I bought a crankshaft position sensor for about $60 online and it fixed mine.

I wasted $300 or so on a filter then a fuel pump 1st.

3 minute installation after ya do it once.

99 ML320 @ 100,000 CPS failed.

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Steve Danville
what i did myself.
CPS
rear shocks
MAS x 3.
SparkPlugs (twice)
Fuel pump & Filter
Window switch
replaced both failed horns with Honda horns.
Cleaned ERG Tube
Oil changes
Oil consumption Fix
Brake Pads
A/C Recharge
Anti-Freeze change X 2.
Front Shocks. Monroe. $90
Mercedes Warrenty Work:
Harmonic balancer,power steering clamp. Cat converters.Drive Shaft Bearing.s
Replaced Outer Lower Tie Rods and front lower ball joints at 156,000 miles

there are two sensors listed, which one would I get

I'd try the CKP sensor like 'DOC says. I've seen LOTS of them fail without setting codes. Drive authorization is probably OK. If the engine cranked and started but then stalled immediately or, cranking was interrupted, I'd look closer at DAS. If DAS intervention occurs a code is set (P1570). Another thing worth checking is whether or not any other failures occur (interior lights, wipers, etc.) when the engine won't start. I've seen ignition switches play some nasty tricks in the past as well as the circuit 15 relay (I think it's k12). Go with the CKP sensor first though. It's the most likely culprit.

Be sure to note if the odometer is giving a strange error code, it'll say "start error" where the odometer is, which means a DAS problem for sure, (try another key if this is the case). I do agree with all the comments though, but don't ignore the obvious if "start error" is displayed.
Gilly

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I have a 1999 ml320 with a similar problem. If the car sits 30 minutes it will crank over fine and not start. 1 hour later it will start. No codes set in the computer, no spark and no fuel pressure. I have seen the problem twice and by the time I found the wires to check the crank angle sensor for alternating current the car started. I got a good signal from the sensor at 12 volts during cranking. After reading this I will replace the sensor and hope the problem will be history. John

Definetly sounds like a crank angle sensor problem to me. just replace it.