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View Full Version : Gas quality and boost fluctuation?



ace33joe
04-09-2006, 06:05 PM
I and my friend have been using gas at Chevron station on Grand Rd (where CA-237 starts) & El Camino Real for about 3 years, but recently their gas quality may have degraded.

I started to use 76 a while ago, so I haven't seen any problem yet, but my g/f's TSX has less power and lower gas mileage recently. My friend's EVO also showed less power, weird boost fluctuation and engine noise at WOT 3rd & higher gear.

We thought boost may leak, but clamps were tight, and the boost fluctuation was not consistent, so we did some OBD II data logging last night, and ECU was pulling ignition timing (as low as -4 degrees timing advance (Actually, it is my first time to see minus timing advance)). After we put 76 on the opposite side of that Chevron station, power seems normal and no more boost fluctuation, although timing was still as low as -4 degrees only at 5th gear WOT near 3700rpm)

Does knocking lower/cut boost also? It almost felt like he lifted off the gas pedal for less than one second when boost was dropping after hits ~20psi.

He said he didn't have those problem when he was using Chevron in Sunnyvale before he moves. I guess that station on Grant road may have water in their tanks?

I heard gas station itself is more important than the gas brand, and it seems it is true.

Dr. Evo
04-10-2006, 07:25 AM
That could very well be the station. Yes, knocking will cause a loss of boost because the ECM will pull timing and boost to save the motor. FWIW I try to only use 76 from one station, unless of course I am on the road, then I try to only gas up at a station with a lot of people there. That indicates to me htat the station doean't have many problems, and that the gas is probably fresher and has less chance of water intrusion. Rememer, fuel does have a shelf life. And a short one at that.