W115 - Will she start? - PeachParts Mercedes-Benz Forum

1975300D · #1 08-06-2011, 07:48 AM

HI Everybody, I'm new here and hoping to get some help to save me some money.

I just took possession of my father's 1975 300D. The car has been stored indoors for the last 5 years.

I installed a new battery, put new fuel in the car, pressed the primer button many times, but she won't start.

I unscrewed the nuts on the fuel lines from the injector pump to bleed out any air that might be there and to see if fuel is flowing. There is fuel coming out of 4 of the fuel lines. The first fuel line however produces nothing it appears. Also, I noticed that the glow plug for the first cylinder gets hot, but the others are cold. Should they all be getting hot?

I know nothing about diesel engines and would love to get this thing to start.

Any suggestions?

Thanks so much.

04 Diesel · #2 08-06-2011, 08:13 AM

Get all new glow plugs, if the glow plugs are not working the car wont start.

nhdoc · #3 08-06-2011, 08:28 AM

Are you following the correct starting procedure? Does the glow plug light come on and then go out? That model is the first with the "automatic" GP system (relay operated). Yours might not be working. While not impossible to start with dead GPs it will take a lot of cranking to build up heat and it would help if the valves were properly adjusted to maximize compression.

1975300D · #4 08-06-2011, 08:34 AM

Thanks guys, I will change the glow plugs. Hopefully it is that simple.

Yes, I am waiting for the light to go out before cranking the engine.

The glow plugs seem to be connected to each other by a metal wire. The first one closest to the rad gets hot, but all the others remain cold. Does that metal rod carry electricity to each of them?

kerry · #5 08-06-2011, 09:01 AM

Something is odd if only one of those plugs is getting hot. Those are series plugs as opposed to parallel plugs (if they are original equipment--do they have heavy squiggly wires between them?). If one plug fails, they all should fail. If the front plug is getting hot, then it would seem there is a problem in the wiring system which is causing power to be delivered to the front plug but none of the others. You'll need to troubleshoot the wiring. I would remove the wire to the first plug at the firewall, remove the ground wire from the plug near the radiator and ohm out the circuit thru the plugs from 1-5. There should be continuity thru all the plugs.
Your starting problems are most likely caused by this issue in the glowplugs. Don't do any more to the fuel system until you are sure all the glowplugs are working.

FinnJohn · #6 08-06-2011, 10:05 AM

If you're replacing the glow plugs anyway, you might want to consider going to the pencil-type plugs. The change they make in cold starting of these cars is nothing short of revolutionary.

Not sure if they work with OEM glow-plug relays on the 115s. When I changed mine out, I installed a different glow-plug relay, which adds to the cost. I think I ended up dropping about $150 on everything, but it made the car much more livable. Instead of 120 to 180 seconds of glow time, I'm up and running after 10.

Cheers!

--Finn

Palangi · #7 08-06-2011, 10:39 AM

Quote:

Originally Posted by kerry

Something is odd if only one of those plugs is getting hot. Those are series plugs as opposed to parallel plugs (if they are original equipment--do they have heavy squiggly wires between them?). If one plug fails, they all should fail. If the front plug is getting hot, then it would seem there is a problem in the wiring system which is causing power to be delivered to the front plug but none of the others. You'll need to troubleshoot the wiring. I would remove the wire to the first plug at the firewall, remove the ground wire from the plug near the radiator and ohm out the circuit thru the plugs from 1-5. There should be continuity thru all the plugs.
Your starting problems are most likely caused by this issue in the glowplugs. Don't do any more to the fuel system until you are sure all the glowplugs are working.

X2

IF only one plug in a series wired string is getting hot, something is wrong with the wiring. It seem very odd that the front plug, which is the last one in the string, is the one getting hot. That does not make any sense at all. I wonder if it is just the ground wire that is actually getting hot?

One thing that this forum seriously lacks, even after all these years, is an illustrated troubleshooting DIY on the two types of series glow plug setups. If I still had my old 240D, I could take some pictures and put one together, but, unfortunately, Nellybelle is no longer with us.

