Flashing check engine, misfires. Bad Gas?

[marquiliuss]

Yesterday evening filled up about 13-14 gal at costco. Live about two miles down the road. Warmed up next morning and took her around 3k onto the highway at regular temp and got flashing cel. Felt a little underpowered as I was around 65-70mph for a few minutes. Shut her down on the off ramp and restarted to a shaky but normal 800rpm idle.
Feels weak moving out of first gear. Almost like only running on four cylinders. Afraid to drive it to auto zone to see what codes are showing.

Could it be bad gas or a coincidence ?

Was searching around similar symptoms and I do recall my fuel filter making small ticking sounds before. It's the stock filter (currently at 92k)

o2 sensor? I recently installed a cat back and feel like I have some leakage where the bolt on to stock cats. Not sure if the o2 sensor puts the car in limp mode.

Any suggestions what to do would be greatly appreciated

[TheSchwa]

As for the fuel, Costco uses Top Tier and I've never had an issue with it after filling up there many times... Maybe call them and see if they've had any complaints lately?

[SpoolBus]

Funny you should start this thread but I filled up my motorcycle last night at a small no name station and about 5 miles later BAM..rough idle, stumbling, stutter..I put in some SeaFoam into the tank per the instructions on the bottle. The low end stumbles are still present but high rpm's it runs smooth.

Worth a try to put in some SeaFoam or HEET if you think it may be bad gas (water in the fuel). It should clear with a treatment and a fresh tank if that's the case.

[Jake@JHM]

Are the misfires isolated to a single bank?

[s4burner]

FYI... I had #8 sparkplug fowl out and cause the car to go into limp mode...

[krew53]

I don't have an S4 but a blown coilpack will cause the flashing cell and misfires like you described.

[blubalz]

this happened to me and it was a coil pack. when was the last time they where replaced? From my experience if one goes, the other ones start to go shortly after. If that is the problem I would change all 8 and do the plugs while your at it.

[Jwheeler]

Not good to drive with the flashing cel. That means bad things are happening to the cat. O2 sensor won't cause a misfire. Get a scan too and see what cylinders are misfiring. If it is just one, coil or plug would be suspect. Multiple cylinders on both banks could be caused by bad gas.


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[dparm]

I don't buy the bad gas scapegoat. I have only been driving for about 13 years, but I have never, and I mean NEVER, had a bad tank of gas.

Until you read the codes, anything is going to be speculation.

[Jwheeler]

I don't buy the bad gas scapegoat. I have only been driving for about 13 years, but I have never, and I mean NEVER, had a bad tank of gas.

Until you read the codes, anything is going to be speculation.

Of course it is all speculation. He hasn't done any diagnosis except say the light is on and ask why. Water gets in underground fuel storage tanks. It does happen.


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[p3u]

I don't buy the bad gas scapegoat. I have only been driving for about 13 years, but I have never, and I mean NEVER, had a bad tank of gas.

Until you read the codes, anything is going to be speculation.

2nd...

[JimmyBones]

Can't stress it enough: You need to get the codes read to see what is going on.

Bad gas is a possibility but I doubt it. It is much more likely that a coil pack died. Worst case scenario is your timing jumped or your camshaft adjuster failed. Did you ever have the coils replaced as part of the recall a while ago?

[Slow4]

Of course it is all speculation. He hasn't done any diagnosis except say the light is on and ask why. Water gets in underground fuel storage tanks. It does happen.


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Unless that gas is DILUTED with water, this theory has me in awe; WTF?

[vacsimile]

I don't buy the bad gas scapegoat. I have only been driving for about 13 years, but I have never, and I mean NEVER, had a bad tank of gas.

Until you read the codes, anything is going to be speculation.

Bad gas is very real but I don't think it's the case here. I'm also afraid that even after the OP gets the codes it will be nothing but speculation. If you take your car to Autozone to retrieve codes you might as well just take it to a shop that knows what they're doing.

[TheSchwa]

Unless that gas is DILUTED with water, this theory has me in awe; WTF?

Does gasoline and water really mix...? Can it really be "diluted" if gasoline floats to the top?

