You could check the resistance on the ignition wires & boots - sometimes these fail or are not correct. I had the same problem, also with all-new ignition (breakerless from Luminition), plugs etc and it turned out to be the wires (that were also only 2 years old). It only started when the engine warmed up. The popping seems to be normal for certain types of distibutors.
Here's a bunch of additional diagnostic tips from John Hassel on Yahoo! a long time ago:
1. Remove the distributor cap.
2. Check the points and make sure that they are not sticking and have the proper gap.
3. Crank the engine and make sure that the points open and close properly.
4.. Connect a voltmeter between the coil positive terminal and ground.
5. "Bump" the starter until the points are closed.
6. The voltage at the coil positive terminal should be about 8 – 11 volts.
7. Bump the starter until the points open.
8. The voltmeter should read about 7 - 9 volts.
9. Leave the ignition ON with the points open and watch the voltmeter. The voltage should remain constant, no fluctuations. Watch it for a good 3-4 minutes just to make sure that it's OK. If the voltage fluctuates widely or
drops completely, the switching unit is the likely cause (however, they rarely fail).
10. If these tests are good, replace the distributor cap.
11. Pull out the coil wire from the midle of the distribuitor cap and hold it about 1/2 inch above the port.
12. Take a small piece of wire and connect it to the positive terminal of the battery.
13. Briefly, touch the other end of the wire to the positive terminal of the coil. You should see a spark from the coil wire to the distributor port.
14. Touch the wire several times; you should see a spark each time.
15. If all of these tests are OK, then the points, coil, ballast resistors and switching unit (the black box under the battery tray) should be good.
16. Similarly, if these tests are good, there is likely another problem, which could be vacuum advance in the distributor, vacuum problem in general, the fuel injector pump, timing, etc. Basically, the steps above will allow you to eliminate the components in the ignition system itself.
Good luck Naj,
Cees
white 1969 280 SL
