Intermittent hard or no start on 4.0T S6 S7 RS7- possibly solved

[Mscarn2014]

Going to add my experience.

Had the same problems. Hard start on a 2013 Stage 3 S6 with the autotech injectors. Always remedied with giving some gas with startups. But always fine during a cold start. If I drove it, let it sit for an hour or two, it would be a hard start. If I let it sit overnight, it would be completely fine. Drove me nuts. It's like there was a vacuum with the fuel to the point that if the vacuum eventually released over a long span of time (overnight), it would be completely fine start up.

Regardless... spent 2K on brand new fuel pumps, autotech injectors, install, etc. Worked fine for 2 months, started up without a problem. And now, starting to have the same failed started after driving it a bit, turning it off for a bit, and turning to turn it on again. Still - if I drive it, leave it overnight, and try it the next day, completely fine. Not sure exactly what the hell is the issue, but it's never NOT started, but may need some gas to start it.

Sounds like many are still having the same issue.

[snohman]

Any updates? How are the new pumps treating you? Fixed the issue?

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Any updates? How are the new pumps treating you? Fixed the issue?

No issues still - been about a month and nothing close to the issues I was having. I’ll wait a few more months and provide more feedback given some are still having some symptoms post new hpfps

[HyunjinsCake]

No issues still - been about a month and nothing close to the issues I was having. I’ll wait a few more months and provide more feedback given some are still having some symptoms post new hpfps

Any updates? Is it something else in the pump itself that tends to fail? or would the "piston upgrades" remedy the issue as well? Just picked up an S7 a week ago and it's embarrassing to have to give it gas to start when I show people my new (to me) car lol

[wiggly]

What fixed mine was fuel pressure regulator. Inside fuel tank on pass side next to low pressure fuel pump. Roughly $150 from Audi and ~1h of work

[trifona]

2018 stock S6 with 55k miles.

Had the hard start / no start symptoms show up a couple of times last winter then they went away. No dash lights and no codes stored according to the dealer at the time; car was still under 4yr/50K mile warranty.

Symptoms reappeared once this past December. Car was not driven again until mid February. Symptoms reoccurred 4x times in the last week. During the latest incident I thought I was going to be stranded and need a tow. Luckily I was able to get the car started, and drove immediately to my dealer which was only 10-minutes away at the time. Car was throwing codes showing both HPFPs were bad. They also confirmed presence of fuel in the oil; I could smell the fuel it in my garage after parking it the prior night. Full cost of the parts & labor to be covered under the 8yr/80K mile emissions warranty; bullet dodged.

[Avantly]

HPFP leaking into the crankcase has always been a known issue with worn HPFP. The 4.0T doesn't have a check valve past the pump, it depends on the metering valve on top of the pump (which isn't available separately last I knew). I wouldn't suspect leaky injectors until the HPFP has been ruled out due to how common this issue is. The pressure test isn't hard to do but requires caution due to the pressures involved; it does require a high pressure test gauge (easier if you have two for 4.0T) and you do have to remove the high pressure lines from the pumps to do it.