Crank-no-start diesel with a high-pressure leak
A BS-VI common-rail diesel van is towed in with a crank-no-start and a strong diesel smell. In the bay an apprentice finds a damp patch around the union of the high-pressure pipe at number two injector and proposes loosening that union half a turn and cranking the engine so he can watch whether fuel pulses out. He is wearing safety glasses on his forehead, has a hot engine bay, and the workshop's parts wash and a space heater are running nearby. The scan tool shows rail pressure of 4 MPa during cranking against a commanded value above 25 MPa, plus a P0087 low rail pressure code. The workshop manual for this engine specifies a guided high-pressure leak test using a calibrated measuring tool and new pipe unions, with a torque figure of 30 Nm and a stated waiting time before opening any high-pressure joint.
1. Identify the hazards in the apprentice's proposal and rank them.
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The single most serious hazard is injection injury. Common-rail pressure runs from roughly 1,800 to 2,500 bar on a BS-VI engine, and a loosened union produces a jet that can penetrate skin without a visible wound, causing tissue necrosis and, if untreated, amputation or worse; the injury is a surgical emergency, not a workshop first-aid case. Second is fire: atomised diesel ignites readily on a hot exhaust manifold or turbo, and the parts washer and space heater add ignition sources in an enclosed bay. Third is environmental and slip exposure from spilled fuel, plus breathing of mist in a confined space. Poor personal protection - safety glasses resting on the forehead rather than over the eyes - compounds all three, and cranking a vehicle with a known open fuel joint also sprays onto the technician, not into a container. The correct ranking is injection injury first, fire second, spill and exposure third, and the answer is that the proposal must be stopped, not modified and attempted.
2. State the correct diagnostic route to the low rail pressure, and how a high-pressure joint should be opened safely if it ever must be.
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Rail pressure of 4 MPa against a commanded 25 MPa or more means the system cannot build pressure, so work logically from the low-pressure side. Check fuel level and quality, lift pump delivery and pressure, filter restriction, and for air ingress on the suction side, then check the rail pressure sensor and regulator readings against a mechanical gauge, and measure injector return flow to see whether an injector is leaking internally. A leaking union at number two may be a symptom of a cracked pipe seat rather than the cause. Use the manufacturer's guided leak test, which collects return flow into a calibrated tool. If a high-pressure joint truly must be opened, stop the engine, wait the specified period, clean the area, use a flare-nut wrench of the correct size, never reuse a distorted pipe, fit new unions, torque to 30 Nm and run the engine at idle while checking for the faintest weep with a dry paper towel - never with a hand.
3. What would you do at the scene immediately, and what follow-up is needed after the repair?
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Stop the job, take the keys, and move ignition sources away: shut down the space heater, keep the parts washer covered, and remove the vehicle from the immediate area if the bay is enclosed. Ventilate the bay, place an absorbent under the leak, and keep a foam or dry-powder extinguisher at hand; clean the spill immediately so nobody slips and so vapour does not accumulate. Raise the personal protection: eye protection worn over the eyes, face shield for anyone near a pressurised joint, nitrile gloves, no loose cuffs. If any fuel penetrates skin, send the person to hospital at once with the words high-pressure diesel injection injury, and do not wait for pain or swelling. After repair, run the engine and check every disturbed joint, road test, recheck rail pressure and codes, then record the torque values used. Finish with a toolbox talk on the ban on cracking high-pressure lines, because this habit recurs whenever an apprentice is rushed.