yesterday morning i went to crank my 85 300sd and had a little trouble getting it to fire up....on cold mornings, below 60 degrees or so, i usually let the glow plugs warm up a couple of times before actually trying to crank it....after i did that, it took a good ten seconds of turning over before it ever fired up.....now today, at like 1 in the afternoon, i went to crank it and it will not fire up at all....the engine is turning over and over, but nothing else....i need some help here guys....i have to get this beast going before work tomorrow, and i dont have a clue what could be wrong with it...

i can tell you that the valves havent been adjusted in quite some time, and about 2 days ago i had to drive on the interstate for about 50 miles one way....i noticed something else too, while on the interstate.....i was doing about 85 or 90mph, and went to pass someone, and put the pedal on the floor and the car downshifted....this car isnt supposed to downshift past 80mph, and it never has until the other night....i immediately let off the gas and let it go back into 4th gear for fear that it would blow my engine, knowing it should never downshift going that fast....im not sure if this is related to the cranking problem, but figured i would say something about it since these problems happened within 2 days of each other.....

now i drive this car mainly to work and back...about 30-40 miles a day, stop and go traffic....havent had any problems with it until today...im all ears, and thanks in advance for the help...this site hasnt let me down yet

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1985 300SD 192,000miles...Astral silver/ Grey MbTex

1983 300D 194,000miles...White/Tan MbTex...my newest addiction

First get a multimeter, check glow plugs.....you may have one or more bad.....I had that problem recently.

Get the valves adjusted, or at least checked, it they are excessively tight it can keep valve open and make it real hard to start......combine that with recent cold weather it would make for a no start condition, that in the heat of summer would still start.

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Proud owner of ....
1971 280SE W108
1979 300SD W116
1983 300D W123
1975 Ironhead Sportster chopper
1987 GMC 3/4 ton 4X4 Diesel
1989 Honda Civic (Heavily modified)
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Section 609 MVAC Certified
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"He who fights with monsters might take care lest he thereby become a monster. And if you gaze for long into an abyss, the abyss gazes also into you." - Friedrich Nietzsche

i think i have a multimeter somewhere around here...what do i need to look for, and how do i go about checking my glow plugs?

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1985 300SD 192,000miles...Astral silver/ Grey MbTex

1983 300D 194,000miles...White/Tan MbTex...my newest addiction

disconnect glow plug harness at relay. measure resistance between each plug contact and engine block. All should be less than 1 ohm.

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'82 300SD - 361K mi - "Blue"

"Good judgement comes from experience. Experience comes from bad judgement."

listen, look, .........and duck.

forgive me for being so green, but where is the harness located? maybe you could show me a picture of it?

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1985 300SD 192,000miles...Astral silver/ Grey MbTex

1983 300D 194,000miles...White/Tan MbTex...my newest addiction

its the black block on the Left front fender.....just unplug it to measure.

__________________
Proud owner of ....
1971 280SE W108
1979 300SD W116
1983 300D W123
1975 Ironhead Sportster chopper
1987 GMC 3/4 ton 4X4 Diesel
1989 Honda Civic (Heavily modified)
---------------------
Section 609 MVAC Certified
---------------------
"He who fights with monsters might take care lest he thereby become a monster. And if you gaze for long into an abyss, the abyss gazes also into you." - Friedrich Nietzsche

While you have the cover off the relay to check resistance, look at the bar fuse to see that it is in good shape. Turn on the key and with one volt meter lead grounded probe the studs at both ends of the fuse to make sure there is voltage at both when the key is turned on.

If you have voltage, even if the plugs pass the resistance test, I would consider replacing all of them. I have been through this many times and found that even if the resistance test is okay, one or more of them will have holes burned in the shell or other problems that prevent them from working very well.

It was much more painless back in the days when pin type plugs were only about $3 each, but even now at $10 each it will almost always solve your starting problems by replacing them if, of course, they are getting voltage.

They are a Tasmanian Devil to replace on the five cylinders. It is easiest to just go ahead and remove the spider web to get at them.

Good luck and Merry Christmas,

ok,guys...thanks for the replies....i just got back from work and tried to check it out with the remaining ten minutes of daylight i had...now i dont know if im checking them right or even if im checking the right thing....i pulled the cover off of the black box located on the fender right behind the left headlight...inside, theres a harness with 5 pins, a smaller harness with 4 smaller pins, and what looks to be a bar fuse....im assuming thats what i needed to check, the harness with 5 pins....went yesterday and bought a digital multimeter, and have no clue if im checking these glow plugs right...i dont know if im supposed to ground the black lead somehow, or if you just put both leads into the plug you want to test....i tried both ways, and got a reading by inserting both leads into each pin socket on the harness....i got a 0.3 ohm reading on every one of the plugs...with the key on and with it off....something tells me im doing this wrong, i thought the readings would vary from plug to plug....i think i need someone to explain to me, in elementary detail, what i need to do....if the black lead needs to be grounded, where can i ground it at?

