FAQ
TL;DR: Tank pump delivers 3.8 bar [Elektroda, klusek1712, post #16183602]; "It lowers pressure, not raises it" [Elektroda, Strumien swiadomosci swia, #16183233]. Verify 12 V supply, PWM duty ≤80 %, and rail pressure >250 bar before replacing the CR control valve. Why it matters: Misdiagnosing the valve can waste €300+ and keep the engine from starting.
Quick Facts
• Supply voltage: 11.5–12.5 V at ignition feed [Elektroda, klusek1712, post #16183137]
• Tank (lift) pump pressure: 3.8 bar nominal [Elektroda, klusek1712, post #16183602]
• Start-up rail pressure required: 250–300 bar typical [Bosch CR Guide, 2014]
• New metering valve cost: €60–€90 (OE) [Autodata Parts, 2024]
• Valve retaining screw torque: 35 Nm (M12, typical) [Delphi Service Manual, 2018]
What does the pressure-control (metering) valve do on a common-rail (CR) pump?
It meters how much low-pressure fuel enters the high-pressure section. The ECU drives the valve with a pulse-width-modulated (PWM) signal; more duty opens it, less duty closes it, raising rail pressure [Bosch CR Guide, 2014]. "Without the engine running, the valve is open" [Elektroda, Daro122, post #16183700]
How do I check that the valve gets the correct voltage on an Astra 1.3 CDTI?
Back-probe the two-pin connector. You should read battery voltage (≈12 V) with ignition on and ≈0–1 V average while cranking due to PWM switching [Elektroda, klusek1712, post #16183137] No voltage means wiring or ECU fault.
What PWM duty-cycle does the ECU use?
Typical light-load duty is 20-40 %. During starting, the ECU may drop below 10 % to build pressure quickly [Delphi Service Manual, 2018]. A constant 100 % duty can dump fuel back and give <5 bar rail pressure [Elektroda, klusek1712, post #16184172]
Can I bench-test the valve safely?
Yes. 1) Connect the valve to 12 V through a 45 W bulb as a current limiter [Elektroda, Daro122, post #16184030] 2) Briefly energise; you should hear/feel a click. 3) Apply light air pressure—closed valve should block flow. Continuous battery feed without a limiter can burn the coil.
Why is all fuel returning to the tank instead of reaching the rail?
A stuck-open valve or zero PWM duty allows >90 % of feed fuel to bypass, leaving rail pressure at 5 bar [Elektroda, klusek1712, post #16184172] Faulty wiring, ECU ground, or metal debris holding the pintle off-seat are common causes [Bosch CR Guide, 2014].
What minimum rail pressure is needed for the engine to start?
Most CDTI engines need 250–300 bar before the ECU enables injection [Bosch CR Guide, 2014]. The forum car showed only 5 bar, well below the threshold [Elektroda, klusek1712, post #16184172]
Could bad injectors mimic a failed valve?
Yes. Excessive leak-off can drop rail pressure even with a good pump. Perform a return-flow test; flow difference should be <4 ml in 30 s at cranking speed [Delphi Service Manual, 2018]. The poster’s injectors passed a bench test [Elektroda, klusek1712, post #16184191]
How can I rule out wiring or ECU problems?
Swap the valve connector with a 21 W test lamp. Crank the engine: lamp should flicker. No light = wiring/ECU fault. Continuity check between ECU pin and valve shows resistance <0.5 Ω typical. Open-circuit or short means harness repair [Autodata Wiring, 2024].
What’s an edge-case that blocks pressure even with a good valve?
Microscopic debris can lodge in the pump inlet or bypass channel; normal disassembly may miss it. One mechanic restored pressure only after flushing with 6 bar external feed [Elektroda, Daro122, post #16183810]
Three-step quick test before buying parts?
- Measure lift-pump output (goal 3.5–4 bar). 2. Back-probe valve for 12 V and PWM flicker while cranking. 3. Read live rail pressure; if still <10 bar, clamp return line for 3 s—pressure jump points to valve leak. Replace parts only if all three fail.
How much does a new valve or complete pump cost?
Aftermarket Bosch-type IMV valves retail €60–€90 [Autodata Parts, 2024]. A reconditioned CP3/CP1 pump for Astra 1.3 CDTI runs €400–€550 plus fitting.
Is it safe to run the engine with the coolant sensor unplugged?
No. An open-circuit sensor reads −40 °C; ECU enriches fuel and may keep the metering valve open, flooding the return and risking wash-down [Bosch CR Guide, 2014]. Fix sensor before further pressure tests.
