My 590SM runs very good until I push it or load it up. When I try to dig into a pile of dirt and give it more fuel it bogs down and starts to stutter even when I back off and sometimes stalls. If I use a lower gear 1 or 2 and let the momentum of the machine dig into the pile, I can scoop it up and dump it in my dump truck. When it does bog down I either have to shut down the machine and wait about 30 sec then restart and all is well or sometimes I have to shut it down and loosen the fuel connection at the injector pump after the fuel filter and pump the fuel pump to get out air. After that it starts fine until I push it again. I replaced the fuel pump, fuel filter, fuel line from the pump to the tank, removed the pick up assembly from the tank and checked for debris or a blockage but all seems fine. No smoke, black or white when it happens. It just seems that it is starving for fuel. Is it possible that they sold me a bad fuel pump? When it's running good I can tack it out at 2300 and hold it there with no problems - it's only under load that this happens. Anyone ever have this problem or have any ideas?
Did you do these things before or after this problem? Obviously under a load the machine demands more fuel. It's sucking in air somewhere between the pump and tank. Couldn't tell you if they sold you a bad or wrong pump.
I actually replaced the fuel pump before this problem because it wasn't picking up and you couldn't prime it by hand anymore. Replaced the pump and all was well. The problem is that we didn't really use the machine to load it up so I'm not sure if the new problem was right away. I also replace one of the return lines from the cooler back to the tank. That was leaking. If the return line is kinked or restricted will the injector pump build up pressure and cause the problem?
Unfortunately this is not my expertise. If you blew air threw all the lines and there is no restriction and all the connections and filters are tight, then anything I would say beyond that would be a guess. Hopefully someone else will chime in. Good luck.
I was wondering if anyone knows if the injector pump pulls fuel or does it only get the fuel supplied from the pick up pump. My thoughts are that if the engine uses more fuel when under load then maybe the pick up pump is not supplying enough that the injector pump needs and then the injector pump would pull down the supply lines to a vacuum and possibly pull in air. It's a long shout but just a thought.
There should not be any air in the system under any circumstances. Whether the engine is under load or not under load, it doesn't matter. with engine shut off try putting about 3 to 5 psi of air pressure in the fuel tank and look for fuel leaking.
Ok, I pressurized the fuel tank and not a drop of fuel from any fitting, filter or hose. I held it for a while and not even a wet spot sighted.
Have you tried loosening the fuel cap when it starts to lose power? There's a 1/4" vent hose shown that connects to a breather on the tank mounting bracket on the end that has the fuel fill? Could be plugged causing a hard vacuum.
I haven't tried that. I did see the 3rd line that is connected to the tank but I didn't know where it went. I think I'll try and disconnect it and blow a little air through to be sure it is clear. FYI I just came in from working on the machine. I disconnected the fuel lines from the pick up pump, checked all connections, reinstalled the pump, primed it up, pressurized the tank again to be sure there are no leaks. I was distracted by a phone call but I'm going back out to test if the machine still bogs down under load. If it does then the first thing I'll try is to loosen the cap. Maybe if it does bog down then I should try it without the cap. Got about a 1/2 tank so it shouldn't slosh out.
Update - I removed the 1/4" hose and blew through it with no resistance. I then pressurized that tank and air came out of the 1/4" port. I put it back together and drove the machine across the street where there is an open field in 2nd gear at full throttle with no bogging down. I back bladed in 2nd gear and after about 30 - 40' it bogged down and almost stalled. I backed off the throttle and it recovered. I then removed the fuel cap to eliminate that and back bladed again and the same thing happened. I put the cap back on and drove it back to my shop in 2nd at full throttle with no bog. This is a very strange problem. Only under load does it lose power and bog down and with no smoke.
Punctured aneroid diaphragm? Might be time to take the injection pump to a fuel shop. I'm assuming this is an early one with the mechanical pump?
I believe it is a mechanical pump but how does the aneroid diaphragm get punctured? Would that suck in air under load? It that something I could replace myself? I appreciate the input lantraxco.
