I've been casually battling this for a year now, occasionally throwing parts at it to no avail.
Wife's '03 A6 2.7t 6MT
Car starts fine/right away when cold/ambient. Drive it long enough to warm up fully, park it, shop 15+min, go to restart and will not start on 1st try. I'll qualify this statement with - if you crank the starter the "normal" muscle memory amount of time it will not start. Try again and it probably will, sometimes 3rd time is a charm.
We have learned over the months that you can expect this behavior and to just hold the key in the cranking position for 3-4 seconds and it will start.
NO CODES. Car runs perfect otherwise. We've had this car 12 years, minimal drama considering...
It is not the Coolant Temp. Sensor. I have monitored/logged that and Intake Air Temp at length. It is not the Crank Position Sensor. I replaced that 1st thing last Oct. I kept the old one, which wasn't that old and have since swapped it back in, same behavior.
I have suspected a loss of fuel pressure and the fuel is just not there on restart, but that doesn't add up given that 100% of the time it's perfect on a cold start. Add to this, sometimes the car sits for days. I have swapped fuel injectors, suspecting leaky injectors that wet the cylinder enough to be too rich on warm restart - that opened a whole other side quest of bad parts that isn't worth talking about, but I'm back to exactly the way it was 11 months ago. On the bright side, I'm a fuel injector swap expert now. I have not 100% ruled them out. I'd like to unfasten and lift the rail up enough so when I cycle the fuel pump (I wired up a momentary button inspired by the test in the Bentley) I can see if any are dripping under pressure. Nice of the engineers to add those injector retaining clips
Because the car is "old" and has a bit over 200k on it, I have slowly been hitting it with normal "tune up" items - spark plugs, fuel filter, air filter, primary o2's...that devolved into the aforementioned fuel injectors and also changing the fuel pump.
Monitoring/logging various channels in VAG COM and all appears normal. I have watched o2's, cylinder misfires, I have had a fuel pressure gauge temporarily plumbed in - all appears normal while running. Prior to fuel pump swap, the pressure did drop off sharply on shutdown, so I added an external check valve. No change in behavior, despite meeting the Service Manual spec of holding something like 36psi after 15 min (don't quote me on the spec., the Bentley isn't in front of me). Fuel pressure gauge/check valve came out at the same time the new pump went in because the temp. fuel line I had rigged up with (hello China!) began to balloon and looked like a fire waiting to happen.
Can anyone suggest any oddball measuring blocks to monitor on warm restart or theories that might reveal the core issue? Recently another enthusiast suggested a cam position sensor, but I would think this would trigger the fault code. I literally have none unless I intentionally unplug something.
I attached a log file from a couple weeks ago where I monitored G70, G62, G42 and others I found (and probably don't apply?) in the 078-907-551-AZA.lbl file. I thought those "Start Adaptation Values" in block 104 might tell me something, but I don't know what's normal or what they are for. In the event some of my numbers seem odd, do know that I live at 9200 feet. Also, to reiterate, the car starts quickly 100% of the time from cold, runs perfect/strong always (even after hard restart).
Happy to hear anyone's theory.
Thanks!
-TJ
Wife's '03 A6 2.7t 6MT
Car starts fine/right away when cold/ambient. Drive it long enough to warm up fully, park it, shop 15+min, go to restart and will not start on 1st try. I'll qualify this statement with - if you crank the starter the "normal" muscle memory amount of time it will not start. Try again and it probably will, sometimes 3rd time is a charm.
We have learned over the months that you can expect this behavior and to just hold the key in the cranking position for 3-4 seconds and it will start.
NO CODES. Car runs perfect otherwise. We've had this car 12 years, minimal drama considering...
It is not the Coolant Temp. Sensor. I have monitored/logged that and Intake Air Temp at length. It is not the Crank Position Sensor. I replaced that 1st thing last Oct. I kept the old one, which wasn't that old and have since swapped it back in, same behavior.
I have suspected a loss of fuel pressure and the fuel is just not there on restart, but that doesn't add up given that 100% of the time it's perfect on a cold start. Add to this, sometimes the car sits for days. I have swapped fuel injectors, suspecting leaky injectors that wet the cylinder enough to be too rich on warm restart - that opened a whole other side quest of bad parts that isn't worth talking about, but I'm back to exactly the way it was 11 months ago. On the bright side, I'm a fuel injector swap expert now. I have not 100% ruled them out. I'd like to unfasten and lift the rail up enough so when I cycle the fuel pump (I wired up a momentary button inspired by the test in the Bentley) I can see if any are dripping under pressure. Nice of the engineers to add those injector retaining clips
Because the car is "old" and has a bit over 200k on it, I have slowly been hitting it with normal "tune up" items - spark plugs, fuel filter, air filter, primary o2's...that devolved into the aforementioned fuel injectors and also changing the fuel pump.
Monitoring/logging various channels in VAG COM and all appears normal. I have watched o2's, cylinder misfires, I have had a fuel pressure gauge temporarily plumbed in - all appears normal while running. Prior to fuel pump swap, the pressure did drop off sharply on shutdown, so I added an external check valve. No change in behavior, despite meeting the Service Manual spec of holding something like 36psi after 15 min (don't quote me on the spec., the Bentley isn't in front of me). Fuel pressure gauge/check valve came out at the same time the new pump went in because the temp. fuel line I had rigged up with (hello China!) began to balloon and looked like a fire waiting to happen.
Can anyone suggest any oddball measuring blocks to monitor on warm restart or theories that might reveal the core issue? Recently another enthusiast suggested a cam position sensor, but I would think this would trigger the fault code. I literally have none unless I intentionally unplug something.
I attached a log file from a couple weeks ago where I monitored G70, G62, G42 and others I found (and probably don't apply?) in the 078-907-551-AZA.lbl file. I thought those "Start Adaptation Values" in block 104 might tell me something, but I don't know what's normal or what they are for. In the event some of my numbers seem odd, do know that I live at 9200 feet. Also, to reiterate, the car starts quickly 100% of the time from cold, runs perfect/strong always (even after hard restart).
Happy to hear anyone's theory.
Thanks!
-TJ
