Did Lots of Work, Now 300CD Won't Start!? - PeachParts Mercedes-Benz Forum

GoldenEagle · #1 12-10-2016, 06:47 PM

1983 300CD 225k miles

I started a couple threads a week or so ago about this car. I'd recently purchased it and discovered it had a shop rag wrapped around the cam under the oil fill cap. It was running and starting fine at the time but I decided to tear into it to get as much of the rag cleaned out as I could. While I had it apart I did a bunch of other work and now that it is back together it just cranks and cranks but will not start. I did the following work:

1. Replaced battery

2. Replaced all v-belts

3. Replaced temperature sensor near glow plugs (dash gauge was not working)

4. Dropped oil pan, cleaned out all of the shop rag remnants, replaced the rubber grommet and mesh screen on the oil pickup, replaced oil pan gasket, new oil and oil filter.

5. Set valve adjustments and replaced valve cover gasket.

6. I discovered that the guts of the vacuum pump valve (screws directly into the top of the vacuum pump and connects to the line that goes to the brake booster) were missing. I am still waiting for the replacement valve to arrive, but I reinstalled the bad valve just to try to get the car started. Would this cause the car not to start?

7. New fuel filters (I made sure to fill the primary screw on filter with fuel before installing).

8. Replaced some of the short vacuum line connectors that were obviously bad.

9. General cleanup/flush-out of vacuum lines, banjo bolts, fuel lines, etc.

Again, this car was starting and running fine before I took it off the road to get the rag issue cleaned up. I feel pretty confident that it is getting fuel because several of the injectors are weeping fuel (another issue I need to address) as they were before I did all the work. I also feel fairly confident that the glow plugs are working (I did not pull all of them out, but I checked the resistances of each plug circuit and voltages going to each plug and everything seemed fine).

I have not done a compression test, but again this car was running fine before I did the work.

Any suggestions? Thanks.

kerry · #2 12-10-2016, 06:56 PM

Pull the brown line from the shut off valve just to make sure there's not a vacuum on it causing the no-start. Am I correct that you have confirmed voltage to the plugs with the key in the glow position?

GoldenEagle · #3 12-10-2016, 07:15 PM

I can try pulling the brown line off but I don't think that's it because I'm getting fuel at the injectors.

You are correct that I checked voltages at the plugs in the glow position.

disqo · #4 12-10-2016, 07:15 PM

Sometimes after having the fuel system open I will leave the injector lines loosely connected at the injectors while I crank to get the air out. I tighten each one once fuel starts coming out.

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BWhitmore · #5 12-10-2016, 07:41 PM

The brown line going to the shut off valve has nothing to do with fuel. Locate the shut off valve (it is connected to the STOP lever) and disconnect the brown vacuum line from the valve. Try to start the car. The absence of a check valve in the vacuum pump will not prevent the engine from starting, but it will prevent you from having vacuum to shut down the engine and also operate other vacuum operated device (power brakes, door locks, EGR valve, transmission shifting, air conditioning). After replacing the fuel filters do you use the primer pump to ensure that the filters were full of fuel and not air?

Dan Stokes · #6 12-10-2016, 07:59 PM

I'm thinking Bill is on the right track. When I replace the fuel pump on Mutt (I've done that a couple of times) I fill the filter and do all the tricks I can think of (lots of pre-glow, etc.) but it never starts afterward. The first time I have to start it with starting fluid (I know, I hate doing that, too) and keep it running with an occasional squirt until it idles - usually about 30 seconds or so though it feels like an eternity. Once running it's fine from then on - it's just that first start-up. Bottom line - you do what you have to do.

When I do the starting fluid starts it's in neutral and I never rev it or anything until the engine is running on it's own - in other words I do everything I can to keep the load at a minimum until it's running on fuel.

Dan

sixto · #7 12-10-2016, 08:39 PM

Based on that list, it has to be air in the fuel system (I do as disqo does) or a terribly botched a valve adjustment. Filing the fuel filter doesn't mean you don't have to prime the fuel system, it just means the priming process has less to do to the fuel filter.