It's a long shot for sure, but the aneroid or whatever you want to call it senses turbo boost and makes the pump increase fuel delivery to match. Since there is some air pressure there when the turbo is working if the diaphragm did have a leak, it might push air into the injection pump? I'm guessing here so....
What series is your 590SM ? Some of them have a fuel tank breather that is not in the filler cap.
Does this machine have an electric lift pump? If so, is it working?
This machine does have a breather hose - not blocked and no electric lift pump. I guess it's time to search for a place to send my injector pump to for troubleshoot and repair. Anyone know of a place that I can ship it to?
I am quoting you because you are saying you have to purge air out of the fuel line at the fitting on the injector pump. If that is what is going on you have a leak somewhere between the fuel tank and that fitting on the injector pump. You should be cracking the fuel lines loose at the injectors and bleeding the air out. It is the only way to get the air completely out of the system. Does the engine misfire on any of the cylinders when it slows down and stalls ? Although there is no electric lift pump there is a pump on the back of the injector pump, one hose in and one hose out.
Before you pull the pump, I'd hook up a vacuum/pressure gauge to a tee added to the fuel supply line just before the injection pump. Keep an eye on that pressure and if it stays steady while the engine stalls, THEN you have a much better idea that the pump is the problem, or the return or aneroid? How about a picture of the injection pump? Or does it have a pressure line from the intake manifold to the injection pump?
I'm not at work now but tomorrow I'll take a pic of the pump and surrounding area. It does have a plastic line from the intake manifold to a square discus looking devise on the injector pump. Also, I'll make up a temp tee with a compound gauge. What pressure should I expect to see under load and no load conditions. I realize that it probably should never go into a vacuum but lets see. Thanks for the ideas.
I don't know the spec, but I'd guess around 5 PSI. It won't be enough to damage a low pressure gauge. The main thing is that it stays steady at various rpm and load. The picture is probably unnecessary, I'm the only one who's not familiar with the pump.
Ok, I cut in a tee in the fuel line leading from the lift pump and before the fuel filter. I put a compound gauge on it and what I found is this: when I started it up I was reading about 5 psi. Then I ran up the RPM to max and the gauge dropped to almost 0 but slightly above. Under load it fluctuated under 0 but would recover. I then put it through a hard run of digging in piles of dirt and the whole time it hovered around 0. After the machine was at full operating temperature I did some back blading and it was then that I noticed the gauge went about -1 or -2 psi and the machine would bog down and start to act like it would stall. I called Case where I bought the lift pump from and they said that the pump only has a 30 day warranty. I purchased it 7/24/15 so I kind of feel pissed that they wouldn't stand behind the pump. Bottom line is, I am sure I have a bad lift pump and the replacement will cure my problem.
The good news is it's probably not your injection pump. If you want to be sure it's the lift pump that's bad, put the gauge between the lift pump and the tank. Or leave the gauge where it was and let the lift pump suck out of a can of fuel for a short test.
Faulty lift pump maybe, don't discount the possibility that something is in the fuel tank,intermittently blocking the flow to the lift pump. I have seen it happen many times on different machines. I have removed weird stuff from tanks. Rags and weeds were the most common. I had a man tell me he had a fuel tank that had a baffle get loose in the tank and every so often it would cover the fuel outlet.
I replaced the lift pump and the machine runs like new. I put it through the paces and no problems. I then decided to do an autopsy on the lift pump and found something very interesting. Inside the intake under the connection where the hose adaptor screws into, is a brass screen. That screen was almost completely clogged with sediment. Obviously I have crap in my tank that needs to be addressed but I can't believe that this was my problem all along. Thanks to all for your suggestions and comments. If I ever have power problems again I now know where to look first. I'm also thinking of installing a pre-filter. PS - I have a spare lift pump on the shelf ready to go LOL.
Yup, lol... been there done that, manufacturers like to hide those screens. I would suggest a water separator/prefilter. Good job!