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So I am not very knowledgable when it comes to cars :eek:. Anyways, I have four codes on my 2002 Saab 9-3... I bought this car at auction a few weeks ago. I have only been putting Regular gas in it. Is it possible that regular gas can set off error codes?

Thanks,
BK
 

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You will get better performance (and depending on your driving habits better mileage too) with premium but the car will run fine on regular. If you are getting error codes it wouldn't be caused by running regular, but switching to premium might help mask the problem if the issue is borderline.

I'd suggest a tune up with new plugs (correct NGK resistor type) and new vacuum hoses. But without knowing the specific codes there isn't much more advice to offer.
 

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Adding your location and model specifics to your profile is a good idea around here.

If you're in the USA, Autozone will read out the codes for you.
 

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imho, old plugs with a large gap and low grade gas will throw codes. It will detect unburnt fuel and subsequently lean out the trim.
 
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just stop being cheap and use the gas that is recommended. trionic does have the capability to adjust knock retard and timing according to the combustion result.
 

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You will get better performance (and depending on your driving habits better mileage too) with premium but the car will run fine on regular.
It actually ended up being cheaper to run premium in my old convertible because the fuel economy increase more than offset the price difference.
 

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It actually ended up being cheaper to run premium in my old convertible because the fuel economy increase more than offset the price difference.
I found that, too, although the cheaper gas gets, the worse of a deal premium is. It always seems to be $.20/gallon more expensive than regular, no matter what price regular is. Now that gas is getting close to $2.00/gallon, it's getting to the point where premium is about 10% more expensive than regular, and I don't think I get 10% better fuel economy with premium.
 

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Around here high octane (aren't we not meant to refer to them has premium since the only guaranteed difference is the octane rating) is 2.40 a gallon and 2.00 for regular, you need a significant swing in mileage to make a difference. Which if most of your driving is spent cruising around at low boost you may not ever see.
 

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Is there any data to support anyone's theories of mileage based on premium vs regular?

You have the car manufacturer on one side claiming what's best because they couldn't care less bout your wallet, and the consumer on the other ranging from all sorts of theories depending on what they're biased towards..doesn't seem like there's a way to make a sound decision on this unless I'm missing something.
 

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It all depends on your driving style and conditions. You will mostly only see the added benefit from the higher octane at higher boost levels or under significant acceleration. If you spend the day slowly driving town from stop light to stop light you will probably never notice a difference, or if you are careful with your right foot on long highway runs. If you drive in a hilly area or like to put your foot in it on some nice back roads or on ramps you more likely will.
 

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It all depends on your driving style and conditions. You will mostly only see the added benefit from the higher octane at higher boost levels or under significant acceleration. If you spend the day slowly driving town from stop light to stop light you will probably never notice a difference, or if you are careful with your right foot on long highway runs. If you drive in a hilly area or like to put your foot in it on some nice back roads or on ramps you more likely will.
Alas, I short-shift my non-turbo with the 10.5:1 compression like a dog in city driving, and at least 91 octane quiets the pinging somewhat. If I was doing all highway driving I'd stick with 87. Even though the 91 octane I'm putting in has zero ethanol (Shell or Ultramar), I don't really see much if any economy advantage. Certainly not enough to offset the steep premium of 15%-25%, depending on the gas station (most Shell stations putting a punitive premium on their "V-power" stuff).

And no, gas stations in Canada don't show any price but the default 87, so you don't know how much they're marking up the higher octane ratings, and it's not predicable either.
 

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Is there any data to support anyone's theories of mileage based on premium vs regular?

You have the car manufacturer on one side claiming what's best because they couldn't care less bout your wallet, and the consumer on the other ranging from all sorts of theories depending on what they're biased towards..doesn't seem like there's a way to make a sound decision on this unless I'm missing something.
I have not run across much lately that supports or refutes claims of mileage increases or decreases when switching from lower to higher octane fuel. As far as performance is concerned, that was tested by Car & Driver back in November of 2001. (The foregoing link is to the full text of the article).

The cars tested were a 5.9-liter Dodge Ram V-8 with a mechanical distributor and no knock sensors, a Honda Accord V-6 with VTEC variable valve timing, a 4.6-liter V-8 Mustang (all 3 of which were designed to run on regular unleaded), a 333-hp, 3.2-liter BMW M3 straight-six with individual throttle by wire for each cylinder, and a Saab 9-5 with a 2.3-liter turbo engine.

The fuel tanks on all the cars were drained and filled with 87-octane Mobil regular unleaded fuel and driven for two days before track and dyno testing to permit the ECUs to adapt to the fuel. The tanks were again emptied and then filled with 91-octane Mobil premium. Once again they were all driven for two days to allow time for the ECUs to adapt to the fuel type. The testing after the 2 day adaptation for high octane fuel was repeated at the same drag strip and dyno. Results were weather corrected (temp and humidity, presumably).

