Spark Plug Coloration Analysis 230SL - Update

[mistertj]

I have been experiencing a minor mis-fire issue at 15 to 25mph ...no load, just driving down the street. No mis-fire when under load. Removed the spark plugs and found plugs 1 & 3 to be a little discolored, 2, 4, 5 & 6 all pretty clean. Any thoughts?

Update - Got the new plugs NGK BP5ES / 7832's. Ran the car for a bit and still had that same popping. Removed the new #1 plug and it's all blackened as well now. Measured the plug wire resistance and it's just like all the rest...around 1K ohm. I know that spark is getting to the plug because that's where I hang the timing light pickup. I am going to swap fuel injectors with a good cylinder to see what effect that has. Could it be valve adjustment? I'm guessing not since the cylinder compression is about the same as the other cylinders. Just pulled the injectors from cylinders #1 & #2. Injector #1 is not looking good. I will "pop" test tomorrow.
(To be continued).

[badali]

Check your points for proper gap.

[mistertj]

Brad - Do you use a dwell meter or feeler gauge?

[badali]

I use a feeler gauge.  16 thousandths is what I set mine at.  It usually runs perfect after I set them.  I get rough running or it stalls when the gap is getting too close.

[mistertj]

The book says 0.012 but maybe I'll go a little higher.

[Pawel66]

Here, just like in case of my car, I see significant difference in colour of the spark plugs between cylinders. Not sure how the three spark plugs shown on picture look compared to the other 3. But the left one suggests significant difference in combustion vs. the middle and the right hand side ones. Difference in mixture? Is it common?

Also: why would points gap setting (or dwell) influence colour differences of the plugs in various cylinders?

[badali]

Point gap would not affect the color of the plugs but could cause rough running when the gap is too close.  This seems to be the only running problem I have had with my car.  There could be many other causes but it is easy to look at the points.

[Pawel66]

I am not challenging, I am learning - thank you, got that.

Now: what about the colour difference?

[badali]

I'm not sure about the color difference.  Hopefully the points adjustment will have it running well.  I keep things as simple as possible.  I think a few of my plugs were not uniform in color but it runs fine anyway.

[mistertj]

Brad - Adjusted the points and now it idles better. The misfire is still there. Kind of mini pops in the exhaust. It's kind of annoying because most of my driving is at lower speeds. At 50 and above...no issues. Appreciate the points comment though.
Tom

[MikeSimon]

If checking the ignition and plug gaps do not yield any results, also check that your intake manifold is connected properly to the head. Small leaks will cause the engine suck air and it will pop.

[mistertj]

Too much air...too lean. Makes sense. I'll try cranking down the adjustment screw as well. Thanks
Tom

[Pawel66]

I remember when I was tuning my engine and it fired in the manifold it was the timing question. Late in my case. Are you sure all the advance/retard related mechanisms, vacuum work ok? is the ignition timing correct?

And the colour difference is what puzzles me the most.

[mistertj]

Pawel - Timing is on my list. I plan to check tomorrow. I generally check at 1500 rpm 15° - 19° BTDC with vacuum hose disconnected.
Tom

[Cees Klumper]

That left one looks too fouled up, I don't usually see hardly any color difference between the plugs, and they tend to be much cleaner looking than these. I would maybe replace the plugs, check the resistance in the wires + boots, the cap, and the injector of that black plug to see if there is any obvious problem there.

[mistertj]

Cees - I am going to swap the injector of cylinder #1 (the black sooty one) with one from the other cylinders (2, 4, 5 or 6) that were relatively clean. Will see what that does.

[wwheeler]

Cees has a good point. How sure are you that the wires are good and have the minimum resistance? Many have the wrong wires that have the 5000K ohm ends on them.

[Pawel66]

I am not an expert by any means, but I struggled quite a lot with engine misfiring, firing in manifold and hestitating, fixed that, now I am into differing colours of the spark plugs.

What I found useful was when I applied some system to the approach:
1. The most basic things first - ignition leads and sparks
2. Valves
2. Basic settings first - dwell, ignition timing (here I went finally for 123 with settings advised on the Forum of 8BTDC everything connected @idle, 38BTDC everything connected @3000rpm)
3. Linkage tour
4. The mixture composition - assessment of overall mixture composition across speeds - just by the spark plug colour, then on idle based on split linkage test before I got Gunson (does not work vice-versa, you have to have mixture across rpm range more or less ok before moving on to idle adjustment)

I am not sure, but if the colour of this one spark plug is different than the colour of others and the others have the colour similar to those two you show on the picture, it may as well be that it is just that cylinder and not overall adjustment is the reason for misfires. And this can be spark plug, ignition lead or leaking injector - as the simplest culprits. Just by the colour of the two spark plugs - I would have thought the settings are ok, you misfire because of that one cylinder, but that is just my thought.

Do not take me literally as I am not qualified enough, but trying to plan some systematic approach will definitely help.

[wayne R]

This may help, from Haynes Manual in colour.

[mistertj]

Thanks everyone...think I have enough to go on for now. Appreciate all the inputs.

[Benz Dr.]

Number one spark plug is toast - throw it away. What plugs are you running? They look like they're too cold for heat range. Color isn't bad and not that rich - more like cold. 

[mistertj]

Benz Dr - The plugs are A 003 15912 03. Admittedly, I do not "run" the car that much. More short leisurely drives like on a weekend now and then. The misfire thing is a recent issue that has arisen. Too add to that, prior have had a nightmare of issues that started with a very rusty fuel tank leading to injector pump problems necessitating a couple trips to Gus at Pacific Fuel Injection. Not sure the pump might not still be be a contributor. I had to adjust it internally to get the engine to stay running below 2000 RPMs. Right now I am 2 clicks counterclockwise wise, to make the mix a little richer. It now idles pretty well at 1000 RPM. If I try to go below that it will but after a few minutes, it will die.

[Naj ✝︎]

Hi,

Your problem may be your plugs.

That MB Part No. cross refers to plugs with resistors.

May be you should try NGK BP5ES (hotter than the regular BP6ES)  since you don't drive the car much

naj

[mistertj]

Thank you. Will try hotter plugs...plugs are cheap! 

[Pawel66]

I think hotter or cooler is one topic, zero resistance is another. You can see what plugs you have from your picture. You have Bosch W 7 DCo. Co stands for copper core. i am not sure if these are R0 plugs or they have resistor. W 7 DC are R0. It is written on the insulator. Does it say R0 on insulator on your plugs?

I had the impression Bosch plugs with resistor are called WR.

If you have R0 plugs then the point remains if they are proper for your climate as they may be too cold, as stated before.