Sixto
83 300SD

dkr · #8 12-11-2016, 12:58 AM

It's kind of strange the way you are listing it.

Generally, when you do a valve adjustment you would turn the engine on at least to make sure nothing is leaking oil.

Likewise, when you change fuel filters or mess with the fuel system, you would turn the engine on to make sure there is no air in the system.

Did you just do each one of the steps listed and then try to turn the engine on and see it does not work?

I think it is probably an air in fuel lines issue. Does your battery have 12.6V before starting?

Dkr.

888 · #9 12-11-2016, 07:17 AM

I have to go with air in the fuel system as well, if you aren't even getting a sputter of combustion while cranking. The first time I did a head gasket on a diesel VW Rabbit I about killed the starter before I realized I needed to crack open the injectors at the head. I know they are weeping but it sure sounds like air in the fuel to me, I wouldn't rest on that one till all of them are showing fuel at the injector by opening them a little.

I also realized the battery has to be at 12.6 V or higher to get it spinning fast enough to start so check on that as noted above.

If it's cold where you are, that's not helping.

I just changed both filters on my 300D, prefilling both as best I could and using the primer pump till I had air/fuel leaking at the nut on top of the main filter housing. It took maybe three tries and on the third I had the characteristic sputter to a start I remember from my VW TDI and NA engines as the cylinders all got fuel and decided to get on board. Until you get 2 or 3 of them sputtering at full speed, I don't think it's going to start.

oldsinner111 · #10 12-11-2016, 07:46 AM

I know on my diesel the plug to the coolant sensor was broken inside.I had to solder new wire on it.It would not allow glow plugs to turn on.

t walgamuth · #11 12-11-2016, 09:32 AM

Quote:

Originally Posted by Dan Stokes

I'm thinking Bill is on the right track. When I replace the fuel pump on Mutt (I've done that a couple of times) I fill the filter and do all the tricks I can think of (lots of pre-glow, etc.) but it never starts afterward. The first time I have to start it with starting fluid (I know, I hate doing that, too) and keep it running with an occasional squirt until it idles - usually about 30 seconds or so though it feels like an eternity. Once running it's fine from then on - it's just that first start-up. Bottom line - you do what you have to do.

When I do the starting fluid starts it's in neutral and I never rev it or anything until the engine is running on it's own - in other words I do everything I can to keep the load at a minimum until it's running on fuel.

Dan

If I have a problem getting the air out of the lines I use wd40. Spray it directly into the intake (not through the filter) and the diesel will run fine on it until the air is bled out. It takes two people but does not risk your engine.

funola · #12 12-11-2016, 11:19 AM

Quote:

Originally Posted by t walgamuth

If I have a problem getting the air out of the lines I use wd40. Spray it directly into the intake (not through the filter) and the diesel will run fine on it until the air is bled out. It takes two people but does not risk your engine.

+1, never use starting fluid unless your life depended on it. Don't forget, WD40 also requires a healthy battery and starter to gives you enough cranking time and RPM to get the engine started.

If one is in the dead of winter in a remote area where no help is near, no passing cars for hours, battery is weak and cranking slow, then starting fluid use is justified in that situation.

GoldenEagle · #13 12-11-2016, 11:47 AM

Thanks everyone! I will definitely try to crack the lines open today to release any trapped air and see what it does. That is, if I can fight my way through this heavy snow we are getting in northern Indiana!

ROLLGUY · #14 12-11-2016, 12:39 PM

Quote:

Originally Posted by funola

+1, never use starting fluid unless your life depended on it. Don't forget, WD40 also requires a healthy battery and starter to gives you enough cranking time and RPM to get the engine started.

If one is in the dead of winter in a remote area where no help is near, no passing cars for hours, battery is weak and cranking slow, then starting fluid use is justified in that situation.

+2 and I would add that the glow plugs need to have NO power going to them while starting fluid is used.