Excavator stalling under load

[RobMonk]

I have a Cat 311B and the last couple of times I was using it, loads that would normally do nothing to the machine are bogging the engine down to the point where a couple of times it actually stalled. The last time I was using it I was frigging around with it a bit and I thought I had cured the problem but about 3 hours into the day it started acting up again. It sounds like a lack of fuel issue because it seems to be intermittent. I can lift a small rock and almost stall it and then lift a huge rock and it does nothing. I am working on the theory of water in the fuel or a bad filter but I decided I would run it by the forum to see if anyone else had this problem in the past.

 

[Bob/Ont]

Is there any smoke when it loads up heavy? Smoke would rule out lack of fuel. That would indicate a control problem.
Later Bob

 

[RobMonk]

Didn't notice any extra smoke. That doesn't mean there isn't any, I just didn't notice anything out of the ordinary.

 

[John C.]

You need to check for fault codes.

 

[mclean]

We had a 320 that would stall after 1/2 hour or so because the fuel cap breather was plugged. Your problem sounds more pump control related though.. Be interesting to see what the computer thinks is wrong.

 

[RobMonk]

So After trying a few simple 'fixes' where nothing was fixed, I think it is time to look deeper. How does one go about getting the codes?

 

[Delmer]

Is there any smoke when it loads up heavy? Smoke would rule out lack of fuel. That would indicate a control problem.
Later Bob

Can't help you on the codes, but smoking or not is a good start.

 

[RobMonk]

No smoke.

 

[Bob/Ont]

No smoke No fuel, check for a clogged screen, think there is one in the line fitting at the pump.
Later Bob

 

[RobMonk]

When you say 'in the line fitting' do you mean like I take the hose off and there is a screen when I look at the line? Can someone verify if this is the location please. I don't want to start messing with the fuel and then needing to prime the fuel again with no results.

 

[Thomasdiesel]

I believe this engine is made by Mitsubishi and is a mechanical fuel system, ( no electronic controls ). I does have an electric actuator to operate throttle lever on pump. Make shire the throttle is operating first. If it doesn't go to full throttle under load, the problem could be in actuator or controls. If it is going to full throttle, you need to check for fuel inlet restrictions. There is a fuel transfer pump the draws fuel from tank and supplies the injection pump. You can install a vacuum gauge on inlet side of transfer pump and chech to see it pulls a vacuum, if vacuum is too high it indicates a restriction. This could be a pluged filter, debris plugging a fitting, trash in tank ect. You also need to check transfer pump pressure. You should be able to get this spec from dealer, or from service manual. You could start with checking pump pressure, if it's ok you could move on. Then check intake air system. Check air filter, intake tubing ect. If that all checks out, you need to inspect turbo charger. If it isn't building boost, the AFC, or what Cat call the ratio valve, won't open up rack in pump for full fuel. Hope this helps.

 

[Bob/Ont]

Look for a banjo fitting on the fuel line at the pump, the banjo bolt should have a screen inside of it.
Later Bob

When you say 'in the line fitting' do you mean like I take the hose off and there is a screen when I look at the line? Can someone verify if this is the location please. I don't want to start messing with the fuel and then needing to prime the fuel again with no results.

 

[rossaroni]

I have a 303.5 that did what you had said. At first, draining out the water separator would help it, but eventually wound up pulling the fuel tank to clean out all of the junk from it. Never happened again.

 

[RobMonk]

Look for a banjo fitting on the fuel line at the pump, the banjo bolt should have a screen inside of it.
Later Bob

When you say pump, do you mean supply pump or injection pump. I haven't looked at it yet but I assume the machine would have both of these.

 

[Bob/Ont]

I forget exactly what yours hooks up like but look at all line connections at the injection pump or what ever transfer pump it has.
Later Bob

 

[Nige]

Looking at the simple things first, does it have a water separator in the fuel lines right near the tank..? If yes have you tried draining it and what came out..?

Also when it misbehaves have you tried cracking the fuel tank cap to check if there is a vacuum in the tank..?

Post a Serial Number prefix so that we can look at your particular machine in the system.

 

[RobMonk]

Just a bit of an update for posterity.

