08/08/2026 6:12 am
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Automotive Q&A
Fuel pressure falls from 55 to 10 psi and hot restart is extended
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A 2010 Fusion 3.0 cranks long after a 20-minute hot soak. Running pressure is stable at 55 psi, then falls to 10 psi within seven minutes after shutdown. There is no external leak. Pinching the permitted supply section slows part of the decay but does not stop it, and cylinder 5 develops a fuel odor at its plug.
What combination of tests would separate injector leakage from the pump check valve without damaging the line?
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09/08/2026 7:43 am
Use only the isolation points allowed by service information; do not pinch a reinforced or plastic line that is not designed for it. Compare pressure decay with the supply isolated, then perform an injector balance and inspect suspect cylinders after the hot soak. A pump check valve affects the whole rail but does not make one cylinder wet.
If cylinder 5 shows fresh fuel and its injector has an abnormal balance result while pressure decay improves after replacement, the injector is proven. Change oil if fuel contamination is present and verify no seal leaks during prime.
Topic starter
10/08/2026 9:38 am
A borescope showed a wet cylinder 5 piston after the soak, and that injector produced the largest balance drop. The new injector held pressure above 46 psi for 20 minutes, hot restart returned to two seconds and the oil showed no continuing fuel dilution.