Have an issue that I cannot seem to find any information on. My car will not run past 140mph. Will redline in 1st, 2nd, 3rd, and in 4th it gets to 140 and just sputters and will not pull anymore, just falls flat. Tuner said tune is fine, he thinks maybe valve springs, but why wouldn't that affect it anywhere else? Traction is off, active handling is off. It feels like there's a governor on the fricken thing, but that makes zero sense. 2011 GS Auto, A&A, long tubes, meth, 20k miles, stock internals I was told but it does sound like it has a slight cam at idle so not real sure on that one. Plugs and wires were replaced with no change

 

What is the RPM when this happens in 4th? What happens when you put it in 5th?

 

4500ish. Hnmm, haven't gone to 5th to see what that does

 

With the GS manual trans, 140mph is probably going to be towards the top of 4th, prob 6k rpm or so

 

It's an auto, and far from 6k in 4th. It's like the damn thing is governed around 140

 

If you have a scan tool or can get your hands one one I’d be looking at your O2’s and fuel trims, MAP and MAF sensor to see what you have when the car falls flat.

 

have you looked at the tune? Maybe it does had a speed limiter programmed in.

 

Look for error codes for those?

 

I'll have to ask the tuner if that's something he can look at. I just bought it in June and took to tuner in August. He said tune was fine on his end

 

OP says tune looks fine.

 

No, I’d be looking at live data during the drive…you would not want to see your O2’s going lean (well below 450mv’s) and fuel trims going positive….if fuel trims are increasing it may be a fuel delivery or MAF sensor issue…MAP voltage should also be increasing under load…you would want to look at as many inputs as possible…if the scan tool has a graphing feature you could look at a few of those inputs on one screen.

 

OP said tuner said tune looks fine. This is out of my realm, hence my questioning lol

 

Yes, there are speed limiters for different reasons, There is one at 158 mph with an A6 and a 2.56 rear gear with stock size rubber. Not knowing the RPM when you were at 140 in 4th or the rear gear or tire size makes it impossible to calculate backwards to find a cause. Try leaving the TC and AH on and don't paddle shift, then turn TC off if it hits a wall at 140.
Since you bought the car in this condition, you probably don't know all the mods. So unless you can contact the previous owner, you need to learn what is still stock and what/how it has been modded.
Have your tuner look at the transmission shift points, both upshift and downshift.
BTW, Do you also have mag shocks?
Report all mods and data back here, so a cause can be narrowed to strong possibilities, vs a WAG.

 

Waiting to hear back from original owner and his tuner. In the meantime...140 in 4th was around 5-5200ish. Tire size is 335/25/20. I did go and have a code scan done today and it showed a P0174 (fuel trim system, lean bank 2). If that can have anything to do with it?

 

Yes, it may have something to do with it…as I had mentioned look at your fuel trims and O2’s under load at the speed it starts to lose power…if those fuel trims go positive (you already have a P0174 and may have elevated fuel trims on the other bank that haven’t set a P0171) you may have a MAF (if not speed density tuned) or fuel delivery issue…you should be looking at live data with a scan tool while your driving to see what’s going on.

 

Just an opinion here, but since you bought a more than average modded car, you need to spend a little money and a LOT of time learning how to care for it. I'd suggest that you buy the HP Tuner programming setup, which comes with 8 credits and then use your personal laptop to download the current tune. Then you can save live scanned data as it happens, to see where the problems exist. Even if you don't make any changes yourself (not suggested until you fully understand how it works), having the info available for a competent tuner to review, means less time to test and no extra cost to buy/pay for credits every time a different tuner needs to inspect the tune. Documenting road and track data is better than dyno data, since you don't drive the car on a dyno.

 

Being new to this world, and not trying to be a smartass, isn't this what I'm paying the tuner for? Maybe he doesn't really know what he's doing? He road tested the car, and came back with the thought that the valve springs were bad. Buying the hp tuner setup wouldn't be a big deal, but why am I buying a tool for him to get data that he should be able to get. Maybe I'm off base here. But, like I said it's all new to me. I am enjoying learning what I have so far with info and suggestions I've been given. But I'm also genuinely curious what his job is. The tune costs a lot to not have it correct when it leaves

 

Tune may be fine, if you got a code you could have another issue causing it. Dont panic its usually something simple

 

Not all tuners work the same way, nor are all the cars equipped identical. But one thing is for sure, that each tuner will charge a minimum fee, even if they do nothing, because they have to buy a credit from the software company, just to look at your tune.. If the tuner guy you said road tested your car, was the same one who tuned the car before you bought it, then he didn't "need" to charge you to look at the tune he already did, since it was already in his computer. The point I'm making, is that if you buy the software system and download the tune to your laptop, then you have control of the tune, no matter who does the tuning.
I'm not saying the tuner did a good or bad job, but it you go to a different tuner for updates if you change parts or fuel, you'll already have the tune in your computer and you won't need to pay the tuner for a credit.
You'll also have the ability to do scans yourself vs needing the tuner to drive the car, who might not drive it the way you do.

Kinda look at it as if a tire dealer used his brand of locking lugnuts when you bought tires. Then the next time you decide to buy tires from someone else. The new guy would cut the old lugnuts off and put on his brand of locking lugnuts Now you paid for two sets of lugnuts and still can't rotate your own tires, because you lack the tool. However, if you bought your own locking lugnuts and the special tool, you could then let any tire dealer use your tool.

When I bought my C6, I had a supposedly top traveling tuner do the first tune. He put in a tune that blew the engine and claimed it wasn't his fault. Then when I had another tuner tune the new engine, I bought the system and eventually learned to tweak the tune to get the best results whenever I made any new mods.

You already have a problem and it sounds like you don't trust the current tuner either. All I'm suggesting, is to protect yourself with control and save a few bucks in the future.

 

If you have or can get a copy, post your tune.