Used a tank of 100 octane, still got CELs
 

I tried a tank of 100 octane 76 using Scott's original fuel and timing maps. After 200 miles I have the following CELs:

P0300 random/multiple cylinder misfire detected
While the engine is running, the PCM counts the number of misfires that occurred at 200 eccentric shaft revolutions and 1000 eccentric shaft revolutions and calculates the misfire ratio for each eccentric shaft revolution. If the ratio exceeds the preprogrammed criteria, the PCM determines that a misfire, which can damage the catalytic converter or affect emission performance, has occurred.
Possible cause:

• eccentric shaft position sensor malfunction
• ignition system malfunction (high-tension lead malfunction, incorrect power supply to ignition coil or ignition coil malfuntion)
• MAF sensor malfunction
• excess air sunction in intake-air system
• fuel line pressure malfunction
• leakage fuel
• insufficient compression (metering oil pump malfunction, engine oil condition malfunction, rised oil pressure, oil passage malfunction, engine malfunction)
• ECT sensor malfunction
• purge control system malfunction
• leakage engine coolant
• PCM malfunction

P0410 secondary air injection system malfunction
The PCM monitors the front HO2S output current when the AIR control is operating. If the output current is more than the specification, the PCM determines that there is an AIR system problem. This is an intermittent monitor (AIR system). The MIL illuminates if the PCM detects the above malfunction condition in two consecutive drive cycles or in one drive cycle while the DTC for the same malfunction has been stored in the PCM. PENDING CODE is available if the PCM detects the above malfunction condition during the first drive cycle. FREEZE FRAME DATA is available. The DTC is stored in the PCM memory.
Possible cause:

• AIR system malfunction
• PCM malfunction

P2020 intake manifold runner position sensor/switch circuit range/performance bank 2 a)
No information in the shop manual exists.

Pending P2096 post catalyst fuel trim system too lean bank 1
The PCM monitors the target A/F fuel trim when under the target A/F feedback control. If the fuel trim is more than the specification, the PCM determines that the target A/F feedback system is too lean. This is a continuous monitor (Fuel system). The MIL illuminates if the PCM detects the above malfunction condition in two consecutive drive cycles or in one drive cycle while the DTC for the same malfunction has been stored in the PCM. PENDING CODE is available if the PCM detects the above malfunction condition during the first drive cycle. FREEZE FRAME DATA is available. The DTC is stored in the PCM memory.
Possible cause:

• Leakage exhaust gas
• Rear HO2S malfunction
• IAT sensor malfunction
• ECT sensor malfunction
• AIR system malfunction
• Leakage intake-air
• Front HO2S malfunction
• MAF sensor malfunction
• Fuel line pressure malfunction
• Fuel pump unit malfunction
• Leakage fuel
• Ignition system malfunction (high-tension lead malfunction, incorrect power supply to ignition coil, ignition coil malfunction)
• Insufficient compression (metering oil pump malfunction, engine oil condition malfunction, rised oil pressure, oil passage malfunction, engine malfunction)
• Fuel injector malfunction
• PCM malfunction

So it seems regardless of the octane gas Scotts base map throws sundry CELs. P2096 sounds like an inherent CEL since turbos run richer than the NA PCM expects. I really wonder about the P2020 code though.

well keep in mind that 100 octane takes longer to competely combust than lower octane fuel. this means there's more unburnt fuel going the way of the exhaust pipe. always use the fuel the map is tuned for. 100 octane would allow you to run a bit leaner and with more advance, but your map isn't tuned for that.

I used 100 octane in redwood city at the woodside rd 76 gas station, almost 5 bucks a gallon, however you def knoticed a difference, or at least i did. Didn't throw any CEL for me and i put in a half a tank of fuel.

assuming it was actually 100 octane and given the code readings it appears that fuel is not the issue behind them

Using that 100 octane fuel could make your misfire code worse. You should stick with 91 or 93 octane and just have your Interceptor map tuned.

not true

Hmmm I have only run 100 once and never had any issues. I ran the tank down for 40 miles with the fuel light on and only put in like 6 gal so it was probobly 98% new fuel too.

Why do you say not true?

