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  #1  
Old 09-30-2012, 06:59 PM
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Return Fuel LIne (AKA) Cigar hose

During my trouble shoot why my 1984 300D all of a sudden did not want to start I replaced the fuel return line (cigar) with standard fuel line to me it looked it it was getting ready to burst.
Come to find it is suppose to look that way.
With the suggestion of several members, I got it started.
What's is the function of the return line looking like it is about to explode, besides return fuel to the tank?
Is the regular fuel line I replaced it with fine?
While I was trying to loosen the screw for the clamp it did not want to move, it resulted to cutting the clamp and a little of the hose.


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Last edited by whunter; 09-30-2012 at 08:11 PM. Reason: spelling
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Old 09-30-2012, 07:47 PM
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Should be okay.

Install new hose clamps.

Its function is to reduce fuel back pressure, or a damper type of item.
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Old 09-30-2012, 08:16 PM
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The purpose of the cigar hose is to dampen the pulsations that would otherwise occur in the return line.

The injection pump gives each injector a shot of fuel on each power stroke. Not all the fuel goes out the end of the injector to be burnt. Some of the fuel is returned through the system to cool the injector tips. The fuel is used as a liquid heat sink for the injectors.

The return flow is not in a steady stream but a series of squirts, one each time a cylinder gets injected. The cigar hose has a larger space inside than a standard piece of hose so the pulses of fuel flow have a chance to slow down and smooth out on the way back to the tank.

If this was not done, the fuel pulsations would make the hard line back to the tank vibrate. Not only is this annoying but it is bad for the hard line.
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Old 09-30-2012, 08:20 PM
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Answer

What does the cigar hose do....
What does the cigar hose do.... - PeachParts Mercedes ShopForum



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  #5  
Old 09-30-2012, 08:22 PM
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Quote:
Originally Posted by jay_bob View Post
The purpose of the cigar hose is to dampen the pulsations that would otherwise occur in the return line.

The injection pump gives each injector a shot of fuel on each power stroke. Not all the fuel goes out the end of the injector to be burnt. Some of the fuel is returned through the system to cool the injector tips. The fuel is used as a liquid heat sink for the injectors.

The return flow is not in a steady stream but a series of squirts, one each time a cylinder gets injected. The cigar hose has a larger space inside than a standard piece of hose so the pulses of fuel flow have a chance to slow down and smooth out on the way back to the tank.

If this was not done, the fuel pulsations would make the hard line back to the tank vibrate. Not only is this annoying but it is bad for the hard line.
Well if the car does not seem the same with a full tank of fuel put the cigar hose back on. Some cars seem to do okay with it out of the circuit and some not as much.

There are too many reasons to go into why this is. On a properly functioning system the relief valve is always off it's seat when the engine is running. The cigar hose moderates the sharp pulses generated in the injection pump as welL.
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