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Replacing 928 Fuel Lines - a guide

 
Old 04-16-2015, 12:39 PM
  #16  
Carl Fausett
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Looks like what we have "all" been doing for the last 10 years
Just trying to educate those that did NOT know how to do it themselves, or that call me concerned that the hoses are NLA.

So it occurred to me that not "all" owners new this.
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Old 04-16-2015, 01:15 PM
  #17  
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Just a few errors. I will clarify and hopefully avoid some disasters, without promoting any of my own products, on Carl's thread.

First of all, the original line you removed has a separste outer rubber sleeve and an inner PLASTIC sleeve. The outer sleeve does deteriorate and look cracked, but since it is simply an outer protective rubber sleeve, it will NEVER cause any leakage. The inner plastic hose carries the fuel and is what is supposed to be leak proof.

While this plastic hose is a fantastic fuel carrying medium, the problem these days, is that the plastic is invariably brittle and leakage occurs in castitrophic amounts when the plastic "shatters". This is almost never a "leak", but a huge "gushing" of fuel....literally a flood of fuel. The resulting fires are always huge and usually "terminal" to the vehicle.

The original "clamps" are not clamps at all, but simply sleeves to keep the outer rubber protective sleeve from curling up at the ends.

The original plastic hose is retained simply by the sharp barbs on the metal end pieces....this is a "push lock" mechanism.

Those barbs are too sharp for rubber hose and will cut the inner layer of rubber, especially when clamped! Rubber hose over these barbs is the wrong application....as wrong as
"wrong" can be. NEVER install rubber hose over a barb originally designed for plastic hose!

Porche ONLY used rubber hose on the '88-'95 engines in one place....and only for about 6 months. This was the fuel return hose to the fuel cooler....which was deemed by the engineers to be a low pressure application. They quickly realized the mistake and superceeded that one hose to the plastic version, because of leakage potential.

Two of the hoses are still available from Porsche....specifically the short hose from the front damper to the fuel rail and the "updated" return line from the regulator to the fuel cooler.

1987 vehicles are unique. They have a regulator with a metal section designed for rubber hose. This goes to a metal adaptor assembly that is bolted to the back of the block, which them has a plastic hose attacked to it, which goes to the fuel cooler.

We always change this menagerie of pieces to the 1988 regulator and the single "updated" return hose. Much safer.
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Old 04-16-2015, 01:44 PM
  #18  
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Unfortunately not the correct hose - you need Cohline #3024-0800 with the polyamide inner veneer and the matching ferrules #7001.1552. And do not use clamps. We stock them if you get stuck.
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Old 04-16-2015, 02:21 PM
  #19  
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Ah. The Greg and Roger show. I'm sorry I posted on to your forum. How dare me.

Greg:

I did not call it a clamp. See post 4 and 5. I called it a ferrule. It is a ferrule. I will remove the word "swaged". My bad.

Greg and Roger:

I disagree that the barbs are too sharp for use with this hose. They are not. See pics below. They are no sharper than gobs of other barbed fittings that use this hose. This is the OEM hose made in Germany for this purpose and I have no second thoughts about using it here.

So while your plastic-lined hose is one way to repair this fuel line, it is not the only way. This is simply another method that also works very well.

To all: in addition to the example pictured, this method is also a wonderful solution for those who own L-Jetronic equipped cars and are looking to replace the small fuel lines between the fuel rail and each injector.
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Old 04-16-2015, 02:31 PM
  #20  
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I have never understood why somebody wouldn't just grind off the sharp edges and use the rubber lined fuel injector hose and clamp and call it a day.
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Old 04-16-2015, 02:59 PM
  #21  
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Sorry Carl I was just trying to help you use the right hose - silly me as I forgot you were a fully paid up member of the SAE.
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Old 04-16-2015, 05:18 PM
  #22  
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No Rog, it has nothing to do with me SAE membership. I just don't subscribe to the religion of the "one right way". There's often many right ways to affect a repair, each of them good.

Standing back from it a bit, I think I see why and how each of us (you, Greg, and I) come to a different conclusion on a topic like this.

Roger, I think you sell more OEM Porsche parts than aftermarket parts. I believe that's fair to say. That's your business model and there is nothing wrong with it. So it follows that, when you are confronted with a replacement part request, your first move is to locate OEM replacement parts to fill the need. Makes sense to me.

Greg runs a repair shop. He has to justify his charges to replace fuel lines on customer cars (parts + labor) and I don't know how much he charges, but I can guess its way more than the $43 I am discussing here that will replace all the upper fuel lines on the 928 engine. So again, I understand why he doesn't like this thread.

Me, I specialize in quality aftermarket bits that fit the 928. I actually sell very few OEM parts as a convenience for our customers, but it is not our mainstay. So, when confronted with a replacement part quandry, my inclination is to figure out what I can use that will work correctly, regardless of the source. This fits my business model, like reaching for OEM parts fits yours.

