I am working on a CAT 311C U serial # CKE1891. Machine pulls engine RPM down when under load to the point of stalling in some cases. I have checked and confirmed main relief pressure. Engine is running well, I believe it to be a hydraulic control issue. Powershift pressure is 300psi with machine at low idle at rest- goes to 400-425psi over relief at low idle. At high idle it goes from 300psi at rest to 200psi when over relief and pulling down engine rpms. I was under the impression Powershift pressure should INCREASE to destroke pumps, found it odd at low idle it does but then changes to decrease pressure at high rpm. Checked voltage back probing connector I see roughly 6.5 volts at rest 8.3v when powershift pressure increase 5.4v when it decreases at high rpm. Any thoughts on this? Thank you
Sounds like the powershift is doing it's job & trying to keep the revs reasonably constant. I had a 312 that probably had the same engine as yours that was doing similar & we found that the turbo was actually seized. The electronic & hydraulic controls were good enough to keep the machine running & working until it had to really work hard.
I will be sure to check that thanks
If anyone can benefit from the resolution to this issue- Connected CAT ET found code 190-8 for engine speed sensor irregular reading. Found break in the harness where the 2 engine speed sensor wires tie into the the harness near the intake heater wire. Repaired wiring and calibrated automatic governor and powershift solenoid and no more stalling.