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'78 240D
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Discussion Starter · #1 ·
many of you have pulled the fuel supply line at the tank i'm sure, the fuel SHOOTS out of there, so why, if you pull the supply line at the prefilter does it just trickle? is it because of the rising and twisting of the line? or is my line clogged? i'm asking because my prefilter is never full when the car is running.
a mechanic told me that the vacuum line at the back of the pump is what draws fuel into the injector. is this correct? i don't think so. i know this has all probably been covered before but try searching "vacuum" or "injection", it's in every post.
while we're at it, no one has ever answered this question for me, and believe me, i've asked, on non turbo models, what does the ALDA do. maybe it isn't called an ALDA on non turbos but you know what i mean.
 

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85 300D (D for Don)
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242 Posts
I don't know anything about the 240's but I know the following for fact on my 300D...

There are 2 banjo fittings on the IP, the one on the rear, passenger side is the fuel IN. The one on the front drivers side of the IP if fuel OUT.

If I pull the supply line off my filter the fuel will not shoot out but will come out quickly. The is with the car facing down hill in my driveway.

Maybe your fuel line is clogged or collapsing. If it's just clogged you should be able ot blow some compressed air through it, this will likely shke up the crud in the tank so you might want to let it settle afterwards and plan to change filters a little later.
 

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1982 300CD
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vtharpe said:
many of you have pulled the fuel supply line at the tank i'm sure, the fuel SHOOTS out of there, so why, if you pull the supply line at the prefilter does it just trickle? is it because of the rising and twisting of the line? or is my line clogged? i'm asking because my prefilter is never full when the car is running.
Yeah, weight of fuel in the tank. The thin elevated line deminishes pressure. The bubble in the in-line prefilter is okay, don't worry too much about it. But, if you get new small bubbles in it all the time, then you have a leak that is letting air in.

vtharpe said:
a mechanic told me that the vacuum line at the back of the pump is what draws fuel into the injector. is this correct? i don't think so. i know this has all probably been covered before but try searching "vacuum" or "injection", it's in every post.
If you're talking about the vacuum line that runs to the shut off valve, no.
The IP is your Injection Pump.

vtharpe said:
while we're at it, no one has ever answered this question for me, and believe me, i've asked, on non turbo models, what does the ALDA do. maybe it isn't called an ALDA on non turbos but you know what i mean.
The ALDA increases fuel when it senses higher air pressure. In the turbo models, it increases fuel to make use of the extra turbo boost. In an NA engine, it makes adjustments for altitude. Different mechanism technically, but same basic operation.
 

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Basically all your questions were answered correctly, except for one that wasn't answered at all. The injection pump itself draws fuel from the tank and pushes it out to the injectors, there is no vacuum line that does anything to the fuel itself. The only vacuum lines on the IP are for the shutoff valve and the vacuum valve. The vacuum valve is basically just a valve that is controlled by the throttle position.
 

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'78 240D
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Discussion Starter · #5 ·
about the injection, i thought so. about the ALDA: all you turbo guys tweak it for better performance, why don't you tweak it for non turbos. and the fuel lines, well, they built 'em that way and they know better than me so, i won't concern myself with that, aside from maybe running some compressed air through 'em. thanks fellas.
 
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