To finish Coastie54’s input here’s what we did today:
Problem solved: replaced HEUI pump (for the second time in only 1500 miles). Apparently our first factory reman HEUI unit was faulty.
While troubleshooting without benefit of CAT ET software diagnoses we replaced the following:
IAPCV valve
Throttle position sensor
These seemed likely culprits for derate condition based on what RV owners have experienced with CAT 3126 series engines.
Engine continued to throw check engine light during acceleration through 35-42 mph range and would derate engine performance every time we tried to go faster than 42 mph.
Once we got to a CAT service facility, the first ET indication of a problem pointed to IAP Sensor for injection oil pressure readings. CAT ET showed IAP erratic code which could be attributed to low sensor signal, excessive oil return from injectors or weak HEUI pump. So we replaced the sensor and this still had no effect. On the up side, noticed oil leak from sensor o ring that had deformed so by replacing this sensor and o ring we eliminated a pesky and mysterious oil leak.
Today replaced HEUI pump at CAT dealer and she runs like a champ. No CEL indications. Much more power and more boost from what my ears tell me.
FYI: after first HEUI failure we flushed all oil galleries. No metal noted. Kept same injectors in service after removing them and inspecting them. No metal noted on second HEUI partial failure so kept original injectors in place. Runs fine.
Just wanted to close this issue out and not leave the thread hanging.
Thanks to all who responded.
Be careful out there and thanks for your service...
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