I was an idiot and ran my backhoe/FEL out of fuel the other day. I believe I now have air in the line preventing the machine from starting. I've come across a few videos online but I'm still not sure how to purge/bleed the line. Can someone explain how I should or can proceed to get the air out? From my limited understanding I believe I can use vacuum to pull fuel out through the return line. I have available a hand vacuum pump from a brake bleeder kit and also a 7 cfm A/C vacuum pump. From my understanding I may have to purge or bleed the fuel line at a few different locations. I've also seen guys loosen injectors to bleed air out. The machine is a 1986 New Holland LB-620. The engine is an Onan 4 cyl diesel. The first pic is obviously not my engine but similar. Second pic is Water Separator/filter? Third Fuel Filter Forth fuel injection pump? Any help would be appreciated. Thanks
Here are a couple other pics
I was able to find what I believe is the fuel lift pump. I was trying to find it using a parts catalog which is horrible. I was able to do a cross reference which shows the level on the pump. Sure enough it's under there but very hard to see. Now, I believe I'm supposed to bleed the water separator/fuel filter first by loosening the nut shown in the red circle. I'll have to review this a bit more for the next step. The final step I believe is loosening the injectors to let air out that way.
Do NOT LOOSEN THAT SCREW! That holds your slurry bowl top, and bottom together. If you don't have the seals for it, you'll most likely cause a leak. Just pump the lever, til the lever kinda falls away, wait a few then do it again. Now crack a line nut loose to an injector. Crank engine til fuel jets from loose line. Tighten line reasonably tight and start.
Thanks a lot. I won't loosen that screw. I'm not sure what you mean by the lever falling away but I guess I'll notice it when I try pumping it. I'm still waiting for my fuel filter to come in the mail before I go any further. I think it should be here Tues. Thanks
Not familiar with this particular engine but if the fuel lift pump is one of those that works off a lobe on the camshaft if it does not seem to be doing anything try turning the engine over maybe half a turn or so and try again. Reason is if the engine stops with the pump plunger on the high side of the cam lobe the hand lever will not do anything, needs to be on low side of the cam lobe. Problem is there is no simple way to know this so it's more or less done by feel on the lever.
This engine is an Onan L series, also known as a Cummins A series. It has a rotary Stanadyne pump which in my experience really don't like to pick up air in the suction. In the last picture in the first post is the injection pump. In the center of it, right above the oil pressure switch in the picture, is the inlet nut. Loosen that or even pull it off a little bit and pump the transfer pump until you get good solid fuel out of there. Then put it back on tight and it should start up pretty quick. I have never found the need to crack injector lines but you can try if it proves to be stubborn. Beware of disturbing the inlet and outlet lines to the square filter because they have a rubber compression ring and they might leak and have to be replaced and not real easy to find.
I see where you are saying to loosen inlet nut. I've read that many injection pumps have bleeder screws to purge at the pump. I haven't found any on this Stanadyne so loosening the line makes sense. When I was looking up Stanadyne pumps I came across this picture where it shows you can bleed at the return line (I circled the inlet with green and the return is the red circle). The return is a little higher so maybe bleeding there would be a better option? I'll probably crack the injector lines because this machine can be stubborn to start regardless. I'm probably overthinking this. I know I just need to get the air out but also don't want to loosen the wrong nut, bolt, or line. I read where someone loosened the wrong bolt on his injector pump and had to pull the whole unit off and bring it to a diesel repair shop. Thanks
TPGsc has not stepped in here but my understanding of this pump is that the first thing the fuel comes to after the center inlet nut is a vane pump, kind of a lame transfer pump part 2. This vane pump does not pump air very well and any air that is trapped ahead of it will take forever to purge so getting fuel right to that point will allow it to start pumping fuel and then the very next thing it does is to start going to the injection pistons so it may well pick up and take off if you do that. Conversely you can pump and pump the separate transfer pump and nothing can pass through the vane pump if the engine is not rotating. The housing bleed screw is that slotted screw in the black and white picture at about the 4 o'clock relative to the red circle but near as I can tell it doesn't do anything different than the return line to the tank so I seldom mess with it. But you can remove it and observe fuel flow if you are not sure if the injection pump is getting fuel, any time the engine rotates, solid fuel should dribble out that screw hole.