There is a Banjo bolt with screen in the line that goes from the filter to the transfer pump. Took it apart and there was miscellaneous gunk gumming things up. Cleaned it thoroughly and put it back together. The machine works good but I did have anything to work it hard on to see if it was fixed or not, although I suspect that was the problem.

The other things I want to do is scream at Cat. What a ridiculous setup. You need to lay down on the top of the machine and put a socket in a place that you can barely get any leverage on it to fix something that will need to be cleaned some what frequently. also a screen in a banjo bolt!?!? why not some sort of in line filter!?!?!

 

[Logan]

Hitachi do it too mate. Ran an ex200-5 with the same issue. If you ran it much below 1/4 tank it played up and I got pretty quick at clearing the banjo filter. Trouble with cat and maybe the other brands too, is the tank inlet that lets fuel out of the tank to go up to the pump, that inlet seems to be the lowest point in the tank on equal footing with the tank drain tap. So regular sample draining and assessment of drained fuel is a good idea for older machines. Water and rust particles caused by the waters presence on the bottom of the tank, migrate to this point, which is brainless from a design viewpoint. I'm considering drilling a hole about 50mm off the bottom as the new supply line. That way I only have to do a fuel sample each week. The old timers that say keep a full tank every night, they knew what they were talking about. I'm also thinking a stainless replacement tank is probably wise once rust starts in there. I now run an inline filter at the tank, a Facet (USAmade) 24volt fuel pump, then a Delphi settling bowl filter inline, then the cartridge filter to cope with the inherited problem but she runs sweet fuel-wise now. Guess I need to get better at sweet talking bankers into buying me a new machine.

 

[Nige]

Just a bit of an update for posterity.

There is a Banjo bolt with screen in the line that goes from the filter to the transfer pump. Took it apart and there was miscellaneous gunk gumming things up. Cleaned it thoroughly and put it back together. The machine works good but I did have anything to work it hard on to see if it was fixed or not, although I suspect that was the problem.

The other things I want to do is scream at Cat. What a ridiculous setup. You need to lay down on the top of the machine and put a socket in a place that you can barely get any leverage on it to fix something that will need to be cleaned some what frequently. also a screen in a banjo bolt!?!? why not some sort of in line filter!?!?!

The screen in the banjo bolt is effectively the last line of defence. If the fuel tank is drained of water & sediment at the correct frequency, and if the correct fuel filter servicing is done, that screen should never get dirty. Also note that there is an optional water separator in the fuel system that whoever bought the excavator new decided they didn't need, it might have been really useful to you.

 

[Edward D. Dixon]

I have a Cat 311B and the last couple of times I was using it, loads that would normally do nothing to the machine are bogging the engine down to the point where a couple of times it actually stalled. The last time I was using it I was frigging around with it a bit and I thought I had cured the problem but about 3 hours into the day it started acting up again. It sounds like a lack of fuel issue because it seems to be intermittent. I can lift a small rock and almost stall it and then lift a huge rock and it does nothing. I am working on the theory of water in the fuel or a bad filter but I decided I would run it by the forum to see if anyone else had this problem in the past.

I'm no expert by any means but may I suggest starting at the cheap end of the problem and working your way to the expensive end. In this case the fuel would be the cheapest part. Drain the fuel and replace with fresh fuel. If that doesn't fix the problem (probably won't) you can put it back in later. Maybe mix it with clean fuel at 1/5 ratio. Look at the bottom of the tank. Is it clean? If not, clean it. Then hoses. I wouldn't worry about losing prime. If everything is working properly, repriming the system is a five minute, super easy process. I would check every banjo fitting for blockages. Then the lift pump. That is an easy check. unscrew the vent on the filter housing and pump the lift pump. If fuel comes out the vent, it ain't the pump. It could still be the inside of the pump though. That lift pump has two sections. The hand pump and the camp activated pump. The hand pump is a ten dollar replacement and the rest of it including a new hand pump is about $60. The fuel filter should be considered as a potential problem. Look closely for a hole in the fuel line also. That was an issue for me once. After all that, is the injector and good luck with that. above my pay scale.