What are the factors that determine HC output at the tailpipe from the 3.0 V6 (Vulcan)? I have this engine in an Aerostar 5 speed, and barely passed emission. It failed at 1.65 ppm (allowable 1.60). But the plugs were > 4 years old. I changed the plugs to Bosch +2s, changed PCV valve, O2 sensor, and the air filter. The dist cap and rotor are < 1 year old. I put in fresh synthetic blend oil (just for good luck) and ran through 1 tankful of gas with "Outlaw" fuel injector cleaner. It was pinging only on heavy acceleration (pedal all the way down) as opposed to every on-ramp, and the engine had quietened down considerably compared to before. Possibly it had better acceleration too. Then I put in another tankful of gas with Chevron Techron injector cleaner, but time was running out, so only about 80 miles into that tank, I filled it up again, gave it a 30 min whirl on the highway and took it in. They tested it right away, and it got... 1.59 ppm.
I can't understand what else I can do...
- cat?
- Was the Techron making it run rich?