I need help, bank fuel trims off please help me trouble shoot

[spacecadet]

adaptation( idle ) bank 1 sensor 1:-1.7%
adaptation(partial) bank 1 sensor 1:14.1%

adaptation( idle ) bank 2 sensor 1:-0.8%
adaptation(partial) bank 2 sensor 1:6.3%

Banks are out.

I have:
-pressure tested
-smoke tested
-replaced bank 2 02 sensor
-swapped injectors from bank to bank


I need:
More input or thoughts on what to look for. Anything is appreciated.

[Grip99]

Is the ecu tuned? Fuel pressure reg. in good shape/right bar?

[vavJETTAw36]

Any recent changes? When is the last time you saw good trims?


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[spacecadet]

ECU is tuned , its a fresh build so this is establishing base line.

walbro 450, ID725, stock rails and fpr.

[vavJETTAw36]

You have to be more specific when you say the ecu is tuned.

Custom tune? Off the shelf tune?


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[zillarob]

You have 1 new and 1 old o2 sensor now?
Id swap them and see if the numbers follow.

[spacecadet]

Actively being tuned by Blake. Made it through break in, cant get into power tuning because banks are off. Someone pointed out to check the fuel filter/fpr/pump so im going to test those out individually.

[spacecadet]

You have 1 new and 1 old o2 sensor now?
Id swap them and see if the numbers follow.

Both are new now, i re-used one after the rebuild kept one. Then when this started i thought maybe the one i reused was old/worn so i replaced it. two new now.

If the fuel testing stuff does not work out i plan to swap the 02's next thanks thats a good idea.

[zillarob]

Ya, Id start there. Easy one to do to rule them out as you work your way up.

[S4James]

verfy primary O2 sensors are in the exact same location on the downpipe.

I was out 7% left to right on partial.

Not enough to worry about relocating, thats all it was.

[spacecadet]

I'm running o2 per bank not two in down pipe.

[slow ride]

I had the same issue, 5-7% off on the drivers side bank (rich) while idle was even. I was also fighting a idle misfire on 4 which is on the drivers side. Compression was slightly lower in that bank on 4/6 and leakdown is showing less seal in the exhaust valves on that side in my case.

[MCP]

Identical problem here(same banks and and idle was even) and went through a painstaking year of swapping in brand new parts(injectors, spark plugs, MAF, FPR, Fuel filter, ect.) and trying to see if it fixed the problem at hand, I eventually contacted Blake to tune my car as I was on a base file and the fuel trims are now Partial B1: -0.7% B2:-2.7%

[chaos2984]

looks like your running a little lean according to those fuel trims. Being lean can be either unmetered air or low fuel pressure. But since your Tuned It could be the mapping as well. To where the injector duration is off. Do you know what your fuel pressure is suppose to be. Do you have a gauge to monitor it? It could be a pressure issue.

[slow ride]

Any misfires going on while running or idling? I'd do a compression test just to see if both banks are even or close.

[S4James]

I'm running o2 per bank not two in down pipe.

Thats not what I was suggesting.

Verify the downpipes have the primary o2s located in approximatly the same spot relative to each other.

In my case my drivers side 02 was mounted about 8 inches further from the turbo than the other side. Causing a 7% difference.

[spacecadet]

Thats not what I was suggesting.

Verify the downpipes have the primary o2s located in approximatly the same spot relative to each other.

In my case my drivers side 02 was mounted about 8 inches further from the turbo than the other side. Causing a 7% difference.

I see now thanks, one is maybe 1/2 inch further away from the turbo than the other.


No missfires, and the car runs great.


I got a fuel filter in yesterday, same issue. getting burnt out on project might give it a few days rest and re group.

[S4James]

did you swap the 02 sensors themselves left to right? It could just be one sensor is out of spec... you mentioned you changed bank2, but its bank one that seems to be having all the trouble, perhaps that one is bad.

if you swap the sensors, and the 14% moves to the other side then you know its an o2 issue right?

I would also inspect the o2 sensor harness, eslpecially the section mounted to the firewall, those wires get baked.

[spacecadet]

yea if i get motivated today ill swap o2's. need a little break from the car the urge to set it a flame is too great :p

[spacecadet]

o2's swapped
fpr swapped
issue persists. I'm sure I've F'ed something up sigh

[erykv1]

you could have an internal leak at the DV's or in one of those 3 green check valves on the intake manifold.

these types of leaks wont show on a pressure test / smoke test.

