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Having To RUN Higher Octane????

 
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Old 24 Dec 2010, 04:23 pm
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Default Having To RUN Higher Octane????

I have been running regular unleaded fuel in my 03 PT cruiser, since 03 with no problems. BUT at 93,000 miles it started running rough. I used Chevron Techron to clean the injectors and that increased the response of the throttle. But it still ran rough and I got a trouble code for the KNOCK. So I switched to the 89 octane fuel. I tried to use regular unleaded after a couple tanks of 89 octane, and it started running rough and not as smooth as it ran on 89 octane. Oh and using 89 octane cleared the KNOCK code.

Does anyone else have this problem and know why it only runs well on 89 (more expensive) fuel???

My father has an 89 Toy with 235K miles and his started dieseling. So he put 89 octane and it cleared up too.

Last edited by tcr1016; 24 Dec 2010 at 04:26 pm.
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Old 24 Dec 2010, 04:58 pm
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Default Re: Having To RUN Higher Octane????

When was the last time the plugs and wires were changed? PCV valve replaced? Air filter replaced? Throttle body cleaned?

At 93K everything has to be cleaned and or replaced if it hasn't been. There's no need to ever run anything but regular gas unless somethings wrong. If bumping up the octane level clears up a problem, your just masking what's wrong and wasting money on more expensive fuel.

Your also heading for the all important timing belt change which controls your engine timing. If that's off, you'll get the rough engine and pinging. Your dads TOY is probably built up carbon deposits which causes dieseling.
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Old 24 Dec 2010, 05:07 pm
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Default Re: Having To RUN Higher Octane????

How do you clean the throttle body???? I did the rest.
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Old 24 Dec 2010, 05:28 pm
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Default Re: Having To RUN Higher Octane????

Well, you can take it off, only a few bolts and connections or get hold of a can of SAEFOAM from your local auto store and follow the directions.

Caution: While Seafoam cleans, it makes a lot of smoke so use it in open spaces.

Sea Foam | How to Use Sea Foam Motor Treatment

How to Seafoam your engine the right way.|| Complete DIY || : General Chat

http://www.matthewsvolvosite.com/200...-instructions/
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Old 27 Dec 2010, 12:49 pm
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Default Re: Having To RUN Higher Octane????

Crewzin is mistaken on this one. Octane is a fuel's tendency to combust. The lower the octane, the higher the tendency to combust. When you have a higher compression engine, lower octane fuel combusts slightly sooner than higher octane. Sooner combustion is known as predetonation. After a while predetonation can lead to pinging and knocking.

This is why modern vehicles are equipped with knock sensors. A lot of people don't follow the manufacturer's recommended octane level, so the knock sensors detect when pinging begins and they slightly retard the timing to help avoid pinging.

In severe cases, predetonation can lead to severe engine damage. This is why manufacturers of high compression engines require premium fuel, or usually at least 89. They don't recommend higher octane simply so you have to spend more money.

There are no problems your engine could be having that would go away simply by changing fuel. Carbon buildup, bad plugs, dirty parts, etc. will not be affected by higher octane.
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Old 27 Dec 2010, 02:50 pm
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Default Re: Having To RUN Higher Octane????

Chris,

You explained it all very nicely and that's all well and good but what is your answer to his problem that he's having that he has to use higher octane to get rid of the knock code and running rough if nothing I said will help?
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Old 27 Dec 2010, 03:26 pm
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Default Re: Having To RUN Higher Octane????

isnt there some octane mixture you can buy and put in your fuel tank before adding fuel?
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Old 27 Dec 2010, 03:55 pm
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Default Re: Having To RUN Higher Octane????

Quote:
Originally Posted by CREWZIN View Post
Chris,

You explained it all very nicely and that's all well and good but what is your answer to his problem that he's having that he has to use higher octane to get rid of the knock code and running rough if nothing I said will help?
Yes. His engine is throwing knock codes because of predetonation caused by low octane fuel. Increasing the octane will alleviate the symptoms and the code can be cleared. That's why the symptoms and light go away when he uses 89.
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Old 27 Dec 2010, 04:29 pm
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Default Re: Having To RUN Higher Octane????

Quote:
Originally Posted by heifetz17 View Post
Yes. His engine is throwing knock codes because of predetonation caused by low octane fuel. But we are supposed to use low octane fuel in the PTIncreasing the octane will alleviate the symptoms and the code can be cleared. So your telling him that he should go up to 89 to alleviate the symptoms? That's why the symptoms and light go away when he uses 89.
Sorry, I don't get it. What you seem to be saying is that there's no way, without going up a grade to 89, that he can fix his problem.
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Old 28 Dec 2010, 09:34 am
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Default Re: Having To RUN Higher Octane????

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Originally Posted by CREWZIN View Post
Sorry, I don't get it. What you seem to be saying is that there's no way, without going up a grade to 89, that he can fix his problem.
That's exactly what I'm saying. The only way to fix a predetonation problem is by increasing the octane of the fuel. I'm not sure how to make it much clearer than that...

I don't know what your manual says, but according to mine and Chrysler the minimum recommended fuel is 89. 89 is not low octane. Chrysler does not recommend "regular" or low octane fuel for any of their vehicles.
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