O2 corrections changing on their own.


New Member
Hey guys,

Today I was messing around w/ the laptop and got the correctoin %s within 3% (+,-), then when I turn the truck off and turn it back on, it seems like it's way out of tune, going up to 20% correction in some spots. It seems to be only happening within the first 30seconds or so after starting, then it's normal agian. Any suggestions? I have my hot cold loop delay at 10seconds. Should I increase the revs to run mode, more enrichment during after-start? This is happening when fully warm.

That is very strange since you can not have any o2 correction applied for the first 10 seconds anyway. 2nd if there's any afterstart enrichment applied there can be no o2 correction, however if there is coolant temp correction being applied you can have 02 correction working.

To see whats going on, log aft correction, cts correction, o2 correction, coolant temp,and i think you can log, where it changes from open to closed loop aslo.This will give us an idea if aft correction is being and how long, do you run this thing closed loop at idle?
Yes, I do run closed loop at idle. After the first 10 seconds it'll go into closed loop and the corrections limits will be way off, then they'll slowyly go back to normal, but lately they have still been swinging alot, from 5.5% to -11%, and that's at idle. I have all the enrichment talbes at 0% at the temps it's doing it.
Well, if you watched it before, and it was fine, then something is fishy. Any minor exhaust leak will cause the o2 to by off, check that. But i do know after a heat soak it will be lean, thats the whole idea of aft correction. Check if the vacuum at idle is erratic, maybe you have a minor intake leak. I am running out of suggestions here. :rolleyes:
Also check your battery voltage. At start-up the voltage will be different until the battery comes back up to full charge.

The injector opening time will change with voltage & often change the idle correction significantly (especially with big injectors). This in not adjustable in the FAST system, even though nearly every injector is different & therefore a significant nuisance. You can try putting a battery charger on the car at idle & see if it changes the correction.

Hope this helps.
Well don't feel so bad my o2 corection goes from -25% in park to +2% in gear. Thats a huge change nothing i can do about it
I'll check my exhaust, it's known to come loose at the collector, and that's the side where the O2 sensor is on. My battery voltage is at 15.3v right when I start it, and comes down to 13.1-13.5 when warm and lights are on.
Don't feel bad, mine does the exact same thing Foxspy. Has forever. Never could figure it out so I just gave up.
16VDC system??

Foxspy said: "My battery voltage is at 15.3v right when I start it, and comes down to 13.1-13.5 when warm and lights are on."

How do you get 15.3VDC at startup? Is this a 16 volt battery/alt system?
No, it is not a 16v system. I have to get my alternator checked out also, I think the voltage regulator is taking a crap. Last night my gauge was bouncing all over the place, lights dimming, and I could feel the power surge while driving.
Found it??

Wild voltage swings could be a contributor to the problem..Keep us up to date once you have it fixed.
While you are working on the electrical system, a look at the condition of the grounds wouldn't be a bad idea...;) :D