Hello All,

I bought this 81-300sd w/ 215K about two months ago for my wife...she loves it. It has always started immediately. I have changed the filters (air, oil, and spin-on fuel) right after I bought it.

Today, the engine turns over quickly and strongly, but nothing is firing. I checked the glowplug strip fuse and obvious vacuum hoses, and nothing. The fuel in the plastic filter seems clear and very little bubbles. I am running on regular diesel.

We had a wicked thunderstorm and about 5 inches of rain yesterday, if that would make a difference.

What could be the culprit? It started great just last night.

Thanks, Don...I will check back often for any follow up questions.

I left the wiper switch on overnight...could that have run down the battery just enough to make it slow on start? I did not think the wiper switch would do that, but... I don't know this car that well.

Thanks, Don

OK, I tried to jump it and it still want to fire... What is the next step?

Don

Is your glow plug light illuminating ? You need that to work or car wont start.Check your fuses,Johnny

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85 300sd SOLD ,85 745i,95 740i,1972 Suburban,1938 International

Johnny,

Thanks for the reply. The glowplug light is working as normal. None of the fuses are blown, but I am not sure what the relays are in the fuse area, as they are not marked. I may try taking out each fuse and cleaning them and the contacts.

Don

Is there any way you can put a meter on the glow plug to see if your getting voltage ? I think there is a relay for the glowplugs,it may not be working.does the glowplug light go out or des it stay on? Johnny

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85 300sd SOLD ,85 745i,95 740i,1972 Suburban,1938 International

Disconnect the Vacuum hose from the shutoff valve on the IP in case your ignition switch or shutoff valve on you IP is the problem, Have you verified their is fuel being sent to the cylinders.

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1979 300D.

dazsa,

2 to 3 seconds for the GP light to stay on is not normal. It should be on for about 10 seconds in warm weather or if the engine is warm and longer in cold weather.

As soon as U energize the starter, the GP shut off. So they may not have been on long enough to get red hot.

Try waiting longer for the GP to get hot before U turn the key to the start position.

P E H

Well, here is the latest:

The battery is giving the 12 volts, but the glow plug relay (with the key on) is not getting anything (unless I am testing it wrongly).

The "hot wires" at the power stage are only getting about 5 volts, so I am going to clean them, next.

hawthorne90250:

I just know that I have fuel to the fuel filters. I am not sure how to check if it is getting to the cylinders.

Don

My wife just told me when she got in this morning and it wouldn't start, the glowplug did NOT come on!

Does this mean that the glowplug relay is bad or something else???

Don

Don,

The way to tell if the injectors are getting fuel is to loosen the injection line nuts (located on top of the injectors) one at a time, have someone turn the key to crank the engine, and look for fuel leaking from around the nuts. Don't expect much fuel to leak out, or a high pressure spray but it will be visable if the IP is pumping fuel.

The dash GP light doesns't mean the GP are working or not working (unless it blinks after starting engine which means you have an open GP). The light is just a timer to tell U how long to wait before U cranking the engine. Often on older MB, the timer is out of calibration, usually showing too short of a time to wait for cranking.

Does the GP relay click when the key is initially turned to the run position? If it doesn't click, that is your problem. I don't know what U mean by the "hot wires at the power stage". If the relay clicks, check the voltage inside the GP relay at the fuse. U should get about 11.5 volts when the GP are working. Check both sides of the fuse. Same voltage: Fuse is OK. Different voltage: Fuse is NG. Sometimes the fuses get an invisable crack and don't conduct electrical current.

P E H

I vote for a glow plug problem. Turn on the dome light first, and then turn the key to pre-glow. The dome light should dim. The big strip fuse at the glow plug relay can look ok and still be bad. It is a 80 amp fuse.

Don't try to spin the engine over too much until you find out what the problem is, because you can load up the engine with raw fuel which will make starting even more difficult, and create a huge mushroom cloud of smoke to impress the neighbors when it does.

When the GP light doesn't turn on, it's supposed to indicate a burned out GP, BUT sometimes if you have 2 burned out GP's the system is 'tricked' and thinks everything is normal. You can check the GP's with an ohm meter, but this too can be tricked. Sometimes when the GP's get hot, they expand and the electrical connection is broken, preventing the GP from fully heating. This is usually the case when you try to remove the electrical wire from the GP and the whole thing turns.

If you plug your block heater in for a few hours the car is more likely to start if you have one or two burned out GP's.

Good luck.

Marty

www.benzbonz./biz

Ok, I tested the power to the GP Relay and it is at 12.49v and both sides of the fuse test the same. I get .8 ohm from each socket on the relay and
12.49v when I switch on the key and quickly test the relay. I get .8 ohm at each GP.

What now...?

I changed out the plastic fuel filter and there was a sucking noise from the fuel line. I primed the plastic filter and fuel has filled the filter and the fuel looked clear and clean.

I will loosen the injector lines to see if I getting fuel. What is going on if the fule is not getting there?

I am really getting frustrated because everything I check out works.

Should I change the GPs anyway?

Don

Here is how to test the glow plug circuit.

http://dieselgiant.com/glowplugrepair.htm

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1981 300D 147k
1998 VW Jetta Tdi 320k
2001 Dodge Ram 2500 141k
1979 300D 234k (sold)
1984 300D "Astor" 262k(sold)
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