‘69 280sl - Rough Idle/Rough Running

[cjpoulos]

I think the main issue with my current plugs is that one or more of them is faulty - I may or may not have knocked two of them off the workbench late one night... They foul very quickly as well, which I'm currently going to blame on the mixture issues and whatever may be causing that. I've ordered an injector tester/cleaning kit from MercedesSource, so I'll start chasing the final fuel issues there. I think between that and the new NGK's, we will be in good shape!

[sens]

If you have a multi-meter you could:

1/ Test the spark plug between the thread that goes into the block and the tip coming out of the ceramic tube. Resistance should be very, very high, infinite.
2/ Test between the same tip and the point where your cap fits on the plug. Should be around 1100 Ohm
3/ Test the wires including caps. Should be around 0 Ohm.


If you clean a fouled plug and sand a little the spark points, you should have a good spark.


Now if this is OK, I would do the split linkage test to see if you are realy running so rich. (I think you do)

Good luck.

[twistedtree]

Another test of the CSV is to remove it from the manifold, but keep the fuel pipe connected.  Then turn on the ignition and let the fuel pump run a bit.   Look for any leakage of fuel from the CSV spray nozzle.  If it's dry, then you know it's not continuously over fueling the engine.

[sens]

Spot on!!

That is a very good test to make sure the CSV is OK!!

[cjpoulos]

That is a great test. I did all the tests mentioned and it turns out that my CSV is working very well, no leaks and it's not stuck open or closed. I think the initial spray at start up is just adding unnecessary fuel because of how rich the mixture already is, so it runs a bit better with the CSV disconnected.

The car will start and run (a bit roughly) every time now! Dwell is set to 36 degrees, points are at .012, and I gapped the plugs down to .027 from .031, which seemed to help a lot - did not think that it would make a noticeable difference, but I'll take it.

Now I'm just going to clean the injectors and throw the new BP5ES's in - the NGK BP5ES 7832 are available on amazon now for anyone who's had trouble finding them. Make sure to buy the 7832 part number, those have the twist of caps (7732 BP5ES plugs have a fixed cap that threads into the ceramic bit).

Almost there!

[sens]

Well you are msking real progress!!
You can exclude your CSV.

On my 280SL I had one plug (No4) that fouled. (see post) The others were ok.

It was solved completely by setting the valve clearance correctly (was far to high) and cleaning the injector No4. It had a bad spray pattern.


So I would check the injectors as soon as you receive the kit!

Please let us know!

Good luck!