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Interesting problem, one I've actually had on a few cars myself........

One thing you might try is changing the angle of the fuel nozzle, and holding it by hand instead of just letting it sit in the tank opening. Sounds dumb, but it can work better than you think. All fuel fill nozzles can sense pressure, they are designed to do that to prevent a fuel spill in the event of being left unattended during a long fill time. They sense backpressure as the gasoline comes up the fill pipe, and can so turn themselves off. The problem may be either the air pressure inside the tank is higher than the outside air pressure, which will confuse the nozzle sensor, or the nozzle outlet is too close to one of the fuel inlet pipe walls, that will also create the same backpressure the nozzle senses to shut off. Try various combinations of nozzle angle and how deep it is inserted into the tank inlet.....
You may also wish to sit with the nozzle in the tank for a few seconds before you start filling, this will allow any extra air pressure inside the tank to escape.

Newer cars have more highly pressurized and better sealed gas tanks than even models made within the past few years, it's mainly to reduce hydrocarbon emissions. However this means your gas tank becomes highly pressurized even under normal driving conditions, and this excess pressure can take a few moments to vent itself after the cap is removed.

Let us know how this works out for you.
 

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mbarton99 said:
Thanks -- I'll try all of these, although I did try different angles -- except for totally upside down and not inserting the pump all the way. The car is at the dealership now -- it will be interesting to see what they have to say!

My other question is can damage to the motor or anything else happen if the dealership put low octane gas in when they filled it up for the first time???

Thanks!
It would be their own fault if they did, they should know better..... I don't think it will harm the engine unless used for extended periods of time, but you may notice a small loss of power. Newer car ECUs can compensate quite well for crappy grades of gas, but the result is less power output.
 

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mbarton99 said:
Think about this -- you spent 4 hours at the dealership getting the best deal, signing the paperwork for a trade-in plus cash deal and then have the sales manager demand your trade-in automobile that day after your salesman has agreed to get it the next day after cleaned out, etc. (keep in mind this was the 3rd new vehicle purchased at this same dealership). I was very FRUSTRATED by that point! Then 3 days later you can't pump gas into the car -- between my husband and myself we probably pumped 1 gallon of gas into the car (also knowing that the dealership put regular gas in the vehicle) -- that's never happened to me before. You then spend about 1 hour on hold with Nissan after the dealership had no idea what the problem was and was told by Nissan that the sales manager would call -- which he didn't and then you call Nissan back and they're CLOSED. The next day my hubby tried to put gas into the tank at THREE different stations -- no luck! He took the car back to the dealership and was told they would need it for at least 4 days -- oh, by the way, sorry they cannot give loaner cars out ------- YES I wanted my 2002 Maxima back.

After ranting above -- the good news. They put a new fuel tank and OVRV valves (whatever that is) in the new 2004 350Z. My husband put gas into it the other day with no problem -- I'm just waiting till the day I try to put gas into it!

Thanks for everyone's help with this matter!
Well at least they took care of it, fixed the problem for you. Some dealerships around here mighta said, "Tough **** , you own the car now, good luck with it"..... Nice to know a few dealers still take care of new car owners without trying to gouge them in the repair shop.
 

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KaRdoN said:
heres my only question, what do you mean by low octane gas, we have 87 down here in FL, and everyone and their dog uses it. I dont think the Z would have any trouble running on a lower octane gas, unless its designed for race fuel.. :rolleyes:
Hmm factory recommended 91 octane, as I recall. 87 might cause detonation to set in, and if the ECU could pull enough timing to stop it, then you'd end up with a lot less Hp.....If not, then you'd end up with engine damage. I generally would not recommend using less than the factory recommended octane.
 

