I am stumped. Short story, had car with new engine tuned with bad headers (leaked, cracked, severely dented) car ran great, replaced headers with new ones, ran great but dislike sound. rereplaced headers with bigger primary tube ones, car runs like crap.

Long story
Ok so here goes. Earlier this year (April/May) I replaced my 2002 Z06 engine with a 2005 LS2, has TF heads, 240/244 cam, FAST 92, 90 DBW throttle body. Car orignially was bought with a set of LG 1 3/4 long tubes. They were aged, cracked and rewelded but still leaked, and had a few big dents in them from road debris.
I get the car back together and running, and I take it to get professionally tuned with the LG headers on it (1 3/4). (ran low on funds and had no choice) Get the car back and it runs wonderfully, tho the headers are taking away (can hear the leaks). So I make plans to replace the headers and start saving.
I replace the LG headers with a set of XSpower headers (1 3/4). Car runs great, performs great also. I just dislike the sound, and I really did not like the A.I.R. ports. So I replan and start resaving to purchace another set. Keep in mind, the car still ran very well.
So after some time, I get a buyer on the XSpower headers and sell them, by this time I saved enough to buy a set of Stainless Works headers (1 7/8, no AIR ports) and buy them. I just finished installing them this past weekend. I start the car up and it fires right off, idles great, and free revs well. I let the car go through a warm up cycle then shut it down to cool down. The next day I take it for a quick run.
When driving through my neighborhood in 1st or 2nd gear, low throttle, low RPM, the car spits and sputters, very similar to a misfire. At this point, I assume it is because the car has sat for an extended period of time so I take it out on the main road and give it 1 WOT accel in 2nd gear to to aprox 5500-6000 and it does fine, then return to the garage. The car still spits and sputters.
I go and recheck everything, all plugs wires are fully connected, check electrical connections and they appear all connected. So I replace the stock AC Delco plugs (new when engine went in) with a set of NGK TR5's. 2nd drive arround the neighborhood results in the same sputtering.

No codes are pending or present other than P0133 which has been there since the XSpower headers (I am ordering new o2's this week). The car has right at 1/2 of fuel, but that has been in the tank since about mid/late June. Plug wires are FireCores and have aprox 600 miles on them. I changed the LS2 coils out for LS1 coils and no change. And I previously mentioned the spark plug replacement. What else am I missing?

The only other thing I did during the header replacement was to add a 4 gauge ground wire from the passenger side of the engine block to the passenger side frame rail, at the stock location of the battery ground. I also added a 4 gauge power wire from the back of the alternator to the positive battery cable. However, I disconnected this wire during the 2nd test run.

I appreciate CF's help and recomendations. I know it is a long read

 

1st of all it takes at least 50 miles of drivimg to let the ECM "learn out" the fuel trims---before that making decisions is based on uselesss information---after it learns out then try to diagnose----I would start with your front 02's --make sure they are bouncing around rapidly between .150 and .950 millivolts---You can check this with most scanners that show real time data---If an 02 is flatlined at .450 or if is moving slowly--it's junk---A faulty 02 will put the ECM into a sort of limp mode--but NO codes will appear--
Next check your LTFT(trims) make sure both left and right are all slightly negative or at "0"--try to drive it at P/T to hit the entire range

 

I have HPtuners, so I will check that tonight. I know the fuel trims and ECU need to relearn, but the car is driving way worse than it should. The car did not act this way when the XSpower headers were put on. I dont think it is directly related to the header replacement, but possibly something happened during it?

 

you said you have had the SAME gas in there since june. Its not REDICULOUSLY old but old nonetheless. Id go purchase a bottle of Techron and see what she does. Start small and work your way up.

 

I was thinking of the same thing last night. I also finally got 2 codes last night when I went to check the o2 sensors. P1133 & P1153, ironically enough, lack of switching on the o2's. Now it is time to trace that problem out too, as I did not have that issue before putting on this last set of headers. Maybe I broke them (a wire on the o2 sensor) or something

 

Did you get the O2 sensors reversed? Its a common thing to do getting them into the wrong places.

