I will start with the obvious - I am very new to this and trying to learn, any advice is much appreciated!
Car is 2005 Corvette C6 MN6 with E40 ECU. It has Halltech CAI, Ported TB, Fast 92, Kooks headers, sports cats x pipe.
I have owned the car for 10 years now, 5 in the USA and 5 back over here in the UK since leaving the military. It had 60k on the clock when I purchased it and now has 115k, mods plus a tune were done by previous owners. It drove great the whole time in the USA both as a daily and doing approx 8 HPDE events a year. Some months before returning it failed two o2 sensors in quick succession (months) and began running/smelling a bit rich.
- Shipped car back to UK 2015 -
UK emissions is far more strict than Nevada! It just made it through its inspection (wink wink) despite having a high measurement on the HC, I was told at the time this was likely due to the tune or the CATS being done. I have taken it upon myself since then to try to get the car to pass completely unaided - up to this point the car still drove as it always had and with hindsight I probably should have left well alone
I started with the simple stuff and got both cats replaced for new - this made no difference at all.
I found a tuner here in the UK who is very reputable but he is quite some distance away. I made the trip to him several hours away and had the car tuned, it initially felt very good but over time I then began having issues. Knowing what I now know about tuning I can see how it was probably totally unreasonable to expect much given the time constraints that day.
The car is now almost exclusively used as a track toy despite keeping it road legal. Finally onto the actual problem...
Some weeks after the tune I was on the way to my local circuit cruising on the highway when I realised the 'throttle' was behaving very strange to what I was used to. When coming off the throttle it seemed like it wasn't fully closing, like cruise control, the revs were decaying much slower than I had previously been used to. It would then begin shunting like the throttle was being lightly pulsed. At the track, although pulling very strong I was finding it harder than usual to achieve a smooth gear change, it was like the throttle/rpm wasn't behaving as normal. I had owned the car nearly 6 years with maybe 30 - 40 track days at this point.
Additionally I was killing O2 sensors every few hundred miles. I spoke back and forth with the chap who tuned the car and he was obviously happy for me to head back down but it was so impractical I began the process I am in now. Firstly I found out that the car had the mother of all Vacuum leaks which I attended to. At the same time I had the injectors serviced and tested and they came back with a clean bill of health as a nicely matched set, no leaks and all within spec.
Lot's of time passes between me being able to do anything with the car as we are also self renovating our house plus winter is a big no no over this way. So it's been a slow process but I purchased HP tuners about a year ago and have been reading and learning as much as possible. I had in fact been reading and learning for about ten years but never considered i'd be having a go at the Vette as a starting point!
I have managed to dial in the fuelling to enable the car to pass emissions all on its own yay! Also, I haven't replaced an O2 sensor for over a year now, I think generally it runs better, the cruise shunt is much more reduced but I have this major pita problem which when trying to drive on the limit is really ruining my enjoyment on track.
Basically, when rolling back into the throttle it acts like a bit of an on/off switch and shunts the car a little. If you have done road course work you'll know what I mean, when you are cornering hard, rolling back into the throttle, trying to be smooth and it is like you go from zero to 10% throttle in an instant it really upsets the balance of the car. I find I am sub consciously driving around the issue which again, I would go as far as saying now it is ruining my day!! It does also still seem to hang the RPMs/cruise a bit but not as badly.
Is it my idle air? Throttle follower? Timing? Please give me a push in a direction or two that I can try.
I am bound to have missed something or other but I reckon that is enough for now lol, if you need any more specific info or need me to log anything just say and i'll get to it right away. This is now getting to the top of the priority list, the patio can wait...
Cheers
Ritch
testrundemo.hplFor the Track2.hpt
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Originally Posted by Hib Halverson
