77 300d wont start - PeachParts Mercedes-Benz Forum

mulchman · #1 04-10-2011, 03:32 PM

I just bought this car, I replaced the glow plugs thinkin that was the problem but still won't start. The glow plug light dosent come on when I turn the key so I'm thinking it might be the relay, does anyone know where it is located or have any clue what could be wrong?

leathermang · #2 04-10-2011, 03:40 PM

Did you drive it home and now it will not start ?
How long have you had it ?
Did the glow plug light come on when you bought the car ?

kerry · #3 04-10-2011, 03:47 PM

First thing I would check would be the strip fuse, on the firewall where the wire to the back glow plug attaches. You should have a series glow pulg system in that car unless someone converted it. Is the ground wire going from the front glowplug to the block attached?

cirrusman · #4 04-10-2011, 04:00 PM

Was the car towed home or it just stopped working? A diesel engine needs 3 things to work: Air, fuel and compression. Temperature is a factor, but since you're in TX, it's not likely an issue. If any of these 3 is lacking the car won't start.
Fuel: Is fuel reaching the engine? Are there any obstructions between the tank and the engine? Is the Injection Pump (referred in this forum as IP) working and delivering the fuel?
Air: Is your filter clean? Any obstructions between the air filter assembly and the pistons?
Compression: If you have the capability you can test the cylinder compression or have a professional do it. Since diesels don't use spark plugs, they rely on engine compression to work.
If you have more details about the car, maybe you will get more detailed help, but hope this helps a bit.

leathermang · #5 04-10-2011, 04:04 PM

OP was online a while.. but looks like he did not refresh his screen ...to see if he had replies...

mulchman · #6 04-10-2011, 04:14 PM

I trailered it back. And it wouldn't start up when i bought it. The piece of wire on the fire wall is not broke

kerry · #7 04-10-2011, 04:17 PM

Quote:

Originally Posted by mulchman

I trailered it back. And it wouldn't start up when i bought it. The piece of wire on the fire wall is not broke

I wasn't referring to the piece of wire. I was referring to the 80 amp strip fuse which is in the little plastic box that that wire attaches to.

leathermang · #8 04-10-2011, 04:20 PM

I suggest that you do a compression test.. or a leak down test..
this will tell you a lot about the condition of the engine...

I am only 80 miles from you...so I know we are warming enough that it should have started without the glow plugs working at all...
The battery, wires, etc all good and clean ?

kerry · #9 04-10-2011, 05:16 PM

Personally I wouldn't bother with any other tests until you get the glowplugs working. Can you confirm they are the series glowplugs with the heavy squiggly wires with insulators at the plugs?

leathermang · #10 04-10-2011, 05:25 PM

Quote:

Originally Posted by kerry

Personally I wouldn't bother with any other tests until you get the glowplugs working. Can you confirm they are the series glowplugs with the heavy squiggly wires with insulators at the plugs?

You are in the NORTH... two days ago it was 97 here.... it should start above 80 without glowplugs... if not.. that tells you something about the engine also...

kerry · #11 04-10-2011, 05:28 PM

Quote:

Originally Posted by leathermang

You are in the NORTH... two days ago it was 97 here.... it should start above 80 without glowplugs... if not.. that tells you something about the engine also...

I agree. It should start but it isn't. If he wants to get it running, fixing the glowplugs may very well get it running even if it has low compression or some other problem. Knowing it has low compression isn't helpful unless he knows whether it is going to run or not. Without the glowplugs, he can't tell.

leathermang · #12 04-10-2011, 05:33 PM

Quote:

Originally Posted by kerry

I agree. It should start but it isn't. If he wants to get it running, fixing the glowplugs may very well get it running even if it has low compression or some other problem. Knowing it has low compression isn't helpful unless he knows whether it is going to run or not. Without the glowplugs, he can't tell.

If we know it is not failing to start due to cold... then why would we not go for something like fuel or compression first ?
I say a 3-5 second shot of starter spray into the air cleaner inlet while the starter is cranking is the next logical cheap fast thing to try...
and NO, it does not have enough btu's to hurt the engine or wash the cylinder walls ( it is gas not liquid )....

This may show that fuel is the problem...

mulchman · #13 04-10-2011, 06:15 PM

Quote:

Originally Posted by kerry

Personally I wouldn't bother with any other tests until you get the glowplugs working. Can you confirm they are the series glowplugs with the heavy squiggly wires with insulators at the plugs?

Yes it is the old style glow plugs, this is my 1st 77 model I'm use to the 80s diesels

mulchman · #14 04-10-2011, 06:20 PM

Where's the gp relay on this car

kerry · #15 04-10-2011, 06:44 PM

It's above the driver's kick panel. Did you check the strip fuse on the firewall. It's a common failure point on that system. The strip fuse is not in the relay like the pencil plug systems.