No problem.
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Old 04-16-2015, 05:26 PM
  #23  
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Sorry Carl I was just trying to help you use the right hose - silly me as I forgot you were a fully paid up member of the SAE.
...and I don't understand why my SAE membership sticks in your craw like that. It obviously bugs you.

I enjoy being a SAE member. I have enjoyed being a a guest lecturer for them, and enjoyed it even more when they invited me back to do a second lecture. I attend what meetings I can, and they are informational and the meals are always good. I learn things from the engineers around me, and that's the big attraction for me.

The crib notes of those two SAE lectures are downloadable in the Articles section of this page:
http://www.928motorsports.com/install.php
They are entitled "Challenges when Racing a Street Vehicle" Session I and II
You are welcome to review them yourself, as is anyone.

I'll remind you that it was Greg who said something about my engineering degree, an assumption he made. I was quick to correct him - it was I who told him that I was not a degreed engineer. Others trot their engineering degrees around this forum, that isn't me. Not trying to be anything I am not.
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Old 04-16-2015, 10:57 PM
  #24  
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Wow !!! the opinions among the top 928 experts vary so much ??? I just bought a MY89 S4 and engine fire prevention is my top priority. Next will be TB/WP, flex plate, intake refresh, chasing electrical issues etc. All I need is a piece of mind that my car's fuel lines don't start spraying gas all over the place and burn my car to the ground. Or in Roger's language I need to rest assured there is no petrol seepage. What gives ?
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Old 04-16-2015, 11:11 PM
  #25  
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I took 50% off the sharpness of the barbs. Enough to take the bite off but still hold good.

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Old 04-16-2015, 11:21 PM
  #26  
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I took 50% off the sharpness of the barbs. Enough to take the bite off but still hold good.

Brilliant !!!

Tony.
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Old 04-16-2015, 11:27 PM
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I took 50% off the sharpness of the barbs. Enough to take the bite off but still hold good.

Did you use a hack saw also ?

Still brilliant !!!
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Old 04-17-2015, 04:11 PM
  #28  
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So the barbs/fittings/connections intended for rubber-lined hoses have no barbs inthe area that's clamped, but do have a bulb at the end so that system pressure that might cause a hose to slide will ultimately cause the clamped section to stop sliding as it reaches the bulb. If you want to use the existing fitting with rubber-lined hose, you need to completely remove the barbs except for the one nearest the end of the fitting, and roll the sharp edge of that barb so there's no chance of it cutting the rubber liner. The 'relieved' area above the remaining rounded barb needs to be wide enough to allow the clamp you are using, with one hose wall thickness between the edges of the clamp and the barb. I don't think there's enough length to that fitting for this to work, even with the narrow Oetiker clamps.

Meanwhile, self-sealing plastic-lined hose requires fittings that have the barbs as initially illustrated in Carl's pictures. Thus there are multiple 'seals', one at each ring, that also hold the hose in place. I like to soften the hose and particularly the lining some in hot water before sliding the hose on. Once installed, the metal collar that Carl cut off keeps the end of the hose from flaring as it ages. It's more cosmetic than functional, but there is some function.

Last but not least, I recommend against using a hacksaw on anything you might want to reuse later. The razor knife on the hose falls into that same category. Carl shows the correct technique for relaxing the hose shell so it can be removed from the fitting. DO NOT use the sharp tip of the blade to slice into the hose, as any scratches on the metal barb will prevent that ring/barb from sealing. A little heat is your friend for softening the plastic enough to pull off the barbed fitting.

... In my limited experience.
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Old 04-17-2015, 04:59 PM
  #29  
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I agree that caution should be taken with the razor not to cut so deep as to score the steel. But it is steel, and not easily scored. I will mention it just the same. Good point.

I don't agree with this however:
If you want to use the existing fitting with rubber-lined hose, you need to completely remove the barbs except for the one nearest the end of the fitting, and roll the sharp edge of that barb so there's no chance of it cutting the rubber liner. The 'relieved' area above the remaining rounded barb needs to be wide enough to allow the clamp you are using, with one hose wall thickness between the edges of the clamp and the barb.
IMO, there are plenty of barbed hose fittings that have barbs beneath the clamps and they work just fine.

Just a difference of opinion. Thanks for your input.
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Old 04-17-2015, 05:55 PM
  #30  
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I wonder, in the name of scientific inquiry: could one conceive of a test to add some sample data to this discussion? Perhaps an accelerated aging test, or an over-pressure test — I guess my question would be: is there an appropriate test one could (at least theoretically) perform to generate comparable results between the two approaches? I'm not qualified to suggest one; just wondering if it is possible.

"In God we trust, all others bring data."

BTW: nice photo documentation and explanation of the approach.
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