1985 325e turns over but won't start
I am new here, but I am looking forward to hearing any ideas you may have as to what may be ailing my car - a 1985 325e. Here is what has been happening:
About 6 weeks ago or so my car started and ran perfectly.
The next week (I only drive the car once or twice a week on average), the car started, but took longer (more craking) to start, but it ran perfectly once it started.
The next week the car took much longer to start, but again ran perfectly once it started.
The following week, the car took so long to start that my battery was weakening due to all the cranking, and I needed to add a jump to prevent the battery from being completely drained, but finally the car did start and yet again, it ran perfectly.
After that the car hasn't started at all.
Originally I was thinking this was just a fuel delivery issue, so I tried replacing the fuel pressure regulator, then the in tank transfer pump, and then the external (main) fuel pump. I also tried swapping both the fuel pump relay and main relay, but none of these swaps fixed the problem. I then checked and discovered that I am not getting fuel OR spark, and I know that my distributor, rotor, spark plugs, wires, and coil are all nearly new and are all in great condition, plus since the car ran perfectly once it would start, this problem seems to be related to just starting the car, and not anything that affects driveability.
Anyway, since I found that I am not getting fuel or spark during starting, I thought that maybe the Motronic ECU was bad, so I tried swapping in a used but supposedly working one, yet the car still won't start - I guess it is still possible that the ECU that I swapped in was not working as I had thought, but it was stored at room temperature away from all heat sources, so I thought it should be ok. I also checked the reference and speed sensors on the bellhousing, and both test out fine, and I checked for the pin on the flywheel and I am nearly certain that I saw it still in place in there, although it is tough to see in the small sensor holes. The other thing that I checked was the fusable link on the positive lead wire about a foot in front of the battery in the trunk, as that fuse had corroded and caused a no start issue for me about 3 years ago, but this time I am getting full 12V on both sides of the fuse, so it doesn't seem to be that this time. I have also checked for any obvious corrosion on any wires or connectors, as well as loose connections, and I have not been able to find anything yet. And finally, my timing belt was just replaced within the past 10,000 miles or so, therefore I don't forsee any issues there.
One further note - I went through the diagnostic check noted in the Bentley manual for testing at the ECU connector, and although the fuel pumps will not run while trying to start the car, they do run when touching pin 20 in the ECU connector to ground in the test (so they work as expected in that test), and they also run when the ground pin of the fuel pump relay (when left in it's socket) is touched to ground with the ignition on.
Is there anything else that anyone can think of that would cause this type of a problem?
Thank you in advance for any assistance you may be able to offer.