I felt like splurging today. My tank was almost empty and I got a tankful of 95 octane gas. It costs more than the sixty-five US cents I pay per gallon for the 91 octane stuff, but what the hey. I also had the pump jockey add a bottle of fuel injector cleaner. I watched as he opened the bottle, broke the seal and poured the stuff in.
Remember my tank was almost empty.
As my engine idled at the pump, I felt a slight pulse in the usually smooth sound. The tach did not indicate any change in idle speed, but I could fee something.
So WTF? Did I get some bad gas? Some good gas with a higher-than-usual octane?
A couple of things come to mind. Since you did not mention year make or model, I am making some generic guess here.
Normal idle fluctuations. As the engine idles and the oxygen sensor switches from rich to lean sometimes this get magnified to the point where the engine idle may appear to skip a beat. Air leaks, old spark plugs, or plugged fuel injectors may magnify this condition. (Fairly likely)
The injector cleaner actually did something, and knocked a piece of crap loose, temporarily giving one injector a bad spray pattern, causing a miss fire. (Not likely)
The new fuel burns somewhat different and when it first went through the engine, it took some time for the engine management to compensate for the difference in fuel. (Also fairly likely)
If it continues to happen, look at #1. If it was a one time deal, look at #3
One of the thing that really annoys me about the way they sell gas is they equate higher octane with “better” gas, which is absolutely not true. The octane rating has to do with how much you can compress the gas before it spontaneously explodes. Running with too low of an octane will cause the gas to explode before it gets fully compressed instead of waiting for the spark to ignite it, which will make your engine run like crap and may actually damage it. The typical symptom of running with too low of an octane is that your engine makes a “pinging” noise.
Running with too high of an octane though is just wasting your money. Some cars can adjust for it, some can’t. I always figured that it wouldn’t provide any extra benefit from running too high of an octane, but it wouldn’t get worse, but Mrs Geek’s Camry proved me wrong. It runs best on 89 octane. On 91 octane it runs worse, actualy losing a couple of mpg.
If you feel like splurging, the fuel injector cleaning was probably a good idea. The higher octane wasn’t, though.
Paul’s car can and will adjust for different octanes.
Most over the counter injector cleaners are nothing more than moose milk. IOW they don’t actually clean the injectors. The exception to this is Chevron’s Techron.
So you’re saying that Chevorn’s gas IS better at cleaning injectors and intake valves than others? I had always assumed that all gas was pretty much the same.
That’s the claim ChevronTexaco makes, though I’ve never seen what they cite to back it up. Still, however, the difference would not be the gasoline itself but the additive.
Techron is the only additive I have ever seen a car maker recommend by name in a technical service bulletin.
Car makers can use any pump gas they want for their emission certification tests. Chevron is not sold in Michigan. All three of the big three auto makers truck Chevron fuel in from Kentucky for their emission durability tests… Cite
BMW, GM, Honda, and Toyota established criteria for "Top Tier " gasoline for the fuel that they would like to see used for the lowest emissions and best performance. Chevron was the first gasoline to be certified as Top Tier, and no reformulation was necessary.
On the way to work today more surging. Then I got a “Check Engine” light and an odd “Slow down or Shift Up” message. I took the afternoon off work and took it to the dealer. The shop manager met me, we are old friends by now. He got me a nice loaner car, a Rexton.
His first guess is the throttle, but we will see.
So a hardware failure at the same time I was gassing up? It could happen I guess.
I agree completely with the sentiments of engineer_comp_geek’s post.
Many people don’t seem to realize that the higher the octane rating, the less easily the fuel burns.
The octane rating is merely a measure of how much you can compress a given fuel-air mixture without pre-ignition. Since many high performance engines have high compression ratios, they require high octane fuel. Putting high octane fuel into an engine that does not require it does absolutely nothing for engine performance, though.
You can leave the car running while filling up? Weird.
My WAG from afar is you had some moisture in the tank, and the gas additive brought it into solution with the gas. Ultimately, the moisture will be out of the tank and out the tailpipe, but you might have some rough running until the “moisturized” gas is gone.
Last question: Are Saudi engines such high-compression that you need 95 octane? Here, 91 is the highest you can normally find.
The morning news was showing a gas station in San Mateo that was charging $3.69 for 87 octane, so I don’t want to hear any complaining!
Musst be an East Coast company. Looks like Sunoco race fuel is sold at about 20 locations in CA (primarily at “76” stations, rather than Sunoco locations) - none are particularly close to here, and no Sunoco-branded locations in CA at all. For comparison, there are more than 20 Shell-branded locations in San Francisco alone.
