Cat 3126 hard to start hot: injection oil pressure
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Applies to: Caterpillar 3126 (HEUI) diesel engines
Symptoms
- Starts cold but cranks long when hot
- Rough running or misfire when warm
- Low power with no obvious fuel problem
Why it happens
The 3126 uses engine oil pressure to fire its injectors. Leaking injector O-rings, a weak high-pressure oil pump or a faulty pressure sensor let injection pressure drop, worst when the oil is hot and thin.
How to fix it
- Check engine oil level and grade.
- Read diagnostic codes and watch injection actuation pressure while cranking.
- Test the pressure sensor and regulator per the manual.
- Inspect injector O-rings and the high-pressure pump.
Tools and parts
- Diagnostic tool
- Injector seal kit
What the factory service manual covers
HEUI fuel system: actuation pressure specs, sensor tests, injector service. The full procedure, specs and wiring diagrams are in the factory service manual for your machine.