Blow Torch

Does anyone know of a reason that my O2 sensors are not "cycling" at idle on my SD tune>>
I have a 98 that has a 02 PCM. at idle (up to around 1400 rpm) the O2s stay in the 900s and the AFR is in the 12s. If I rev it up to around 1400 in gear, the O2s cycle perfectly and the AFR is close (VE needs tweaking)
I purchased new O2s and it didn't help, so the original ones are actually in it right now
I have been fighting this issue for around a month, but a crazy work schedule, the holidays and consistent rain every weekend has hampered any testing. I'm ready to get this thing back on the road

tblu92

I believe on a SD tune the front 02's-MAF and fuel trims are NOT being used---so their reportiing is not important----An SD tune uses the VE table solely to command fuel----Even on a stock OL/CL tune at WOT the 02's are not being used--the fueling is commanded by the PE table in your tune---

RonSSNova

Tom,

It depends on how the tune is set up.
SD most certainly will run in closed loop. I have my turbo car running CL and it's a 3 bar SD tune. Works very well.

It's also possible to set up any tune to be open loop at idle and switch to closed loop at 1200 or so rpm.

Ron

Russ K

The front O2's do control the fuel trims (once in closed loop) in SD or Maf mode. And yes, the O2's don't control the fueling at WOT.

Blow Torch, post your tune.

Russ Kemp

tblu92

I agree somewhat---However there are several versions of an SD tune----Some use OL some use CL and some use both---But a true SD tune uses neither---No MAF NO fuel trims--NO 02 input---This type of tune is generally used only on dedicated race cars---
Most people running an SD tune have no idea which version of an SD tune their tuner used----