This pretty much confirms what you described in removing the inlet line for bleeding. The filter outlet is a bit higher but I don't want to disturb that connection if you think it may leak. When bleeding at the injectors it's saying to open the throttle wide open and crank the engine to purge the air. I guess the transfer pump is only for supplying fuel to the injector pump? This was from a John Deere manual and also states this is for Stanadyne rotary pumps. The difference is they're saying to bleed at the return line. Not sure why it's different.
So I guess this is why the instructions I posted say the engine needs to be cranked to bleed at the injectors..........
Well, in theory, the pump only so much fuel into the injection line per stroke. If the line is full of air it will push it in but never reach nozzle opening pressure and spring back into the pump when the injection event completes, thus never purging the high pressure injection lines. In practice, once you get good fuel to the pumping elements, whatever they are, the engine will start, in my experience. I suppose they still have a considerable amount of fuel in them because once the pump runs out of fuel it cannotreally pump the fuel out and the high pressure lines full of air. So the long and short of it, don't overthink it, just get fuel to the central nut with the priming lever, tighten it up, and let it rip.
As long as you have fuel TO THE INLET of the inj. pump, the inj. pump will take it from there.. You just have to get the AIR out of the lines GOING TO the injectors.. Loosen a couple or ALL of them & crank the engine till fuel squirts out & tighten.. Have the throttle wide open. I would leave the return alone.. The pump will bleed itself.. Good luck.
I have a much better idea of how the fuel system operates now. Thanks everyone, hopefully this is the last you'll hear from me.
No, you have to come back and tell us how it went after you have it running again, you can't leave us hanging.
Ok, will do. Looks like Wed as long as the weather permits.
Yes as Birken says be sure to let us know what you did and what worked. Nothing pi$$e$ of many people as giving advice and then never knowing if it worked. Also this is not just to give warm fuzzy feelings to those that have helped. Someone else five years from now might find this site while trying to solve the same problem and your reply might be just the information they need to fix their problem!
last time, huh?? Until the flex ring goes out.. I see the lead seals on you pump have ADS stamped/pressed in them.. which means the pump has been off before & taken into an ADS shop.. Hopefully they put in a solid weight retainer?? {EID} IF NOT.. We'll be see'n ya..
Some people have good eyes! Not that the letters on the tag would have meant anything to me! But it is always good to know there are people out there who can spot things like that.
Pulled the inlet line off and manually started pumping the lift pump. It felt like I was only pumping air and no fuel was coming out. Checked the fuel tank and it's pretty much empty even though I put a good 5 gallons in last week. I'm not sure why there's no fuel, I didn't have a leak before. Right now there's snow on the ground and the machine is soaked. It will be a few days before things dry out. Hard to find a leak in this weather.
Leaks on suction side are a challenge. Since they pull air rather than leak fuel. Try priming her up from an alternate source like a 5 gallon jug of fuel. That way you can see if your fuel level diminishes while priming
Seems like it's not pumping much fuel. Is this correct?
That's pretty weak, looks like check valve might be hung open. Are you getting full stroke on the pump lever, or do you have a long dead spot followed by a little resistance?
Here's another video. I have the tube hooked to the inlet "stub" where the filter sits on. That's about as full swing with the pump as I can get. About 1/2 to 3/4 of the way I feel a little resistance like it's starting to pump. It doesn't seem like much but I don't know.
That second video doesn't look too bad? How the pump works isn't intuitive. The lever and cam lobe pulls down the diaphragm against a spring, which pushes the fuel out. If the outlet is blocked the fuel will maintain pressure by the spring and the diaphragm won't return and there won't be pressure on the arm, just the little external return spring. (that diaphragm wouldn't last an hour at full stroke at engine speed). If you get much more pressure than the main spring, then you might be pulling against a blocked suction side. Disconnect the inlet and see if it gets easier to go the whole stroke. Then find your blockage on the suction side (reconnect, then go one step at a time checking for vacuum with the pump). Or hook both sides of the pump up to a can of fuel and see how it pumps when you block the inlet, outlet, etc.
