Cold starting.

[Paul Heath]

Good afternoon, I am fairly new here and share a beautiful W113 280SL with a good friend. I have had a fascination with all thing mechanical since a young age and went on to become a mechanic.

Although I no longer do this, I feel I have a good knowledge of most things motoring and I maintain an interest with my current car collection and do a lot of work myself.

So on to my issue, recently the SL has developed a little chugging on start up almost like a miss, this runs for a while and is then punctuated by little spurts of smooth running and then back to the chugging/missing.

The spurts of smooth running get progressively longer until it will run perfectly. The car will then drive as normal until it is left maybe overnight or for a couple of days then it returns.

This morning the chugging just continued and the car runs poorly, having very little time I popped a spark plug which was extremely black indicating running rich? The plugs gaps have recently been set, the leads distributor cap and rotor arm are all in good condition. The air filter has recently been changed.

Any help would be gratefully received, and i may well have many questions going forward regarding the nuances of this lovely car.

Thanks in advance,
Paul.

[mrfatboy]

I had the exact same symptoms.  When starting in the morning it would be rough or miss for 1.5 to 2 minutes then have a nice idle after. It happened every morning.

I tried all of the WRD,  CSV,  FIP cold starting adjustments with no luck.

In my situation, it turned out to be a blown head gasket that was leaking a little coolant into one of the cylinders 😩.

To diagnose I took my car to a smog testing shop and they stuck a sniffer in my expansion tank and sure enough I had extremely high HC's.  It took 10 seconds.

Tyler S also pressurized my cylinders to verify and we could hear the air bubbles.😩

The head came off an hour later😜

[ja17]

 Make sure your spark plugs are non resistor type. You might also want to check the spark plug wires and the resistor ends with an ohm meter. Make sure that the plug wires are solid and not carbon type.
Sounds like you might be  running rich during cold starts. Confirm this with our "split linkage test". Next make sure the WRD (regulates fuel mixture and additional air during warm-up), is operating properly. There is a lot of information already posted on these items. So a little research and get back with us. Ask questions.

[Paul Heath]

Thank you gents, just pooped back up the check the WRD filter and slider which seems ok. I took the oil filler cap off and seem to have a lot of fumes coming out of here. Burnt out valve? Compression test next.

Hope thats not it as it was running really well recently without issues.

Thanks, Paul.

[Benz Dr.]

I agree with Joe. Even with new Bosch plug wire sets I've found that the coil wire is often carbon core. This may look like a small thing but it will make your engine run poorly, sputter, hard start, and appear to run rich. Always make sure your ignition system is 100% before moving on to fuel problems. It could save a lot of time and frustration.

[Paul Heath]

Thanks Gents, I have a multi meter so will test those tomorrow.

Paul.

[Benz Dr.]

For best results the coil wire should have zero resistance.

[Tom in seattle]

I experienced the same problem except after warming up mine would eventually die and would not restart until it cooled off. I went trough all the cold start tests, linkage tour, ignition etc to no avail.  Someone here advised to check the fuel filter. Bingo!When I removed the filter canister the paper fiber filter came out in 50 pieces.  Apparently the filter chunks were blocking the fuel exit. With new filter it runs like new. You might take a look in this area.

[Paul Heath]

Afternoon Gents, went back tot he car this PM with a multi meter. The leads have got radio resistance stamped on them. The one from the coil to the distributor cap gave a reading of 19.85. The leads from the distributor to the plugs gave no reading at all?
Trying to do some research on plug leads and resistance but what do the figures above mean?
Thanks again.
Paul.

[Paul Heath]

The leads are Hypalon Graphite core?

[mrfatboy]

What year is your 280sl?   I believe the earlier ones should measure 2k ohms from end to end on the spark plug wires (with connectors) and the coil wire (with connectors) should be 1k ohms. The wire core should be solid copper for best results.

[Paul Heath]

Thanks it is a 1969 model, in the process of sourcing some copper core leads, Magnecor do them.

[mrfatboy]

I just measured the resistance on my plug set and updated my post above.

[Shvegel]

Sometimes the cheapest alternative may be the best.  For cars like ours simple cheap copper core wire with Bosch resistor ends seem to work the best.  I tend to steer clear of Magnecor etc unless I can see that the core is a substantial copper conductor rather than tiny copper wires wrapped around a carbon core. 

