1981 300GD I need help in getting this to start - PeachParts Mercedes-Benz Forum

RussK · #1 12-16-2014, 10:35 PM

I just acquired a 1981 300GD, I need help in getting this to start, it sat for 10 years , so let me start at the beginning.
The primer pump was the old plastic type, it wouldn't pump up, and was leaking very bad, so I replaced it ( new style) and the fuel filters.
It still wouldn't start, I got 7-8 psi from the mechanical lift pump, BUT only when blocking the line.
when priming it builds pressure, and you can hear the regulator hiss when you reach its limit.
But the pressure falls back to 0 psi real quickly (3-5 SEC), and the lift pump cant build enough pressure when its turning over trying to star it.
you can pinch the feed line to the pump, or return line, or both at same time and it still looses pressure.
Any help would be greatly appreciated.

vstech · #2 12-16-2014, 11:39 PM

After priming you need to bleed the injection lines at the injectors. Crack the line nuts loose and crank the motor until fuel seeps out of all 5 air free.

RussK · #3 12-17-2014, 09:10 AM

Quote:

Originally Posted by vstech

After priming you need to bleed the injection lines at the injectors. Crack the line nuts loose and crank the motor until fuel seeps out of all 5 air free.

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Thanks for the help, I got fuel from #1-4 cylinders , none from #5 yet. how long should it take to get them to bleed?
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Also when I prime it, should the pressure drop back down? or should it hold pressure?

vstech · #4 12-17-2014, 09:31 AM

I don't know on the pressure, but I'd think it would drop down.
since you have fuel to 1-4, close them, and keep cranking... the motor will likely start though, so be ready to tighten it when the fuel starts spraying!

RussK · #5 12-17-2014, 09:58 AM

Quote:

Originally Posted by vstech

I don't know on the pressure, but I'd think it would drop down.
since you have fuel to 1-4, close them, and keep cranking... the motor will likely start though, so be ready to tighten it when the fuel starts spraying!

Again thanks for your help

Its still a no start, I had already checked the glow plugs circuit and checked the ohms on the glow plugs and they were all close to one another. what is the ohms reading they should be at?

PS I'm in Atlanta now, but from Murphy NC. But that's a long time ago

vstech · #6 12-17-2014, 10:28 AM

glows should pull around .7 ohms... but it's hard to tell from a ohm reading if they are the problem.

how fast is the starter spinning the motor?

do you have a block heater? is the air filter clean? did you get fuel to all 5 injectors?

let the battery fully charge, and the starter fully cool down, then try again. keep the motor plugged in if you can, or shove a hair dryer into the intake if you can't.

RussK · #7 12-17-2014, 10:43 AM

Quote:

Originally Posted by vstech

glows should pull around .7 ohms... but it's hard to tell from a ohm reading if they are the problem.
how fast is the starter spinning the motor?
do you have a block heater? is the air filter clean? did you get fuel to all 5 injectors?
let the battery fully charge, and the starter fully cool down, then try again. keep the motor plugged in if you can, or shove a hair dryer into the intake if you can't.

Letting battery charge back up right now, I removed one glow plug, and it lights up as it should, so no problem there.
Still haven't got fuel to # 5 yet, but keeping a eye so I can tighten it up when needed.
No block heater, that I know of, but I will double check
Didn't think about hair drier, that's a good idea will try it
and let you know how it goes.
This thing has only 76k on it but it did set for a long time.
Thanks again.

RussK · #8 12-17-2014, 04:14 PM

Tried to start it with a hair drier, still nothing, still no fluid from #5 line.
It did start and started to rev yesterday, I panicked and killed the key scared of a runaway, maybe something in the IP bad?

uberwasser · #9 12-17-2014, 05:32 PM

If you were able to kill it with the key it isn't a runaway. Check around to see that the accelerator linkages are all free to move. Something may be stuck.

RussK · #10 12-17-2014, 05:43 PM

Quote:

Originally Posted by uberwasser

If you were able to kill it with the key it isn't a runaway. Check around to see that the accelerator linkages are all free to move. Something may be stuck.

I had read that that was the most common issue with a high rev, runaway, I checked the linkage and all is good and free, I just panicked a little.
It did let me know that the motor is good, but I still doubtful on the IP.
Still cant get fuel on #5, I haven't looked for a remanufactured unit yet.
I hope that I don't need one.
Thanks for the help, it greatly appreciated. RussK

RussK · #11 12-17-2014, 07:47 PM

UPDATE;
I started from the beginning, to double check myself, make sure I didn't miss anything, and to try to keep from spending more money than I have.
So here it is,
primer and lift pump is working, I dead headed it, and it held pressure and I stopped turning it over when it quickly pumped up to 15PSI , and it had positively no leak down.
Removed filter housing bolt and checked o-ring and it was good.
The stop lever works with the key, which I assume is correct.

I cracked all the lines to the injectors and started thinking , I'm seeing fuel on cyl # 1-4 and never got it to #5 , also the amount of fuel getting to the injectors is a very small amount, with lines loose,(I'm talking VERY LOOSE) how much fuel should be coming out and at what pressure when cranking?
How much does it take to get past the poppet style injectors?
again I appreciate all the help I can get.

vstech · #12 12-17-2014, 07:58 PM

The volume of fuel is very slight during cranking, the pressure when closed will eclipse 2100psi.
Have you closed all injector lines?

engatwork · #13 12-17-2014, 08:30 PM

You really need to sell it to me and don't sink anymore $$ into it

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If you are getting fuel to 4 cylinders it should run. Disassemble throttle linkage and lube everything up real good. Also, go ahead and plan on adjusting the valves. I'm not so sure I would not go ahead and change all the fuel lines around the fuel injection pump and the filters too.

Let me know and get it down here if I can help you with it.

RussK · #14 12-18-2014, 09:00 AM

I lubed the linkage, already changed filters and fuel lines.
It almost started, just kind of chugged on a couple cylinders.
When I'm trying to start this , is it better to apply some fuel? I'm talking accelerator, not adding either or nothing. I thank you all for the help I am receving.

engatwork · #15 12-18-2014, 09:58 AM

Yes, press on the gas pedal during attempt to start.