Well there's basically 4 things that are likely to affect knocking in the circumstances you describe:

1) Octane. Presumaby you chose a high octane at the gas station, but perhaps you got a tank of bad gas? If problem occurs over multiple tanks from different sources you can pretty much rule this out.

2) Temperature. When the intake air gets hotter, the engine's more likely to knock. So if the weather gets hotter it's going to knock more. But if you've got good gas, it shouldn't knock at 10 psi unless it's *really* hot out (110+ degrees?).

3) Timing. You set the timing at idle. But, if the boost-retard function on the distributor isn't working, it may be too advanced under boost. Might wanna connect a vacuum tester to the advance unit and make sure it's not leaking.

4) Fuel. From everything you say, this seems like the most likely culprit. A bad O2 sensor can make it lean much of the time, but it should ignore the O2 sensor when the throttle is wide open (assuming throttle switch is okay). A bad FPR could lower the fuel pressure and make the mixture lean. Anything else that lowers fuel pressure can be a problem too: clogged fuel filter, failing pump (probably main, not "pre" pump), restriction or debris in the supply line.

As others have stated, connecting a voltmeter to the O2 sensor output may tell a lot. A low voltage from the sensor (< 0.2) means mixture is lean. High voltage (> 0.7) means it's rich. What should happen is at under steady-state conditions except wide-open throttle, the voltage will "cycle" high-low-high-low about once a second. When you floor it, the voltage should go high and stay there. If it ever goes low when floored, you're not getting enough fuel.

Eric Law

posted by 206.96.16...

• Knock+, roman, Thu, 1 May 2003 05:55:23
  • typo meant 3.0 *bar* not bad n/m, roman, Thu, 1 May 2003 10:46:16
  • Re: Knock+, Eric Law, Thu, 1 May 2003 10:17:22 <-- Viewing This Message
    • Thank you Eric, more questions for you+, roman, Thu, 1 May 2003 10:45:21
      • Re: Thank you Eric, more questions for you+, Eric Law, Thu, 1 May 2003 12:01:28
        • Not to be too trustic but sorta like leaves rustling +, roman, Thu, 1 May 2003 12:37:31
          • read: too rustic n/m, roman, Thu, 1 May 2003 12:38:32
  • How is your O2 Sensor??, 93CSE, Thu, 1 May 2003 07:18:45
    • There really are not more symptoms, I suppose+, roman, Thu, 1 May 2003 07:42:28
  • Re: Knock+, Chad, Thu, 1 May 2003 06:53:50
    • Ha? I installed 3.0 FPR AFTER knocking began n/m, roman, Thu, 1 May 2003 07:38:13
      • Re: Ha? I installed 3.0 FPR AFTER knocking began n/m, Chad, Thu, 1 May 2003 07:44:12
        • "I hope if feels good+, roman, Thu, 1 May 2003 07:51:14
          • It does!, Chad, Thu, 1 May 2003 07:57:57
            • I know what you meant, but I thought you'd realize +, roman, Thu, 1 May 2003 08:06:04

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