1990 E250D glow plugs/light
 

i posted this already, can anyone advise me why my old E250D sometimes puts the glow/heater plug light on the dash before starting and sometimes doesent, either way it often comes on during normal driving, and IF it does come on when its supposed to it will stay on as long as i don't turn the engine over, it doesent seem to work on a timer, also the car starts lumpy and smokey for 20 - 30 seconds like it needs some of the glow/heater plugs replaced, any advice??

RE: 1990 E250D glow plugs/light
 

I don't know how different you Euro E250D is from the 240D... or for that matter, even the year of your 250D. But the first thing I'd check is the glow plug strip... If your 250D is 1979 and earlier, your gp's are the looped in series type and the glow plug strip could be under the dash. The following is from Kent Bergsma of Mercedessource.colm : To check glow plugs etc. on a 1979 or earlier 240d , put a 12 v meter or test light on the end of the wire coming from the firewall to the rear most glow plug. If you get nothing then either the fuse is blown, the under dash relay is bad or something may be wrong in your ignition switch. If it has power in that rear most gp, check the next one. . If you have no power to the next in line then the rear most gp is burned out. Since they're in series, if the tip of one gp is kaput, the others won't fire up.
On the other hand, models 1980 to 1985 uses a pencil style fast glow plug wired in parallel. The best indication that your gp's are bad is the engine will run rough for the first 60 seconds after a cold start up. If your glow plug dash light blinks after engine start, you probably have a bad gp, or three, or all.
BTW, the gp fuse strip is in a black box behind the driver's side headlight.. Snap off the top of the box and you'll see the metal strip between 2 bolts. It very often looks good, but has hair line cracks that not visible to the naked eye... It must be taken loose to check... and, according to Henry Schuman of schumanautomotives, if bad, it often falls apart..