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1985 300SD 192,000miles...Astral silver/ Grey MbTex

1983 300D 194,000miles...White/Tan MbTex...my newest addiction

85drtysthbenz,

First, you need to confirm you have the right connector. The black box on the driver's side fender, forward side, has a couple of wire ways entering it. The one that comes from the engine (it should be visibly traceable to the glow plugs) has five connections in it, and one blank spot, with an orientation pin so you can only get it on one way. If you look at the underside of the connector after you get it off, it should have "1, 2, 3, 4, 5" labels for each cylinder's glow plug kind of cast into the plastic. Once you confirm that is the plug you have, you put the red lead from the multimeter to the electrical connector (a sleeve) in the plug, and the black lead to the valve cover or some other covenient grounded surface. The multimeter should be set to the lowest scale you can pick over 1 Ohm as the reading should be around 0.9 Ohms.

Go from connector pin to connector pin. Make sure you get a good contact between the sleeve and the red multimeter lead probe, and on the black, ground probe.

Write down the values. If they are less than the 0.9 Ohm value, report back. If they are barely more than that, report back. If there is a dead short (zero Ohms) or a break, or a few or more Ohms, the plug is bad. Like Larry said, if one is bad, you might as well replace them all, and keep the ones you think are good as emergency spares. I found the new ratcheting box end wrenches from Sears worked wonders for removing and replacing glow plugs as I just did one on my 1982 240D. No cut up hands and I got around the fuel delivery tubing. Good luck, Jim

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Own:
1986 Euro 190E 2.3-16 (291,000 miles),
1998 E300D TurboDiesel, 231,000 miles -purchased with 45,000,
1988 300E 5-speed 252,000 miles,
1983 240D 4-speed, purchased w/136,000, now with 222,000 miles.
2009 ML320CDI Bluetec, 89,000 miles

Owned:
1971 220D (250,000 miles plus, sold to father-in-law),
1975 240D (245,000 miles - died of body rot),
1991 350SD (176,560 miles, weakest Benz I have owned),
1999 C230 Sport (45,400 miles),
1982 240D (321,000 miles, put to sleep)

1982 300sd
very similar problem. It's in 20's here. My #2 glow plug was totally dead. Had to use block heater to get started. Changed front two glow plugs and she fires right up in 20degree weather without the block heater.

Just had my valves adjusted. It really makes a HUGE difference in cold weather and the engine idles better and runs smoother.

I took my multi meter, disconnected the relay for the plugs, put the ground to the chasis and started putting the red lead into the holes in the harness to the glow plug relay. Got the same ohm reading on every plug except #2. I got no reading. It was a dead one. Easy fix. But go to sears and buy a 8mm and a 12mm ratchet box end wrench first. 12mm for the plug and 8mm for the nut on the wire. Dont get an offset wrench, but a straight one. Then you can do the job without having to disconnect the injector lines and having to bleed the fuel system.

ok, a little progress today....i decided the digital multimeter i bought was crap, and didnt work....or im just too stupid to use it properly.....anyway, i went and got an analog multimeter a while ago....came back, filed off some paint on the chassis to ground, and took readings on each plug....plugs 1, 2, and 3 gave no reading at all....plugs 4 and 5 gave a reading of 5 ohms, both of them....not 0.5, but 5 ohms...im assuming that i need to replace all plugs and do a valve adjustment and go from there....whats sad, is the fact i can do all this myself, but i was in an accident last year and can only open my hood about halfway....now that i have to perform all this work, it means im going to have to pay someone to fix my hood for me....so, ill have to tow it to a body shop, and then tow it back, just to even think about working on it....and all a week before Christmas....hard to feel all warm and jolly without being able to drive my pride and joy ...

thanks again for the advice, this site would be crap if it werent for all you nice folks out there.....and if you have any plug changing tips for me, im all ears

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1985 300SD 192,000miles...Astral silver/ Grey MbTex

1983 300D 194,000miles...White/Tan MbTex...my newest addiction

well, i finally got to replace some glow plugs today....i only replaced two of them before i ran out of daylight, but that did the trick....the car started up just fine after i jumped it off, ran the battery down trying to crank it the other day....

i noticed something wierd though....before, and ever since ive had this car, the glow plug light in the dash would come on for about 2-3 seconds and then go out....ive never trusted this as proof my glow plugs were warmed, so i usually just wait about 15-20 seconds and then turn it over...but now, since i replaced two of the plugs, the light doesnt come on at all....even after its running.....what could make the light not come on at all after i replaced 2 plugs? should i go ahead and replace the other 3 and see if that does anything? or could there be something wrong with the relay?

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1985 300SD 192,000miles...Astral silver/ Grey MbTex

1983 300D 194,000miles...White/Tan MbTex...my newest addiction

Since you have confirmed that all five glow plugs were bad, providing any theories on why the light does not work with three remaining bad glow plugs would be a fruitless exercise.