylinder ? Work backwards from sparkplug to distributor to locate the problem. All cylinders ? Start with the dizzy and coil and work towards the sparkplugs.
3. If observing yellow or yellow/blue flashes it means your engine is running rich, which may cause fouled or wet plugs hence bad ignition. Adjust mixture and replace sparkplugs
4. Observing blue/white flashes means your engine is running lean which may cause engine overheating and burning up your sparkplugs . Adjust mixture and replace sparkplugs
STEP3 : LINKAGE SET UPFor a smooth running engine you need an optimal mixture of air and fuel ,the AFR ,or air-to-fuel- ratio. This means that your venturi throttle plate opening angle( read : the amount of air) and the FIP delivered amount of fuel should match to achieve a correct AFR ratio over the whole rpm range.
In other words : they need to be synchronized . Tampering with ,or just a little bit of wear/play over the years of your linkage sytem will disturb synchronisation. Replace worn parts.
The linkage tour gives you all the guidance and details to achive a proper linkage setup.
https://www.sl113.org/wiki/Restricted/Linkage-tourSome topics mention to increase the lenght of the FIP rod a bit to overcome minor running problems. Reading the above this is not the way to go. Fuel adjustments should be made at the FIP only !
If you observe anything incorrect in my text please PM me so I can adjust it.
To be continued with part 2 and more..
Rob "rosch"
Halle ,Netherlands
