I have the Denso o2 sensors, and back a while ago when I was tuning my cam, I finished and put it in closed loop, the AFRs went wild. I just put it back in open loop and forgot about it because I was tired of tuning. Anyways, yesterday I had EFI live open again for the first time in months and noticed the o2s weren't switching. Could this be because of them not getting hot enough with my headers? WOuld it be worthwhile to stick the stock O2's in there and see if they heat up better?

 

I can't see the Denso sensors as being an issue, FWIW, I'm running the same ones as you and they're functioning flawlessly. Even with heat escaping through the headers, the sensors should switch, just very slowly. Which way are they stuck, lean or rich? If you rev it up to about 2k-2500 rpm do they start to switch properly?

 

I do think it's the sensors, because they worked perfectly in the stock exhaust, with no other changes.

 

I had bocsh in mine and both started getting lazy about 8 months later they will not stick one way or the other for to long but they threw my fuel trims way off. I wouldnt see the heat as being an issue since they are heated. I would swap the sensor with the other ones you know are good and see how it goes from there.

 

Post up your tune, the problem is probably in it

 

hmm, just put it into CLSDMAF and it's showing them switching on the scanner. Weird. Before they were stuck around .850 and would only switch when I got off the gas.

As far as gas mileage goes, I don't think there's any helping this thing. My trims are around -4 to -7%, so I'm hoping the PCM will help bring things more in line. It sees around 5.5 mpg pulling from a light, and around 12 mpg with very light throttle around 35-45 mph. Coasting down from 40-50 mph it hits 28 mpg. Kinda sad considering my father's Malibu averages 28 mpg Only reason I make a big deal about the mileage is that in the upcoming months I'll be driving all over the midwest for job interviews and it's extra $$$, but still cheaper than getting a rental car. I'll be interested to see how much closed loop helps highway mileage, if at all.

 

are you still tuning with trims or did you get a wideband? is B3605, B3601, B3801, B4108, B4105, B4205, and B4206 stock?

 

It seems to me that closed loop while highway cruising is crucial to achieving a good highway MPG, as well as helpful in so far as allowing you to set the target (switching point, thereby altering target AFR) in the computer load vs. fueling tables, helpful if trying to implement psuedo lean cruise.

 

I tuned it with my LC-1 a while ago.

 

Well since you tuned it with the wideband, in order to get your trims to line up afterwards, you have to adjust the switch point tables to bring the trims inline to match your wideband readings... You use the wideband to insure your predicting/calculating the correct airmass, a correct AFR is a bi-product. Since your O2 sensors are just like ever other sensor (map, maf, etc), they need to be calibrated as well to your unique setup.... Developing a map that simulates the closed loop modes and logging your ltft average after the wideband tuning is the final step the result of that log will allow you to correctly adjust the switchpoint table... A step that many people omit... which is funny because those trims make you calculate a different airmass, which basically voids all the previous work you did with the wideband, excluding the WOT stuff...