DPnSider

New here, but not to the LS scene. Got the wife a 2007 vette that is bone stock (to my knowledge). Thought I'd run this past the community:

It had some serious KR - audible under any real load. So, first thing I did was swap in some TR6 plugs and a set of wires, which made the car run better but really didn't change the KR very much. FWIW - The plugs that came out were obviously melted. The tips had gone liquid. Center electrode looked like a pyramid with a bead on the top point. not to mention bubbly ceramic.

So, hooked up HPT and started logging and the VVE table is pretty much off in entirety by 15%. Lean. So, I verified fuel pressure, which was a solid 58 psi. Bumped the entire VVE table 15%, calculated new constants, and then a few logs to fine tune the VVE constants. Then, I went to MAF only mode, and 15% lean AGAIN. So I bumped the MAF curve 15% and then logged a few times to dial it in, and the KR was completely gone.

Lo and Behold - It will now take 26 degrees timing with no KR, and MPG went UP 2-mpg.

Is it normal for the stock LS2 tune to be that far off? My first thought was a hypertech tune or something stupid, but I doubt hypertech would have the timing at 19 degrees.

I'm thinking the next move will be to replace the stock balancer with an ATI just to improve the vibration damping - not so much for the UD.

BlindSpot

What were FTs doing before the HPT intervention?

DPnSider

LTFT + STFT were +10 to +25% depending on which cell you were looking at. Nothing at all was negative or even close to zero.

BlindSpot

So you were running + 25% LTFTs?

Just a couple more:

What do the O2 sensor switching patterns look like?

No CELs?

BlindSpot

If it takes you some time to get back, and I'm not meaning to ask 25 questions, but:

A bone stock engine with a supposed stock factory tune, fueling should not be walking off the path on its own like that. Also, a bone stock LS shouldn't need TR6s to run right.

I probably would have pursued a different first path than a complete refueling with some cold plugs. I would have first looked to some possible mechanical issues that would cause a chronic lean condition, BC if you jump to refuel and, lets say you have a serious vacuum leak, then you've just tuned in a mechanical failure.

Other than that, the +25% LTFTs concern me w/o a CEL. That MIGHT indicate that the tune has been manipulated in the past afterall, but, I still am stuck on the first comments I've made about a mechanical lean issue.

DPnSider

O2's were very active and centered. They look like they should. And no codes at all.

DPnSider

That's why I was asking. It seemed weird to be that far off, but it definitely liked and needed the fuel. I didn't check for vacuum leaks, but the only times I've had vacuum leaks bad enough to affect the fueling 25% on other cars, they'd struggle to even idle. Although, since the LTFT were making up the difference I guess that could have been negated.

BlindSpot

A little late now, but before you did the VVE and MAF, you could have pulled up a stock tune from the HPT library and could have done a compare (love that feature). Compare would have highlighted any changes if someone did go in and manipulate the tune before you owned it.

You could still do that. Especially check your tune in HPT - Engine Diagnostics > DTCs > P0171 & P0174

Are they SES enabled? Disabled?

Anything else disabled? Check ALL the Sensor 1 and sensor 2s both banks. If any are disabled, THEN we might have first signs the tune has been manipulated in the past.

DPnSider

I should have done that. But good idea. If anything is deactivated that'll be a big clue.

BlindSpot

Yep!

BlindSpot

So, I hate theories, but let me throw one out there. Let's say the owner before you had a blower kit installed, something like an ECS or an A&A, and had it tuned correctly. Then decided to strip everything off, return the car to stock before he sold it, but left the tune in it.

Assuming he was running at least 60lb or 80 lb injectors, then returned to the 40 lb injectors without correcting the injector data, then both the injector data and the fueling would be way off, lean....and the timing would have also been retarded in the boosted tune. 19* is pretty high for any boosted tune, but...just something to keep you awake tonight.

DPnSider

Well, I remembered on 3.4, there is that feature that automatically logs changes and saves the old tunes, and I opened up the original tune I pulled from the car and compared it to stock, and the VVE constants and MAF curves didn't match. Was definitely not on a stock tune.

The emissions were all still turned on.

I'm betting on a box tune like hypertech

BlindSpot

Only thing is - all of these "Kiddie Tuners (Kiddie tooners)" - Hypertech, Diablosport, SCT, etc, don't really do much in canned tunes. They cannot, with any degree of accuracy, "can" program fueling.

All they do is bump the high octane table up a couple of degrees, maybe relax some torque management and same with the auto trans settings. They'll call these 91 Octane tunes, or 93 octane tunes. Users are going to feel more in their butt dynos especially on a colder/crisper day (when we all feel it), and the tune is safe, BC of the knock sensors.

How were the spark tables?

schpenxel

How were you checking fuel pressure? If you were just logging the PID for fuel pressure then you weren't getting a real reading.

Regardless, sounds like you have it more in the ballpark now. I'd still pull a stock tune for that year from the repository and see how it compares

DPnSider

The spark was a little advanced. The low octane table wasn't touched, but the high octane table was. It was mostly more advanced in the midrange. Same high RPM values (>5000) as the stock tune I pulled to compare.

I used a mechanical gauge to verify fuel pressure. It's easy enough and accessible and leaves no question. I'll do the same with oil pressure if it ever looks squirrely too.

schpenxel

Good deal, just making sure. A lot of people think it's a real reading and think their fuel pressure is REALLLLY steady

DPnSider

LOL - yeah, no. I've seen similar crap though. If someone is handy, I'll have them rev while I look at the gauge and make sure it's holding