w123 cannot bleed air from hard fuel lines - Page 2 - PeachParts Mercedes-Benz Forum

Silber Adler · #16 11-14-2012, 08:47 AM

I have a question, I replaced my fuel filters. and primed them back up with the hand pump. The engine starts and runs.

Do I need to crack the fuel lines before the injectors to bleed them as well? Would not they self prime with the high pressure of the IP?

Just asking.

Stretch · #17 11-14-2012, 10:40 AM

Quote:

Originally Posted by Silber Adler

I have a question, I replaced my fuel filters. and primed them back up with the hand pump. The engine starts and runs.

Do I need to crack the fuel lines before the injectors to bleed them as well? Would not they self prime with the high pressure of the IP?

Just asking.

If the engine runs as it should - then don't fix what isn't broken!

For the situation described in this thread where the engine will not run it might be necessary to make absolutely sure that there is no air between injector and injector pump...

Govert · #18 11-14-2012, 10:51 AM

Quote:

Originally Posted by Silber Adler

I have a question, I replaced my fuel filters. and primed them back up with the hand pump. The engine starts and runs.

Do I need to crack the fuel lines before the injectors to bleed them as well? Would not they self prime with the high pressure of the IP?

Just asking.

If you just replace the fuel filters, than the hard fuel lines to the injectors will not have air in them. Only the low-pressure area can/will have some air in it.

The hard fuel lines will be empty if you remove them for some reason, but even then the air will be pressed out by the IP, that is probably the reason why the FSM doesn't prescribe bleeding the hard fuel lines.

If your car doesn't start, opening the injector lines at the injector can be used to determine if fuel reaches the injector.

loneranger · #19 11-14-2012, 02:22 PM

for the next time. Go to the auto parts store and by an electric fuel pump. Put it in the line after the small in line filter. I put the switch for it in the counsel that has the power window switches but an under the hood switch would be just fine. If you run out of fuel etc. let this pump run for a minute to get all air out of the low pressure side of the IP. When I bleed injectors I usually do one at a time. If you have one or two that remain dry you may have problems with the IP. The engine should run on 4 cylinders which will help clear the fifth out. Only crack the line half a turn. Hope this helps. If the car has been sitting the filter in the tank my be plugged up. Or the purge may have busted some crude loose and plugged something up. Good luck.

cook · #20 11-17-2012, 01:38 PM

PM Send to UPOD

Glad your car started!!

tskraemer · #21 03-27-2017, 11:30 PM

'85 MB 300DT - was a daily driver until a couple hours ago. Replaced the fuel filter twice in the last two days and had no problems getting it going. Now, I can't seem to get the car started. Primed, etc. (Significantly leaky, but appears to get fuel to the filter) First time no problem. Second time it doesn't start. Even put the original fuel filter back on to see if it was just the wrong part (first time it was the wrong filter even though parts store said it was right).

So, having issue after replacing fuel filter. Is it possible that over tightening fuel filter bolt will prevent aspiration of the fuel pump? After checking and trying to bleed hard lines, cylinders 1,2 and 3 do not appear to be getting fuel. 4 and 5 show liquid when cracked, but have not opened them up all the way. Trying to decide if there is debris in the lines between the IP and the cylinders or if I am just not doing something right. With 1,2 and 3 open, no matter how much cranking am not getting fuel delivery.

Diseasel300 · #22 03-27-2017, 11:40 PM

If you have the "white" style primer handle, its been suggested to replace it as they can leak air as they age and make it damn difficult to prime the pump.

If you have a fair amount of air in the system, crack all 5 lines and crank the engine with the fuel pedal pushed to the floor until you're squirting out of all 5. Then tighten back down and try starting normally. The pedal to the floor will cause the IP to deliver more fuel and pump out quicker, especially if you have a lot of air in the system. With the injectors cracked, the engine isn't going to start, but you need the air out.

barry12345 · #23 03-28-2017, 12:03 AM

Using the primer pump it should get harder to push. If so get a helper to constantly keep the primer pump going as you crank the engine. Even after it starts. If that works you may have a very weak lift pump.

If when pumping the primer pump it does not get substantially harder to push. You have a defective primer pump or open relief valve perhaps. The injection pump is probably just fine as the engine was running somewhat normally.

