PeachParts Mercedes-Benz Forum - View Single Post

Maxbumpo · #9 01-18-2017, 08:46 AM

Ok, I think a little perspective is in order. The car is 32 years old (or more) and probably has a couple hundred thousand miles, likely more. Its an _OLD_ car, and so things will break and need to be diagnosed and repaired. I fail to see how any of this justifies converting to a manual pre-glow system. All the parts to repair this are available if you have time to wait for them to be shipped. You even have a choice of MB original parts, or aftermarket.

One of the systems that has three components (relay, fuse, glow plugs) is acting up. As designed, the light in the dash is telling you that there is something wrong. There is a diagnostic circuit inside that compares the current draw of the first glow plug to the other four, and if that comparison indicates a problem with any of the glow plugs, the circuit will tell you (the driver) that there is a problem by either not lighting the dash indicator, or lighting the dash indicator after the engine is started, or maybe both. You had three bad glow plugs, replaced them with used plugs, and the light was happy for awhile. Another plug failed, light told you, so you've replaced that. Now the light sometimes thinks there's a problem, and sometimes doesn't. In other words, the system is telling you that it is not really happy about the used plugs.

Why wouldn't you simply install the new glow plugs and be done with it, or then also replace the pre-glow relay with a new relay? Generally the relay fails in one of two ways: Doesn't work at all, or randomly turns on and drains the battery.

Last note: The indicator light in the dash doesn't mean plugs are energized or not energized. If the key is turned but the light doesn't come on, power is STILL going to all the glow plugs unless the fuse is blown. The car MAY still start, with a failed plug or two, because the other good plugs are heating up.