Piston Slap: The Gassy Goat and Its Forum Saviors

Sajeev Mehta
by Sajeev Mehta
piston slap the gassy goat and its forum saviors
Luke writes:

Sajeev, I was hoping you’d have an answer to my unusual problem and post my letter so I may get some feedback from the brilliant people who visit your website. I bought a 2004 GTO (automatic) back in September ’09. It’s in beautiful condition, yet has an unusual plight. Here goes:

If I fill the gas tank 3/4-full, the engine chokes and surges and will often times stall. Engine speed drops and then it revs and drops and revs again… and sometimes drops so far it just quits. I get the impression it’s drowning in gasoline and gasping for air. I don’t always fill my gas tank and was able to diagnose the syndrome myself after the 3rd irregular occurrence. It’s downright dangerous in heavy traffic, slogging around town, as I nearly lunged out into cross traffic the last time it happened. I was able to jump on the freeway and keep the engine revving. By the time I made it to my friends house I had burned off the first quarter tank and the car was back to normal. For the past 4 months I’ve been careful to keep the tank below 3/4 full and the car runs great. Having moved to Knoxville, TN, only about a year ago, I don’t have a network of trustworthy acquaintances. I’d rather not take it to a shop that’ll cash in on me. One wanted to rip my engine apart for $1000 dollars. It’s only got 40K miles on it. I’d love to go in knowing what I need.

I’ve done as you asked and took my car to Advanced Auto to check for stored codes. There were none found. It would have been important for me to note that my engine light did come on one time and one time only. In the midst of the first occurrence, I accelerated hard and the engine light began to flash. I slowed and the light shut off after a few seconds. The light did not come on during the second two episodes under normal driving conditions. My owners manual states: “If the (engine) light is flashing, a misfire condition has been detected.”

Sajeev answers:

Consulting with car enthusiasts that have no financial ties to your vehicle’s repair needs is pure brilliance. That said, I better start armchair quarterbacking: I can’t believe the GTO didn’t throw a code, save it in the computer and eagerly share it with your scanner. But here we are!

Given the problem(s) presented, the Goat must have a problem with the evaporative emissions system. A quick check of LS1GTO.com found an extremely relevant thread. After clicking on that link, there’s nothing more I can add!

Bonus! A Piston Slap Nugget of Wisdom:

Just kidding, there’s more to discuss: everyone who cares about their car and/or wallet should be a (somewhat) active member of their ride’s on-line forum. As someone who’s been in the forum moderation business for a decade, I know there’s no better source for model specific problems. So just do it.

(Send your queries to mehta@ttac.com)

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2 of 13 comments
  • Nrd515 Nrd515 on May 20, 2010

    I had a problem like this on one of my old cars, almost causing me to get into a couple of wrecks before it got fixed. It would rev/surge, sputter, stall etc, and it took me a while to figure out it was the Evap system, and filling the tank all the way up made it happen, or made it a lot worse. Gas could be smelled in a closed garage when the tank was full, but it wasn't all that strong, at first. I started checking around under the hood when it got really strong, and the evap canister was full of gas and was very heavy. I took it to the dealer, and they knew what it was, and I don't remember how much it was, but it wasn't bad at all, like maybe $100 total. I think it was a check valve someplace had stuck open, and it let raw gas be sucked into the canister.

  • Lukemo2 Lukemo2 on May 20, 2010

    Thanks, everyone, for your input. And thank you, Sajeev, for posting my letter. I have enough information now and know where to begin with this. I am a member of LS1.com and did my best to search it and LS1GTO.com for subject matter similar to my problem, but I had a difficult time finding anything. That is when I decided to write in to TTAC. This venue provided me with the terminology I was looking for in order to search for the information I needed! Thanks, again!

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