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? ;-) :poke:

[tchr49]

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

Takes too long to get to the point

[STL_G8GT]

Takes too long to get to the pointYeah, 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? ;-) :poke:

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]

:watch:

[-Ray-]

Yeah, sell it. Buy someone else's problem. That could be easier to fix.

[STL_G8GT]

I hadn't considered that. That's actually quite reasonable. :-)
Yeah, sell it. Buy someone else's problem. That could be easier to fix.

[STL_G8GT]

Wire traced the fuel injector and coil for cylinder #2. No issues, no shorts that I could find.

Slightly raised idle fuel pressure.

Replaced bank2 header gasket.

Visually watched valve train during crank to see all rockers/springs/valves moving. They were.


No change. Bank2 climbs lean at idle.

[wyome]

Something in the tune?

[STL_G8GT]

Something in the tune?

I really don't think so, but that's not my forte. The tuner didn't see anything initially that is jumping out at him, but it's all remote, which is tough.

He suggested maybe swapping the valve springs on that lazy cylinder with ones from another bank. I'm going to give that a shot at some point, but honestly I would think a valve spring issue would show up at higher rpm, not at idle.

I went back and looked at the oldest log I have, from 2013. 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.

This is consistent with the idle performance today, a +5 differential on Bank2.

[STL_G8GT]

Going to do a hot leakdown test, and compression test. Going to check spark strength at 200deg.

Then I'm pulling the blower and heads. Going to replace intake gaskets, lifters, springs (it's time, anyway), and upgrade to the ls9 head gasket.

[-Ray-]

Going to do a hot leakdown test, and compression test. Going to check spark strength at 200deg.

Then I'm pulling the blower and heads. Going to replace intake gaskets, lifters, springs (it's time, anyway), and upgrade to the ls9 head gasket.

Wait! It's gonna be driving season. Turn the light off and go. Freak.

[STL_G8GT]

Haha!

Hot leakdown was fine, spark has plenty of strength.

Its all out.

Gutted the cats this afternoon.

[-Ray-]

Haha!

Hot leakdown was fine, spark has plenty of strength.

Its all out.

Gutted the cats this afternoon.

I see what you're doing. You're trying to get out of working on the property. LOL

[STL_G8GT]

Wellllllllllllll

got it back together with new gaskets, new injectors, new springs, and new lifters... still drifts. However, now it starts Bank1 @ -3% and Bank2 @ 0% and then at about 16mins through 20 mins Bank1 will go to 1% and Bank2 will climb to 5.5-7%.

It seems that both banks will climb slowly, but bank 2 climbs exponentially more. These trims are significantly better than before, however the drift is still perplexing.

Things that are new:
Blower sealant
Head Gaskets
Exhaust Manifold Gaskets
Injectors
Springs
o2 Sensors
removed Cats


Inspected, no faults found:
Pushrods
Valves
rockers
piston tops
Lifter trays
Spark plug wires
Ignition Coils
Wiring and both engine grounds
Exhaust clamps/system
Tested Spark distance @ temp and @ startup, both fine
Fuel crossover @ blower

If I think about this a bit differently, because both banks technically richen up, it really could only be bottom of the engine (extremely doubtful), a fuel pump issue (as fuel rails get hot and/or fuel pump heats up), or a ridiculous wiring issue that is temperature specific (again, doubtful).

Oh well, at least she's got new springs in her!

[donkeyGT]

Shit man...how much do you charge for labor? The boss and myself could take a road trip to CO and we could stay at your place while you (and my expertise of course) could do a DOD delete/cam swap:) this would be cake for what your dealing with..

[STL_G8GT]

Shit man...how much do you charge for labor? The boss and myself could take a road trip to CO and we could stay at your place while you (and my expertise of course) could do a DOD delete/cam swap:) this would be cake for what your dealing with..That's not a terrible idea, but I don't tune, so that might be a tough one. I did replace one of the axle/cv shafts and seal in my truck as a break, which was nice because it was a clear start/finish kinda deal!!!

[STL_G8GT]

Wellllllllllllll

got it back together with new gaskets, new injectors, new springs, and new lifters... still drifts. However, now it starts Bank1 @ -3% and Bank2 @ 0% and then at about 16mins through 20 mins Bank1 will go to 1% and Bank2 will climb to 5.5-7%.

It seems that both banks will climb slowly, but bank 2 climbs exponentially more. These trims are significantly better than before, however the drift is still perplexing.

Things that are new:
Blower sealant
Head Gaskets
Exhaust Manifold Gaskets
Injectors
Springs
o2 Sensors
removed Cats


Inspected, no faults found:
Pushrods
Valves
rockers
piston tops
Lifter trays
Spark plug wires
Ignition Coils
Wiring and both engine grounds
Exhaust clamps/system
Tested Spark distance @ temp and @ startup, both fine
Fuel crossover @ blower

If I think about this a bit differently, because both banks technically richen up, it really could only be bottom of the engine (extremely doubtful), a fuel pump issue (as fuel rails get hot and/or fuel pump heats up), or a ridiculous wiring issue that is temperature specific (again, doubtful).

Oh well, at least she's got new springs in her!


Figured I'd circle back here once more.

Replacing all of those parts, freshening up the top end, putting in new injectors (incidentally the old ones came back from testing and ID said they're good as new), and a tune adjustment for the new injectors has the fuel trims more balanced / zeroed at idle. The long idle (20mins +) issue is still somewhat present, although greatly reduced. I did notice that it starts to drift at the 15-16min mark (idling, no throttle manipulation, in park), and then at the 25min mark the other bank starts moving as well. I can't imagine a scenario where I would ever idle it for a half hour, and even if I did, with the exception of the fuel trims adjusting, there are no ill effects. As soon as I put it in drive, and then return to park, it starts over again. I did check fuel temps at different points, and it's never high enough to truly cause an issue. I did find out that my fuel pressure gauge in the car displays 2psi higher than the actual sensor is putting out, so I adjusted the controller to 42psi at idle logged in HPT via the interface input. ( I believe it's a ground issue, although I've tried two stock ground points with no change. )

The car starts, runs, drives just fine.

I don't have any idle logs to compare to, to see if this is a newer issue or if it's always been present, but because of the way that it shows up over a LONG idle, I'm guessing that it's always been this way. The only thing that got me looking into it was the p0174 that may have been thrown because of any number of small leaks that I found and addressed, before fueling/airflow was adjusted because of the larger intake tube.

I still would like the tune cleaned up for transients, eoi, and flex fuel, but remote is the only option, and that's a real pita.