We have a 992 g that sometimes runs fine ,and sometimes the engine smothers under load. This usually happens when the machine is getting warmer , and when riding and hoisting , but mostly hoisting is killing the engine. Now the local dealer wants to pull the engine , but I have the feeling that it is something of a sensor or sensing problem. Because the engine is not smoking when it nearly dies, I'm thinking hey the e.c.u. or something else is not letting the engine getting enough fuel. Anyone had this problem or similar?
I would start with trouble codes, then fuel pressure ( manual gauge ), boost pressure.
Seems a bit drastic to pull engine right away, what kind of trubleshooting has been done previously? My gut feeling is fuel supply problems.
As always - what's the Serial Number..? or at least the S/N prefix. Early machines were 7HR, followed by ADZ, the last ones before the 992K came in were AZX. I'm with Per & OW. What sort of diagnostic codes and/or events is it throwing when it misbehaves..? The thing I'd look for is when the machine starts "acting up" to run a Datalogger either on VIMS or ET - which one depends on whether or not the loader has VIMS, a lot of the early ones didn't. However the VIMS datalogger gives a much more comprehensive set of data. One thing that immediately comes to mind on 992G is the famous "Dig Trigger Strategy" that caused all sorts of complaints about loaders allegedly lacking power when it was introduced - I'm actually old enough to remember that far back. The machine electronics look for 3 factors - trans in 1st speed forward, ground speed less than 1mph/1.5kmh, & boom angle sensor less than a certain amount, the actual number escapes me. These 3 factors indicate that the loader is in the pile filling the bucket. At that point the Powertrain ECM activates the Dig Trigger which commands the engine to go from 1850 RPM High Idle down to 1400 RPM. The reason for this is that the engine produces its maximum torque at 1400 RPM but the converter can't absorb all of it, leaving the difference to be used to power the implement pumps. I wonder if for some reason the Dig Trigger is not DEACTIVATING..? Easy to tell because the RPM will stay bang on 1400. That would make the machine slow in hydraulic performance, especially when large fluid flows are required to move the cylinders fast - that needs max engine RPM. Here is a graphic of the theory behind how the system works. The blue line is the torque produced by the engine, the red one the capbility of the converter to absorb the torque, and the green the difference between the two @ 1400 RPM that is effectively the torque/power available to run the implement pumps. It all makes sense when you see it explained like this but try explaining to an operator that giving him less RPM will actually give him more power....!!
Thanks for the replies guys. The engine won't stay on 1400 rpm.. wish it was true. It drops all the way to 700 or sometimes if you hold the controls it parishes. Don't know about the serial.. I'll have a look.
Ah, why is it that all operators think more pressure is better no matter what pressure it is, I've been trying to explain for a few days that a lower powershift pressure on a Cat digger gives him more hydraulic power and not the other way around.
Usually I set the rimpull to low , it depends on the material..
Better that than spinning the tyres......... I usually disable the rimpull control at assembly time so that operators can't get maximum rimpull (only the reduced values) right from Day 1. So far I've had no complaints and with a good operator in the seat loader cycle times are usually world class. Ok, so we can assume the Dig Trigger is working OK. When the loader hits the pile and you're filling the bucket does the engine RPM fall from 1850 to 1400 just after you hit the material and then go back to 1850 again as soon as you engage reverse..? Note this is without trying to lift the bucket at the same time.
It's a 7HR
Oh, an old one then - well at least 15 years old anyhow. So here come the questions ...... 1. Does it have VIMS installed..? A lot of machines from that era had what was known as VIDS which looks like VIMS from in the cab but only displays parameter information rather than recording it to memory. You can check this by trying to activate the data logger function. Press the keys DLOG in that order then hit the key. If the machine has VIMS 4 small lights should start to flash in the top RH corner of the Message Centre Display. 2. What about my question from post #8 about what the engine RPM does when you hit the material then when you engage reverse..? You should see it go 1850 -> 1400 -> 1850 whether the machine is having problems or not. Do NOT try to use the hydraulic system other than lifting the bucket a minimum amount off the ground while you do this test. 3. Are there any strange noises from pins that might indicate something in the bucket/arm linkage is binding somewhere..? Not likely I know but let's answer the question just to rule it out. 4. Has anyone put a pressure gauge on the engine fuel rail and run it to the cab so that you can see what the fuel pressure is doing when the engine RPM falls..? 5. Did the problem start suddenly or has it been building up for a while..? Does the machine suffer from the problem more frequently today than it did say 1 week or 1 month ago..? In other words is the problem slowly getting worse..? I need to look into the hydraulic system a little bit regarding the implement pump control logic. Can't remember it 100% off the top of my head. I will most probably come back to you with some more questions once I've had the chance to read the book a little........ Edit ........... Well, that didn't take long. This machine has 2 implement pumps, one is fixed displacement, the other is variable. If the variable pump is not de-stroking properly when the hydraulic system is under high load then this will of course drag the engine RPM right down - although I would have expected that it would be also accompanied by black smoke as the engine ECM frantically tries to inject more fuel to maintain engine RPM at the required value. My first suggestion would be to put a gauge on the fuel pressure manifold and see what the fuel pressure does while the engine is at low RPM. My second suggestion would be to try to run a data logger on it while the machine is suffering the problem, using VIMS if possible but if not then Cat ET could do it. The problem is that either method will require a laptop equipped with the relevant software to download and analyze the results. If you have no-one on your job site then it will be a case of getting the dealer in to do the work.
Hey thanks Nige for this input. Have to try the dig trigger. My point exactly with the smoke.. is the variabele pump steered bij the ecm to or only the controls? Also (this machine is not my regular as I am on nearly every machine on site) I am pushing the inching pedal like hell ( on a 988h its a breeze) and still not get the result I want in slowing down the machine... the treshhold between decelerate and brake is very not to my likings
The inching pedal issue probably means that the torrque converter Impeller Clutch solenoid valve requires recalibrating (or maybe even replacing). Generally nobody bothers - we do them every 100 hours and it's a simple 2-step process. 1. Calibrate the LH pedal sensor. Type 7378 (SERV) on the keypad and hit . Use the right arrow (>) key to scroll through the menu options until you find the one for the left pedal position sensor. When you find the correct parameter press again and follow the on-screen instructions. Before you do this make sure that the back side of the pedal is not blocked up with mud so that it can return to the correct position. I've seen loads refuse to calibrate because there wasn't enough angle of movement in the pedal. 2. Calibrate the Impeller Clutch. Best done when the transmission is up to normal operating temperature, it can take up to 20 minutes with a cold machine but with a warm one only about 5 minutes. As before, type 7378 + and again use the right arrow key to scroll through the parameters. IIRC the Impeller Clutch calibration is the one after the LH pedal position sensor. As before, press once you find the correct parameter and follow the on-screen instructions. Let me know how the calibration process goes. It may be that the IC clutch solenoid valve is not working correctly (in which case it will probably need replacing and calibrating again once the replacement is installed) but you have to try the calibration process first and see how it goes. If everything calibrates correctly you should see an immediate difference in left pedal response.
Mecanics replaced a govenorvalve? and there was 1 injector slowly dying.. replaced that 2 , and the engine is running on all 8 again and seems to operate within specs now...