Piston Slap: A Gassy Problem From a Hibernating Audi

Todd writes:

Hello Sajeev, I have a 2001 Audi TT (225hp) that cranks but wont start, not even a sputter. Thus far I’ve checked for fuel and spark and both seem to be in working condition. I verified fuel by unplugging the return line and watching fuel come out as the motor was cranked. I can hear the injectors ticking so it seems they’re working as well. I popped off a coil pack and grounded it to a screwdriver to verify that I also have spark. At this point I’m thinking the fuel in the tank has gone bad because the car has not been significantly driven in 18 months. I literally haven’t started or driven it in nine months, and when I did drive it nine months ago it was for about 3 miles. There was less than a 1/4 of a tank of gas in it while it sat for those 18 months and I just added about 3 gallons of premium to the tank with no result. There also seems to be an odd smell coming from the exhaust when I crank the car, almost like a paint remover or super glue smell. Is this bad gas? I’m really stumped here because I feel like even if the gas is bad it would at least sputter or run rough.

Any help would be greatly appreciated that you or TTAC’s best and brightest can provide. Key points:

1) Car has sat for 18 months, but ran once for three miles nine months ago.

2) Car has fuel and spark.

3) Car has no DTCs.

4) Battery was weak in the TT, but was recharged and jumped with my other car. The TT cranks strongly.

5) Odd smell from exhaust when cranking, no smoke whatsoever from exhaust.

6) Timing belt is good.

Sajeev Answers:

Quick answer, stated in a question, did you verify the actual pressure of the fuel? Having fuel in the line means nothing, you need a certain pressure to work with your car’s EFI system. So checking the pressure and verifying it’s within range enough is the first thing to do.

Todd Replies:

I did a visual and aural check, meaning I only watched the fuel squirt out of the return line while it cranked over and listened to the injectors tick. Where should I hook the fuel pressure gauge up to?

Sajeev Answers:

There’s a schrader valve (like a tire) on the fuel rail, and this is where a gauge tests fuel pressure. That’s about all I can say, because proper diagnosis requires research on VW/Audi forums, here and here. Which is technical, somewhat complicated and far too boring for TTAC’s format. I’m falling asleep just thinking about it!

So here’s the quick overview: EFI won’t work correctly with too little (or too much) fuel pressure. Since the Audi sat for a while, I recommend changing the fuel filter first. If it gets even a little better that’s a good indication the fuel system is at fault, and the fuel pump is more than likely the problem. If a new filter and pressure test turn out okay, then its time to address weak/inadequate spark condition. But I am 100% sure that fuel it your problem.

Bonus! A Piston Slap Nugget of Wisdom:

Why 100%? Because my Fox Body Cougar sat for 11 months, waiting for me to pull it’s cracked dash and failed heater core. Once I got it done, the Cat was fairly happy, even if the 1988-vintage fuel pump was already undersized (60 liters per hour, feeding 155 stock horses) for my conversion to 5.0 Mustang status (90lph, 225hp) about 11 years ago. But things got worse: idle, power above 4000rpm, and fuel economy. Then it ran flat above 2500rpm. Then it wouldn’t run above 2000 rpm. And then it just stopped running, period.

I hooked up my fuel pressure gauge only to find out its connector doesn’t work on the non-Mustang fuel rail. Fan-frickin-tastic. I replaced the filter, on a hope and a prayer, as the (running) pump shot fuel from the disconnected filter. The car did indeed sputter and stall after that, but a new pump was in order. I went to the 5.0 aftermarket, getting a pump with over four times more flow for future power upgrades. Which is awesome, except the new pump now exposed a leaky fuel rail.

After I was done cursing up a storm in my gasoline soaked driveway, I gave up and towed the Cougar to my trusted mechanic. I know when I’m beat, so here’s the Wisdom Nugget: enjoy the Audi once you fix it, but don’t be surprised if another component fails after that long slumber. It happens.

Send your queries to mehta@ttac.com. Spare no details and ask for a speedy resolution if you’re in a hurry.