87 300E DIY diagnostics?

[Camohall]

Is there anyone out there who knows how to do DIY diagnostics on a 87 300E W124 M103 engine? My diagnostic plug is a 9 pin plug that sits in the engine compartment just above the ignition module.
It won't start. It was running well and then dying out when it got up to running temps and then won't restart. It was only restarting after cooling down for a bit. But just recently, it won't even start anymore. The starter turns the engine over but it won't catch. Thinking it was the CPS, I replaced it but there weren't any changes.
I have fuel, I have spark.
Any ideas anyone? Ignition module?
I'd love to run diagnostics but would like to avoid the unnecessary $105 at the local benz shop...thanks guys.
Cam