[allroadmark]

I don't buy the bad gas scapegoat. I have only been driving for about 13 years, but I have never, and I mean NEVER, had a bad tank of gas.

Until you read the codes, anything is going to be speculation.

its all bad, if you knew what was in tanks at stations you would probably buy an electric car!

[Fritz_S4]

Gas stations have a lot of filters to filter out crud and other impurities, not to mention take out the bigger impurities and water in the gas.

Yes pretty much all underground tanks will have water in them simply because of air condensation as they go through the fill/empty cycles, not to mention water infiltration around seals in the tank inlet/outlet/gauge ports.

Water is the least of the contamination going on in the tanks, just think of how much crud is at the bottom of your gas tank after 100,000 miles and multiply that by 100,000 for a very safe estimation.

That's why they have all the filters and strainers for each individual pump (aside from very old stations which sometimes have just on filtering system for the entire station), so that no contaminants goes into your gas tank.

Each of those pumps has a filtering system behind that lower portion underneath the display.

Now of course there will be some contamination but nothing warranting that you get horrible misfires and a flashing CEL.

When you get "bad gas" your car will idle slightly less smoothly, kinda like if you're running 87 or 89 instead of 91/93 but maybe a bit worse.

It won't get a flashing CEL unless your station mixes up the tank fill ports and puts in diesel instead of gasoline in which case you engine will grenade much faster than you'd really expect.

[marquiliuss]

Thanks for all the tips guys. Yes, a lot of speculation here off what knowledge I had at the time.
The bad news:
Took it to autozone on the way to the shop to know what I'm dealing with beforehand. Cylinders 1&2 misfires. Didn't get the codes.
Shops diagnosis was two fried spark plugs causing misfires.
Opens up a whole new problem because I just had them replaced no more than 5-7k miles ago. I think I may have some internal issues going on. Been using generous amounts of oil (2qt+/1000miles).

A while back Audi service borescoped the engine and said I had scored walls. I never went back there because they wanted to drop the block and overhaul for $6k... Anyway... Damn audi problems

[Slow4]

Does gasoline and water really mix...? Can it really be "diluted" if gasoline floats to the top?

I don't think so....I just recall watching my dad wash his paint brushes in gasoline and water. The gasoline would eventually mix with water but my original point was about the idea of THAT much water residing in the station tanks sound ridiculous.

A while back Audi service borescoped the engine and said I had scored walls. I never went back there because they wanted to drop the block and overhaul for $6k... Anyway... Damn audi problems

Overhaul the block for scored cylinder walls;
what's that consist of, sleeving the walls?

[marquiliuss]

It was awhile ago. Some tech was explaining to me the fix process things like removing piston heads and sending them to Minnesota to be remanufactuered. I stopped listening when I heard the price of all this so I decided to take it to another shop. There they diagnosed and fixed something completely different that was the problem.

[allroadmark]

Gas stations have a lot of filters to filter out crud and other impurities, not to mention take out the bigger impurities and water in the gas.

Yes pretty much all underground tanks will have water in them simply because of air condensation as they go through the fill/empty cycles, not to mention water infiltration around seals in the tank inlet/outlet/gauge ports.

Water is the least of the contamination going on in the tanks, just think of how much crud is at the bottom of your gas tank after 100,000 miles and multiply that by 100,000 for a very safe estimation.

That's why they have all the filters and strainers for each individual pump (aside from very old stations which sometimes have just on filtering system for the entire station), so that no contaminants goes into your gas tank.

Each of those pumps has a filtering system behind that lower portion underneath the display.

Now of course there will be some contamination but nothing warranting that you get horrible misfires and a flashing CEL.

When you get "bad gas" your car will idle slightly less smoothly, kinda like if you're running 87 or 89 instead of 91/93 but maybe a bit worse.

It won't get a flashing CEL unless your station mixes up the tank fill ports and puts in diesel instead of gasoline in which case you engine will grenade much faster than you'd really expect.

not all stations have filters fitted some only a mesh strainer and some have nothing and there are problems with petrolium products that filters do not fix and besides that filtered fuel is still poor quality! you sound like you have some knowledge on this topic, are you in the industry?