1975300D · #8 08-06-2011, 01:42 PM

Okay, so if there is no continuity through the plugs, then that means the plugs are bad? But why would power be getting to the last plug in the series?

Where is this relay you guys mention?

Thanks!

barry123400 · #9 08-06-2011, 01:57 PM

Slow down a little. The older loop type plugs are wired and function exactly like old fashion christmas tree lights. If there is a problem with any one of them it will affect all of them in some fashion. Not very probable that they are all bad. Try the site archives for directions or get a friend that understands this better.

1975300D · #10 08-06-2011, 02:08 PM

Right, but since the last one in the series is getting hot, then it would indicate that there is no continuity problem if the circuit starts at the firewall. I'm trying to avoid having to pay for a tow to a diesel mechanic, who, upon seeing the tow truck, will know he has a captive audience.

Palangi · #11 08-06-2011, 02:14 PM

I have no idea where the gp relay is on a 115 300D, probably under dash somewhere, but, if you're getting voltage anywhere on that circuit, it means the relay is working.

Each glow plug should have a wire on the input side, and a wire on the output side. There is an insulator on the threaded shaft of the gp to separate the two. Often where people go wrong is, they get both wires on the same side of the insulator, thus bypassing that plug. Or else they manage to create a short somehow.

Starting on the rear plug, see if you have voltage on the shaft of the gp. Doesn't matter too much exactly how much voltage. Let's say maybe 9 or 10 volts. (Measured when the gp light is on. of course). If yes, measure voltage on the wire between the 4th and 5th plug. Should be a volt or 2 less. Then measure on the wire between the 3rd and 4th plugs. Again, it should be a volt or two less than beetween 4 and 5. Keep moving down the line towards the front. Wherever the voltage disappears, or, is not lower than the previous plug is where the problem is. When you get to gp #1, there should be about 2 volts or less on the input side, and close to zero on the output side, as that is a ground wire.

Again, a reminder that voltage measurements must be made when the gp light is on, which means you only have 15 seconds or so for each measurement.

Test and report back.

Palangi · #12 08-06-2011, 02:15 PM

Where are you located? Maybe there is someone nearby who can help...

1975300D · #13 08-06-2011, 02:53 PM

Thanks Palangi, I will do what you recommend.

Is it possible for the current to flow the other way and this is why there is heat at the last plug?

In the '80s, the car was hit with lightning and the electrical system was knocked out. I remember my father telling me he got the car working again after rigging up some kind of bypass. I don't know what he meant. I'm just wondering if what he did caused the current to run in the opposite direction and it is really the last plug that is the problem.

I'm in Aurora, north of Toronto.

Palangi · #14 08-06-2011, 03:11 PM

Quote:

Originally Posted by 1975300D

Thanks Palangi, I will do what you recommend.

Is it possible for the current to flow the other way and this is why there is heat at the last plug?

In the '80s, the car was hit with lightning and the electrical system was knocked out. I remember my father telling me he got the car working again after rigging up some kind of bypass. I don't know what he meant. I'm just wondering if what he did caused the current to run in the opposite direction and it is really the last plug that is the problem.

I'm in Aurora, north of Toronto.

That's interesting. I suppose it's possible that after the mishap, someone may have wired it from the other end. The circuit has to have a voltage source on one end and a ground on the other end. As far a the circuit goes, it really doesn't care one way or the other.

At this point, you don't need a diesel mechanic, in fact, he may do more harm than good. What you need is someone who understands simple DC circuits and has a bit of common sense.

1975300D · #15 08-06-2011, 07:41 PM

Well, I took a look at the problem this afternoon, and yep, there is no continuity anywhere between the 5 plugs. And the reason was clear to see.

Corrosion. The wires that connect the plugs to each other were corroded, and the plugs themselves were corroded where the leads attach. The retaining nuts were corroded. One was so bad it took the threaded shaft of the plug with it. I've included a couple photos of the worst offenders.

So I removed all the plugs and will install new ones. I assume the porcelain spacers come with the new plugs?

Thanks for all the help up to this point!

Mark