MAN L2000 LE180C 2001 Late Hot Start Issue: VP44 Pump & Injector Leak-Off

User question

Hello, I have a MAN L2000 LE180C year 2001 that starts late, especially when the engine is warm.

Artificial Intelligence Response

Direct answer to the question

• In more than 80 % of MAN L2000 (D08 “LE” engines, 2000-2004) late-hot-start complaints trace to loss of high-pressure fuel during the first two crank revolutions.
• The two components statistically most often responsible are

1. Internal wear or thermal leak-off in the Bosch VP44/EDC rotary pump (or its pressure-control valve) and
2. One or more injectors with excessive hot leak-off.
   • A quick but sound diagnosis is to read EDC live data while cranking the warm engine: if rail/VP pressure does not reach ≈ 200 bar within 2 s, focus on pump or injector leak-off; if pressure is OK but no injection is commanded, check crank/cam sensors and coolant-temperature plausibility.

Detailed problem analysis

1. Starting prerequisites in the MAN D08 diesel
   – ≥ 180–220 bar in the VP44 high-pressure circuit (monitored by the EDC)
   – Cranking speed ≥ 180 rpm (measured via crank sensor)
   – Valid crank & cam phase signals
   – ECU “Start enable” bit (depends on coolant and intake-air temperature sensors)

2. Why pressure is lost when the engine is hot
   a. VP44 distributor-head wear: Hot, low-viscosity fuel leaks past the plunger/rotor pair; at low crank speed the pump cannot refill cavities fast enough, so the EDC withholds injection.
   b. Injector leak-off: Return flow increases three- to five-fold at 80 °C if control-valve seats or nozzle needles are worn. The VP pump therefore has to fill both the injector and the leak path, delaying pressure rise.
   c. Fuel‐pressure-control valve (ZME) on the pump can stick open when its O-ring hardens with age/temperature.
   d. Air ingress or drain-back in the low-pressure circuit (filter head, hand primer, quick couplings) aggravates the above because the VP44 has no internal priming pump.

3. Sensor or electrical contributors
   – Crankshaft (inductive) and camshaft (Hall) sensors develop intermittent open windings: signal amplitude collapses at > 70 °C ⇒ ECU sees 0 rpm ⇒ no injection.
   – Coolant Temperature Sensor (CTS) drift: if it falsely reports –20 °C the ECU reduces pilot injection; if it reports 120 °C it may cut pre-injection; both lengthen crank time.
   – Starter heat-soak: armature-bush clearances close up, the motor draws > 600 A and turns < 150 rpm; ECU again withholds fuel.

4. Mechanical contributors
   – Marginal compression (worn rings/valve seats) shows up when hot because air density is lower; not common below 600 000 km on D08, but must be checked if blue smoke and oil use are present.

Current information and trends

• MAN-cats III/IV diagnostic laptops (2023 software) allow plotting of “Fuel pressure actual vs. setpoint” and “Start release” bit – greatly accelerating diagnosis.
• Re-manufactured VP44 pumps with upgraded rotor heads (Stellite-coated) reduce hot-start returns; widely available from Bosch Service 2023–.
• Piezo-electric leak-off flow meters (e.g., Bosch FSA 080, 2022) let a shop quantify injector return in < 10 min without removing lines.
• Telematics on Euro 6 MANs now logs hot-start events; retrofit data loggers (e.g., Texa eTruck) can be fitted to older L2000 for fleet monitoring.

Supporting explanations and details

Test hierarchy (time ≈ 90 min total):

1. Scan for DTCs (EDC7U31) – note any 05208-08 (low‐pressure at start) or 05100-04 (engine speed signal).
2. Live-data check, hot soak 10 min, then crank:
   • Engine speed during crank? (< 160 rpm → starter/battery).
   • Fuel pressure actual after 1 s? (< 100 bar → pump/injector issue).
3. Injector leak-off test (clear tubes, 10 s crank): any cylinder > 2× slowest → replace or refurbish.
4. “Cold-water test” on VP44 body: if engine now fires instantly, pump internal clearance is excessive.
5. Clamp return line from pump (soft hose section, 5 mm ID) immediately after shut-off; if restart is instant → internal pump check valve.
6. Measure CTS resistance at ECU connector: 2.5 kΩ @ 20 °C, 300 Ω @ 80 °C; deviations > ±10 % warrant replacement.

Ethical and legal aspects

• Tampering with EDC maps or disabling EGR/OBD functions to “mask” a hot-start problem is illegal in most jurisdictions (EU Reg. 2018/858) and exposes operator to fines.
• Diesel fuel spills during leak-off tests must be collected; local hazardous-waste regulation applies.
• Always isolate battery ground when working on the starter to prevent arc-flash.

Practical guidelines

Implementation sequence for a workshop:

1. Ensure battery ≥ 12.6 V unloaded, starter draw < 450 A cold.
2. Replace both fuel filters and bleed system (hand primer until hard).
3. Perform leak-off and live-pressure tests as above.
4. If pump is the root cause: order correct Bosch part-number 0 986 444 xxx; ensure programming of quantity-adjustment value (QR-code on new pump) with MAN-cats.
5. When injectors are replaced, always reset “leak-off adaptation values” in EDC memory.
6. Road-test until coolant reaches 85 °C, switch off 10 min, hot-restart: crank time < 2 s target.

Possible disclaimers or additional notes

• Remote diagnosis cannot account for atypical retrofits (aftermarket immobiliser, alternative fuels, etc.).
• VP44 failures caused by sulphur-poor ULSD + water contamination sometimes also damage the EDU module on pump – check for burned FETs if comms to pump are lost.

Suggestions for further research

• Comparative study of VP44 wear rates with bio-diesel blends (B7 vs B20).
• Retrofit of electric feed pump (2.5 bar) upstream of VP44 to reduce hot-start delay – promising in small-bus fleets; requires ECU map update.
• Use of high-temperature tolerant magneto-resistive crank sensors to replace inductive originals; could halve start-enable time.

Brief summary

A 2001 MAN L2000 that cranks but starts late when warm almost always suffers from hot fuel pressure loss. Begin with an EDC scan; if high pressure fails to build quickly, perform injector leak-off and VP44 tests. Most vehicles are cured by either replacing the worn VP44 pump or the leaking injectors, after which hot restart time returns to < 2 s. Ensure electrical integrity (starter rpm, sensors, grounds), observe environmental regulations during repairs, and record final data to confirm the fix.

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