MFJ

iTrader: (4)

New engine build with 1k miles on the build so far.

It started throwing the P0171 and P0174 about 4 days ago. I thought it was because I had to take the exhaust off (ran off the road avoiding an accident and it hit the frame, header and exhaust) and now I have open headers, but I usually do that everytime I go to the strip anyway. Normally it makes the engine run rich not lean.

Engine idles fine and stft's look ok at idle and when under heavy throttle. When cruising or light throttle they shoot up. Last time it threw the code STFT's were 56% LTFT's were 26%.

Here's what I've done so far:

1) Cleaned the maf

2) Checked fuel pressure 60 psi at idle 59 psi wot

3) Checked the intake bolts since I put new gaskets on the intake

4) Sprayed carb cleaner on everything with no change in idle

5) Changed the bank 2 o2 sensor since that's the side that got hit

6) Did a pcm relearn (worked for a little while then ft's went back up

7) Checked the vacuum lines that run around the intake and to the brake booster (which are all brand new)

8) Checked all the header bolts and also can't hear any leak around the flanges where the bolt into the head

Like I said it idles fine and at idle the stft's look pretty normal, but under light throttle they shoot up.

Motor info just in case someone needs it.
Mahle forged pistons, blueprinted and balanced, ARP's, stock cam, crank, maf, P/P throttle body, A/C delete, P/S delete, Stock LS6 intake, upgraded oil pump.

I need help. This is my daily driver. I may be able to get my hands on a smoke machine.

I can also watch the readings live.

MFJ

iTrader: (4)

Here is a theory I have going. Since the o2's are at the back of the LT's I think fresh air is getting to the o2's while cruising and making the pcm think the engine is running lean and dumping fuel to try to compensate for it, which is why at idle and wot the fuel trims go back to normal.

As I was scanning it a few minutes ago I got the usual P0171, P0174 and now P0306, which is probably a fouled plug from being pig rich.

Any thoughts on that theory?

2xLS1

iTrader: (25)

You can't run closed loop with open headers. If you must run open headers, unplug the O2s so it stays in open loop. P0171 and P0174 don't necessarily mean it is running lean. It means the fuel trims have exceeded +20% attempting to keep the a/f at stoich.

MFJ

iTrader: (4)

Yeah, it's definitely not running lean (which is a big relief), it's actually running rich as hell. It's just fooling the pcm into thinking it's running lean. I just pulled and changed all the plugs and they are black. I'm going to add extensions or try to modify my duals this afternoon and hopefully that'll fix it.

Won't running in open loop be rich too?

2xLS1

iTrader: (25)

OL fueling is pretty close to stoich not in PE when fully warmed up but the fuel trims are ignored and don't add any additional fuel. It will depend on how accurate your air model is in the tune. Disconnect the battery so the trims get reset to 0.

MFJ

iTrader: (4)

Alright, I'll disconnect the positive and unhook the o2's and see how it goes. It has a Frost tune in it so I have no idea what my air model is in the tune.

delta3

I just installed 1 3/4 long tube ARH headers with the catted ypipe. Frost did my tune as well. Just yesterday I had the same DTC come up when I hooked my Verus up. My LTFT is as 25%. I was running mac mids before and never had an issues. I've added NGK iridium plugs (0.050), MSD plug wires and cleaned the MAF. My 02 sensors are new Bosch 13111. I bought them off Steve's recommendation. Any ideas where else to look?

joecar

Are you saying the header got damaged...? Is it sucking air ahead of the O2S...?