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jeff91C2T jeff91C2T is offline
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Join Date: May 2001
Location: Central Coast
Posts: 278
The bouncing is the frequency valve doing it's thing. If you disconnect the 02 sensor it will settle down. I've played with going unplugged vs plugged for the 02 sensor in many different scenario's (autox, track, around town, hwy cruise) and for the C2T the computer does a good job. By that I mean best fuel mileage, sharpest throttle response and over all running. Keep in mind for any on boost / load / or higher RPM's the 02 sensor is not used and the frequency valve goes to 50% duty cycle.

When you get over 3k rpm it's going open loop, that's why the afr's settle down (mine does that too actually).

Adjusting is long as you have the wide band o2 sensor installed. The system wants ~14.7 so all you have to do is adjust to get to that value (with sensor unplugged). You can also set it a little richer or leaner but the computer will compensate and try to get it back to the programed value.

For gas...if I'm doing a sniff test I'll run oxygenated gas. All other times I go to a local station that sells "pure" gas. A little more expensive but the engine likes it better and I feel better not having to worry to much about the lines.

Originally Posted by lucittm View Post
I run with the O2 sensor plugged in because I'm scared to find out what might happen if I disconnect it. The car runs great, so why risk it?

Funny that you mention the bouncing AFRs. Mine bounces too but I think it is the opposite from you. I think I have some cylinders that are running rich and it is sampling a rich-lean condition. I also notice that the inside of my exhaust is a bit sooty and black, not a nice chocolate brown that you would expect (and want).

I think you may have better gas than we do.

I read about someone on this board who used a IR temperature gun to determine which of his header pipes was hotter than the others (too lean) and then he adjusted the offending orifice on the fuel head. I plan to do a similar operation except I will be looking for the cooler (too rich) header pipe and try to adjust that injector source.

One thing he said was that he had to adjust his CO each time he made a change and that scares me because I don't know how to do it and I might make it worse.

Did I mention that the car runs GREAT! Cruising at exactly 3000 RPM and above my AFR is solid and a hair over 14. I mean "a hair" and under 3000 it bounces. Is that the WUR or the frequency valve? It is repeatable.

Old 06-18-2011, 09:35 AM
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