[mbzse]

.../...simple cheap copper core wire .../...

As for ignition wires for our M-B 6-cyl engines of the sixties, never use anything but normal copper wire type. This is as specified from both the M-B factory, and also for 123 Ignition aftermarket distributors

[Paul Heath]

Good afternoon gents, well the problem persists. Whilst on holiday I had new copper leads made, ordered a new coil and fuel filter.

These arrived and I duly fitted them. The car started quicker than it ever has but the missing is still there.

I removed the spark plugs and all were black with soot, also 3 and 5 were wet with fuel. Over fuelling, insufficient air, CSV maybe?

Any help as to where to go next would be much appreciated.

Thanks
Paul.

[stickandrudderman]

Try swapping injectors around to see if the "wetness" follows the injector. If it does you know your injector is bad.

[Paul Heath]

Thanks, will try that tomorrow. The other black plugs could be because it's not getting warmed up?

[franjo_66]

On top of what has been suggested above, I'd recommend checking the CSV to ensure it isn't leaking.

[ja17]

I recently ran across a similar problem. The condenser was loose on the side of the distributor. It must be tight and grounded to the distributor or  you will have a random ignition miss.

[Paul Heath]

Hello guys, thanks for the responses, swapped injectors today and the car will not start at all. Car has electronic ignition, checked the CSV and it looks fine, also disconnected it this morning before trying to start the car and this made no difference.

It fires but won't start so the problem is getting progressively worse. I think I'll get the injectors tested next unless anyone has other suggestions?
Getting frustrating now!

Cheers
Paul.

[ja17]

The car will start if you have: spark (on time), fuel (adequate pressure), and compression.  Most likely your plugs are fowled. Check for spark first, then change then out. 

[Pawel66]

Let me throw in my two cents - I do not know how fluent/experienced you are in this. I am not, but I went through similar trouble, so from an amateur perspective - there is a couple simple things to check before you go for big $$$ on injectors - I do not know if the injectors test you did is, in this case, conclusive.

On the fuel side the two simple reasons for rich condition (there are more factors, but the simple ones) are CSV and WRD:
1. Are you sure you checked the CSV as per procedure (safety first - get a small bowl under the CSV, unscrew the small screw on the side of CSV, switch on the pump and see if you have fuel leaking). Also: if you unplug the CSV, you will not start the car easily.
2. WRD - when you start the car cold you hear a loud noise of air being sucked through the filter on the FIP. This noise should fade away after a minute or so. If the noise stays - your WRD is not working and you have rich mixture.

On the ignition side:
1. How old are the spark plugs? Have you tried new, proper ones? Have you cleaned the ones you are putting in and removed soot?
2. Do you have spark on all of them? When you check it, be careful you hold them through insulation and away from the hole in the cylinder. The spark should be strong, blue and nice.
3. Are the ignition wires sitting tight in distributor cup and on plugs? Are the wires sitting tight in the plug connectors and cup connectors? Is the distributor cup sitting tight on the distributor? Is the distributor screwed tight (distributor does not turn) in its seat (that allen bolt there sometimes just surrenders)?
4. Do you have ignition timing ok across the rpm ranges - a simple check, but you need to have a stroboscope.

You have an electronic ignition, so I guess dwell check and ignition points cleaning do not apply.

I think if all of the above is ok, then there is time for further digging. Someone on this forum wrote that going systematically through these things will save time and money in the end vs. "shooting from the hip" approach.

If you know all this and did all this, just ignore it.

[Paul Heath]

Well gents, pulled the spark plugs and have a good spark but cylinder 6 is spraying coolant out of the plug hole.

Head gasket 

Will keep me busy for a while, thanks for the input , I may well be back for advice for the cylinder head removal.

Cheers
Paul.

[mrfatboy]

Sorry to hear that Paul. That was my original assumption at the beginning of this thread.

I just went through the same thing and actually just finished the job a couple of weeks ago with Tyler S's help. I could not have done it with out him😀

The good news is that you can take the time to detail the engine and fix all of the other issues,  if any while everything is out. 👍