I understand what a tune is that's why I asked "Can this be shut off without a tune?" The O2 simulators are what I was thinking about but forgot what they were called. It would seem from Spin's post I'm better off to bite the bullet and get a tune or don't mod if I'm afraid of losing the warranty

You are correct on your other statements. The dealer won't honor my warranty with a tune.

 

My choice of wording was poor as I wasn't insuiating that you didn't know what a tune was.

I was trying to say that the only way to shut off the O2 sensors was to do it by accessing the PCM and by GM definition that would be considered a "Tune".

I had never heard of those O2 stimulators, but had heard of using some kind of spacers to mechanically defeat the rear O2 sensors, but have never seen one in action.

And we all know that once any of the oriiginal PCM calibration are changed, the powertrain warranty is then voided. That kind of sucks because if your doing something as simple as running a different size tire setup and want your speedo to be correct; you need to enter the PCM to recalibrate it.

And once again GM states that if you change any of the original PCM Calibrations; your powertrain warranty is voided.

I'm hoping that Guy rings in and states how and under what conditions the engine can be damaged from installing an aftermarket CAI and/or exhaust headers and not recalibrating the AFR MAP tables.

He's seen everything at least once and I'm sure he'll have an excellent example with pictures and video to boot.

 

I'm hoping that Guy rings in and states how and under what conditions the engine can be damaged from installing an aftermarket CAI and/or exhaust headers and not recalibrating the AFR MAP tables.

He's seen everything at least once and I'm sure he'll have an excellent example with pictures and video to boot. [/QUOTE]

Me too!

 

It may help you to understand the purpose of the four different O2 sensors. The front O2 sensors are monitoring air/fuel ratio for each bank and reporting to the ECU which is then adjusting fuel inputs.

The rear O2 sensors are also monitoring air/fuel ratio, but are behind the Cats. Therefore the rear O2 output should be flat (the Cats should burn all the O2 and fuel remnants). Occasionally, the ECU runs a Cat check right after engine start up. It is checking that the Cat output is still 0. The Cats are normally installed right up next to the cast iron exhaust manifolds. This is so they heat up to operating temp immediately and "light off".
When we add long tube headers, we relocate the Cats further down the pipe and now they take longer to light off. Thus, even when you use Cats in a long tube header car, you will occasionally get a check engine light because it did not pass the initial Cat start up check.
Tuners will turn off this report by having the ECM ignore the rear O2 sensor inputs. You can also use O2 sensor simulators, or even use a hand held tuner to turn off these codes.

 

The CEL is there because you are outside the car's ability to compensate to get it back to stoic. Its running lean at part throttle (thats bad). The PCM uses the part throttle reading to detwermine how much fuel it has to dump at WOT; since you're 24+% lean it will dump +24% more than the way too much fuel at part throttle it already has from the factory. The car runs too rich bone stock and with headers and a CAI it will be adding 24% more fuel than the already too much fuel it has from the factory.

Summary: Running 15.5:1 at part throttle will kill the cats and running 11.2:1 at WOT will be carbon deposit city on your pistons and combustion chambers which makes a car prone to detonation.

I have seen carbon deposits on stock engines run their entire life ingesting oil and running rich from the factory. They ping and pull 10+ degrees timing and can never get to the level of power it would have had if the owner had simply addressed these issues long ago.

You need a tune and lame fixes like using rear O2 sensor simulators to input a false reading isnt going to make it run right.

I have said it before 100 times, find a dealer who is mod friendly or does mods themselves and pay them to do the tuning or leave the car stock. If you do mod, you dont deserve a warranty and a dealer shouldnt be held responsible for thing you do to your car including incorrect fueling ratios from headers installed without a tune.

Jay/Spin

 

All headers alter A/F ratio so its not always a rear O2 issue that causes a CEL so i wouldnt assume thats what its from.

I have used LG, AR, and Kooks all on the same car with various mods....all with cats...and none ever gave me a rear O2 code. Proper tuning makes the rear O2's work without being turned off.

What is 100% fact is that the A/F ratio is altered from optimum with a header install.

 

I agree, a good tune is always preferred.

However, most Corvette LS engines come with a rich tune. Depending on configuration, adding headers tends to lean it slightly.

 

No, not ture. Headers make it run lean only in closed loop. The long term fuel trends are then sampled to see how lean it is and then that percent fuel is then added at WOT to keep a servere lean condition occuring at WOT. So if you are +24% lean at closed loop it adds 24% more fuel during WOT to make the car not be lean under those conditions.

I have seen headers make a car 10.8:1 at WOT from a factory rich of 11.8 to 12.2:1.

Adding headers always makes you richer at WOT.

 

Maybe one of the forum members near you has a code reader or HP Tuners to show you what codes are triggering the CEL then run a scan to see where the fuel trims are. Then go from there. Don't just think by shutting off the rear 02 sensors will solve the issue. You are not addressing the real problem....your CEL is saying something is out of bounds. If it turns out to be the LTFT, then changing the tune is best thing for your engine's long term health.

If you intend to keep the headers, take the car to respected tuner. The warranty issue may be an issue for certain warranty claims but it won't totally void the warranty for the whole vehicle. Talk to your service manager because headers is really not a big deal.

 

What I gather from Guy's post if the following:

Installing LT Headers absolutely requires a tune of the MAF MAP tables to insure proper AFR's at both idle, under load and at WOT.

While there are a few "chop shop" methods that can be employed to defeat the CEL from coming on by simply disabling the rear O2 sensors, it's certainly not advisable as all you're doing is building carbon deposits within the combustion chamber and potentially damaging the engine.

What I gathered from his post was that once carbon really builds up inside the engine; there's no way to ever return the engine to optimum performance even with tuning.

So the bottom line is that if you're going to install LT Headers; plan on having the engine professionally tuned.

If you're currently under a powertrain warranty and that's important to you; don't install the headers as you're going to damage the engine anyway by not tuning it.