I just did this test on my 85 300D with 159k miles and it took about 29 seconds (if you subtract the 6 second pause in between).
Engine was cold from sitting over night.
Ambient temp around 85 F.
Glow plug relay connector disconnected.
throttle pedal half depressed.
I have not serviced the injectors or taken a compression test and do not know what condition they're really in but engine starts great with glow plugs in the coldest winter day. I am wondering if 29 seconds is too long w/o glow plugs for a 617 when my VW 1.6 IDI Jetta with 230K miles starts w/o glow plugs in about 2 to 3 seconds of cranking. The VW has compression ratio of 23 to 1 and the 617 is 19 to 1. Could that explain the difference?
Can you try it on your 617 and report results?
BTW, the cranking RPM was 1/2 of reading shown (started at 185 and ended at 195 RPM). The timing light (which was getting the signal from the diagnostic port) was on the wrong setting.
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