I live at 6000' in Show low Arizona. This weekend I went down to Phoenix which is less then 1000'. The car ran totally different. It even sounded different. The motor had more of a roar. I'm sure this is due to the oxygen. It had better Low end and when the boost kicked in it was even better. I am running 10LBS of boost peak on a stock motor. About 500RWHP at the wheels.

I was having a fun ride home through the canyon's. 60MPH where there was a recommended MPH of 30....etc. Of course as I was getting a little closer to home and the elevation started getting higher, I started have less power.

---The problems come in on the way home. The gas gauge went to empty and I experienced an even greater loss of power. Less then usuall when I am home. I immediately went to the gas station. When I started to open the gas cap there was a huge suction. I slowly opened it and it sucked air for about 15 second. The pressure appeared to lessen so I removed it. Once removed it still sucked air for another 15 seconds. I started to put gas in and it did not want to take it. It kept clicking. After only getting 1/2 a gallon in. I started the engine to hopefully get the fuel pump going. The gas gauge went up to half a tank where it should be.

Any ideas what happened? Anything I need to take care of? Maybe the Boost a pump? I would appreciate any help.

Mark G.

 

Sounds like a EVAP problem?

 

Are you running boost referenced? What is your fuel pressure set at?
If you run less than about 45# or less the siphon pump will not transfer fuel to the drivers side tank. Given you can pull a few more lbs of vacuum at the lower altitude, at normal driving the back pressure on the siphon pump becomes less. So as example ie you are set to 50 #s pressure with conservative driving you might be pulling 7#s vacuum which would mean 43#'s at the siphon pump. So just a guess if you are close to where the siphon pump is not working, the elevation could have had this effect.

 

----no codes where thrown.

----maybe the elevation change changed the pressure? Hopefully it will be okay now?

 

bmp

 

One of the things that makes the gas gauge show empty suddenly is if the right side tank is fuller than the left one (which should never happen under normal circumstances). But that would throw a P1431 code. There's a certain amount of difference that is acceptable, so it could be a delayed symptom of driving in PHX that may have nothing to do with the higher altitude itself.
Any problems since? Have you checked your gas cap?

 

I have not had any apparent problems since. The drive back was pretty hard. A lot of twisty curves and acceleration into boost. Maybe the shifting of the car back and forth affected the Fuel. I was hitting it pretty hard. 50MPH on 25MPH curves. What should I look for on the gas cap?

 

This is based on general EVAP knowledge, not the Vette in particular (everybody, please chime in if I'm wrong): Gas caps have a check valve that allows air to enter the tank (as the fuel level gets lower), but not fumes to escape into the air. From your description, it sounds as if that check valve was blocked, causing a vacuum in the tank as the engine sucked out fuel?

 

Thank you, this is some really good information. Is it just a strange occurence? Or do I need a new gas cap or a performance gas cap if there is such a thing? What do you recommend?

 

No idea. But it seems to me that, if the gas cap was indeed faulty, you would notice it every time you refuel. May have been just a fluke?!?

Disclaimer: I'm not a mechanic, I just slept at the Holiday Inn Express last night...