bigrpm

Looking for some help. I have an 08 Z06 that was modded with the following, ARH headers, Torquer 110 cam, WCCH stage 2 heads, KB2 CAI and was tuned by ECS. The car ran very well but I was not happy with the combo. I just installed a custom grind Chris Straub cam, Morel lifters , Ported Fast 102 and NW102 throttle body. The car is in the process of being tuned with HP Tuners but the bank 1 and bank 2 fuel trims are always off by 7-10(negative) percent so you can't even start tuning never mind getting on the throttle. Here is what I have done to try & cure the issue. I installed new GM O2 sensors to take that out of the equation, checked for exhaust leaks, checked all fittings and intake for vacuum leaks, changed plugs and wires. I also pulled the intake to make sure the seals didn't move. The car idles well, starts well and cruises fine but the ECM is always adjusting the short and long term fuel trims but you can't play with it because of the bank to bank issue. Any ideas of what to try next.

realcanuk

I have the same issue and after many, many hours of trying to resolve it, I have determined there is nothing you can do. It could be due to variations in cam lobes, head ports, or who knows what. I run with LTFT turned off and my STFT are off by about 5 to 8% from side to side. I just tuned to get them as close as possible to 0.....(meaning for example one reading -4 and one +4, rather than one reading 0 and the other +8). I went through the same thing of checking and rechecking all the things you mentioned. If all those are good I would just live with it. You can tune around it anyways. Trying to get trims less then 5% in all conditions is just an exercise in futility. The computer will adjust that no problems. Trims don't work once in PE anyways so don't worry about getting into it.

TurboLX

Why not tune it properly in open loop (no corrections, O2's off) using a wideband first? Get this done right in steady state, then see if there is any need to chase trims afterward.

bigrpm

Thanks for the responses. I thought about tuning around this but my thought is if they're out by 10 % that something's not right. I am very new to HP Tuners and that's why I am asking. Are the trims being out that far normal for a modded combo or is there a problem.

Unreal

Because if you tune it in open loop, spend all that time, then just put it back in closed loop for the factory o2/feedback just to mess it all up.

I see ~3-4% difference side to side, nothing I've ever worried about.

edge04

can you post a log and tell us more about how you are tuning

realcanuk

Its common from what I have seen. If you really want to know whats happening, you can put a wideband in each bank, but as I said, I wouldn't worry about it.

realcanuk

Unreal

If you are going to keep it open loop, then do open loop tuning. If it is closed loop, then you have to play nice with the car. No point in going open loop just to have the car go +15% on all fuel trims.

tblu92

As long as they are negative I agree I would not worry--
Try resetting the fuel trims with your data logger with DVT---see how fast the trims return--If quickly--just mostly the nature of the beast--
Many heavily modded cars will simply turn the fuel trims OFF permanently anyway-beacuse of this same reason of always chasing them down----when re-setting them see how much the idle changes--if somewhat seamless----it's not a big deal to turn them OFF

jim2092

Since this "is the guy who wrote the book on it", several of them to be exact and DVD's, etc., I would think you would want to do this first anyway. A properly placed wideband tune (on both sides if you like) at steady state in open loop. Then turn your O2 sensors back on and see what's up. If you have a nasty cam they will jump around. Narrow band O2 sensors really don't like overlap at low rpm. Nature of the beast.

bigrpm

Sounds good. I will shut the long terms off and see what that does. The cam is pretty stout and the car sounds bad ***. I had one tuner tell me the intake and throttle body was junk and I should go back to stock but that's not in my plans yet. Tuning with HP is very new to me so I am taking this all in and learning. I will report back.

tblu92

I just had similar issues with a heavily modded Z06---Idle was eractic pipe were always sooty blk--I experimented with many tables one at a time to isolate the issue
His main issue were his LT headers--they move the front 01 bungs about 3 ft aft so his actual CL AFR was always pig rich--
I eventually increased the idle speed to 675--
Set the minimum timing at idle to "0"(stock was as high as- 5*) So his car at ilde would bounce around from 3* to 16* which would create a surge at idle black sooty pipes--stumble at take off--poor fuel mileage
When I set the min idle timing to 0 the timing w=changed to 7-16*
No more stumble--smooth idle--pipes started to burn off the soot and clean up
Also---because of the bung locatios of the LT's now moved 3' back I adjusted the 02 switching points --Originally they were reading as an average about 380 millivolts I raised them 100 points and now they are switching at 489 Millivolts--( more in line as LT's tend to make PT closed loop fueling way rich !!--Totally cleaned ip the bootom end and around town driving---
I did have an issue with fuel trims that were a weird +10 to a -17 on the same cell--
From What I've learned a large # is OK but nor optimum as long as they are ALL negative #'s So I tweaked the MAF table to only show all negative trims and tried to keep them below 10% As a tuner the 427 is a hard engine to get perfect but it make so much power even when not running 100% no one seems to care!--
Result---The owner feels like it is a whole new car--it is easy now to drive in the city
Idles a steady 675 with no dips--and faster than ever--mileage way up and after 1 week the tailpipes can be swiped with your finger and there is 0 black soot---
LTs are great but unless tuned correctly can cause major headaches and in some cases even make LESS HP than stock manifolds