Posting for a friend:
We have a 1999 Cat 953C track loader with an attitude.
The history is: The engine was just rebuilt, which entails cab-off. After rebuild, the head shop which did the heads botched the job and the cab and engine came out again.
The problem is:
Now...the engine runs sweet. It's all hydrostatic and ECM controlled. At full throttle it takes off and then slows to a crawl in 30 ft. Engine still at full rpm. Bring the trans into neutral and it will again take off and slow down slowly to a crawl.
Now, if you keep the rpm 200 below the recommended operating setting (full rpm)....it works just fine, but lacks the governor response of the full throttle setting.
Cat has put their computer on the ECM and downloaded the data. Also two occurrences of low voltage, which was the battery going dead after sitting a while, which they said are not important. One weak track sensor was found and replaced. No difference. It has been operated for hours with the ECM on wireless and the laptop recording all data. Nothing shows up as the errors occur.
At this point they have given up on it. Cat has a unique form of doublespeak which really means "We are stumped, but give us all your money and we'll try to figure something out." (So BP-ish)
Has anyone dealt with or heard of a similar problem in any Cat hydrostatic drive systems?
Was the machine operating fine before the engine work was preformed?
How many hours are on the machine?
Has any work been done on the drive pumps?
Sounds just like our local stealer umm I meant dealer.
A couple of questions, is the is ECM connected to the hydraulic control system on the loader? Yes
When the loader slows to a crawl, are the other hydraulic systems fully functional and at speed?Yes
Drive coupler to pump stripped?I don't think so
I'm thinking it's in the oil supply to the pump, is there a hose collapsing internally? I've seen rubber hoses that the inner liner collapses in cutting off flow.
Any way of checking the hydraulic oil for aeration? If there's a defect in the drive pump, it could be pumping air into the oil at higher RPMs. This is worth checking out, but aeration usually causes jerky operation of hydraulics. But IIRC, this is a multiple section pump, so the drive section could fail and the hydraulic section work ok, but sucking air should affect them all
This statement point me to the governor doing something abnormal (the ECM may think it is acting perfectly) could it think it running to fast and go into a default slow you down controllably mode, shifting to neutral resets things? Yes, this points to the govornor or ECM
You said the engine was re-done, but were any of the hydraulic lines cracked open to gain access to the engine?
If the 'puter & sensors are checking out ok, I would next suspect something blocking a rotary valve in the hydraulics or something that is dumping pressures after it moves a bit. Knowing nothing about the hydrostatic systems of the Cat, I would hesitate replacing parts until I knew what was really wrong.
I believe the lines were left intact and the pump removed from the engine. All controls are electric over hydraulic. The owner is hesitant to replace parts willy nilly (sensors are $400 plus) and he blames the shop as it worked perfectly before the rebuild. That said...with the amount of blowby coming out of her before the rebuild, it may not have been able to reach top rpm and so this may not have shown up.
Silly idea, but there are strainers in the hydraulic tank. Have you drained the tank and checked them?
Also there should have been no need to disconnect hoses, but if you drain the tank down, check the supply hoses to see no-one's left a plug in there.
My 953 was doing the same thing. A filter/fluid change fixed my hydrostat. But then mine is an 1984 cat. not one of these new machines.
I know it's an old-ish thread but was searching and found it,
calibrate calibrate calibrate. its something you can do yourself,
and then i would lower the engine RPM and then i made a thread on how to adjust the governer (its a 3 min job).
i would also check the WOT (wide open throttle) switch for proper function.
There is TWO drive pumps on the machine and arent driven off a "coupler" off the end of the crankshaft,....more of a flywheel looking thing,
BTW;....how do you define a "weak" track speed sensor??
I would also change the charge filter.