1996 W210 E300 turns over, won't start

[JacB]

Greetings,

I have an issue with my 1996 (W210) Mercedes E300D not starting. The engine turns over fine, but never catches, even on the 70+ degree days we had earlier this week in CA. I would really appreciate any pointers in just getting it started. It’s normally pretty reliable.

When the engine turns over:
* There is no glow plug light on the dash now, always showed fine before. (I wait 20 seconds after turning the key to position 2 before continuing)
* The engine turns over without hesitation, but never “catches”. I keep turning it over for 15-20 seconds 4 times in succession, but no luck.
(I trickle charge the battery overnight to make sure there is a good charge each day I try)
* A voltmeter shows each of the holes in the 6 pin plug on the glow plug relay is getting 12V. (the pins and plugs are clean)
* When the key is at the second position, where the glow plug light would normally occur, there is a loud buzzing from the front passenger side of the engine compartment, underneath the air filter box. The noise lasts as long as the key is on position two, 10 minutes is the longest I tested. I'm assuming it's a pump of some sort.
* There are no errors showing on the dash, the interior lights work as usual, and the rearview mirror does not flash green/red. Rearview mirror does light the usual colors with the keyfob lock/unlock.
* The cheapo code reader I have says no codes. (I have a better one on order)
* The car has been parked on an incline outside, nose up, for the last week.
* I checked the fuel lines, the only bubble I see is in the line going from the fuel filter (#5 in this diagram) when I remove the key from the ignition.

Any ideas on what to try? I don't have access to a lot of tools, and technically can't work on a car at my condo parking lot anyway. Hoping your help and suggestions can get me on the road again.

I read through the posts on here already, and the ones that apply to the later glow plug relays didn't reveal much. Cables were tight, connections not corroded, jostling the cables made no difference. There is no strip fuse in the 96 W210 glow plug relay. The K40 relay was replaced about 6K miles (24 months) ago. I checked it out and made sure it's clean and no obvious issues. All the connections/plugs seem fine and no corrosion is present.

I tend to commute by train so only drive on the weekends.

Thanks!

[Jeremy5848]

If your meter can measure resistance, check each glow plug (from each pin of the 6-pin plug to ground) with the plug disconnected from the preglow relay. If one or more glow plugs are bad the light in the dash won't illuminate. If the glow plugs are good, there could be a problem with the relay. Finally, if you eliminate the preglow system completely, check for proper fuel delivery. Loosen one hard line at its injector and see if fuel squirts out when you crank the engine.