The Dodge Ram experienced a few HP more on the dyno with high octane but the strip performance was essentially the same as with lower octane. The Mustang showed 2 more HP on the dyno but showed a .3 second lower ET using the higher octane. The Honda actually lost 2.6 percent power on the dyno with higher octane and suffered a 1.5% decline in ET. The BMW could not be dyno'ed due to ECU programming, but suffered a 6.6% performance decline at the strip when running lower octane fuel as compared to higher octane. With the T7 9-5, dyno measured power loss running lower octane was 9.8% and strip performance on lower octane suffered a 10.1% decline.

These results pretty much speak for themselves. Engines that have sophisticated and powerful engine management systems (the V-TEC Honda being a very strange anomaly) and that have aggressive timing (and boost in the case of the Saab) programming will tend to perform significantly better with higher octane fuel.

The article noted that neither the BMW nor the Saab (the two cars tested in which the manufacturers specified use of higher octane fuel) suffered any mechanical ill-effects when using the lower octane fuel.
 

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Even though the 91 octane I'm putting in has zero ethanol (Shell or Ultramar), I don't really see much if any economy advantage. Certainly not enough to offset the steep premium of 15%-25%, depending on the gas station ...
I believe the theoretical difference in MPG with 10% Ethanol is a 6% decrease in MPG. That's based on the actual difference in burn value of the alcohol vs. gasoline.

We don't have the option of no Ethanol where I am. There's a strong farm lobby in the USA.
 

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Isn't there a school of thought that premium gas should always be run on the T7 cars to have a more complete combustion cycle to help prevent the pistons from overheating and blowing up?
 

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These results pretty much speak for themselves. Engines that have sophisticated and powerful engine management systems (the V-TEC Honda being a very strange anomaly) and that have aggressive timing (and boost in the case of the Saab) programming will tend to perform significantly better with higher octane fuel.
That's not quite what I got out of the article. Their last paragraph starts out with:

"Our tests confirm that for most cars there is no compelling reason to buy more expensive fuel than the factory recommends, as any performance gain realized will surely be far less than the percentage hike in price."

Most cars don't recommend premium fuel, regardless of their timing or programming. Our cars are an exception to that rule, and obviously do perform better with premium. I wish they had extended their test to do some fuel economy comparisons, too. My wife and I think we get about 10% better fuel economy running premium, but then our fuel economy could easily vary by 10% from tank to tank with Seattle's horrible and unpredictable traffic.
 

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That's not quite what I got out of the article. Their last paragraph starts out with:

"Our tests confirm that for most cars there is no compelling reason to buy more expensive fuel than the factory recommends, as any performance gain realized will surely be far less than the percentage hike in price."

Most cars don't recommend premium fuel, regardless of their timing or programming. Our cars are an exception to that rule, and obviously do perform better with premium. I wish they had extended their test to do some fuel economy comparisons, too. My wife and I think we get about 10% better fuel economy running premium, but then our fuel economy could easily vary by 10% from tank to tank with Seattle's horrible and unpredictable traffic.
And I agree with their statement. It applies to most cars and limits itself to to saying it makes no sense to buy higher octane than the manufacturers of most cars recommend.

If you read the entire article many times over, as I have since I first received it in the mail 14 years ago, you realize that C&D was making a great many points.

1) Nearly all cars that do not require higher octane gas will realize, at best, very small and insignificant performance gains by using it. And any such gain will almost always be a loser when examined under a cost/benefit analysis. By performance gains, the article was referring to measurable performance increases, as in producing higher horsepower and lowering ETs (quicker acceleration), since the article did not address increased or decreased mileage as a performance criterion being evaluated.

2) The article indicates that the BMW and the Saab were cars of a different classification as compared to the other 3 being tested. It stated that BMW and Saab specified higher octane (premium) fuel for these vehicles. Additionally, it took pains to mention their powerful and sophisticated engine management systems. As well, the article measures the performance results differently for the two classes of cars. The first three cars' results are expressed as performance differences achieved using higher octane fuel over or under those as compared to the baseline results provided by use of regular unleaded fuel. The BMW and Saab results were expressed as performance decreases observed when those cars used the regular lower octane fuel as compared to baseline results achieved when they used premium higher octane fuel.

4) The results essentially verified that the lower tech (i.e. less electronically sophisticated) vehicles like the Dodge and Ford realized only the tiniest measurable performance improvements by switching to higher octane and the Honda was an almost unexplainable anomaly, causing the consulted experts to surmise that its slight but measurably decreased performance results might fall into the realm of expected test-to-test variability.

5) The cars designed to run on premium higher octane fuel were the two that were able to extract the greatest and most significantly measurable benefit from using it. As car guys we know that this MUST result from the engine being able to utilize more advanced ignition timing (in the case of the BMW) and from a combination of more advanced ignition timing and boost (in the case of the Saab). We know this because we know that premium higher octane fuel is not more powerful or more volatile or more flammable than lower octane fuel and that it does not contain more energy than regular lower octane fuel. We know that it is the increased AKI of premium fuel (which is really just another way of saying it has a higher octane rating) that permits an engine capable of detecting its presence and taking advantage of it to run more aggressively and efficiently (i.e. with more advanced ignition timing in the case of naturally aspirated engines, and in the case of forced induction engines, to run more aggressive ignition timing and higher boost).