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Nik33615 said:
I agree you won't damage the engine or any other part of the car by using 87 octane once in a while. If the recomended gas is 91 or higher then that is what you should use to get the most power the engine can produce. Todays cars can adjust ignition timing and such to compensate for lower octane fuel but don't produce their potential power on less than the recommended octane in most cases.
To a point that is true. However, the latest gen ECUs are very much more aware of what goes on with the engine than any previous, all except maybe the standalone aftermarket units. Continued use of too low an octane level of gas can cause the ECU to go into a version of "limp mode", which it sometimes won't correct until reset. On VVT-type motors that means no cam advance, on most all others the ECU switches to a very low output fuel/ignition map, and sometimes the engine will run about 2/3 the Hp. Reseting a newer computer is much harder, it's not the simple "disconnect the battery" anymore. Most ECUs now have a small internal backup battery.
All this because you wanted to scrimp a few bucks on gas. My advise is, if you can't afford the gas, don't buy the car......
 

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IreiMember said:
always try to stay with what oem specs are and what they reccomend. the rating on fuels is nothing other than a ping rating. absolutely nothing will ever happen if you use 87 it may not burn as clean as 91 obviously. but as far as power gains lol please... thats like saying puting in 110 octane in a car with a compresson ratio of 9:1 is gonna make it faster
If its a turbocharged car, it will........ ;) Why have race gas, then, by your way of thinking.....
 

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IreiMember said:
race fuel is for race engines
Wrong. Race fuel is useable on all engines. I noticed a definite difference between running 91 octane pump gas in my car, and running 104 race gas in it. NA engines are mostly the ones that don't require an increase in octane, unless you increase the compression ratio and/or the valve lift. Turbo engines, when you increase the boost, you effectively increase the compression ratio.
I've also learned the problems of running low octane in a higher octane required engine. My motorcycle requires 91 octane. I attempted to run 85 in it, and the pinging was painfully obvious. I promptly drained the tank and put the proper grade of gas in it. And this was in a carburated 15 year old motorcycle. Modern engine electronic controls will cause massive loss of power when low octane fuel is sensed by the knock sensor and the 02 sensor. You can't argue with the facts, and those are.
It used to be that running too low a grade of fuel, in older engines, simply caused the head gaskets to blow, due to knocking, and other major problems. Now, thanks to modern technology, we don't have those problems any more, the effects are simply seen as a loss of power as systems compensate for the low grade. So people no longer seem to see the severity of the situation , as they may have 20 years ago before modern electronics.
 

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BlankgazeX said:
not to mention what would happen if the knock sensor crapped put... major engine knock and leading to fuct pistons...
Blown head gaskets, too. Depends on the engine. Some engines, such as the 4G63, simply melt the pistons before the headgasket goes. I have personal experience with that..... ;)
 

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BlankgazeX said:
ok idiot, run 87 in your car, but dont tell other peole to, because you are too ignorant to realize IF THE KNOCK SENSOR FAILS A 350Z WILL BECOME SERIOUSLY FUCKED UP WITH 87 OCTANE GAS! and like i said, you lose power with lower octane BECAUSE of the sensor, is that what you are disputing? or are you disputing my statement you WILL NOT gain power from higher octane?

its a high performance car, use high performance gas... god i went through with this shit in the qr section with spec V's, some dumb ass is gonna have 100 people fuck up thier cars to save 30 cents at the pump...

in the end, if your car says 91, run 91, 87 will hurt it, 100 wont help it, use what is recomended...
We've already shown that 100 octane will help it.....
You'd lose power in a car running 87 octane that should be running 91 octane, knock sensor or no. Why? Because the knock is incomplete combustion..... The typical engine only uses 33% of the energy contained in a given amount of fuel. When improper octane levels cause knock, that means far less is used.
Knock is improper flamefront propegation in the combustion chamber. Typical knock can be best explained as too fast of such propegation, instead of uniting as a single "wave" and creating the powerful push on the piston, it splits up, "echoing" off the walls of the combustion chamber and charging the middle, where one or more meet and cause a reverberation effect. All of this is supersonic and takes place in milliseconds, your brain registers it as a high frequncy tapping sound.......
Anyway, what I'm trying to say , is that you would lose power whether the knock sensor heard that noise or not. Knock sensors are designed to hear that certain frequency of where 90% of all knock occurs. However, it can happen at a much lower or higher frequency, especially if the car has any modifications that affect airflow. Air density affects knock frequency. It's possible to have knock the the sensor will not even notice, especially in older vehicles.
 

