Supermarket Vs Brand name fuel

[Dangermouse]

Question for you combustion experts on the difference between supermarket gas and brand name gas

I have been neglecting my D because of my newest DD, which is turning out to be a SOB.

On my DD (with variable valve timing) I have been having a check-engine light on intermittently for a few months. When I check the OBD codes there is always a P0015 - B Camshaft Position Timing Over Retarded.
There were various mechanical things that I looked at, without success, so on the suggestion of another owner, that it was ‘something in the fuel system that was causing the timing problems’, I switched gas brands. I had been using Kroger 91 octane and I switched to Shell 91 octane, and within 15 miles, the code was gone!


So what’s the mystery ingredient? I thought that supermarket brand gas just didn’t have some of the detergents that the brand name stuff does.

Of course I’ll be filling the tank with Kroger the next time to see if it comes back, as a confirmation that it just wasn't luck.

[krs09]

Shell-Exxon-BP are considerd top tier fuels and have a higher concentration on cleaners in their fuel where supermarket (bottom tier) fuels have the goverment mandated levels of cleaners. Thats why top tier fuels a more expensive (added cleaner expense) Stay away from Wawa and Sunoco - very high levels of carbon and leave a lot of deposits behind after burning. What do you have as your DD?

[Dangermouse]

That's what i thought - that you were paying extra for the cleansers etc, but I though that the octane level was the same, by code/law etc. The two stations are next door to each other and the gasoline tank farm that they both get supplied from is about 20 miles away.

I'm just wondering about why the timing would be affected.

It's an 07 BMW X3 with the N52 PITA engine, btw.

[Flicky]

Could be that place has a bad tank or something. Like water got into it. I also suspect that some places selling Premium are really pumping out low grade. I hate that the stations now are using 1 hose to pump all grades out. Even if they aren't trying to jook you, it makes like 1Gal that is someone's nasty leftover 85 octane. Not a huge deal when filling from empty, but on my motorcycle I try to find a place that still has the pumps with 3 hoses.

I usually don't mind supermarket stations since they are busy and I figure the gas is fresh.

<EDIT>
Oh, I see it was going on for a number of months, so probably not a one time water thing. I guess see if it comes back on you with the other gas. How many miles on the car? Ever pull a plug and see if what things look like? Even if the CE light doesn't come back I'd drop some techron in if over 30K miles.

[NightFlyer]

Stay away from Wawa and Sunoco - very high levels of carbon and leave a lot of deposits behind after burning. What do you have as your DD?

My DDs have been diesels for quite some time now, so I haven't really kept up with what's going on with gasoline.

But when I fill my D, I go out of my way for Sunoco, so I'm not sure why you're saying that it's bad fuel.

This is from Sunoco's website:

Sunoco fuels significantly exceed U.S. Environmental Protection Agency (EPA) gasoline detergency standards. All grades of Sunoco fuel contain the same level of detergent.

In addition to government-mandated detergency tests, Sunoco fuels are subject to additional testing by an independent, third-party lab to further ensure their quality.

Sunoco fuels contain other additives such as corrosion inhibitors and antioxidants, which help to ensure fuel quality.

They also promote a longer “shelf life”, which means the fuel will last longer in between uses.

Dispensers at Sunoco gas stations filter and trap particles as small as 10 microns from the gasoline before it gets into your tank.

Sunoco fuels meet every car manufacturer's specifications for oxygenated and reformulated fuels in areas where those fuels are required by law.

Sunoco fuels do not contain methanol.

As stipulated by most automobile manufacturers, Sunoco fuels contain no more than 10% ethanol.

Sunoco fuels do not contain MMT, a manganese-based fuel additive banned by the EPA in certain types of fuels.

And let's not forget that Sunoco is the official exclusive fuel of Nascar and many NHRA tracks. Sunoco's are also your best bet to find ethanol free fuel here in the state of Michigan anyway.

[David T]

The variable valve timing is trying to adjust the valve timing based on the octane of the fuel you are using. If the octane is below what is required it can't adjust enough. Check the octane requirement. It is in your owner's manual and usually on the fuel door by the gas cap. No name brands sometimes cheat on the octane so you may think you are buying 91 when it is really 88.

[Dangermouse]

I am thinking that this is what's happening. I get the gas from the same station but different pumps so it's unlikely to be a fault in the pump.

The manual recommends 91 but notes that the engine will operate on 87 also.

That was my understanding of VVT control and that's why I was wondering why two fuels of the same octane have different effects.

[mluder]

The variable valve timing is trying to adjust the valve timing based on the octane of the fuel you are using. If the octane is below what is required it can't adjust enough. Check the octane requirement. It is in your owner's manual and usually on the fuel door by the gas cap. No name brands sometimes cheat on the octane so you may think you are buying 91 when it is really 88.

+1
My wife's Mazda was running really crappy recently - To the point where passengers would ask "What's wrong with the engine?" Then the other day I filled up at Costco on an almost completely empty tank. The rough idle disappeared - or at least was greatly diminished.

We always fill with premium fuel as the owner's manual specifies. Best I can guess is either she accidentally put lower octane fuel in or the gas jockey (we only have full service gas stations here) put the wrong gas in.

Cheers
Steven

[Dangermouse]

I just noticed an error in my first post. Both stations actually sell 93 octane (as well as 87 and 89), so it should have been higher than the "preferred" 91. I drove through both of them this morning in case the Kroger was 91 and the shell 93, which would explain it, but they both sell the same choice of grades.

I wonder if there is a way to test the octane from a sample batch?

No Sunoco down here Josh.

[David T]

I just noticed an error in my first post. Both stations actually sell 93 octane (as well as 87 and 89), so it should have been higher than the "preferred" 91. I drove through both of them this morning in case the Kroger was 91 and the shell 93, which would explain it, but they both sell the same choice of grades.

I wonder if there is a way to test the octane from a sample batch?

No Sunoco down here Josh.

Without the proper test equipment there is no easy way to test octane. Getting a full tank of each on the same car and trying it is as close a way to compare octane as you can. If it runs crappy on one tank but good on the other, one tankful has lower octane or more water. It can also be the additives are different or even stale fuel. House and no-name brands can be lower quality than nationally branded stuff.