w123 cannot bleed air from hard fuel lines - PeachParts Mercedes-Benz Forum

upod · #1 11-13-2012, 12:28 PM

FYI this is on a 1980 300TD wagon

For the life of me, I cannot bleed the air from the hard fuel lines going into the fuel injectors #1 and #2.

I have had all of the hard lines cracked a full turn at the injectors while I crank the engine. After SEVERAL tries of doing this (20 seconds per time so as not to stress the starter motor) #3, 4 and 5 all have fuel coming out of them and are wet on top. However, #1 and 2 are BONE DRY on the top of the injectors, indicating to me that no fuel is coming from the hard lines to the injectors at #1 and #2. No fuel, nothing. I even unscrewed them some more and they're still bone dry.

I have bled fuel lines many times before without so much of a problem as this. I'm hoping it's not a defective IP because the engine started up and idled fine yesterday and ran for about 5 minutes! I've read numerous posts on this and also consulted the manual under section 07-140 which talks about venting the fuel lines. I've

And I've had to recharge the battery 4 times already and it's starting to get frustrating as nothing has changed! FYI, I'm cranking the engine for about 20 seconds per attempt with several minutes in between attempts, and then an hour or two while I wait for the battery to be recharged. Before attempting, I prime the hand primer pump (brand new, bosch) as per the factory manual section 7-140. I originally had the front tires of the car on ramps but have since put it back on flat ground, hoping that would (perhaps!) make some difference, but alas, no improvement.

Some background: I am finishing up an install of a replacement engine and the car DID start up on a dime yesterday with diesel purge in the primary fuel filter. The car was sitting over a month and the engine for about 5 months. The car was low on fuel so I poured in about 2 gallons of fresh diesel so it would be able to have enough to run on. I'm not sure if it had been run dry, but somehow, air must've been sucked into the line since the car had been sitting before I did the engine swap.

oldsinner111 · #2 11-13-2012, 12:31 PM

I can't bleed my w126 either.So I bleed to get most air out.Then take a 2x4 and depress brake pedal and wedge 2x4 to seat,holding it down overnight.I repeat until all air is gone

Stretch · #3 11-13-2012, 12:36 PM

Quote:

Originally Posted by oldsinner111

I can't bleed my w126 either.So I bleed to get most air out.Then take a 2x4 and depress brake pedal and wedge 2x4 to seat,holding it down overnight.I repeat until all air is gone

I think that that is a good tip for brakes but it won't help much with a fuel injection system.

Stretch · #4 11-13-2012, 12:47 PM

Here's what I'd try and do to save the battery a bit. I'm not 100% certain this will work on a hand pump but it is a little bit like the high pressure timing check detailed in chapter 07-109.

Find where begin of delivery on #1 cylinder should be just about happening - start at say 30 degrees BTDC on the compression stroke. Pressurise the fuel system with the hand pump after cracking the hard line at the injector for cylinder #1. Turn the crank to about 24 to 20 BTDC and see if you can get any fuel out. If the hand pump is strong enough you should start to get some fuel out.

If that works then I'll work out where to roughly put the crank for the compression stroke on #2...

(I assume that you haven't been doing a drip test since the engine last ran)

upod · #5 11-13-2012, 12:51 PM

Thanks, I'll try that, Army.

No, I didn't do any drip test to set IP timing, nor did I check timing chain stretch either. My main concern was to first at least get the car running before doing those.

Stretch · #6 11-13-2012, 12:57 PM

Quote:

Originally Posted by upod

Thanks, I'll try that, Army.

No, I didn't do any drip test to set IP timing, nor did I check timing chain stretch either. My main concern was to first at least get the car running before doing those.

No that's fine - I was just thinking that if you'd removed the pressure valve on the output on #1 on the IP then you might have put it back in wrong or something and perhaps that was stopping flow...

...which leads me on to think about an alternative if this doesn't work! Can you guess what it is yet? (See chapter 07-110 para 4!)

