27/06/2026 6:12 am
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Automotive Q&A
Hot diesel long-crank: injector 3 return flow is more than double the others
Review the evidence, add a focused answer, and distinguish confirmed measurements from assumptions.
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A 2016 Sprinter 2.1 diesel starts quickly cold but cranks for six to eight seconds when hot. During the failed hot start, rail pressure stalls near 180 bar while the enable threshold is about 250 bar. Low-pressure delivery is steady. In a timed return-flow test, injector 3 fills more than twice the volume of the other injectors.
Is the return imbalance sufficient evidence, and what should be repeated before fitting an injector?
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28/06/2026 10:50 am
Repeat the return test at the temperature and crank duration that produce the symptom, using equal-length hoses and matched containers. Confirm no external leak, air entry or pressure-control valve fault is lowering the whole rail. A single injector returning substantially more fuel can prevent the rail from reaching start pressure, but the comparison must be repeatable.
Check the replacement coding requirement and inspect the injector seat and hold-down hardware. Common-rail pressure is hazardous; use only the specified closed test equipment and never loosen a high-pressure line on a running engine.
Topic starter
29/06/2026 7:36 am
A second hot test gave the same result: injector 3 returned 31 ml while the others were between 11 and 14 ml. After replacement, coding and leak inspection, rail pressure crossed 250 bar within two seconds and hot starts matched cold starts.