'79 300D won't start - PeachParts Mercedes-Benz Forum

clarknova · #1 09-27-2003, 03:55 PM

So I began this adventure by replacing the primary and inline fuel filters, cleaning the injectors, replacing the seal washers and return hoses and charged the battery.
I attempted to run some Diesel Purge through it directly, but she just won't fire up.
When I crank the engine she'll cough but won't actually fire and run.
Suggestions?

#2 09-27-2003, 04:40 PM

After cleaning the injectors there is likely not any fuel in the injection lines or filters. Crank it while holding the throttle at 50%.

clarknova · #3 09-27-2003, 05:22 PM

I've primed the pump several times and cranked her about a dozen times after that but still no luck.
The other bit I noticed is the idle adjust on the dash doesn't appear to be hooked up. Would this have any adverse effect?
Also, there is a two inch round can thingy (looks sort of like an EGR) on top of the injection pump that has a barb for a vacuum line? that isn't connected. The PO said it was part of the governor, not sure if that has anything to do with it.

P.E.Haiges · #4 09-27-2003, 10:21 PM

Clarknova,

Idle speed adjustment won't affect starting. Later model didn't have the idle speed adjuster and they all started.

Pump the hand pump rapidly 30 times and then try starting. If that doesn't work, try pumping it 50 times more and try starting.

If that doesn't work, let me know.

P E H

unkl300d · #5 09-28-2003, 01:13 AM

Isn't that thing ontop of the injection pump important?
If it does not work correctly, the car can't be turned off with the key. If it is installed incorrectly, the engine can run off on you and tach out........maybe you should plug it in.

#6 09-28-2003, 01:33 AM

That should be the aneroid compensator(ALDA), it adjusts the fuel injection based on altitude (Atmosphere pressure). It should not be a source of problems on a NA engine like it can on turbo models.

#7 09-29-2003, 03:09 PM

On the 79 non turbo there is a metal tube that angles out from the ALDA. It looks like a vac line should be attached to it. If you pull a vacuum on it with the engine running it will shut the engine off. I tried for some time to find the function of that but I have never been able to find anything.
Just forget about it. It is on all of those early diesels and never have seen anything usefull hooked up to it.

Lycoming-8 · #8 09-30-2003, 01:35 AM

So what does the ALDA on a non-turbo 300D actually do? I was surprised to find what looks like one on the IP of an '80 300D parts car I have. It is, however, slightly different in appearance from the one on the '83.

Fisherman · #9 09-30-2003, 10:50 AM

There is a very real chance that the compression on this engine is a little low and as such if it has been siting it will not build much compression anymore since the scylinder walls are washed clean of oil.
I have on occasion shot a few pumps of either atf or 30 wt into the cyllinders and let it sit over night to help build compression.

The other item not mentioned is the glow plug system. If this system is not working then it will be hard to start your car if for some reasont eh starter does not spin as fast as it used to or the cylinders are a little low on comrpession. Make sure the glow system is working correctly and if needed try to build the compression via a little oil/atf in the cylinders...

This has always worked for me.

p.s. The alda is a spring loaded device that in theory reacts to atmospheric pressure and adjusts the rack on the IP to compensate for more or less air pressure/density. There should not be a hose on the alda on the older cars that I know of.

Stevo · #10 09-30-2003, 11:28 AM

clarknova

When it sounds like in MAY start keep the starter cranking, do not let up. Of course you dont want to over heat the starter motor (check it by touch), but if it sounds like she wants to start that means at least one cylinder is firing and the others should kick in as the air leaves the system.

clarknova · #11 09-30-2003, 12:38 PM

Ok, so there is no missing hose to the ALDA?
good, that clears that up.
She started running yesterday, but wouldn't stay running. I think it's just bad fuel in the lines (drained the tank almost dry and refilled with good diesel, just haven't circulated the last of the old stuff out of the IP and lines). That 50% throttle on cranking brought her to life on the purge.
Thanks again for all the great advice, this is my first MB and this forum is an incredible help.

Lycoming-8 · #12 10-01-2003, 10:20 PM

Based on the previous responses, "The alda is a spring loaded device that in theory reacts to atmospheric pressure and adjusts the rack on the IP to compensate for more or less air pressure / density." and "If you pull a vacuum on the alda with the engine running it will shut the engine off. "

It seems that if you go from Oklahoma to Denver a N/A 300D will really suffer a performance hit because the ALDA is going to be reducing the fuel charge because the air is less dense at 5200ft. How does this help, my 190D and 220D already had this problem withoout benefit of the ALDA?!?

P.E.Haiges · #13 10-02-2003, 09:27 AM

Lycoming-8,

THe alda will keep a Diesel engine from spewing black smoke at high altitudes because without it the mixture it too rich for the thinner air.

I had my 240D in the Smoky Mountains and it smoked like crazy. But my 300SD has been thru the Rocky Mtns. many times and it never smokes more than at low altitudes. With the turbocharger on the 300SD, there is little power loss at altitude except at less than 2500 RPM when the turbo is not as effective.

P E H

#14 10-02-2003, 11:38 AM

On the 300D NA engine I tore down, the alda had an "adjusting screw" on the top of it. Could this be adjusted to help in high altitudes like it can help a turbo model?

clarknova · #15 10-02-2003, 02:27 PM

Here's what's transpired so far...
'79 300D NA
Was running about a month ago.
Stopped running and sat for a few weeeks.
Compression is good on four of five (#3 is low but always has been).
Injectors cleaned and washers replaced.
New return hoses.
Old fuel drained and refilled with fresh diesel and treatment.
Inline and primary fuel filters replaced.
Fuel lines purged of air (old screw type pump, weeps a little when using but otherwise seems OK, considering getting a new type).
Tested glo-plugs, getting power and heat on pre-glow but not hearing the relay (will test tonite).
After many attempts she fired up on a jar of LubroMoly and ran briefly with 50% accelerator, but wouldn't stay running.

HELP - I'm sure I'm just missing something obvious, but it won't start and is getting frustrating. It's been cold and foggy lately, so that isn't helping either.