I havent been following your troubles closely enough, but I also got misfire codes from what I think was an unbalanced pressure plate. Removal eliminated the code. I am not suggesting an answer, just providing data.

I don't see the logic there. Higher octane means the fuel needs a higher ignition temp to combust but once that process starts I don't think it takes longer to actually burn. Can you cite references?

I have put 100 octane in a NA V8 tuned for 91 octane without any problems or codes. (Ran out of pump gas @ 3pm on a track day). Granted I didn't gain any performance benefit to running higher octane in that car but it didn't cause problems either.

The common possible causes from P0300 and P2096 are:

• ECT sensor malfunction
• MAF sensor malfunction
• Fuel line pressure malfunction
• Leakage fuel
• Ignition system malfunction (high-tension lead malfunction, incorrect power supply to ignition coil, ignition coil malfunction)
• Insufficient compression (metering oil pump malfunction, engine oil condition malfunction, rised oil pressure, oil passage malfunction, engine malfunction)
• PCM malfunction

So it's possible a single common problem is causing both CELs. Note that I have seen these codes using 91 octane as well. I really hope it's not ignition or compression.

one of us is talking from direct experience

the other is theoretically talking out their tailpipe

care to take a guess? :angel:

:nono: rkostolni is right. The only reason to burn higher octane is to prevent pre-detonation. That means it is harder to light-off the mixture. Misfires occur when you fail to light the mixture. Hence, absurdly high octane will lead to more misfires, unless your engine was designed (or modified) to light it.

It is particularly a problem on rotary engines because of the partially fouled spark plugs found in most rx8's. Have you ever pulled yours to see what they look like? Dirtiest plugs I have EVER seen and with only 12k miles of use.

But you should only run the octane required to prevent detonation at whatever hp level you are trying to achieve. Anything higher is wasting you money, and can infact be bad for your engine because it can make it more difficult for the combustion chamber to reach the temperatures required to burn off carbon buildup. There is no more performance to be gained by increasing the octane alone, unless that allows you to advance your spark timing, or lean out your mixture to achieve a faster burn.

I did the exact same thing, no issues?

Assuming you aren't tuned to use it, agreed.

Also agreed. We are not debating this.

Here (like with epitrochoid's claim higher octane gas burns slower) I'd like to see some references. Are you suggesting higher octane gas burns at a significantly lower temperature? That claim sounds suspect to my (admittedly) uneducated ears.

Here's a reference that refutes epitrochoid's claim:
http://www.cs.uu.nl/wais/html/na-dir...faq/part3.html
The antiknock ability [of higher octane gas] is related to the "autoignition temperature" of the hydrocarbons. Antiknock ability is not substantially related to:
1. The energy content of fuel, this should be obvious, as oxygenates have lower energy contents, but high octanes.
2. The flame speed of the conventionally ignited mixture, this should be evident from the similarities of the two reference hydrocarbons.

The FAQ also states, "high octane fuels produce end gases that take longer to autoignite" which epitrochoid may have misread to mean it burns slower.

It's an interesting read. It also mentions AFR does have an effect on flame speed (leaner AFR has slower flame speed): "The normal flame speed is fairly consistent for most gasoline HCs, regardless of octane rating, but the flame speed is affected by stoichiometry." It also says "an average increase of 2 (R+M)/2 ON is required for each 1.0 increase (leaning) of the air-fuel ratio"

deam and showoff,
Are either of you turbo'd? If not, why make the comparison?

believe whatever you want, it's no skin off my back :Peace:

just don't expect anyone who unequivically knows better to take you seriously :slap: :hahano:

I believe neither are. They are making the comparison to show NA cars tuned for 91 (or lower) octane can use 100 octane without any problems or CELs. Rkostolni and epitrochoid claim using a higher octane gas than what you're tuned for will actually cause problems.

If you have direct experience then why not share the details rather than just say, "'cause I know better"?

Why don't you offer up even a shred of technical reasoning back-up these statments that you are throwing around? I don't mind being mistaken - if you can prove me wrong. So far, you haven't done anything to prove you "unequivically" [sic] know beter.... You can't debate someone who won't step up to the plate.

I see now. I think that there are a variety of things that make the turbo more susceptible to misfire than a NA: higher chamber pressure, colder plugs, rich AFR, maybe timing changes, too.