Help with bleeding air from fuel system... - PeachParts Mercedes-Benz Forum

Fidens · #1 10-07-2012, 08:15 PM

So I did a diesel purge and filter change in my new 83 300d, and am having a really hard time getting it started. What I've done so far:

-After purging, I swapped out the filters,(I partially filled the canister with diesel), however I forgot to prime it with the hand pump. It started and ran fine for 20 seconds and then died.

-I then used the hand pump to prime the system until I had fuel coming out of the top bolt on the secondary filter. I then opened the lines at the injectors and cranked the motor.

-However after wearing down the charge in the battery, I only have fuel just weeping from two injectors.

Am I on the right track, and should I just keep trying, or should I begin to suspect something else is wrong? Maybe air is getting into the system somehow? How long does it normally take to bleed the air out?

Diesel911 · #2 10-07-2012, 10:15 PM

In this case get on the Hand Primer and start pumping until you hear a squishing or buzzin sound; then pump a little more.
Loosen the Fuel Injection Hard Line Nuts at the Injectors and crank the Engine until Fuel comes; that allows the Air trapped inside a way to escape.
The tighten up the Fuel Injection Line Nuts at the Injectors and attempt to start.

Fidens · #3 10-07-2012, 11:38 PM

Quote:

Originally Posted by Diesel911

In this case get on the Hand Primer and start pumping until you hear a squishing or buzzin sound; then pump a little more.
Loosen the Fuel Injection Hard Line Nuts at the Injectors and crank the Engine until Fuel comes; that allows the Air trapped inside a way to escape.
The tighten up the Fuel Injection Line Nuts at the Injectors and attempt to start.

Should I open up any bolts when I do this? When I pump with everything sealed up, all I get is fuel squirting out at the bottom of the primer pump.

Zacharias · #4 10-07-2012, 11:53 PM

Yes, 911 said you should loosen the nuts that connect the steel hard lines to the injectors.

HOWEVER, you should never have fuel coming out of the primer pump, no matter how you are doing it.

What does your primer pump look like? Is it a big black button, or a white knob with a hollow centre that you have to loosen in order to pump?

If it's white, then you have an old pump and it sounds like it's leaking. In that case you need to replace it.

If you have the newer style, black primer pump, then you should check that it is screwed in tight at its base.

Fidens · #5 10-08-2012, 09:26 AM

Quote:

Originally Posted by Zacharias

Yes, 911 said you should loosen the nuts that connect the steel hard lines to the injectors.

HOWEVER, you should never have fuel coming out of the primer pump, no matter how you are doing it.

What does your primer pump look like? Is it a big black button, or a white knob with a hollow centre that you have to loosen in order to pump?

If it's white, then you have an old pump and it sounds like it's leaking. In that case you need to replace it.

If you have the newer style, black primer pump, then you should check that it is screwed in tight at its base.

I have the old style with the white nob. Will I be able to bleed it out enough to get the car started even if the pump is bad, or should I just wait until I get a new pump before I go any further?

cho · #6 10-08-2012, 09:54 AM

.

I would check both valves on the lift pump first. tight them up
and try again.... if possible tight lift pump itself...

if that does not help
I would get a new pump ... it is 15 bucks or so....

.

cho · #7 10-08-2012, 10:06 AM

Quote:

Originally Posted by Fidens

Maybe air is getting into the system somehow? How long does it normally take to bleed the air out?

few months ago while I was replacing my hard lines it took me 10-15 sec
cranking to see fuel on all tips

everything was primed before so it is not exact situation as yours...

.

ytmtnman · #8 10-08-2012, 12:36 PM

I once had a leaky white primer pump. I unscrewed it to its useful position then wrapped some Teflon tape around the handle just below the mushroom head. Then I screwed it back down tightly. This seemed to help stop any air infiltration for a temporary fix.
I guess another way to prime would be to suck diesel through the return line. It doesn't taste good but can get you started in a pinch. I guess you could use a pump instead but I always have a mouth nearby...

Zacharias · #9 10-08-2012, 03:01 PM

Quote:

Originally Posted by Fidens

I have the old style with the white nob. Will I be able to bleed it out enough to get the car started even if the pump is bad, or should I just wait until I get a new pump before I go any further?

You won't be damaging anything to try to prime with the existing pump, so you may as well try it again.

Loosen the nuts where the hard steel lines connect to the injectors and try pumping. If you don't see any diesel coming out after 60 seconds of pumping, however, I would leave it be until you have the new pump.

Govert · #10 10-09-2012, 10:32 AM

Quote:

Originally Posted by Zacharias

You won't be damaging anything to try to prime with the existing pump, so you may as well try it again.

Loosen the nuts where the hard steel lines connect to the injectors and try pumping. If you don't see any diesel coming out after 60 seconds of pumping, however, I would leave it be until you have the new pump.

You cannot get diesel out of the hard injector lines by means of the hand pump. The hand pump is there to fill the low-pressure area of the IP with fuel and to pressurise it. When you hear the buzzing sound, that is the sound of the relief valve opening, that means that the low-pressure area of the IP is under pressure and is free of air.

Now you can go beyond what MB advices and loosen all the lines at the injectors and operate the starter. Stop when you see fuel at the injector. Have some rag ready for the mess. Tighten the lines (25 Nm) and now attempt to start the car. It should not take long for the engine to start, only slightly longer than normal. Don't stop starting upon the first ignitions and sometimes you need a high idle in the first half minute or so.

Diesel911 · #11 10-09-2012, 03:48 PM

Quote:

Originally Posted by Govert

You cannot get diesel out of the hard injector lines by means of the hand pump. The hand pump is there to fill the low-pressure area of the IP with fuel and to pressurise it. When you hear the buzzing sound, that is the sound of the relief valve opening, that means that the low-pressure area of the IP is under pressure and is free of air.

Now you can go beyond what MB advices and loosen all the lines at the injectors and operate the starter. Stop when you see fuel at the injector. Have some rag ready for the mess. Tighten the lines (25 Nm) and now attempt to start the car. It should not take long for the engine to start, only slightly longer than normal. Don't stop starting upon the first ignitions and sometimes you need a high idle in the first half minute or so.

X2 on no Fuel out of the Hard Lines using the Hand Primer; the Springs on the Delivey Valves are too strong for that.

haromaster87 · #12 10-09-2012, 06:47 PM

Don't know if I read it wrong, but when I had to bleed the lines like that, I was told to crack open one injector line at a time, have a buddy turn over, and close the line as soon as you see fuel coming out. Granted, this is hard to do if you don't have said buddy around, but is there any benefit to the one at a time vs. the all at once?

Diesel911 · #13 10-09-2012, 07:52 PM

Quote:

Originally Posted by haromaster87

Don't know if I read it wrong, but when I had to bleed the lines like that, I was told to crack open one injector line at a time, have a buddy turn over, and close the line as soon as you see fuel coming out. Granted, this is hard to do if you don't have said buddy around, but is there any benefit to the one at a time vs. the all at once?

If Air gets trapped in the Hard Lines it compresses a lot and mover only a little bit and it takes a lot of cranking to get it out.

Only loosening one line only bleeds the Air out of one line at a time. The theory here is that if you bleed the Air out of one line at a time the hope is that you will allow a few Cylinders to fire and that those firing Cylinder will have enough oomph to keep the Engine running and clear the Air from the unloosened Hard Lines that Still have Air in them.

This method is also more dependent on the health of your Engine. An Engine with good compression, timeing and good Injectors is going to start and run more easily on a few Cylinders than one that does not.
Your Battery and Starter need to be in good shape also.

You can use the method you prefer to use.