p0171 and p0420 and thunderbolt cats ?s

[MMAFIGHTER121]

Ok.. I have been hunting a gremlin here. My car will throw either one of those two codes every 5 or 6 days. I double checked all the seals on my vacuum lines.. I cleaned my MAF. The car idles wonderfully, doesn't stumble at all, pulls smoothly with no misfires, but that bright yellow light throws me into an OCD rage. Ill pull my codes and it will be either the 171 or 420 the code will go away for a few days, then pop back on. I have noticed it seems to happen when I trigger something that would require a bigger strain on the engine (one time just after my ABS triggered on ice, another time after I turned on my defroster on) and my battery is on its last legs. Possible issue there? The post cat O2 sensors are new, and the entire exhaust system is new including the thunderbolt high flow cats. So - a few questions.. anyone have this experience with the thunderbolt high flow cats? Any other ideas what could be throwing the codes? I've considered the MAF but a bad MAF would cause poor drivability issues wouldn't it? Is it worth replacing the upstream O2s as well? Why won't this code stay away??

 

[lincoln ls_250k]

when you have brand new downstream O2 sensors its VERY likely to get lean and below threshold readings on the cats

the upstream sensors will read LESS than the downstream because they are old

upstream will read LITTLE GAS therefore u get a lean condition

when u have a lean condition the ecm adjusted and INCREASES the amount of fuel making the car run rich

when u have a rich condition the downstream sensor will notice this and set the below threshold on the cats.

A bad battery will make a car like the ls act up b/c of the amount of electronics on the car. replace the upstream sensors and the battery, that should fix the problem

If you can get a scanner to read the short and long fuel trims post the results here and i will help u.

 

[MMAFIGHTER121]

Sense. You makes it.

 

[MMAFIGHTER121]

Replaced the upstream o2s and then read the trims at idle:
St ftrm1%: between -4.0 and 2.3
Lt ftrm1%: 13.2
St ftrm2%: same as 1
Lt ftrm2%: 16.4
Will drive for a few days to see if the code returns. Out of funds for a new battery.

 

[lincoln ls_250k]

Did you reset the computer after installing the O2 sensors?

On the fuel trims you want them as close to 0 as possible

so on the short trim is close to where it needs to be

Long fuel trim is adding an additional 13% - 16% fuel to the mix

Unplug the battery hook it back up 3 mins later, start the car let it idle for 5 minutes, then turn on the a/c let it idle for 5 minutes, then go for a drive (drive it ez) 10 mins or so, get fuel trim readings again

 

[MMAFIGHTER121]

No I just swapped them and turned it on and pulled them. I didn't have much time. Without the battery reset will it self adjust eventually while my short trim is in the right range? I thought resetting the code reset the long trim..

 

[lincoln ls_250k]

you should just unplug the battery and be done with it, it will fix itself but the sensors will get blasted with extra fuel for no reason.

 

[MMAFIGHTER121]

I did the reset anyway. We'll see if the code returns or ill pull new trim readings if I get a shot.