I usually fill up at the same gas station everytime I get gas. They have 93 octance, today I had to fill up at a different station that only had 92. When ever I fill up at the station with 93 my wideband gauge at wot is about 12.5. Now on this 92 octane gas at wot it went all the way down to 10.9. Can the difference in octane cause this or is something else happening? This is the first time it went that rich.

 

Bet it runs like **** on the gas that makes it run 10.9 too doesn't it??? I had a similar occurrence in my 403 Camaro. I run dual channel Haltech widebands in it and constantly monitored how everything was going. Anyhow I normally use shell 93 gas and had gone to the track and just ran some 10.70's. The very next day I got in it to take a drive up to the dyno to see what kind of power it made. My lambda was dialed in to within half of a percent at the track the night prior. Stopped and filled up in an unknown town at an unknown gas station and went on up to the dyno. Did the first pull and it was instantly 10% richer than before and laid down some fairly shitty numbers to boot 44x hp if I remember correctly. I ended up pulling the fuel out of it and got HP up to 48x hp but was still puzzled. I did a few WOT pulls on the way home and got the same results. Ran that tank of gas out being curious and filled up with my normal gas station with shell 93 and did a little WOT pull and now was lean... put the old tuneup back in it and was perfect again. I never did get a chance to take it back to the dyno (before I had my own) but the car was noticeably different power wise.

My guess is the gas that was shitty had alot of water in it or something because it didn't seem to burn very well at all.

 

That's pretty interesting James. I would not think it's water though. If it were water, it would have less fuel per volume than previous, yielding a leaner mixture.

I would think if everything were identical (specifically pulse width) then with nothing more than a fuel change, octane difference won't mean squat when it comes to A/F ratio. You would have to some how end up with more fuel than previous. A 10% swing is very substantial.

 

Car doesnt seem to run any different between the fuels, doesnt feel sluggish or anything.

 

Yeah that's what I thought too however the car misfired and acted stupid. Could have had diesel mixed in with it for all I know or been an extreme mixture of ethanol like 30+% instead of the normal 5-10% for my area.

 

Not sure how the diesel would affect it, but a higher level of E should lean it too. Don't mean to sound like I'm arguing because I'm not, just interested in the conversation. I have not seen anything like this (change of fuel causing a huge change in A/F to the rich side) and am interested in the 'why'. Things that make ya go hmmmm......

 

Yes with all things being like they should it should have gone leaner due to not as much volume of fuel for the E content but something was definitely different about that gas and those three things are the most plausible things that could have been mixed but the richness doesn't make sense. I'll see if I can dig up the old datalogs to show the difference. I saved all the logs from the dyno and the track the night before that and you can see lambda feedback as well as pulse width with the two different tanks of fuel.

 

Cool, I'd like to take a look if you don't mind. Really curious about this. If you don't wanna post you can email them to me. I'd like to see a data log of it on the junk fuel, and one of it on good fuel.