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Old 09-28-2001, 10:05 PM
rushman53
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Unhappy no fire

Ok, I'm new to the Mercedes forum, but I need some advice. I bought a 78, 300 D about 3 weeks ago.. It ran great, but the guy did say it needed glow plugs and a battery. (As he had to use starter fluid to get it to start, it sounded reasonable to me) After it was started once in the morning, it would start by itself for the rest of the day. It seemed to be a little slow accelerating, but we weren't looking for speed anyway!
That was 3 weeks ago. A couple of days ago, we tried to start the car, but while it would turn over, it wouldn't fire. We figured the glow plugs had finally given up( the glow plug light on the dash started working occasionally and then not at all) So we replaced the glow plugs and battery-still no glow plug light on the dash and no fire
Now we are looking at the glow plug time relay. Is there anyway to test it without paying 100 plus to get a new part that I might not need? Any thoughts as to anything else I should check? Can glow plugs be tested one at a time? Maybe one or all of the new plugs are defective?
It does try to start- in fact with the new battery, it almost starts without the glow plugs. The plugs seems to be getting some electricity,but they don't seem to be heating. Could there be a ground problem?
It is getting fuel to all the injectors and we changed all the fuel lines for the injectors as they were slightly cracked.
We really love the car and would like to get it back on the road.
thanks

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Old 09-29-2001, 01:10 AM
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Join Date: May 2001
Location: Florida
Posts: 1,105
have you checked the 80amp fuse? sometimes these get hairline cracks in them and work intermitantly. Also, try turning the key to the "glow light" position two, and count to 20 with the key in position two. Sometimes my glow light doesn't come on with my 83 300SD, and i count to ten and it fires right up. I would also be VERY, VERY carefull using starting fluid with a diesel. I have heard heads can be blown off of them by starting them with this.
Ryan
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Old 09-29-2001, 01:56 PM
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Join Date: Aug 2001
Location: Evansville, Indiana
Posts: 8,150
Ron:

DO NOT use starting fluid on these engines -- they pre-ignite terribly, can ruin the starter, break down the ring lands, etc -- basically ruin the engine. Please don't!

You can check the glow plugs several ways. The best way is to use a voltmeter and check for voltage at each glowplug -- the voltage should drop at each plug and the resistor links (the wavy ones). The thermo timer (big plug in the head near #1 glowplug) can also go bad, in which case no electricity goes through the glowplugs even though they show voltage. Check for voltage on both sides of the thermo timer before comdeming the relay.

The resistor links will get red hot if you leave the key on and the system is working even if the light on the dash doesn't come on.

These engines simply will not start cold unless the glow plugs are on. They will start, somewhat reluctantly, if warm and the glow plugs don't work. If it does, then your compression is OK.

Just to test -- I don't recommend this for regular operation -- you can get a set of large wires with aligator clips on them and connect the glow plugs directly to the battery -- remove the wire at the rear plug and the wire at the front plug from the thermo timer, and connect the wires to the battery, positive in back, negative in front (or just to a good ground). Use heavy wire, or the insulatio will melt -- they draw upwards of 50 amps! If the car starts well, you have a relay or thermo timer problem (or a bad wire). If the resistor links get red hot and it still won't start, you have other problems.

To get good acceleration out of this car, you need to really mash down on the accelerator pedal and close the kickdown switch -- otherwise it starts off in second gear! Winds up like crazy, but that is all right -- redline is 5000 rpm!

Peter

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1988 300E 200,012
1987 300D Turbo killed 9/25/07, 275,000 miles
1985 Volvo 740 GLE Turobodiesel 218,000
1972 280 SE 4.5 165, 000 - It runs!
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