I am having stalling trouble with a 1994 311 Excavator SN 9LJ00380. It blows black smoke and stalls, or nearly stalls, when putting a load on the machine, or when the cylinders for the boom, stick, or bucket are bottomed out. Also when turning machine. All filters have been changed and I verified machine was not in "limp mode" at the switch. Anyone have any ideas how to diagnose and repair this problem? I have read a few other post with some other machines having the same trouble, but not a 311 Excavator, so, I don't think they will pertain to this excavator. Please help! Thanks in advance for any help...
the problem will most likely be the signal (or more correctly the lack of one) that destrokes the main hydraulic pump to avoid overloading the engine. Don't read too much into the fact the fact you haven't seen the problem on a 311 but on other models in the Cat range. They all work pretty much the same. I'm sure one of our resident excavator experts will be around shortly to help you. BTW kudos for posting your machine Serial Number right from the get-go. Most posters don't and especially with excavators there can literally be dozens of variants of the same model. A question. You don't specifically mention it but have you done the basic checks on the fuel system (drain sediment/water from the tank, drain/replace water separator, change secondary filter, etc, etc) just to rule that side out..?
Thanks for the reply G..G..G.. Yes I have done all the basic checks. I did notice that the engine speed would not even try to increase rpm when the engine was put under a load. I watched the linkage from what I believe is a governor and it didn't move at all as the engine started losing rpm......
Basically what happens is that when you have the throttle control at maximum the implement hydraulic pump flow is controlled by a signal from the electronic system which moves the pump swashplate to keep the engine at full load all the time. If the demands of the hydraulic system exceed the power the engine can put out then the engine is going to give all the signs of having "low power" when in actual fact the engine is turning out all the power it can but the hydraulic system wants more than the engine can give, if you get my drift. What sounds like is happening with your machine is that the signal to destroke the pump to balance the demands of the hydraulic system with the power output of the engine is not coming. If you want a copy of a document explaining how the system works send me a PM with your email address.
I think it might the PRV solenoid, but, I don't know where it is located, or how to diagnose it.....my email is [email protected] . Thanks for your help..
I got the files Nigel. Thank you very much. This is just what I needed!