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Discussion Starter #1
For years now, I've been complaining about my car being underpowered and getting not-quite good enough gas mileage.

Last weekend, I helped out a mechanic who repaid me with a tank of gas. On a whim, I told him to put in mid-grade gas (89) instead of economy (87). On the drive back home, I noticed that I was getting 86 mpg instead of the 73 that I got going there.

It appears that my 10 year old car has a problem common to older cars - carbon buildup. This has caused an increase in the compression ratio which causes the car to need a higher octane fuel. Because I haven't been putting it in, the knock sensor has been retarding the timing all this time.

I took a drive last night that was similar to my test of a few weeks ago. I started from home, drove about 50 miles down the Garden State Parkway, turned around and came back. I did not use MIMA at all. Last time, I averaged 77.5mpg. This time 87.8.

 

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I would definitely like to investigate how prevalent this phenomenon is. I've always been a staunch advocate of using the fuel grade that your car was designed for, but obviously that doesn't take into account things like carbon build up that can happen and are rather dependant on an individuals driving habits/conditions.

I think I don't have problems with this in my cars because I tend to drive them hard. Insight #1 usually sees redline a few times a day, and has for the last 3 years and 72,000 miles. I've never been able to notice a difference either power or fuel economy wise when using different fuels. I wasn't even able to detect a MPG or power increase by using 100% gasoline(no ethanol).

I'd like to look into being able to see what the knock sensor sees. Or a way to be able to tell if the ignition timing is being retarded. Hmm.
 

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I used a bottle of Gumout with regane(clear bottle with gold fluid), and a bottle of Chevron Techron on two separate full tanks of gas in my Insight and it cleared up the herky jerky from when I bought the car. 22k miles later and I'm about to run the same thing through as it starting to have the herky when the engine is cold again, just waiting to need a gas fill so I can put it in and fill the tank full.

Using both of those back to back cleaned the carbon that I could see on the piston heads that I noticed on my other car when changing the spark plugs, checked after both tanks and they were spotless afterwards. You might find the same thing works for you. I'm not sure which one does the trick the best so I just use both but not in the same tank.
 

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2001 5S "Turbo"
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Eli:
Use your scan gauge to monitor the timeing. Been doing that for years.
HTH
Willie
 

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Eli:
Use your scan gauge to monitor the timeing. Been doing that for years.
HTH
Willie
Yes, but I don't know what the total range is, or is supposed to be?

I've seen something like -4 to 18 degrees since I've been watching it?
 

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Unfortunately everything would have to done under extreme control in order to determine the benefit of reg. vs a higher octane. Carbon buildup can increase the compression ratio but the wear on the rings, if the engine has high mileage would negate any benefit. The highter octane would allow the engine to run a little more advance than normal.
I run regular most of the time and by useing the scan gauge and the rpm I try to keep the timeing around +6 which seems to be the sweet spot. Even under "boost, too much and the timeing goes way retarded, ease off the boost and get the rpm around 3200 at +6 degrees and it feels "right".
When an engine runs a lot of retard on the timeing the engine heats up real quick. I have no idea what is programmed in the ecu. They are more than likely useing load & rpm as a governing factor on the timeing. (Just my opinion)

Willie
 

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Did the car actually get fixed? If you return to normal fuel, will the mpg go back down to what it was before?

I have also noticed my car (@200k) seems to run better and give slightly better mpg when running mid or premium gas.

I wonder if we use one of those carbon cleaning products (seafoam etc...) will the fix last longer.
 

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Discussion Starter #9
Did the car actually get fixed? If you return to normal fuel, will the mpg go back down to what it was before?

I have also noticed my car (@200k) seems to run better and give slightly better mpg when running mid or premium gas.

I wonder if we use one of those carbon cleaning products (seafoam etc...) will the fix last longer.
The "fix" is that this car now requires more than 87 octane gas. The difference in gas price is FAR less than the mpg improvement, so that is just how it is from now on.
 

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As I mentioned introducing liquid water into the intake at a fast Idle will totally remove all deposits from every surface of the combustion chamber and piston top.
 

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As I mentioned introducing liquid water into the intake at a fast Idle will totally remove all deposits from every surface of the combustion chamber and piston top.
I wouldn't suggest doing this unless you know what you're doing...

But yes, it will.
 
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