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  #1  
Old 09-15-2013, 12:11 AM
Fulcrum525's Avatar
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617 Gwagen low on power...

OK bit of a stumper here....

I drove another 300GD cabrio a few weeks back and realized that I have been down on power since I bought the truck (I never had a basis of comparison so I never realized)

In order to check the tank strainer I ran diesel purge directly from a bottle under the hood and noticed only a little improvement afterwards. (And no drastic change while driving either)

Getting frustrated I dropped off my truck last week to my Mercedes mechanic to go through a few things to see if we couldn't sort of the source of the problem. He did a valve adjustment and tested the injectors and found that one of them was 'pissing'. He also checked the timing chain for stretch (Just a small amount) and he put in a new chain tensioner, fuel priming pump and injector. I also put in new fuel filters. Hoping that I had cracked the nut I was disappointed to see a maybe 10% improvement. The truck has a bit more pep and responds a little bit better. So at least i'm getting somewhere.....here is where things get odd though.

My mechanic mentioned that after buttoning everything up that he had a hard time getting the truck restarted (I never had a problem with this before) It would crank and cough a bit but it took a lot of cranking to get it going. I didn't think much of it at the time because when I picked it up it started perfectly. (And a few more times throughout the day)

Last night however while leaving work I cranked the engine and it started with a bit of a stumble but then died after idling for about 5 seconds. I primed the heck out of the pump two times and it wouldn't even start. At this point the truck was parked uphill so I turned it around to more level ground and after another attempt was able to get it going. This morning, same problem. I said "Alright, fuel flow, that tank strainer must be clogged." The screws on the access panel were so bad that I had to drill them out and what a mess underneath it....There was so much dirt, grime and particles under the panel that I couldn't even see the lines. I vacuumed everything out and ran straight into problem #1. I don't think I can even get the lines off....and even if I do I will probably breaking them. (As is what happened when I removed the sending wire.....one connection snapped right off.

My girlfriends father who was helping me came up with the idea of running compressed air down the lines to unclog it. I should note at this point that priming the pump didn't seem to be drawing much fuel but after blowing the lines it seemed to be flowing much better. It still took some doing and we cracked the injector lines to remove any air but the truck eventually started again.

My girlfriends father thinks I might have a weak injection pump. I'm still on the thought of clogged strainer.

Any thoughts will be highly appreciated. (I have a few pictures which I can upload tomorrow)

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1982 300GD Carmine Red (DB3535) Cabriolet Parting Out
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1991 350SDL Blackberry Metallic (481)

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  #2  
Old 09-15-2013, 12:53 AM
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What about the fuel pump?

- Peter.
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  #3  
Old 09-15-2013, 01:03 AM
JB3 JB3 is offline
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Replumb the engine to run off a 2 liter bottle of diesel in the engine bay. Sluggishness gone, then its an issue with lines or tank. Sluggishness remains, the issue is on the engine side
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  #4  
Old 09-15-2013, 05:46 AM
t walgamuth's Avatar
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I thought it might be a hole in a fuel line on the suction side letting in air.
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  #5  
Old 09-15-2013, 09:53 AM
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Swap inlet and return lines and see what happens. If the situation resolves it's probably a plugged screen. But since you already ran the truck on a bottle of fuel, it doesn't seem that this can be the problem.
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  #6  
Old 09-15-2013, 10:16 PM
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Update

I had a tough time starting it again while leaving work (The longer it sits the worst it gets) a mix of some serious priming and holding the pedal at full throttle finally managed to get the engine running and holding. This time however while I was priming I noticed that I was getting air bubbles from the top bolt on the main fuel filter (Which made me absolutely furious ) I didn't have an adjustable wrench on me so I left it alone till I got home. When I did get to it I got a good 4 turns on the bolt so air was definitely getting into the system right there. I also noticed that a return line on my injectors was routed under the throttle adjustment rather then over it and was a bit kinked (Which also didn't make me smile)

Now I should mention that I do trust this mechanic. Factory trained with a good 20 years experience 90% of which has been on Mercedes at the main local dealer. He went independent a few years back and he did a flawless head gasket job on my SDL some time ago. I think the difference is that on that job HE did the work but that this job was done by one of his employees that he has since hired.

I will try to start it first thing in the morning and should know in about ten seconds if that was the source of the hard starting. (Fingers crossed)


Back to the lack of power issue and to recap on a few things.

1. When I ran diesel purge a few weeks back I did it from a bottle under the hood and there was no difference in performance. (Starts to rule out a clogged strainer or line.)
2. The tank leaks above 50% but I have never seen it leak from the seem so it is possible that the leak is from a line.
3. It was reported to me that my chain only has a minor stretch in it.
4. When blowing air down the lines to the tank the cap was off and I could hear the air coming through loud and clear.
5. My mechanic did a valve adjustment and installed the following: chain tensioner, one new injector, hand priming pump, new main fuel filter,(Although apparently not tightened....)
6. My Indy talked about doing the drip timing on the pump but it was not actually done.