I decided I'd try putting it back together. When I loosened the injectors some fuel came out but it wasn't spraying out like it was under high pressure. I did get it to start for about 1.5 secs on two occasions but that was it. I'm not sure if I flooded it, it's the weather, or something else but it won't start. I'm charging the battery now and may try again tomorrow. By looking at the smoke from the exhaust it looks like it's getting at least some fuel. Seems it to me but I don't know.
MAKE SURE the throttle is wide open when trying to start it or bleed it.. Do you have an air compressor?? Loosen the lines at strategic points, before the filter, at the pump inlet, ect. & pressurize the system..
^^^^^^^ What he said , except, regulate air to no more than 5-6 psi. Any more and you may wind up with unintended consequences
Back to basics though. If and when you pressurize the fuel system start at the lift pump inlet, you should have steady flow. If you do not, one of 3 things. Insufficient fuel or damaged stand pipe or obstruction in supply. If this occurs, run off alternate source. It's hard enough to diag no start but to do it with unknown source really causes grief.
Or just dump fuel into the tank 5 gallons a day whenever you get home, until it is nearly full, you know it ran fine before so no reason it should change now.
That's a clue that your suction is plugged. Which is why it stalled after starting. Look for another problem all you want, or find the problem you have. If it's sucking air, then it would be blowing air out with the little bits of fuel and not having added resistance 1/2 -3/4 of the way on the pump stroke.
Can I bypass the lift pump using gravity to feed the injector pump? I could put a fuel source above the injector pump and siphon it into the fuel filter outlet port so it feeds into the injector pump. Would this work or do I need pressure at the inlet port of the injector pump?
That should work, bearing in mind that the pump returns quite a bit to the tank so once it is running, it will pump out the gravity tank pretty quick. Also I would not under any circumstances run unfiltered fuel into an injection pump. Maybe just gravity it into the lift pump inlet.
This seems like the easiest thing to do next. I could try pressurizing the system but I don't have the correct fittings. Anyone see why gravity feed to the injector pump would not work? I did try to bleed again at the injector inlet and then at the injectors earlier today. I'm not getting much fuel out of the injector lines. I'm hoping it's not the injector pump.
Are you philosophically opposed to finding the problem for some reason? This seems simple, find the problem, fix the problem, done. I don't see what you get by using a temporary tank in this situation. If it starts and runs until the temporary tank runs out, then you know you have a blocked fuel supply, which you already know. Why not find the blockage and fix it? You can use the priming pump to find the blockage, or pressurize the tank and see where you get good flow and where you don't. A piece of inner tube with the valve stem attached, held over the fuel filler opening is an easy way to get a pound or two of air pressure in a tank. Or if there's an overflow/vent tube, hook a clean tube to it and blow by mouth.
The reason I wanted to try the temporary fuel tank was to see if the injector pump is working. I guess I want to hear the engine run. I'll try pressurizing the system and see if that works. I have small air pump and will need to pick up a schrader valve. It will be a couple days because of work.
If you have a regular air compressor a helper with a rag shoved on the gas filler and a blowing air hose in there as well will do it, just watch the line to the IP and tighten it on when fuel shoots out, then it should start right up same as it was before it ran out.
I got it fixed. I temporarily changed out all my rubber fuel lines to clear pvc so I could see what was going on. I think the water/fuel separator was leaking just enough to not allow me to draw fuel up. After I got it put back together I ran it with the pvc line temporarily to make sure air wasn't getting into the line. I've changed it back since this video. I learned a lot from this and everyone here. Thanks everyone for the help.
Just adding this video that I realized I had taken. I was able to start the machine using siphon/gravity from a 5 gallon tank. Once I lowered the tank the machine kept running. The clear vinyl/pvc tubing allowed me to see what was happening. In the video you can see a significant air leak coming from the water/air separator. The rubber grommet on the bottom the water/air separator had a very small leak which I didn't see what the machine was not running. Thanks again for everyone's help.