Stretch · #7 11-13-2012, 12:59 PM

Oh yeah I forgot to mention an important part of the first method (that might or might not work) you need to have the throttle wide open =>

which could indeed be the trouble with the bleeding on the starter that you have at the moment...

upod · #8 11-13-2012, 01:06 PM

Yes, removing the spring and pressure valve, as is done when doing the drip test! I suppose if no fuel is flowing with those elements removed, it would indicate something wrong inside the IP itself.

Stretch · #9 11-13-2012, 01:30 PM

Quote:

Originally Posted by upod

Yes, removing the spring and pressure valve, as is done when doing the drip test! I suppose if no fuel is flowing with those elements removed, it would indicate something wrong inside the IP itself.

Indeed but the pump still needs to be in a position when it is supplying fuel to the injector so you still need to hunt about for begin of delivery by turning the crank by hand and (perhaps to make it easier on the hand pump) open the throttle a bit (or a lot!)

EDIT:-

Make sure you read the FSM and unscrew the bit you are meant to unscrew - and not the bit you're not!

upod · #10 11-13-2012, 02:38 PM

Well I think I finally was able to bleed the air! However, the engine will turn over but not start. The glow plugs are all brand new. The starter is only 2 years old. I also have the battery connected via jumper to another car I have for extra cranking power. I'm not sure if this car has been flooded with too much fuel in the prechambers or not due to repeated cranking attepmts with the throttle wide open.

If that's the case, I don't know how to reverse that. Right now, I'm recharging the battery yet again. I'll have another shot at it shortly.

Army, I was going to set the crank to 30 degrees BTDC and use the hand pump, but as I have the fan installed and fan shroud in place I was in no mood to remove it once again. But I will keep this in mind should this happen again!

For anyone else with this problem, here's what I did: Since #3,4,5 were getting fuel from the hard line to the top of the injectors, I tightened those off. Then I cranked the engine some more. I think 4 or 5 more times and I had the battery charged again in between those Finally, something came out of #2, so I tightened it up. Still nothing out of #1, however at this point. I then decided to take the hard injector line completely off at both the injector and the pump and blew it out with compressed air to make sure there was no gunk in it. When I removed the hard line, I saw a small puddle of diesel fuel at the injection pump and fuel dripped out of the lower part of the line that was connected at the IP. That told me that at least the pump was supplying fuel, at least. I then blew out the hard line with compressed air, didn't find any obstructions (or if they were, they blew out faster than I could see!). Then I replaced the hard line, and tightened it down at the IP and only loosely connected the hard line at injector #1. After 2 attempts to crank, finally some fuel dribbled out! Then I tightened down the hard line connection at injector #1.

upod · #11 11-13-2012, 02:42 PM

here's a couple pics

Diesel911 · #12 11-13-2012, 03:15 PM

I have been trying to think of something that would help.

I would be inclined to check and see if the Glow Plugs are really working or not.

If it is a low compression issue perhaps cause be sticking Piston Rings you might try pluggin in the Block Heater and getting the Block nice and warm before you attempt to start again.

Also the lower amperaged charge for a longer time is better for the Battery.

Also when you are stressing the Starting System it is a good time to make sure the Cable connections are in good shape.

You did not say if you thought the Engine was cranking normally fast?

Stretch · #13 11-13-2012, 03:21 PM

I'm glad to hear that there's fuel coming out where it should now - I conclude that moving the throttle helped - so that'll probably be my top tip if I come across this problem again.

As the engine was running recently I reckon you just need a bit more juice in that battery and to then try again.

Have you considered tow starting?

(I don't follow the fan shroud bit though - but never mind!)

upod · #14 11-13-2012, 04:40 PM

Well I got it to start!

Turns out that the 80 amp glow plug fuse was not properly connected on the firewall. Once I cleaned the connections and connected it snugly, the car started up!

Govert · #15 11-14-2012, 05:00 AM

Quote:

Originally Posted by Army

Oh yeah I forgot to mention an important part of the first method (that might or might not work) you need to have the throttle wide open =>

which could indeed be the trouble with the bleeding on the starter that you have at the moment...

Not really, during starting the governor is in the starting position, meaning that the control rod is in the even-more-than-full-load position.

As you can see in 07-140 of the FSM there is no description of venting the hard fuel lines, as it is not necessary. In my experience there is no difference in time too between starting the engine with closed injector lines and open injector lines.