PeachParts Mercedes-Benz Forum - View Single Post

Jeremy5848 · #12 10-20-2009, 02:16 AM

Ah, I missed that, sorry. You should already have an after-glow relay in your '93. I suspect (but do not know for sure) that all 602 engines will have the same glow plug -- and possibly the 603 as well. You can confirm that in EPC, the Mercedes Electronics Parts Catalog, available free to USA residents here.

If new glow plugs (they do wear out) do not fix your problem, you might try measuring the current to the glowplugs, see if they are getting their rated current. If not, the relay contacts in the preglow relay may have gotten burned.

Another possibility is that the after-glow circuitry or the temp sensor has failed so that you are no longer getting afterglow. Quick way to check this is to wire a small 12 volt bulb to any one of the glow plugs and run the wires for the bulb into the passenger compartment so you can keep an eye on it. If the bulb is lit then the glow plug is getting voltage (whether it is drawing sufficient current is another question).

If the engine is cold, the bulb should stay on for at least 30 seconds, depending on the afterglow timing for the '93 model-year. If it does not stay on for at least 30 seconds then you may have an afterglow failure. If the bulb stays on but the engine still stumbles then you may have bad glow plugs or bad relay contacts.