Hard Hot Start After Heat Soak - Failed FPU VSV Replacement

Fuel Systemintermediate✓ OP Confirmed

Problem

1987 7MGTE turbo automatic would not restart properly after a hot soak period of 15-30 minutes. The car started fine when cold but after driving and shutting off, it would catch briefly then stall, requiring careful feathering of the throttle to keep running. Too much throttle would stall it.

Engine catches within seconds when cranking hot but immediately stallsRequires very light, gradual throttle to keep running after hot restartToo much throttle causes stallProblem only occurs after 15-30 minute hot soak, not when coldOnce finally running, idle drops to ~500 RPM briefly before recovering to 750 RPM

Root Cause

The FPU (Fuel Pressure Up) VSV (Vacuum Switching Valve) had failed in the closed position. Although it tested within spec for resistance (4 ohms, no short to body), the solenoid would not actuate when 12V was applied. This meant the VSV could not redirect vacuum away from the fuel pressure regulator during hot cranking, so the regulator was always receiving vacuum and reducing fuel pressure. During heat soak conditions, the engine needs full fuel pressure to overcome vapor lock, but the stuck VSV prevented the pressure-up system from engaging.

Confidence

High confidence — Original poster confirmed this resolved the issue

View Original Thread →Posted December 2015 on SupraForums.com