 

It is possible that they got switched, would that really have that large of an effect on it? I can not accelerate from 1000-2500, it bogs down and then after awhile the car wil snap your neck trying to accelerate.

I can keep the throttle in 1 place and it will just break up trying to run until I depress the pedal farther. I need to get a log off it, I think it clears up when the car goes in to PE enrichment.

 

When my headers were put in the shop switched the sensors. It wouldnt run for crap and would cut off if I pushed it past 1500 rpms.

Switched the sensors and it ran perfect.

 

I just ordered new OEM sensors from 1 of the dealers in town. $58 per front sensor didnt seem bad and figured it was time to replace anyway as they looked like the original sensors. I should know tomorrow afternoon if this fixes it or not.

 

Have you pulled the codes recently to see what its having issues with?

 

yes I have. only codes that are coming up now are P1133 and P1153

 

My car ran rough and rich.... soot all over the butt, gas mileage way down...
code P0133....

The headers had damaged the wiring harness for the drivers side O2 sensor. Replaced the sensor and the body side pigtail and at 140K (s)miles she was running like the track star she was.

 

P1133 Heated Oxygen Sensor (HO2S) Insufficient Switching Bank 1 Sensor 1
P1153 Heated Oxygen Sensor (HO2S) Insufficient Switching Bank 2 Sensor 1

Its sort of looking like you might have gotten them reversed. Start looking...

 

Yeah I'm an idiot. I went to put the new o2's in and found the old ones just hand tightened in, and they were reversed. Ontop of that the new o2's are wrong, they have the wrong connector on them. I know the new 1's are what's suppose to be in the car, but it looks like the car has the rear sensors as the front's now. I tried to locate the correct front o2 body harness but could only locate the square o2 sensor plugs (2 square ones on the driver's side, one on the passenger side) so the old ones went back in, but in the correct placement. Car runs like a champ now, except for the rattling of the mid pipes, I need to get it on a lift and properly readjust the fitment of the pipes.

So I'm off to get two new rear o2s and give my z06 a bath finally!!!!

 

Ok...wait a minute....who's turning the wrenches on this car?

It is common practice to use an adapter(s), and use the rear O2's in the front locations, due to better heater circuits, in which case, the rear 02 locations are blocked off, the the rear codes are turned off when it's tuned. It is common that in doing this (by a novice), that the O2's get crossed in the front positions, which causes issues.

 

I am turning wrenches, always have on my cars. I just forgot to tighten them when I put the headers on. I knew people used the rears as the fronts with adapters, but didn't think about it when I ordered my replacements. When I was under ther yesterday, I did not see any adapters at the plugs, they were all the square o2 plugs, I looked and felt arround up the bellhousing area and tried to trace back the harness to see if there was an adapter farther up but still did not see any. I still need to get new o2's because the codes are still piping up, but not as frequent (still running the old sensors).

 

Something doesn't make sense. You said the rear 02's are now in front positions. If there are no adapters, to facilitate the use of the rear sensor, connected to the front harness..............that would mean the rear sensors are all that is connected.....

 

I agree that it does not make sense. I spent 30 mins looking for a flat 4 pin connector on either side but could not. Only found the squared 4 pin connectors. The o2 sensors that are in the car have leads that are about 18 inches long, maybe a bit longer. The new ones that came from the dealer (new fronts) only had 4-5 inches of lead wires. I plan to get the car up in the air on a lift tomorrow after work and look some more.

 

Got the car on a lift and found the driver's side does have an adapter, looked on the passenger side and no adapter. Maybe someone cut it off (factory plug) and wired in a rear o2 plug? Ordered 2 new Bosch rear sensors today for $61 each, lets hope these come in correct tomorrow.

Side note, the fitment of the new exhaust is a PITA. I am about to realign it all for the 3rd time to try to remove the rattling against the frame, rear diff, and rear crossmember.