Can my tune "change"
Thread Starter
Racer
Joined: Apr 2008
Posts: 265
Likes: 0
From: Wesley Chapel Florida
Can my tune "change"
My car 99 frc has ported 243's, ported ZO6 intake, tb, .600 plus comp cam, dynatech headers, magnaflow x-pipe and catback, puts down around 425 at the wheels. When these changes were made, and the tune was done, I wasn't completely happy with the tune but was told it was the best that could be done. The car varies the ilde rpm from 600 to 1100 frequently and after some heavy driving, it likes to stumble and I have to tap the gas to make it stay running from time to time. It didn't do that when I first had it tuned. Also, I am getting pinging at low rpm's lately, I haven't noticed them at higher rpm's but it might be there, and I have changed gas stations a couple times, and even added octane booster ONCE just to see if it helped, which it didn't. What should I do? The tune is about 10 months old, so I don't think the tuner will mess with it again, and for geography purposes I am in Tampa, Florida, and haven't changed anything on the car since the tune. Thanks for any ideas.
Pro
Joined: Mar 2004
Posts: 653
Likes: 0
The weather has changed since 10 months ago, and this includes things the PCM uses as inputs...intake air temperature being a big one.
Fuel blending also does predictable but strange things to my car's LTFTs up here in the Northeast, the extra oxygen in the Winter blends has my trims up ~5-8% across the board after a few weeks each year.
Are you running a Speed Density tune, with the MAF removed and the car running in Open Loop mode?
Fuel blending also does predictable but strange things to my car's LTFTs up here in the Northeast, the extra oxygen in the Winter blends has my trims up ~5-8% across the board after a few weeks each year.
Are you running a Speed Density tune, with the MAF removed and the car running in Open Loop mode?
Thread Starter
Racer
Joined: Apr 2008
Posts: 265
Likes: 0
From: Wesley Chapel Florida
No, it isn't a surge, the car wants to die with the a/c on after I drive it for a while. It will stumble quite noticeably to the point that I have to tap the gas to keep it running. Now, when I am driving just normally, the idle will stay at about 1400 rpm, then slowly ( and i do mean slowly) settle to the 650 rpm idle speed. Its almost embarassing to sit at a light and have to wait 10 - 15 seconds to settle down and rumble. Without the a/c on, none of these issues occur, except of course for the pinging.
Pro
Joined: Mar 2004
Posts: 653
Likes: 0
I'd get scan data on it, EFILive can read the stored LTFT table for all cells and this tells a good bit about the accuracy of the VE and/or MAF tables.
Comparing this table's values between left and right cylinder banks also gives some indication of injector performance, as an underflowing injector will often show up as a significant imbalance in the LTFT % between the two banks.
Comparing this table's values between left and right cylinder banks also gives some indication of injector performance, as an underflowing injector will often show up as a significant imbalance in the LTFT % between the two banks.
Corvette Stories
The Best of Corvette for Corvette Enthusiasts
Top 10 Most Expensive Corvettes Ever Sold on Bring A Trailer
Brett Foote
10 Things Every Corvette Owner Needs (2026 Edition)
Michael S. Palmer
8 Most "Only Corvette Owners Understand" Quirks and Problems
Pouria Savadkouei
10 Reasons the C6 Z06 is Still A Performance Benchmark After 20 Years
Joe Kucinski
How Much Horsepower Every Corvette Engine "LOST" in 1972
Joe Kucinski
Top 10 DOs and DON'Ts for Protecting Your Convertible Top!
Michael S. Palmer
Top 10 Most Explosive Corvettes Ever Made: Power-to-Weight Ratio Ranked!
Joe Kucinski
150 hp to 1,250 hp: Every Corvette Generation Compared by the Specs That Matter
Joe Kucinski
8 Coolest Corvette Pace Cars (and Replicas) of All Time
Verdad Gallardo
Former Vendor
Joined: Aug 2005
Posts: 16,897
Likes: 412
From: Lewisville TX
St. Jude Donor '03-'04-'05-'06-'07-'08-'09-'10-'11-'12-'13
Any trouble codes?
Are all sensors reading correctly?
Is it using the correct spark plugs and are all firing correctly?
Manifold or Vacuum leak?
Sounds more like the tune is not correct to begin with if all sensors are performing correctly, and nothing mechanically is wrong.
The tune is hard programmed into the car and does not get lost due to battery on or off. What will change is how the car learns it's fuel trims and idle settings. Think of it like installing windows (base tune) on your PC. Every time you power on and off your computer windows is always there. Now what you typed into Word (long term fuel trims) or some other program may not be there but the base program is.
Are all sensors reading correctly?
Is it using the correct spark plugs and are all firing correctly?
Manifold or Vacuum leak?
Sounds more like the tune is not correct to begin with if all sensors are performing correctly, and nothing mechanically is wrong.
The tune is hard programmed into the car and does not get lost due to battery on or off. What will change is how the car learns it's fuel trims and idle settings. Think of it like installing windows (base tune) on your PC. Every time you power on and off your computer windows is always there. Now what you typed into Word (long term fuel trims) or some other program may not be there but the base program is.