P0174 Issue, 09 G8 GT

[STL_G8GT]

Chasing a P0174 on a 09 G8GT. At startup and entering CL, (at idle) bank 2 will go up 1.6/2.3/3.1 until the ltft climbs a couple points. After the ltft adjustment, the stft will steady for a moment and then add 1.6-3.1 until the ltft jumps again. It will continue this to up past +15% ltft on that bank alone. If I disable ltft, the stft will push past 15%. This is all behavior at idle. It's possible that this issue follows (gets worse) engine temperature rising. Otherwise, I don't understand why the fuel trim wouldn't immediately climb the 15% it eventually settles at. Bank1 trails between 5 and 10 behind Bank2.

(Edit: I went back and reviewed logs from 2013, which are the oldest I have. I had a +5 differential on Bank2 vs Bank1 at idle. I wasn't able to view a log to see if that number climbed over time, however after acceleration or deceleration and then idle (such as at a stop sign), the fuel trims drop to B1:0/B2:+5)

Fuel pressure is measured at the drivers manifold on the s/c, and reads correct @ 42 psi at idle. It's a boost referenced system and has shown no changes from previous readings.

Here's the rundown:
2009 G8 GT, 38k miles
Rotofab intake, PatG Cam w/ls7 lifters & pac beehives, ARH 1-7/8, ID850 injectors @ 10k miles
Ported Mag2300, RCR Heads, ls7 maf, CTSV pump with vaporworx controller @ 17k miles. (pac beehives were tested at this point and spec'd out as like new)
Upgraded 4" intake, exhaust work (Added midmuffler) @ 35k miles
Swapped Comp Trunions for Smith Bros bushings @ 38k miles

The car sits and isn't driven October through June each year.

About a month ago I tossed around the idea of going to the 09.5 ecm. So I swapped in the ecm and we started the tune... but before we could make any progress, the tuner recommended that I look for a vacuum leak or misfire on bank2. I swapped coils, plugs, injectors, new injector orings, wires from bank to bank and the problem stayed on bank2. That was the first I knew of the issue.

I ditched the ecm swap, went back to my original and the issue is still there. This is when I did the trunion to bushing swap, so it's not part of the issue. The two mods that happened between the last log without the issue (in 2015 I have a log without the issue present - but the trim differential of Bank2 +5% trims is present) were the exhaust work taking out the xpipe and replacing it with a mid muffler and the change to a 4" intake tube.

Here's what's I've tried so far...
+Swapped all fuel/ignition components bank to bank.
+Cleaned injectors on the bench, twice. Ensured s/c crossover lines were clear. (fuel enters on bank 1)
+Swapped o2 sensors bank to bank.
+Smoke tested the top of the engine. Had some seeps at the catch can and maf adapter, addressed those. Held the supercharger bypass open for this test to allow smoke past the blower. No smoke near intake manifolds under blower tub.
+Disabled injectors 1 by 1 in HPTuners & disconnected each coil manually, each produced a noticeable change.
+Smoke tested the exhaust. Had seeps near clamps on the exhaust by the axleback, addressed pretty well. Could see a very trace amount near the bank 2 collector but wasn't able to pinpoint.
+Tried propane near each header primary to manifold connection and each fuel injector oring. No change.
+Replace spark plugs (cyl 2 still "browns" first, and darker) (5/18)
+Removed and replaced header gasket on Bank2 (5/19)
+Verified rockers move with cam, all lifters "lift"
+Slightly raised idle fuel pressure (5/19)

Things I haven't done yet...
Pull the blower and install new intake gaskets.
Remove the header for a real close look for cracks/damage.
Remove the heads and look for valve damage/cylinder condition.


I don't know where to go from here... any suggestions welcome!

[-Ray-]

Sell it.

[STL_G8GT]

Sell it.

Have you thought about a career as a motivational speaker? ;-)

[tchr49]

Have you thought about a career as a motivational speaker? ;-)

Takes too long to get to the point

[STL_G8GT]

Takes too long to get to the point

Yeah, sometimes I wish he was more direct.

[STL_G8GT]

Cylinder Plug for #2 (the first cylinder in bank 2) is darker than any other plug on that bank, by a mile. Not oily or wet, just dark/sooty.

[STL_G8GT]

Cold engine compression test has all cylinders on bank 2 @ 165. Bank 1 ranges from 162 to 165.

[-Ray-]

Have you thought about a career as a motivational speaker? ;-)

I'd like to remain anonymous.

Have you considered you have an under performing spark plug? Perhaps consider a spark plug in a higher heat range for that location.

[STL_G8GT]

I replaced all plugs in it, but will watch that first cylinder. Not sure it's actually connected to my issue... because...

Today I swapped fuel injectors bank to bank, tried a known good coil out of the truck, and put in new plugs. Issue persisted on the same side.


I took it for a drive and noticed something right away... If I'm idling in Park or Neutral, the issue is present. As soon as I put it in gear, the trims even out. So basically this is an issue only when the engine is under no load at all, which is a bit odd.

If I ignore the dark plug, and chalk it up to another issue (maybe a fouled injector that I cleaned when I swapped, or something along those lines), then I still just have a lean on bank 2 issue. With that in mind, most of my research points me to an exhaust leak on that side before the o2. The only things I have not changed are the intake gaskets and the exhaust manifold gaskets. There's also the possibility that my header is physically damaged itself, somewhere on either the collector or the manifold. I've got a different smoke machine coming tomorrow and I'm going to try and smoke the exhaust again with the car hot as that's when the issue is worst.

That smoke test will happen tomorrow and hopefully I'm further down the road with this thing.

[donkeyGT]