I just bought new headers and I read somewhere that the stuff that burns out of these headers for the first few mins will kill the o2 sensors. So can I just get plugs for in the bungs of my headers and run it a while then install the 02's?.....I do realize that it will run rich but how bad will it run? Also how long do you guys recommend I run it before I reinstall the sensors? and FWIW they are uncoated Pacesetter LT's .....Thanks

 

Appears your headers are not cera-metallic coated (e.g. Jet-Hot) inside and out. The coating is what may cause a problem with the O2 sensors. Headers without this coating are not a problem.

Actually, its not positive it will run rich, lean or correctly without the O2 sensors. If it does run rich or lean, the PCM will not know and will not be able to correct for it. Run real rich and you dilute your oil. Run real lean and you get detonation. Not likely, but possible.

 

Thanks, they're painted headers so I'll just put them in and run it

 

On a cold start, won't the PCM ignore O2 sensors for the first 4-5 minutes and use the long fuel trim averages to set fuel rates? You could use a series of short, cold starts with 2 or 3K rpms for 2 or 3 minutes to "condition" the new exhaust. Alternately, if the MAF is unplugged won't the PCM manage the engine in SD mode and not reference the O2 sensors? That shouldn't be too far off on fuel values.
Just a thought ...

 

Defaulting to speed-density will cause more problems that it will help. The only difference between speed-density and MAF is the way the PCM finds out what the mass air flow is. In speed-density, it calculates it from the RPM, IAT, MAP and VE tables. In MAF, it gets the mass air flow directly from the sensor. If the VE tables have not been updated to match any "breathing" modifications (intake, exhaust, cam, etc), the whole speed-density calc gets thrown off. MAF picks those changes up.

Once the PCM gets the mass air flow rate, it runs exactly the same.... it divides the mass air flow by the target A/F ratio to get the mass fuel flow, then calculates the pulse width required to deliver that much fuel. The O2 sensors aren't involved in the calculation, unless their feedback has altered the long term fuel corrections. The LTFT's are used in both open and closed loop. The only real difference between open and closed loop is that learning is disabled.

Yes, you could run for less than 205 seconds (the timer element in the closed loop transition), but its not likely you would keep the headers hot enough to "gas" the cera-metallic coating. I SUSPECT it happens at high temps. The "coatings ruin the O2 sensors" is to some extent based on speculation, and not necessarily scientifically proven. Of course, without the O2 sensors functioning, it isn't even going to go into closed loop at all, so the whole idea is sort of meaningless.