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And I should perhaps point out that Irei is incorrect as to how the knock sensor hears the sound. It is not listening to the sound of the antifreeze. Not on gasoline cars anyway, that is reserved for the newer diesels. No, it is listening to the sound of the engine block itself. The metal is of a known composition and will conduct sound almost always in the same way. Composition of antifreeze can change, and could change how much or how little of that particular knocking sound is actually heard by the sensor. Go ahead, pull the knock sensor on any car, it is not in a water jacket...
 

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bridrive55 said:
And also, conversely, noise that the knock sensor recognizes as knock that is really harmless engine noise. Subaru's have huge problems with overzealous knock sensors.
I see what they were saying above though. Running C107 race fuel in a 350Z will not increase power, because all that a higher octane rating does is increase an engine's knock tolerance threshold. With a stock or even slightly modified VQ35DE, this isn't a consideration, because it doesn't knock with 91. 91 octane will deter 100% of knock just as well as 107 octane will. 87 octane however, might make the engine knock, which would activate the knock sensor, which triggers the ECU to retard the timing.
Actually the Subarus (the STi) are having problems because the EJ25 was designed to run on 95+ octane gas.... The 91 octane salad oil we have completely freaks out the ECU. This problem is solved with an ECU reflash, but then the STi is not longer 300 Hp.... ;) The 350Z, as JamesZ has already said, responds better to 100 octane fuel. Engines are specified to run the octane they are to balance fuel economy, Horsepower, and warranty. Also, cars that require higher octane can be offputting to potential buyers, especially with the prices we pay for gas these days. At 10.5:1 compression ratio, I would say that 91 octane was barely adequate to control knock in the 350Z. The 91 ZR1 Corvette, at a 10.1 ratio, specified 91 octane. Half a point higher, it makes sense that more octane would be required.
Something else you don't realize, almost all engines experience knock at some point. Could be one out of every 30 power cycles. Could be one out of 100. Knock sensors start to wake up when a threshold point is reached, which is about 1 out of every 10-20 power cycles. At 5000 rpm, you do the math. ;) What higher octane does, is create smoother more useable power for the engine. Higher octane of itself is not more powerful, higher octane actually slows down combustion, makes it more useable by the engine. It lowers the chance of having knock in the threshold range of the sensor, and lowers knock in general, which means the engine can make power on every stroke, not just most of them......
 

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I'll put this into perspective for some of you. What do a 79 308 GT Ferrari, an 86 Porsche 911 Turbo, a 94 ZR1 Corvette, and a 2004 350Z have in common? They all require 91 octane gas.... Even with such disparate power applications. What I'm trying to say is, factory octane requirement is a generalization. Especially for modified vehicles, factory octane requirement goes right out the window. Octane requirement is also specified the same for all altitudes, which is hugely incorrect in a place like Colorado.....
 

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NickZac said:
Might as well also add, when fuel is reformulated (oxygenated), I have always been told to consider bumping up octane as it can cause pinging or premature burn, especially vehicles with excess carbon build up. I know that MD is reforumlated in winter months, and PA is not. Premium is generally 93 here, and 94-98 is readily available. I would imagine Cali is oxygenated. The STi may simply not be able to take reformulated 91 octane without having a serious reduction in timing.
Aside from a few gas stations catering to the racers around here, the best we get is 91 octane. Kind of odd, since at higher altitude, we should get the higher octane stuff.
 

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Most cars have multiple spark and fuel maps stored in the ECU. Most cars run fairly conservative timing advance and injector pulse width depending on what the knock sensor and 02 sensor sees. Most cars also run a touch rich from the factory, turbo cars definitely do. This is to protect engine warranties, for no other reason. What happens when the knock sensor hears less knock, is that it lets the ECU advance timing until it once again hears threshold knock, within the fuel maps capabilities to do so..... If timing can not be retarded enough to combat knock, a lower value fuel/spark map is switched to. When less knock is heard, the ECU advances the timing til it gets threshold knock, or if it comes up on the out of range of a low end map, switches to a more aggressive one. This is why putting higher octane gas in a modern vehicle can have big results. Older vehicles with less advanced ECUs, or even no ECUs at all, don't really benefit from using higher octane gas, except to combat piston deposits, as was mentioned before.
 
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