[spacecadet]

I don't have any of that stuff any more.

[spacecadet]

Out of pure frustration I was manually moving through every block in the engine tab hoping to find something that would help me.

Nothing really until I hit block 093.

bank 1: 2, bank 2: -9 or vice versa i cant, quite remember.

I don't understand how these got off that much, I used a crank lock pin and cam lock bar so who the hell knows.

I have found a few other threads where people have had similar issues where they just pull the valve covers, pop the cam gears, and vice grip the intake cam into position.

I'm currently working on doing the above. Who knows anymore.

As always i appreciate any input.

[slow ride]

Good find, with my issue I was ok on block 093 (1 and -2 or something). I found from compression and leak down tests that my drivers side bank was slightly weaker and had more leakage on the exhaust valves (#4 the most as it had a misfire issue at idle).

[spacecadet]

Welp I successfully moved it from -9 2 to -8 3 smh

[zillarob]

Just put the cam bar and crank pin in, pop cam pulleys, and tighten them back up?

The sensor wheels on the cams ha a little play and prob not difficult to jack up if somebody got ape fisty in there.

A few people have munged up the end of the cam where the cam bar holder gizmo goes on.
This can prevent them from indexing the cams properly with the cam bar.

[spacecadet]

ive used cam bar and crank pin everytime, i must be doing something wrong

[slow ride]

Are you applying torque to the tensioner when locking the cam gears down? As Rob said above sometimes the cam keys get mucked up (sort of rounded over) as mine were do to t belt failure years ago so check those.

[slowSfaux]

I also was having trouble with my timing the first time I did a timing belt, but round 2 I pretensioned the adjuster before I tightened the cam gears and that took care of my issue.

[zillarob]

Ya, pretensioning is mandatory if you want everything to line back up nicely after the test 720deg thing.

90in/lb seems to be the number for getting the pin and bar to slip back in nicely after the 720deg test and works well for me.
I think some do more (like 25nm), and I can see some good/bad reasons for it, but dont expect the bar and the pin to slip back in without a fight.

[erykv1]

correct me if im wrong, but I believe as long as you are not more than 6* away from each bank it is ok

[vavJETTAw36]

Ya, pretensioning is mandatory if you want everything to line back up nicely after the test 720deg thing.

90in/lb seems to be the number for getting the pin and bar to slip back in nicely after the 720deg test and works well for me.
I think some do more (like 25nm), and I can see some good/bad reasons for it, but dont expect the bar and the pin to slip back in without a fight.

What is meant by pretensioning? im trying to paint this picture in my mind and I just cant. You meant turn the cam slighly?

[spacecadet]

What is meant by pretensioning? im trying to paint this picture in my mind and I just cant. You meant turn the cam slighly?

with the cam pulleys loose, you turn the timing belt tensioner to like 14 nm. Then you torque down the cam gears.

[slow ride]

Doing so with the crank locked puts tension on the belt to act like it would while running. You do this step before pulling the pin on the auto tensioner. As said above also look into the intake cam timing rings to be sure they are not damaged.

[slowSfaux]

Doing so with the crank locked puts tension on the belt to act like it would while running. You do this step before pulling the pin on the auto tensioner. As said above also look into the intake cam timing rings to be sure they are not damaged.

You do this after pulling the pin on the auto tensioner, but before tightening the cam gears.

[slow ride]

Correct, my bad I was lost thinking about my old DSM days ;)

[spacecadet]

uh oh, just tested bank 1 and all 3 only @ 90psi.

[S4James]

oh dang... tweaked valves i guess?

[zillarob]

What is meant by pretensioning? im trying to paint this picture in my mind and I just cant. You meant turn the cam slighly?

After you pull the grenade pin, you put and allen socket in the eccentric gizmo and rock it with a torque wrench to stretch the belt a lil and make everything happy before tightening the cam sprockets.
It is a lefty tighty gizmo iirc.

The rs6 has an extra eccentric pulley and is extra fun to do this on.


90 is way low. I think I usually see 140ish not opening the tblade, and would be a bit more if you did it properly.

[slow ride]

I'd be suspicious since all 3 read 90 that closely. Leakdown will help you some I think. Edit, just noticed you are in CO so cranking compression will be down some, but not sure about 90.