Kalevi

I installed long OBX tube headers, no cats, and disconnected the rear O2 sensors. The LTFT was reading down to -17.2%. Is this normal? I haven't let the engine warm up yet but I want to make sure the engine isn't running too lean to begin with.

NOTE: I bought HP Tuners during the install of the headers so I do not have any idea what it was before.

Mike's LS3

It's running rich in closed loop (cruise or idle) and the computer is pulling fuel. Ideally, + or - 5% on the LTFT. At wide open throttle, you need a wide band to read air fuel ratio. With the addition of headers, I recommend a tune.

phils C5 vette

Matt. I answered your Email, but I thought you were talking about the Camaro not the corvette. HP Tuners 3.0 can be a little tough to set up when you first get it, but Ill take care of the Corvette when the build is finished.

From the screen shoot its a little tough to determine of you were coming off the throttle coming to a stop which would effect the trims

Phil

schpenxel

It's fine for part throttle/riding around. It just means the air model is off by 17% in that spot so it's subtracting 17% of the fuel it would otherwise inject to get you back to stoich.

Not ideal but not going to hurt anything.

It's actually off closer to 27%.. STFT's are in the -10% range too.

Unreal

But he didn't' even let the car warm up, so data is kind of useless. Let it warm up, drive around, collect data. Logging while it warms up doesn't tell you much of anything as LTFT don't even kick in until a certain ECT.

schpenxel

That too

Mike's LS3

Looks like his ECT's were at 147*F. Usually, you see LTFT kick in around 100*F. But, yes logging is more accurate once the engine warms up.

Unreal

Even so, 60 seconds from 100 to 147 isn't enough time for LTFTs to properly adjust. Probably just looking at the LTFTS from before the header install.

Kalevi

Hi Guys,

Thanks for the input on this. I had the car sent to the dealership due to the ABS/ASM/TC system not working. Turns out I managed to over look connecting the alternator battery feed cable so the car was running off a near dead battery the whole time; which would explain why the battery wouldn't charge.

I'm going to have the car sent over to the exhaust shop to get the cats installed (Flowmaster 2230130 223 Series) as well as the rear O2 sensors. I would do it myself, but I need to have the header flange modified to accommodate the cats and I can't do that in my garage due to lack of a cutting torch and welding machine. That should all be done by the end of the week.

None of the dealerships keep the rear O2 sensors in stock in Central Florida apparently so they are pulling them from their warehouse which should arrive tomorrow.

Which me luck!! I'll post when I have an update.

Cheers,
-Kalevi

Kalevi

Apologies for the extreme delay in updating.

Since the last post, it was found that the problem with ABS/ASM/TC was due to low voltage as a result of failing to connect the battery charge cable after the header install (Don Mealey Chevrolet was kind enough not to charge me for the embarrassing mistake). The cats were installed by S&G Exhaust.

The issue with the high fuel trims was due to an inaccurate MAF table. Once the table was adjusted, everything stabilized.

Cheers,
-Kalevi

P.S. @phils_C5_vette: You were right, tuning engines is easy given my background in engineering. I've been studying HARD swallowing the information from my books (and I need more) and testing. Not as big of a learning curve as I thought. The only struggle so far is reverse engineering GM's algorithms.