Hi, I have a 2004, 2.0TD, HDi Volvo S40, which has suddenly developed an intermittent( can run ok for days then fault appears, sometimes for several attempts at starting, then disappears) only at start, hot or cold, a very very very loud knocking/rattle from gearbox/flywheel area. Sounded like the dual mass flywheel. Changed flywheel and clutch, still the same. Have now noted that when noise is present, if the clutch is dipped the noise disappears and it is apparent that the engine is running very rough and is not rotating smoothly, causing it to snatch, and causing the transmission noises. If engine restarted, fault usually disappears and runs ok drives well. No excessive exhaust smoke, fault present or not. No error codes being logged, live data looks good. Replaced crank sensor behind crank pulley (pulley ok) in case of distorted trigger pulse, fault still present. No 1 cylinder injector has very slight “leak off” whilst offers or dry. Test driving the car revving hard through the gears, shows good performance and no noises. Have noted that from a cold start, the engine cranks for 2-3 seconds before it fires, but runs ok when it does fire.
Any ideas? Bernard.
Further testing has shown that this problem can be related to cranking speed. If the battery is 100 % charged then it starts on first revolution of crank, but if continued cranking is attempted to bring on the fault, starting gets less instant, and after about 20-30 tries, about 6-8 revolutions before it starts, initial idle(4-8 seconds) is slightly noisy. But if you continue, the fault then becomes apparent, whilst cranking is still reasonably quick, and starting should still be good, the very rough idle then occurs and if any throttle is applied it gets horrendous and continues until ignition off. Try again, and it usually runs ok!
Battery load test is very good and this vehicle is fitted with a large battery, charging ok, starter current draw is normal, all battery connexions and earths good, approx 20mA quiescent current drain.