1. That's hard gas line, so
2. I doubt it's a problem.
3. The flex fuel input line,
4. Could be collapsing under high RPM load,
5. But I doubt it.
6. The easiest way to tell,
7. Rich or Lean conditions... look at your plugs.[*] A black sooty coating indicates a rich running engine[*] A brownish tan coating indicates lead contamination[*] A powdery white coating indicates silicone contamination.
8. Or, put a volt meter in parallel,
9. With the 02 sensor voltage.
10. O2 sensors are somewhat generic,
11. The closer to 0.8 volts on the meter,
12. And the system's running rich.
13. The closer to 0.2 volt on the meter
14. The system's running lean.
15. You may want to make up a jig,
16. Clipped from junkyard connectors,
17. To install that Voltmeter,
19. Or just clip into the wire itself,
20. The choice is yours.
21. Now when you're monitoring the voltage,
22. Raise the RPM,
23. The ECM will hunt for the correct air fuel mix.
24. Now use some pliers,
25. To pinch off the flex fuel line,
26. The chokes things down...
27. And you should see the 02 sensor leaning out.
28. Clear as mud?