Also on occasion when you get no resistance increasing when using the primer pump. You might observe fuel going back and forth in the primary clear filter.

This usually will be both the check valves in the lift pump are pretty much open all the time. The number one and two injection elements do not decide to work occasionally and then not. Chances are high that you have no fuel under pressure in the base of the injection pump. Double check that your glow plugs are still operational as well.

tskraemer · #24 03-28-2017, 12:23 AM

Thanks Diseasel300 and Barry12345 for the input. Will definitely try all suggestions in the morning and report back.

tskraemer · #25 03-28-2017, 07:10 PM

I tried everything you suggested and the only conclusion I can come to is that the primer pump is the issue. It does not get increasingly difficult upon priming and it just sprays diesel everywhere. It does get pressure to the filter and there is fuel going into and out of the filter housing, but it must not be enough pressure to get to the IP. Again, I did see some fuel leaking from the injectors when I cracked them, but even starting and pumping the primer pump at the same time was not enough. I am assuming there is an air bubble in the IP itself? Ordered a replacement primer pump, so hopefully this will resolve the issue. Also tried sealing everything back up except for the fittings at the cylinder heads and still no fuel at cylinder 1,2, and three no matter how much turnover.

Strange thing is I put the new filter back on and it sounded like it might give it a go for a minute (like maybe cylinders 4 and five were trying to fire) but eventually it just died down to the engine just trying to turn.

I thought about the glow plugs, but have not had a problem with them previously and indicator light on the dash (while I know is not necessarily trustworthy) operates correctly.

It should still have roughly a quarter tank of fuel and it has been a daily driver so I am not necessarily worried about the quality of the fuel as everything I have sprayed on myself is clear and the fuel looks good in the primary filter.

I guess I'll just wait for the new primer pump and go from there. Any other comments or suggestions in the meantime would be appreciated.

Thanks to everyone so far for your comments and support.

Diseasel300 · #26 03-28-2017, 07:32 PM

If the primer pump is making a big mess, it's time for a new one. The fuel system on the 617's isn't self-priming like the later cars are. If you don't burp the air out, you'll be there forever trying to get the thing started. Additionally, if the primer pump is leaking air, you'll not be getting the fuel pump to move fuel either.

It's extremely unlikely that you have an injection issue, merely a lack of fuel supply. Failed primer handles are very common and typically cause similar issues to what you're having.

barry12345 · #27 03-29-2017, 12:09 PM

Well if the primer pump did not substantially increase resistance when pumped. You have a problem. It may be the primer pump or something else.

Of course the primer pump is the first thing to replace in your case.

tskraemer · #28 03-29-2017, 07:44 PM

So current update is I got the new primer pump installed (correctly, I think). It is definitely not leaking and takes much more force to continually pump. After a while (several minutes of continuous pumping) there is a squeak every four pumps or so and some hissing, but after priming and trying to turn over the engine there is a dramatically better response. I cracked the cylinder 1 injector fitting at the IP and there is fuel leaking out. However, battery died and is charging now.

In the process of the trying to remove the old primer pump which took gorilla strength with a pair of vice grips, I managed to break two connections on the small hoses in the array above, I believe coming off of the exhaust line going to the brake cylinder master? One definitely goes to the IP housing. I am going to try and doctor up a temporary fix just to see if I can get it started, but I may need some help isolating and locating somewhere to get the fixtures. They are not listed in the Haynes manual I have so I will have to do some research and maybe post a picture.

However, I seem to be making progress. Once the battery is charged and I have some temporary fixes to the hoses I will continue to try and bleed the engine and report back.

Thanks again for all of the help and guidance

Diseasel300 · #29 03-29-2017, 08:30 PM

The lines you broke may be vacuum lines from the sound of your description. If so, you should be able to find a vacuum line chart for your year and model of vehicle. Some 1/8" vacuum line (not fuel line, it's too hard) will make a handy coupling and a suitable temporary repair.

Junkman · #30 03-29-2017, 08:34 PM

Are you absolutely sure that the glow plugs are getting current? I've never had a huge problem starting a 617 when the engine spins, there is compression, fuel and glow. Usually, 3 cylinders pumping fuel is enough to get it to run. The other cylinders fill and the engine smooths out once it starts. Synthetic fuel makes a huge difference when it is even down to the 20s or 30s.