At this point i'm still suspecting the injection pump and on a related note, I just received a used injection pump and 5 injectors from an 85 Euro 300D NA so I have a second pump which I can get tuned to spec if the need arises.
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1982 300GD Carmine Red (DB3535) Cabriolet Parting Out
1990 300SEL Smoke Silver (Parting out)
1991 350SDL Blackberry Metallic (481)

"The thing is Bob, its not that I'm lazy...its that I just don't care."
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  #7  
Old 09-16-2013, 01:32 AM
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Smile

I say give up on it, cut your losses, and sell it....to me!!

sorry, serious G series envy.

hope you get it sorted out. keep us updated!
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  #8  
Old 09-16-2013, 06:41 AM
JB3 JB3 is offline
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I'm not sure, but did you verify that the white G had the same diff ratio as you? Also didn't you have taller tires?

I don't have any idea what the different G gear ratios are and what year difference your trucks were, but let's say for example he had a 4.10 diff and you had a 3.60 diff, that could explain a huge difference in pep off the line and impression of power.

My 74 240 was considerably faster off the line than my 83 240, both with 4 speeds, and even with the 83 having the more powerful 616. The difference was all rear end gearing, but of course the 74 was a 55mph vehicle wound out, and the 83 will easily do 70.

On top of that you have your tire sizes that could be impacting the ratios. First thing id want to do is make sure my comparison was equal. What tire sizes on both trucks, what ratios on both trucks, ect, jut in case I wasn't trying to solve a gearing difference.

Were they the same years? I thought I remember the white G was very early, while yours is later?
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Old 09-16-2013, 10:01 AM
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Alright the hard start problem was resolved from the loose main fuel filter bolt (Of all the dumb little things.....)

Quote:
Originally Posted by JB3 View Post
I'm not sure, but did you verify that the white G had the same diff ratio as you? Also didn't you have taller tires?

I don't have any idea what the different G gear ratios are and what year difference your trucks were, but let's say for example he had a 4.10 diff and you had a 3.60 diff, that could explain a huge difference in pep off the line and impression of power.

Were they the same years? I thought I remember the white G was very early, while yours is later?
They are pretty close; Dude's was an 80 and mine is an 82. It is possible that I had lower ratios but we checked and our trucks are identical in most respects (He has hard top switchgear and I don't, he has power and I don't, but I beat him hands down for rust )
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1982 300GD Carmine Red (DB3535) Cabriolet Parting Out
1990 300SEL Smoke Silver (Parting out)
1991 350SDL Blackberry Metallic (481)

"The thing is Bob, its not that I'm lazy...its that I just don't care."
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  #10  
Old 09-16-2013, 03:28 PM
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Linkage hitting full stop? New style primer?
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  #11  
Old 09-16-2013, 04:04 PM
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Quote:
Originally Posted by winmutt View Post
Linkage hitting full stop? New style primer?

Linkage is good, the primer is a week old and of the new Bosch variety.
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  #12  
Old 09-17-2013, 07:13 AM
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Quote:
Originally Posted by Fulcrum525 View Post
Linkage is good, the primer is a week old and of the new Bosch variety.
Cheap fix is to find another pump and swap it, if its better get the old one rebuilt. After you run it off a water bottle of diesel and verify the performance is the same. The governors are just a bunch of weights and springs, even diesel mercedes wear sooner or later.
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Old 09-17-2013, 09:50 AM
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Have you taken timed runs? Butt dynos can be very subjective taking consecutive runs. Best to drag race him.

How many miles on the engine? Have you done a compression test? Pop and balanced injectors?

The inline pump is lubricated by oil not fuel and can have a very long life if not mistreated. I doubt that is your problem.
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  #14  
Old 09-17-2013, 01:00 PM
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Quote:
Originally Posted by winmutt View Post
Cheap fix is to find another pump and swap it, if its better get the old one rebuilt. After you run it off a water bottle of diesel and verify the performance is the same. The governors are just a bunch of weights and springs, even diesel mercedes wear sooner or later.
Funny thing is I ran the bottle a few weeks back and there was no change. Someone on the Gwagen forum brought up a good point which is that I ran the bottle with the old main fuel filter and that I should run the rest again with a new filter.


Quote:
Originally Posted by funola View Post
Have you taken timed runs? Butt dynos can be very subjective taking consecutive runs. Best to drag race him.

How many miles on the engine? Have you done a compression test? Pop and balanced injectors?

The inline pump is lubricated by oil not fuel and can have a very long life if not mistreated. I doubt that is your problem.
Yeah timed runs are not needed.... The difference between my truck and the other 300GD were pretty drastic. I actually had trouble getting it into 1st gear because I wasn't expecting it to take off like it was. From then on every gear pulled like crazy and the engine actually reacted to inputs perfectly. In my truck I pretty much have the pedal pushed all the way down all the time.

When I bought the truck the odometer was stuck at 86,000 and the owner said it was broken for about a year. I'd say the engine has around 100,000 miles, probably a bit more. Compression is good, and my mechanic pop tested the injectors, only one was 'pissing' and has been replaced.
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1982 300GD Carmine Red (DB3535) Cabriolet Parting Out
1990 300SEL Smoke Silver (Parting out)
1991 350SDL Blackberry Metallic (481)

"The thing is Bob, its not that I'm lazy...its that I just don't care."
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  #15  
Old 09-17-2013, 06:11 PM
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Check the length on the pressure relief valve spring on the Eng side of the IP. Rebuild kit for the lift pump is cheap. I have a spare ill let go for a 6pack.

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1994 E320 Cabriolet
1995 E320 Touring
2001 Eurovan FOR SALE
1985 300D car, sold and missed.
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