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Setting a Code When Going from 104 Unleaded -> 93 Unleaded

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Old Jun 12, 2006 | 01:12 PM
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Question Setting a Code When Going from 104 Unleaded -> 93 Unleaded

I was at the track the other night and was getting close to empty on the tank of 93 octane and there were no close gas stations, so I got a half tank of 104 Unleaded. The car is tuned for, and normally runs 93 octane only.

Everything was fine until ~150 miles later when I filled the car back up with 93 octane - It set the check engine light!

I will not have a chance to get the code scanned until this weekend. Has anybody ever heard of this before? What do I need to do to fix this? Your experience is greatly appreciated.
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Old Jun 12, 2006 | 01:17 PM
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Try unscrewing your gas cap and re-tighten (click it 3 times). Until the code is scanned, it's anyone's guess what the problem is. At least this is a quick/easy possible solution.
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Old Jun 12, 2006 | 07:13 PM
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It'd help if the code was read and a little guesswork would be eliminated.

E
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Old Jun 12, 2006 | 08:09 PM
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Yeah, the gas should have no effect as long as it was unleaded. I have ran 100 without problems a lot. Chances are it could be a loose gas cap since it happened right after you filled up. That or you could have pinched the rubber seal when you put the cap on. If thats the case it will trip an evap code, most likely a P0442. That would be my first guess.
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Old Jun 23, 2006 | 09:19 AM
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Well, it actually triggered two codes:

P0135
P1133

I'm running Corvette O2s up front (13111) and none in the rear, they've been deleted from the computer. No cats here...

I did a search and found that Macon had a similar problem: https://ls1tech.com/forums/showpost....12&postcount=8

That was the only problem I found that was similar. I ordered a new 13111 but I'm hoping that my code goes away like Macon's did after a tank or two. Any further ideas folks?
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Old Jun 23, 2006 | 11:49 AM
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- They may not have given you unleaded fuel, even though that was what you asked for. Or the can may have been contaminated with some leaded fuel left over from another fill if they got the cans mixed up.
- Another possibility is that the switch from one fuel to the other has nothing to do with the codes & you might just need a new O2 sensor(s).
- Also, do you have a cutout? Sometimes at idle the O2's can get contaminated by air having the cutout open

Just a few thoughts FWIW
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Old Jun 23, 2006 | 12:48 PM
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Originally Posted by Cyborg
- They may not have given you unleaded fuel, even though that was what you asked for. Or the can may have been contaminated with some leaded fuel left over from another fill if they got the cans mixed up.
- Another possibility is that the switch from one fuel to the other has nothing to do with the codes & you might just need a new O2 sensor(s).
- Also, do you have a cutout? Sometimes at idle the O2's can get contaminated by air having the cutout open

Just a few thoughts FWIW
Thank you for the input, Cyborg. I did verify that the fuel was unleaded with the track's gas-guy, but as we all know, **** happens. It very well could have been leaded. Wouldn't that kill both sensors, though? Bank 1 is the only one thats dead.

I do not have a cutout - TSP true duals here.
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Old Jun 23, 2006 | 01:01 PM
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104 unleaded uses that lead substitude to increase octane that turns everything brown and will kill sensors pretty fast if the car is running somewhat rich. I use sunoco 104 unleaded exclusively and a set of lead safe denso sensors lasts a season for me then they get slow. Leaded gas kills them in 1/2 a season..
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Old Jun 23, 2006 | 01:17 PM
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Hmmm....another thread with problems and Bosch O2's. Coincidence???
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Old Jun 23, 2006 | 01:27 PM
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Originally Posted by JoeyAnderson
It very well could have been leaded. Wouldn't that kill both sensors, though? Bank 1 is the only one thats dead.
Eventually, but not right away. It takes a little time to take out the bosch sensors with lead, a few gallons won't completely take them both out right away. Especially if it's a small amount of lead like from a little contamination. Just a guess as to if that's what happened though.
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Old Jun 23, 2006 | 10:39 PM
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Originally Posted by Cyborg
Eventually, but not right away. It takes a little time to take out the bosch sensors with lead, a few gallons won't completely take them both out right away. Especially if it's a small amount of lead like from a little contamination. Just a guess as to if that's what happened though.

A sensor thats almost dead will take four or five passes with leaded gas to start throwing codes, been there. 104 unleaded gas isnt much easier on cats or O2 sensors then leaded gas and they dont claim it to be. Only thing they claim is that it is unleaded and not legal for highway use, says so right on top of the drum.
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Old Jun 26, 2006 | 12:02 AM
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Put a new 13111 in bank one, and all is well. Hopefully Bank 2's sensor will hold up for at least a little while longer. No more 104 for me.
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