Post by deezell on Jan 27, 2024 22:28:18 GMT
My 2015 A6 C7 tdi with CRTE diesel has developed an odd fault. Car has 245K km.
On returning from a flawless 2 day 600km journey, car would not start the next morning. Cranking no start. At midday it started after 5 seconds crank. It ran perfectly for 3 days. On the 4th day it failed to start 2 hours after stopping. Engine was still hot after the previous one hour journey. Multiple attempts were made over an hour,no start, and we had to arrange transport home. Next morning it started first turn. No codes stored either time. It has started multiple times in the next two days. Today it took 4 seconds cranking to restart after 2 hours stopped. Live data scan when normal idling shows high pressure fuel specified value at 250000 hPa (250 bar), rock steady, actual value at 249700, with minor swings plus and minus a few hundred. Immediately after the faulty long crank start, specified and actual were varying widely from these figures, but after a 30 min drive they returned to the steady idle. I suspect the common rail pressure regulator valve, as attempts to settle at a steady idle state intermittently vary widely, and this coincides with the subsequent long crank no start. On the Audi self study guide 840193 og 38 it states failure of the Fuel pressure regulator will cause non running. If this was intermittently unresponsive to PCM control voltages, pressure would be erratic during idle, and starting would not be possible unless it closed sufficiently to reach injector pressure. Other devices in the system, fuel temperature sensor, fuel metering valve, will not prevent starting, but will result in limp mode. On some starts it rough idles with considerable misfiring for 4 to 7 seconds, and with the accompanying widely swinging specified/actual pressure.
Any comments on this condition would be welcome in solving this. There appears to be a similar issue with the A6 C8 series which was sorted by a firmware update, but I suspect the C7 issue is one of sensor or actuator which is intermittently losing full connection.
On returning from a flawless 2 day 600km journey, car would not start the next morning. Cranking no start. At midday it started after 5 seconds crank. It ran perfectly for 3 days. On the 4th day it failed to start 2 hours after stopping. Engine was still hot after the previous one hour journey. Multiple attempts were made over an hour,no start, and we had to arrange transport home. Next morning it started first turn. No codes stored either time. It has started multiple times in the next two days. Today it took 4 seconds cranking to restart after 2 hours stopped. Live data scan when normal idling shows high pressure fuel specified value at 250000 hPa (250 bar), rock steady, actual value at 249700, with minor swings plus and minus a few hundred. Immediately after the faulty long crank start, specified and actual were varying widely from these figures, but after a 30 min drive they returned to the steady idle. I suspect the common rail pressure regulator valve, as attempts to settle at a steady idle state intermittently vary widely, and this coincides with the subsequent long crank no start. On the Audi self study guide 840193 og 38 it states failure of the Fuel pressure regulator will cause non running. If this was intermittently unresponsive to PCM control voltages, pressure would be erratic during idle, and starting would not be possible unless it closed sufficiently to reach injector pressure. Other devices in the system, fuel temperature sensor, fuel metering valve, will not prevent starting, but will result in limp mode. On some starts it rough idles with considerable misfiring for 4 to 7 seconds, and with the accompanying widely swinging specified/actual pressure.
Any comments on this condition would be welcome in solving this. There appears to be a similar issue with the A6 C8 series which was sorted by a firmware update, but I suspect the C7 issue is one of sensor or actuator which is intermittently losing full connection.