Will not start

[wgl0]

68 280SL Early production  It was running fine I parked it for a couple of days it would not start the next time that I tried to use it. I have replaced plugs, rotor, cap, points coil, ballast resistor. The following trouble shooting has all checked out ok.

Fuel pump running, 12 V to CSV, fuel to CSV,  plug wires from new cap in time with firing order, points gapped to .012 or close enough so that it should run.

The motor turns over fine, strong battery, it just will not catch and fire.

Any thoughts?? Thank you

Bill Lindquist
280 SL Signal Red

[hands_aus]

fuel, air, spark......what is missing?

You have replaced almost everything in the engine electrics
Have you checked the dwell, timing, spark, fuel delivery volume and pressure, plug leads for continuity and equal resistance/impedance, the fuses?
lubed the shaft of the distributor.

Bob Smith (Brisbane,Australia)
RHD,1967 early 250 SL, auto

[glennard]

Bill, 1- Is there spark to a seventh spark plug(from any of the six spark plug wires) grounded to the block?  2-If there is spark, squirt a little Starting Fluid(carefully) in the intake manifold-does it fire?

[Naj ✝︎]

Bill,

I'm interested to find out which coil and ballast resistor you've fitted?

naj

68 280SL

[wgl0]

Hi naj

After your last suggestion I took the numbers that you had given me to the MB store. The parts person wanted to do some checking. He called a couple of days later and said that your numbers were correct for an early production 68. The coil that I am using is 000-158-49-03-67. The 67 I think they put into their computer to alert them that early 68 might be fitted with a 250 coil. The ballast was 000-158-17-45. I sure appreciated your help with this.


Thanks again

Bill Lindquist
68 SL Signal Red

[Bob G ✝︎]

I was going to suggest the coil and ballest. I own a 1968 model and in the first month of ownership I got stranded more times then I could count. The car would just quick. No responce when you went to turn the ignition key. Very inbarrsing because with traffic behine you and no electrical the flashers would not work.

As soon as the engine cooled, the engine would start with no problem. While tinkering in the engine bay one day I spotted a crack in the top of the coil. Turned out that was my problem. I guess I was lucky. I did not know what coil to purchase so what came out was replaced with the same a black coil with the orange top. My car  is an early 1968 so Tom Hanson told me after seeing the coil it was a  250SL coil. Well it works fine so fare.
Bob Geco
1130440012001906
April or june 1968 production

[Naj ✝︎]

Hi, Bill,

Seems like you ended up having the 'red' coil and matching 1.8 ohm ballast resistor.
In my opinion, 0.012 is too small a gap. I would go between 0.014 and 0.016 to be nearer the optimum dwell angle.
Try using a jump lead from the battery +ve to the coil side of the ballast resistor to see if it starts.
Once running, remove the jump lead but also check the battery voltage. Should be over 14 volts. I had a lot of these starting problems because the regulator was only charging upto about 12.5 volts!

Hope this helps.

naj

68 280SL

[wgl0]

Hi naj,

Thank you for the wiki information, that was just what I was looking for.

Bill Lindquist
280 SL

[Mike Hughes]

Check for closed or barely opening points.  When the point gap gets too small they will start to pit, which is just a transfer of point material from one contact to the other.  Once enough material has transferred the points can maintain contact in the area of pitting, acting as if they are closed, even though they appear to be opening!  I tore the whole fuel delivery system on my car to bits last year only to find that the rubbing block on the points had worn down due to dried up lubricant, causing a huge pit.  There is a fine line between an engine that runs and one that doesn't when it comes to distributor points.

- Mike Hughes  -ô¿ô-
  1966 230SL Auto P/S
  Havanna Brown (408)
  Light Beige (181)
  Cream M-B Tex (121)

[hands_aus]

A member of our local MB club had his distributor shaft worn cylindrically smooth because of no lubrication to his distributor shaft and the points rubbing block.
The car just wouldn't go. He had driven it 2500Km with very poor economy along the way.
He needed a replacement 051 distributor which are not readily available in small country towns.
Recently he installed a Pertronix unit.
I advised him about adding a few drops of oil to the felt wick and the oil point on the outside every six months.

Bob Smith (Brisbane,Australia)
RHD,1967 early 250 SL, auto

[ja17]

Hello Bill,

If you have spark on time,  fuel, air and compression it will run.

Air: is a given.

Spark: As per glenn, you can check for a spark by unhooking a spark plug wire at the spark plug, install a spare spark plug on the wire end and touch it to engine ground. Have someone crank the starter and watch for spark.
 Sudden loss of timing can happen if the distributor jumps time. Do a static timing check. (turn engine by hand with ignition on and the distributor cap off and watch to see if the points fire to #1 plug wire  when the crankshaft pointer moves roughly to 0 (top dead center compression stroke #1). The last check for spark are the spark plugs themselves which may have fouled and are not functioning. Inpect at least one of the spark plugs for fouling.

Fuel:
Next check for fuel, the fuel pump must be running.  Give the engine intake  a squirt of starting fluid. If it fires momentarily you are not getting fuel to continue running. Caution intake backfire.

Compression:
Sudden compression loss is not likely, but could happen if the timing chain jumps. Checking compression involves removing one or more spark plugs for taking a compression reading.

Follow these steps and you will surely find the problem or be pointed in the right direction.

Joe Alexander
Blacklick, Ohio