6) The BMW's measured performance at the strip was 6.6% better with higher octane fuel than with lower octane fuel, and the Saab's dyno performance was 9.8% better while its strip performance was 10.1% better. These are substantially and significantly larger performance gains achieved using the higher octane fuel than the teeny-tiny gains realized by the other cars that proved incapable of extracting the most from their use of the higher octane fuel. Such gains are, in a word, significant. The only reasonable and rational explanation for these measured results is that the engine management systems of the cars designed to run on regular unleaded were not designed or were not sophisticated and powerful enough to permit sufficient upward adaptation to the higher octane premium unleaded fuel, while the engine management systems of the cars designed to run on premium were.

7) If the manufacturer specifies premium fuel for the car but the engine management system is sophisticated and powerful enough to adjust or adapt for lower octane fuel (i.e. adapt downward by retarding ignition timing, perhaps adding additional fuel if necessary, and in the case of forced induction, dialing back boost) under the existing ambient circumstances, no immediate harm is likely to result from using lower octane fuel. I say immediate here because the article did not present results of a long-term test and thus could not draw a conclusion as to long-term consequences from using lower octane fuel over an extended period under widely varying circumstances, such as towing, significantly higher ambient temperatures, carbon build-up on piston crowns over time, etc.

Accordingly, the article concluded with:

Cheapskates burning regular in cars designed to run on premium fuel can expect to trim performance by about the same percent they save at the pump. If the car is sufficiently new and sophisticated, it may not suffer any ill effects, but all such skinflints should be ready to switch back to premium at the first sign of knock or other drivability woes.
So, I stand by my synopsis.
 

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I agree that 10% is very significant, although MPG gains are going to be directly related to how and where you drive.

Here's my usual analysis, adjusted for today's gasoline prices.

15000 miles/year @ 28pmg = 536 gallons of gas.
536 gallons of 87 octane @ $2.09 = $1120
536 gallons of 93 octane @ $2.34 = $1254

Maximum possible savings in a year, before any loss of power or MPG is $134. Yes, $134 for the entire year.

If you gain 3mpg, you break even on the money AND have the additional power and performance you paid for. Even if you don't gain MPG, you still get all the additional power and performance for a measly $134/year.


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One note: Premium gas used to cost $0.20 more per gallon consistently (and artificial amount, but the going rate). As gas prices rose to ~$4 per gallon, the gasoline companies hiked the charge for Premium so that the differential was more like $0.40 per gallon. As prices decreased in the last couple years, some have kept the same $0.40 differential, even with gas back down near $2/gallon. You might need to shop a bit to find stations with even $0.25 gallon differential now - some have held them at $0.40/gal despite the decrease in their costs.
 

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one compounding factor in the cost analysis is that those likely to run premium gasoline (in cars that can take advantage of it, mainly modern forced induction) for the extra power are probably going to USE that power... and of course the heavier your foot, the more gas you're going to burn!

that said, i think we should start rating things in smiles per gallon. :cheesy:
 

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The position of the EPA:

Why do some manufacturers require or recommend the use of higher octane gasoline?

Higher octane fuels are often required or recommended for engines that use a higher compression ratio and/or use supercharging or turbocharging to force more air into the engine. Increasing pressure in the cylinder allows an engine to extract more mechanical energy from a given air/fuel mixture but requires higher octane fuel to keep the mixture from pre-detonating. In these engines, high octane fuel will improve performance and fuel economy.

What if I use a lower octane fuel than required for my vehicle?

Using a lower octane fuel than required can cause the engine to run poorly and can damage the engine and emissions control system over time. It may also void your warranty. In older vehicles, the engine can make an audible "knocking" or "pinging" sound. Many newer vehicles can adjust the spark timing to reduce knock, but engine power and fuel economy will still suffer.

Will using a higher octane fuel than required improve fuel economy or performance?

It depends. For most vehicles, higher octane fuel may improve performance and gas mileage and reduce carbon dioxide (CO2) emissions by a few percent during severe duty operation, such as towing a trailer or carrying heavy loads, especially in hot weather. However, under normal driving conditions, you may get little to no benefit.

Why does higher octane fuel cost more?

The fuel components that boost octane are generally more expensive to produce.

Is higher octane fuel worth the extra cost?

If your vehicle requires midgrade or premium fuel, absolutely.

If your owner's manual says your vehicle doesn't require premium but says that your vehicle will run better on higher octane fuel, it's really up to you. The cost increase is typically higher than the fuel savings. However, lowering CO2 emissions and decreasing petroleum usage by even a small amount may be more important than cost to some consumers.
 
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