Fuel only dribbles from removed injector line when cranking at WOT - PeachParts Mercedes-Benz Forum

luke4 · #1 03-20-2011, 01:30 PM

Is this a problem? I had a spin on filter with a lot of dark reddish crap in it (did LM diesel purge and now have Star Tron in the tank) and wonder if some has plugged up the IP so much that the diesel purge didn't touch it.

Should the injector lines, when disconnected at injectors and cranking the engine at WOT "shoot" fuel out? Or should it just dribble out?

Car runs, but has no power (0-60 in 21 seconds).

thanks

Luke

scottmcphee · #2 03-20-2011, 02:37 PM

Injector lines cracked open at the nut will appear to leak, not spray, or gush.

Unless you have a pinhole in the line (as when it might if it were being rubbed against something) diesel will not shoot far.

luke4 · #3 03-20-2011, 03:33 PM

Thanks for replying Scott! They all drip a bit, so I guess they're doing what they're supposed to.

Several lines have rubbed against each other and worn down quite a bit. If there's a pinhole, there would be a visible leak of fuel right - or is there suction in those lines and thus no fuel leaking?

whunter · #4 03-20-2011, 04:00 PM

Quote:

Originally Posted by luke4

Thanks for replying Scott! They all drip a bit, so I guess they're doing what they're supposed to.

Several lines have rubbed against each other and worn down quite a bit. If there's a pinhole, there would be a visible leak of fuel right - or is there suction in those lines and thus no fuel leaking?

The steel lines are over 2300 PSI.

.

luke4 · #5 03-20-2011, 04:05 PM

Wow, 2300 PSI! Lots of pressure, but not much volume - which I suppose is why they appear to just dribble a little fuel out.

With that much pressure, if there were a pin hole in the line, I guess it would be obvious - i.e. some fuel coming out of the suspect area.

Diesel911 · #6 03-20-2011, 04:24 PM

Quote:

Originally Posted by luke4

Is this a problem? I had a spin on filter with a lot of dark reddish crap in it (did LM diesel purge and now have Star Tron in the tank) and wonder if some has plugged up the IP so much that the diesel purge didn't touch it.

Should the injector lines, when disconnected at injectors and cranking the engine at WOT "shoot" fuel out? Or should it just dribble out?

Car runs, but has no power (0-60 in 21 seconds).

thanks

Luke

Look at the facts; not what you think it might be. If the Car Starts and runs as you say it does you know you must be getting enough Fuel at cranking speeds.

Swap the Fuel Inlet Hose with the Fuel Outlet Hose and you will bypass the Fuel Tank Screen an draw Fuel from a Higher Position in the Fuel Tank.

Be sure the Fuel Tank never gets below 1/2 Tank when doing the above.

If it still is doing the same thing you may need to change the Filters again.

luke4 · #7 03-20-2011, 06:15 PM

Thanks Diesel911,
doing that right now.

Orv · #8 03-21-2011, 01:48 AM

Quote:

Originally Posted by luke4

Wow, 2300 PSI! Lots of pressure, but not much volume - which I suppose is why they appear to just dribble a little fuel out.

It's a positive displacement type pump, which means it moves a fixed volume with each stroke and the pressure will rise as high as necessary to let that volume flow. With no resistance to flow there won't be any pressure. With the lines sealed, the injectors block the flow until a certain pressure point is reached, then they "pop" and let the fuel out.

Codifex Maximus · #9 03-21-2011, 02:40 AM

Turbo?

luke4 · #10 03-21-2011, 10:52 AM

Thanks Orv, this is a great thread to answer the question:

"How forcefully will fuel come out of injector lines"

Suggestion for the moderator: I think it does a better job than the thread of that title listed under the Diesel Injection DIY link at:
Diesel Injection:
That post is http://www.peachparts.com/shopforum/diesel-discussion/194197-how-forcefully-will-fuel-come-out-injector-lines.html#post1563783

luke4 · #11 03-21-2011, 10:52 AM

Codifex - yes, my car is a turbo

Diesel911 · #12 03-22-2011, 12:57 AM

Quote:

Originally Posted by Orv

It's a positive displacement type pump, which means it moves a fixed volume with each stroke and the pressure will rise as high as necessary to let that volume flow. With no resistance to flow there won't be any pressure. With the lines sealed, the injectors block the flow until a certain pressure point is reached, then they "pop" and let the fuel out.

I used to think the same. There is a thread that go deep into the subject of the positive displacement. I believe it was Numbercruncher that disproved that.
The argument over that was hot enough that ForcedInducton got banned.

Apparently the Piston is pushed positively in one direction against Spring Pressure but on the way back the Spring Pushes the Piston. This means that that if the Outlet of the Fuel Supply/Lift Pump was Plugged the Piston being pushed back under Spring Tension would not move until what is blocking the Outlet is removed.

luke4 · #13 03-22-2011, 02:30 PM

That (mostly) makes sense. thanks!

Orv · #14 03-23-2011, 12:56 AM

Quote:

Originally Posted by Diesel911

I used to think the same. There is a thread that go deep into the subject of the positive displacement. I believe it was Numbercruncher that disproved that.
The argument over that was hot enough that ForcedInducton got banned.

Apparently the Piston is pushed positively in one direction against Spring Pressure but on the way back the Spring Pushes the Piston. This means that that if the Outlet of the Fuel Supply/Lift Pump was Plugged the Piston being pushed back under Spring Tension would not move until what is blocking the Outlet is removed.

I see, so the pressure can never rise higher than what the spring tension can produce? That makes a lot of sense. Otherwise one clogged injector would likely destroy the pump.

Diesel911 · #15 03-23-2011, 01:29 AM

Quote:

Originally Posted by Orv

I see, so the pressure can never rise higher than what the spring tension can produce? That makes a lot of sense. Otherwise one clogged injector would likely destroy the pump.

The Injection System is separate from the Fuel Supply System.

In the Fuel Supply System the Fuel goes into the Fuel Supply/Lift Pump passes through the Secondary Spin-on Fuel filter goes into the Fuel Injection pump housing (this is where it supplies Fuel to the Elements that create the high pressure for Fuel injection) and passes through the Fuel Pressure/Bypass Valve (that controls the pressure of Fuel Supply System) and from there ends up back in the Fuel Tank.

If the Secondary Spin-on Filter became entirely plugged the Spring Loaded Piston of the Fuel Supply Pump would protect something from popping. But, of couse the Engine would also stop if the Secondary Filter was entirely plugged.

The Fuel Injection pressure build up in the Elements, Hard Lines and Injectors and there is no sort of relief valve (in a sense the Injector itself is the relief valve) in that part of the system to deal with any blockage.

And, in fact I have twice seen where a Mechanic managed to get something inside of the Fuel Injection Hard Lines that blocked the Injectors.

Both time it cracked the Fuel Injection Hard Lines.
In one case the Hard Line cracked in 2 pieces.