Rough start up when I fill up - Pontiac G8 Forum: G8 Forums - G8Board.com
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post #1 of 27 (permalink) Old 04-27-2015, 10:13 PM Thread Starter
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Rough start up when I fill up

Hi guys, just picked up a 08 G8 V6. Liquid red with GT trim. Ive only filled her up twice with Exxon 89 octane fuel. I start her up immediately after filling up and both times she had a rough time starting. Just wondering if anyone else has had the same issue.
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post #2 of 27 (permalink) Old 04-27-2015, 10:41 PM
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Maybe injector issues, or spark plugs..


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post #3 of 27 (permalink) Old 04-27-2015, 10:44 PM
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Spark plugs.

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post #4 of 27 (permalink) Old 04-27-2015, 10:51 PM
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Don't over fill it. There is some vacuum system with valves and sensors that gets messed up if you overfill. I forget how it affects the engine control system.
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post #5 of 27 (permalink) Old 04-27-2015, 11:48 PM Thread Starter
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I just got done putting more gas about 30min ago. I only put 20 bucks in (3/4 tank) and it did the same thing. Should I just try changing the spark plugs first?
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post #6 of 27 (permalink) Old 04-28-2015, 03:15 AM
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Could be several things hard to know fow sure from here. I'm thinking maybe leaky injector or bad plug. Maybe bad gas cap. As u say only when u put gas in it.

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post #7 of 27 (permalink) Old 04-28-2015, 05:34 AM
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Check for codes even though no dash lights are displayed. But changing plugs is a cheap thing to do and would eliminate a chief suspect. Also you can pull the plastic cover off the engine and start the car in the dark and look for arcing from any cracks in the plug wires.
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post #8 of 27 (permalink) Old 04-28-2015, 05:41 AM
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Quote:
Originally Posted by whatnext View Post
Check for codes even though no dash lights are displayed. But changing plugs is a cheap thing to do and would eliminate a chief suspect. Also you can pull the plastic cover off the engine and start the car in the dark and look for arcing from any cracks in the plug wires.
No plug wires in the V6. But yes check for codes if any.

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post #9 of 27 (permalink) Old 04-28-2015, 09:19 AM
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I see the issue now...v6... lol


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post #10 of 27 (permalink) Old 04-28-2015, 09:54 AM
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awe...C'mon man...^^ what whatnext was saying seems legit, im still stuck on the only when you fill up thing. I would definitely pull the plugs and see if they look fuel fouled, possibly a bad fill valve allowing gas to go into the charcoal canister? esentially flooding it when you start it? lots of possibilities.

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post #11 of 27 (permalink) Old 04-28-2015, 10:26 AM
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I have not witnessed this issue in the g8. But Im a Hyundai tech of 15 yrs and this occurs when you fill up the tank. Caused by a stuck open purge valve that sucks up extra fuel or vapor and basically what acts like a vacuum leak. This will make it hard to start and run rough for a few minutes and rarely ever throws a code. Have to remove and see if you can blow through it. Its a normally closed valve. (purge valve)
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post #12 of 27 (permalink) Old 04-28-2015, 10:51 AM
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^^^^^ I think that same condition can (and I believe has) happened with the G8 in the past. Every time the ECM requests the purge valve to either open or close, and the valve responds with a proper signal back to it, then you would not log in a fault code an turn on the check engine icon. But if the valve actually failed to close properly, I agree that fuel vapors will start loading up in the intake during fueling. In my mind, that would make for a stumbling start an run condition, until the engine had purged all of that extra fuel/vapor out of the system.


Added thought >>>>> In the meantime if you want to try this at your next fuel fill up, try the *Clear Flood Mode* procedure to see if the engine will fire up and idle correctly, on it's first post fill up. Step on the pedal to the WOT position (an leave it there). Then move the ignition to the start position and allow the engine to crank for a few seconds. This action causes the ECM to shut down the fuel injectors (for as long as the WOT position is maintained). This action would allow the engine to purge itself of any excess fuel vapors that might have entered the cylinders. BUT be prepaired to release the throttle, just in case the engine try's to light off (even thou the service manual says it won't).

Last edited by GOPHERIT; 04-28-2015 at 03:54 PM. Reason: added thought
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post #13 of 27 (permalink) Old 04-29-2015, 12:12 AM Thread Starter
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[QUOTE=GOPHERIT;2880665]^^^^^ I think that same condition can (and I believe has) happened with the G8 in the past. Every time the ECM requests the purge valve to either open or close, and the valve responds with a proper signal back to it, then you would not log in a fault code an turn on the check engine icon. But if the valve actually failed to close properly, I agree that fuel vapors will start loading up in the intake during fueling. In my mind, that would make for a stumbling start an run condition, until the engine had purged all of that extra fuel/vapor out of the system.


Added thought >>>>> In the meantime if you want to try this at your next fuel fill up, try the *Clear Flood Mode* procedure to see if the engine will fire up and idle correctly, on it's first post fill up. Step on the pedal to the WOT position (an leave it there). Then move the ignition to the start position and allow the engine to crank for a few seconds. This action causes the ECM to shut down the fuel injectors (for as long as the WOT position is maintained). This action would allow the engine to purge itself of any excess fuel vapors that might have entered the cylinders. BUT be prepaired to release the throttle, just in case the engine try's to light off (even thou the service manual says it won't).

I'll give that a try next fill up. If it purists I'll change the plugs and go from there. Thanx for the info guys. I'll keep you posted.
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post #14 of 27 (permalink) Old 01-07-2017, 07:02 PM
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08G8V686 it's been almost one year since you had the issue at start-up right after fueling. Can you please update on what was the problem? I have the exact same issue with my '09 V6 G8. I suspect it is the purge valve. Thanks!
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post #15 of 27 (permalink) Old 01-09-2017, 07:52 AM
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Years ago I had same issue after filling up and topping off;car would have an extended cranking before starting,it was the purge valve that was faulty,I replace the purge valve.So now when I fill up and the gas nozzle kicks off I don't top off.problem solved never again had the issue

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post #16 of 27 (permalink) Old 09-26-2017, 11:40 AM
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Same Problem

Where is the purge valve located to replace?
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post #17 of 27 (permalink) Old 09-26-2017, 11:19 PM
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^^^^^ On the V6, they show in mounted (in a horizontal plane) on the drivers side. It looks to be right near (or between) the #4 an 6 plug area.
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post #18 of 27 (permalink) Old 09-27-2017, 07:29 AM
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Quote:
Originally Posted by GOPHERIT View Post
^^^^^ On the V6, they show in mounted (in a horizontal plane) on the drivers side. It looks to be right near (or between) the #4 an 6 plug area.
Yes you are right. Its held on with a 10 mm bolt. Its attached to the upper intake manifold.

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post #19 of 27 (permalink) Old 09-27-2017, 10:39 AM
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When you shut of your V6 do you hear a "humming/whining???" sound for 3-5 seconds followed by 2-3 clicks under the hood.
My purge valve went last year and with the new one installed this sound became more pronounced as it it apparently the purge valve doing its job.
In a nut shell if this is not happening under your hood it most likely is the purge valve.
Hope this rather vague sound/click thing helps but its the best I can explain.
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post #20 of 27 (permalink) Old 09-28-2017, 07:07 AM
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Hah, always thought that sound was coming from the throttle position sensor on the throttle body. The part number for the vapor canister purge valve/solenoid is etched directly on the front.

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