i just got a new set of l.t. headers put on along w/ some new O2 sensors.....with these headers will i need to get my car (air/fuel ratio) re-programmed? the car sounds a little starved right now.

 

I doubt that it is running lean. Unless it was tunned that way. Im running rich after long tubes's just as im sure most people who put long tubes on there car are running rich.

 

yeah i think most people run more rich than lean after an LT install...but no you really don't have to get your car tuned. You can, of course, and make a little more power but I would only get a tune if you make a little bit of bigger mod (like a cam)

 

So where do all you people that say that you run rich after LT's come up with that statement?

 

Well in closed loop(idle and part throttle conditons) the PCm will use the fuel trims to maintain 14.7 AFR no matter what. At WOT though you very well could possibly be lean due to added airflow through the engine without the added airflow being reflected in the MAF and VE tables.

Dont listen to all the people that say that Lt's make you run rich, that is pretty much just an Internet myth.

 

What?!? The internet is all I have

But in all seriousness, he's right. Your car's PCM will correct for it one way or the other (rich or lean), and it usually won't fall anywhere in the middle. And there's really no way to tell without getting some wideband data.

When I had my car dynoed after my exhaust install, Speed Inc's wideband showed I had an A/F ratio of about 12.5 all the way across the board, as measured at the tail pipe. When I installed my wideband O2 sensor, it was saying it was more like 11.8-ish at WOT, as measured at the header collector. Even widebands don't agree

 

good point...i stand corrected but that is why i said i think and not I know

 

Learn something new every day. thanks

 

The reason everyone runs rich at idle (VERY BAD) and cruse is because O2s work off of heat. No heat = lean.....

With stock manifolds, the O2s run hotter due to being so close to the exhaust port. As such, they "switch" around a higher voltage and this "switch" voltage is what the computer takes as being the correct area (the computer directly tries to keep the O2s around this voltage).

When you install headers, the O2s move way down the line to the collector (WAY away from the exhaust port). As such, during low flow times (idle and cruse), the O2s run cold. This cold running makes the O2s switch around a lower voltage which the computer takes to mean "not enough fuel." As such, the computer dumps loads of fuel into the mix in order to heat up the exhaust (this fuel is actually burning inside the exhaust) and as such boost the temps.

When you retune, you adjust this "switch voltage" to tell the computer "no....that is indeed the correct voltage to be at when in this cell."


You will run lean at high RPM, you are flowing more air than the MAP/vs./RPM table indicates. The MAF somewhat compensates for this but it is never perfect.

 

My ide was dead on 14.7 when i installed LT's. I checked it with my wideband, they only difference was it did switch a tiny bit slower though. The car will still not be rich at idle.

 

When I put LT's on my car, it was rich. I'm not going off of the internet, I'm coming from personal, been there, done that experience.

 

alright, i'll just have to get on the dyno and see where i stand....thanks for all the help fellas.

 

Rich at WOT or idle/part throttle?