No start after changing glow plugs and filters. (What did I knock off) - PeachParts Mercedes-Benz Forum

Judge · #1 04-15-2007, 03:37 PM

Ater changing the glow plugs and filters on a car that had sat for nine months the 1976 300D won't start. Likely I knocked a vacume or linkage off. What is likely?

Other observations. All the filters were very dirty. The loop glow plugs were intact, but harder than it seemed right to pull out after being unscrewed.

The clear small fuel filter has a air bubble in it after I installed it. That looks wrong.

As far as I can tell I reinstalled all the vacume lines, but I've only got the basic knowledge.

Thanks

#2 04-15-2007, 03:39 PM

Did you pump the primer?

Judge · #3 04-15-2007, 03:40 PM

Is something wrong to have air in that filter.

#4 04-15-2007, 03:41 PM

A single large bubble is normal.

Once you have primed the pump, it may take ~30 seconds of cranking to clear all the air out of the injection lines.

Judge · #5 04-16-2007, 11:28 PM

There seems to be some difference of opinions on what it necessary/ adviseable to open to help bleed the system. I didnt solve the problem yet

patbob · #6 04-18-2007, 08:25 PM

Quote:

Originally Posted by Judge

There seems to be some difference of opinions on what it necessary/ adviseable to open to help bleed the system. I didnt solve the problem yet

The manual primer pump is supposed to clear all the air out of the fuel system. I think the manual says pump it for a minute or so. But like Forced said, I don't think it can clear the air from the hard lines that run to each injector. Cranking the engine will do that.

You said it sat for 9 months. Did it start before you did this work? If not, then maybe you did everything right and something unrelated is wrong.

mespe · #7 04-18-2007, 10:06 PM

Check the continuity of the glow plugs, If memory serves correct, they are in series and the last one must be grounded,,, memory going back 20 years,,,,

Also when you pump the primer, can you see air bubbles moving in the fuel lines? (this verifies that the pump is pumping)

Do you have a block heater? have you tried using it?

And probably the reason your car wono't start,,, have you adjusted your valves?

Judge · #8 04-18-2007, 10:39 PM

While the car sat for 9 months, we started it, and I drove it about 80 miles. Starting it up about 10 times. A friend who sold it to me also gave me a set of glow plugs and filters that he had bought for it but never installed.

Since it smoked, I thought I would start with those items. And since the fuel had sat for several months, I thought it important to change the filters.

I believe that the valves had not been adjusted in many years. Like 5 to 7 years.

As to the ground after the glow plugs, the year of the car is a 1976. And according to the Chilton manual that was also given to me with the car, the glow plug and preheating system is different than any other year. As I tried to read the schematic this morning, I thought that the sensor cuts the ground connection when the engine is already hot(?)

After the last glow plug, rather than being grounded to the engine block, it is grounded to something that looks like an oversized temperature switch. A second wire come out of the "oversized temperature sensor" and goes back to the instrument panel according to the Chilton diagram, and seemingly a quick visual inspection.

Sorry for too much detail, but I've just bought the car, and I am afraid that I have turned it into a boat anchor.l

biobenz240d · #9 04-18-2007, 10:45 PM

my 300D won't start unless I press on the accelerator a little. Worth a try.

vstech · #10 04-18-2007, 11:20 PM

oooh, there was a thread on here a few weeks ago that talked about the difficulties of converting that system to the pencil plugs. THAT is what I would do. but it's unlikely that is what is causing the no start problems you are having.
I would open all the nuts on the hard lines going to each injector, and crank the motor over and over until fuel squirts clear without any bubbles escaping from the nuts.
did you fill the spin on filter with fuel before you put in on? it will take a LONG time to hand prime a dry spinon.
John

Judge · #11 04-19-2007, 01:15 AM

Yes, I forgot to fill the bigger fuel filter. . . I didn't know that it would be so serious of a mistake.

Tommorrow I'm going to take the advice of cracking the hard lines at each injector, and keep cranking until I see clear fuel passing. (Thanks, any more hints)

vstech · #12 04-19-2007, 01:09 PM

only other thing I can think of is to loosen the spin on top bolt, and pump the handle until fuel squirts out of the top.
John

Judge · #13 04-19-2007, 06:42 PM

Ahh.
We couldn't figure this thing out. I brought in a professional mechanic and also he brought someone with experience in auto electric, who also happens to own three mercedes diesels. Together we couldn't get it stated.

It is true I messed up by trying to start the engine without filling the fuel filter, but we thought that problem was fixed. We have made sure that the system is primed, fuel comes out of the top of the filter when it is cracked. And when cracking injector lines, the fuel is squirting.

Well tomorrow is another day, and the mechanic has a source for a real shop manual rather than my Chilton version. He will also calibrate the valves.

I am still looking for advice. Our conclusion is it should start, but it isn't.

barry123400 · #14 04-19-2007, 09:25 PM

Sounds like time to check out the glow plug circuit for it's funtion. I do not think the average engine will start usually from ambient temperature without them.

Judge · #15 04-19-2007, 11:08 PM

We've tried starting by bring positive directly to the first glow plug. (This is a 1976 300D, so the Glow plugs are in Series.) And the ground after the last glow plug is also working.

I agree that I must have messed up something, and since we have double checked that fuel is getting to the injectors, and that the glow plugs are on, I stretching to figure out what else I might have done wrong.