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Thread: need a fuel system diagram. fuel leaking?

  1. #1

    Default need a fuel system diagram. fuel leaking?

    I just bought an 85 diesel jetta with no fuel pressure at the tank. the next morning I saw fuel on the ground just in front of the right rear tire. the guy I bought it from suggested I replace the fuel lines but the leak is coming from a bolt on the bottom of this pump thing. I could really use a diagram to help me understand how the system works. this is my first diesel project and I appreciate any help that can be given.

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  3. #2
    Junior Member greenlight is on a distinguished road greenlight's Avatar
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    Default Re: need a fuel system diagram. fuel leaking?

    I the fuel leaking from a black plastic box? I have a 92 gas model but I'm wondering if it uses the same fuel pump. Mine was leaking in the same area.

  4. #3

    Default Re: need a fuel system diagram. fuel leaking?

    It is like a black box. There is a lot of info about the primary and transfer pumps, but I cant seem to find out much on that. I can see the fuel line coming out of the tank and into this box and then to the motor. Ill have a book soon and knowing what this thing is called will really help me fix this leak. let me know if you find something out.

  5. #4

    Default Re: need a fuel system diagram. fuel leaking?

    ok i have not found a diagram but I pulled all the fuel lines and found a bad check valve. I still dont know what the plastic box does but Ill just hook it back up and hope it does not leak any more. also there is only one pump on the diesel fuel system, and it is driven by the timing belt. Now on to timing.

  6. #5

    Default Re: need a fuel system diagram. fuel leaking?

    The plastic box you are referring to is called the fuel pump reservoir. Mine was cracked and leaking a year ago and it took me a month to find where to buy one. Used is always an option and much more affordable if you can find one. But search around they are available but very expensive (around $150)

  7. #6

    Default Re: need a fuel system diagram. fuel leaking?

    I'm new to this site....and a month late to reply to this.
    The plastic box/container is a water separator and they crack over time. Pretty much everyone simply removes these from their cars. I certainly did on three of mine). Remove the box and simply patch the line from the tank to the line to the front of the car with a new piece of appropriately-sized rubber fuel line. It is as simple as that. Make sure you use good clamps to keep air from being pulled into the splice.
    Then, get on with your life. These water separators are not needed as you have a fuel filter with a drain.

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    Digifook. CafeRacer is on a distinguished road CafeRacer's Avatar
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    Default Re: need a fuel system diagram. fuel leaking?

    I've seen a few of these removed for the same reason. If you live in an area with a lot of snow or rain like most of Canada I've seen guys use a bigger fuel filter/water separator. My old high school auto shop teacher did a nice job of re installing it on the passanger side of the rad support so it was easy to plumb and easy to get at to drain. The one he used was from a smaller Volvo diesel marine engine. It was easy to get a replacement filter for and the unit he bought used off a marine mechanic, It bolted very easily to the ran support with no extra bodging around. With that thing in there and some rebuilt upgraded injectors that thing ran really nice.

    He did a pile of neat things like that to the engine in his Jetta. His reasoning was he lived out in the country where the fuel tanks at stations were never that clean and the conditions he drove that car thru sometimes were terrible. He made his own updated glow plug system using bits and pieces he bought from a farm equipment shop aswell as added an oil pan heater, and one hell of a block heater. All the fuel lines were insulated and the tank had a heat pad too. All of the plug in accessories plugged into 2 bits of wire hanging out of the lower grill, including the battery sustainer. He made the most well sealed skid plate I've ever seen, that he made after hours at the school. By the time I was graduating He was fitting a cyclonic oil separator and catch can to it.

    Somedays I miss working on the old 1.6L diesel and T diesel engines. They're so easy, and rugged as hell.

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    Default Re: need a fuel system diagram. fuel leaking?

    Does this also go for the unleaded 1.8's? I have the same leak in the same area and I have a hard time starting and when it does it sounds like a lawn mower but then it'll fire up after a bit.

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    Default Re: need a fuel system diagram. fuel leaking?

    Quote Originally Posted by joshuat View Post
    Does this also go for the unleaded 1.8's? I have the same leak in the same area and I have a hard time starting and when it does it sounds like a lawn mower but then it'll fire up after a bit.
    Gassers aren't as simple. You have an in-tank transfer pump that feeds the main pump under the rear passenger seat. Depending on the year/engine in the car the pumps are almost identical but the filters differ.

    Gassers don't need a fuel/water separator because moisture unfortunately dissolves into gasoline. Diesel is an oil and water will not dissolve into it. Instead the moisture collects at the lowest point of the tank and gets sucked up via the pick up. Without a water separator you would end up running water thru the fuel system and stall the engine outright.

    On later model cars that have a Digi engine they use less pressure and the filter uses two hose clamps to hold the fuel line to it. That is a common place for leaks, espessialy if the hoses are old and hard. Tighten them down a bit to check. If that stops it or slows it down replace those bits of rubber hose and away you go.

    Earlier cars or CIS cars use a full hard line set up that uses more of a threaded hydraulic fitting and crush washer style. They also can leak but its usually when they haven't been tightened properly. The issue is depending on the age of the filter those fittings and stick them selves on VERY well. You end up needing 2 very long wrenches, and even better yet proper hydraulic fitting wrenches so you don't round them.

    If checking and tightening either style doesn't solve it the pump housing itself may be shot or cracked. New ones aren't cheap. Before you throw money at it lift the back of the car and lay under it, see if you can spot exactly where its leaking.

  11. #10

    Default Re: need a fuel system diagram. fuel leaking?

    I am guessing your 1.8 gas car has a defective fuel accumulator and this is what causes difficult starting and "putt-putt" when the car has been stopped for 15 or so minutes when the engine is good and warm....worse on hotter days, yes?

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    Default Re: need a fuel system diagram. fuel leaking?

    Quote Originally Posted by Dakota View Post
    I am guessing your 1.8 gas car has a defective fuel accumulator and this is what causes difficult starting and "putt-putt" when the car has been stopped for 15 or so minutes when the engine is good and warm....worse on hotter days, yes?
    Depends on the year and fuel system. Pre 88 I'd say accumulator, Post 88 Id say return check valve in fuel pump.

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