H3 Fuel Trim (ST)

[08H3]

What extremes does anyone's STFT go between? Mine is about + to - low 20%. Back story: Had a cracked exhaust manifold. I let the shop do it because I didn't want to screw with broken bolts, etc. Reputable independent shop. New up and downstream Delco O2 sensors. Had a P1133 set after 24 miles, the coolant temp went crazy, then quit working. Also started going between open and closed loop more or less at random. Took it back to the shop which said a bad ECT sensor could cause the 1133. Not so sure, but I'll take his word....for now. Replaced ECT sensor, car ran fine for 101 miles then 1133 set again. Car still runs fine with exception of the fuel trims being erratic going from one extreme to another. This, of course, results in a slightly variable idle. Sensor voltage is varying, so it is working. Is it possible the code doesn't stem from something else and I just got a bum sensor that truly isn't feeding the PCM info fast enough? I'm not a person to throw parts at a problem, so I wanted to get some input first. Thanks in advance.

EDIT: I think this mystery may be solved. I'll get a few hundred miles on it and post back.

 

[CaseyS]

Why did you change the o2 sensors? Do you still have the old ones?

 

[08H3]

Changed them out because the old ones were so frozen in the manifold that I expected they would probably be damaged trying to remove them. I was right on the upstream....it broke off when removed.

 

[Airborne]

Do you have hp tuners?

 

[jakesz28]

Check the connections for the O2 sensors. If corroded Mabee it's a poor connection.
Exhaust leaks are fixed? Did they use any high heat RTV?

What are the LTFT?

 

[08H3]

Thanks for the suggestions. 99.999% sure the problem is solved. The shop installed the pre and post cat sensors in the wrong positions. Switched those back around and so far so good.

 

[08H3]

UPDATE: I have about 1200 miles on it since the O2 sensors were correctly installed. No lights, no issues, so it was just a mistake at the shop. All is good.

 

[CaseyS]

Interesting. So the sensors are different yet have the same harness?

 

[08H3]

I'd have to check again, but I think the harnesses are different. It would have seemed logical to me to have different threads on the upstream and downstream so it was impossible to switch them.

 

[CaseyS]

I think the threads into the exhaust are the same. However the harness connector for each sensor are far enough apart that I don't think you could stretch the wires far enough to plug one into the other.