Hard Restart
Thread Starter
Racer
Joined: Aug 2011
Posts: 343
Likes: 10
Hard Restart
Everyone,
My 2008 A6 for some reason has a rough time restarting after shutting off and warm. The cold starts are perfect, it fires up strong with no issues. Its throwing no codes. I did repace the vacuum purge valve in the engine bay because it was easy and it didnt change anything. Anyone else have this issue?
My 2008 A6 for some reason has a rough time restarting after shutting off and warm. The cold starts are perfect, it fires up strong with no issues. Its throwing no codes. I did repace the vacuum purge valve in the engine bay because it was easy and it didnt change anything. Anyone else have this issue?
Burning Brakes
Joined: Feb 2021
Posts: 771
Likes: 399
2022 C6 of the Year Finalist - Unmodified
My old 1989 Formula 350 TPI had this same problem..... Turned out to be leak down on one of the injectors. Basically flooding the motor.
Not saying this is what is happening, but giving you a for instance.
Not saying this is what is happening, but giving you a for instance.
Thread Starter
Racer
Joined: Aug 2011
Posts: 343
Likes: 10
Thanks for the responce. I kind of doubt thats the problem with me because the cold starts are perfect. If I had a leaking injector I would think that the starting issue would happen all the time, but who knows anything is possible.
Thread Starter
Racer
Joined: Aug 2011
Posts: 343
Likes: 10
It turns and and eventually starts. I have to throttle it some. And the idle is a little weird. Sometimes it’s a little harder then other times. Again this is after it is warm and I shut it off.
Melting Slicks
Joined: Apr 2019
Posts: 2,499
Likes: 1,165
From: Northern Wisconsin
As always, it's fuel/air, compression, ignition required to fire, so investigate those things. A change in fuel pressure between cold and warm conditions might somehow be part of the problem. Lack of compression could be caused by something weird like the valves being held off the seat or a problem with piston rings. A compression test or leakdown test would help (cold and warm). Ignition is easy to check, but it seems unlikely that you have spark when cold, but not when warm.
Burning Brakes
Joined: Feb 2021
Posts: 771
Likes: 399
2022 C6 of the Year Finalist - Unmodified
It would only give me the issue when I would first crank and drive a short distance....... Long distances after the first crank and it was fine. Multiple cranks in and it was fine. Just on that first crank and short distances. I had to let it idle at the store by the house so it would not do it. When it did do it, I had to let it sit for awhile then it would turn over and run.
Moderator, Tech Contributor
Joined: Sep 2013
Posts: 15,540
Likes: 4,020
From: Cape Coral, Florida
Faulty cam sensor can cause these “hard” starts…maybe even a crank sensor….when it doesn’t start look at your Tach during cranking…if no movement of Tach possible bad crank sensor.
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Thread Starter
Racer
Joined: Aug 2011
Posts: 343
Likes: 10
Tach and everything is fine. I recently replaced the crank sensor too when the issue first started and no change. I’m completely baffled.
Moderator, Tech Contributor
Joined: Sep 2013
Posts: 15,540
Likes: 4,020
From: Cape Coral, Florida
Did you use an OEM or aftermarket crank sensor…aftermarket are JUNK !!…without some good diagnostic equipment like a factory scan tool and a scope you’ll just waste money changing parts…find a diagnostic shop in your area…they will find the issue !!
Last edited by C5 Diag; Mar 24, 2023 at 06:04 PM.
Thread Starter
Racer
Joined: Aug 2011
Posts: 343
Likes: 10
I used an OEM crank sensor. My buddy has a Tech 2. Hopefully it shows a code. Just weird that it shows no code and no engine light.
Moderator, Tech Contributor
Joined: Sep 2013
Posts: 15,540
Likes: 4,020
From: Cape Coral, Florida
Well if he has a Tech 2 and not knowing if he knows how to interpret live data but that is what you should be looking at…if the Tach moves it may be the cam sensor….like I said without some good diagnostic equipment you’ll only be firing the parts canon…I’d be scoping cam and crank sensor, injector and coil pack current.
Racer
Joined: Aug 2022
Posts: 410
Likes: 167
From: KS
Back in the day when a car had this symptom, one would think it had vapor lock, which is when some of the liquid fuel has vaporized in the fuel system preventing the fuel from being delivered as it should. Is it possible the heat of the engine is vaporizing some of the fuel in the fuel system?
I'm a fairly new owner and don't know if this is even possible on a C6. I saw another thread on this forum discussing this BTW. Make sure none of the fuel lines are close to the exhaust system
I'm a fairly new owner and don't know if this is even possible on a C6. I saw another thread on this forum discussing this BTW. Make sure none of the fuel lines are close to the exhaust system
Thread Starter
Racer
Joined: Aug 2011
Posts: 343
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Burning Brakes
Joined: Jun 2022
Posts: 750
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From: Florida
Look at I've data with a scan tool, key on engine off you should see a reading of ZERO on the MAF, I had a Pontiac do what you are saying and when it was warmed up the MAF sensor was reading airflow with the engine not running, this caused too much fuel to be added, pressing the throttle lightly would make it start right up. Replaced with a Hitachi (oem for GM in the early 2000s) and worked perfectly. Just something else to check.
Race Director
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Thread Starter
Racer
Joined: Aug 2011
Posts: 343
Likes: 10
Blownbayou may be correct. A leaky injector may not even be a consideration when cold, as a cold engine needs extra fuel. That isn't the case once it's warmed up. Could be flooding a cylinder, though it should still fire up and run rough until that cylinder clears out. Maybe you have more than one leaky injector?
Thread Starter
Racer
Joined: Aug 2011
Posts: 343
Likes: 10
Blownbayou may be correct. A leaky injector may not even be a consideration when cold, as a cold engine needs extra fuel. That isn't the case once it's warmed up. Could be flooding a cylinder, though it should still fire up and run rough until that cylinder clears out. Maybe you have more than one leaky injector?
Hope it cures your ailment.......