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Stumbles or hesitation at high speeds

1236 Views 13 Replies 6 Participants Last post by  Coupe14
Good evening everyone.
Driving the coupe A6
yesterday and did a high speed pass. Car was running strong then I noticed the car stumbled a few times right around 120-130mph. Drove car today and did same thing around same speed. At this speed I’m just at top of 4th gear. 1 through 3rd no hesitation throughout rpm range with foot to floor. Scanned car and no codes are stored no check engine light! Inspected belts everything looks good. Noticed that air filter wasn’t secured on end of elbow inside box so I snugged it up and retighten. Also I cleaned MAF sensor. Will do another high speed pass tomorrow! Anyone have any ideas
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I drove today and consistently it starts to brake up and hesitate at top of 4 gear around 120 mph. It hesitates the flattens out then hesitates back and fourth at the high speeds. I’m thinking maybe time for injectors or fuel pump. Car just had lower pulley and tune a couple months ago. But I remember now it did the hesitation once before the work was done.
Try gumout fuel injector cleaner, full bottle on a full tank, run it till 1/4 tank, refill and try the run again. also double check that ground screw under the air intake tube and the middle nut on the fuse panel in the trunk.
I suggest you log it with HP tuners, that should tell you if it’s fuel or spark related.

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Thanks family! I will do gum out this weekend and I’m taking to tuner next to scan everything! I scanned it with my obd2 and no codes so tuner should find out something
I would definitely do what Karch said and log. You could be getting massive knock retard due to detonation. If you have fuel or excessive timing problems you will run lean and detonate/possibly blow your engine. Logs will show this long before you feel it. I would not do another pull like that again until you see what is going on. Another thing to look out for is the boost limit settings in your tune. If it is hitting above the KPA specified or p0106 is not disabled the car will pull spark to lower the boost. If it detects excessive boost w p0106 the car will abruptly pull spark and go into a boost limp mode Also another thing to know is did this happen previously? It might be too that the cooler air has increased the amount of fuel needed or boost levels due to the density.

Also are you on stock injectors? What pulley size did you go with?
Yes stock injectors. Lower 18% pulley. I’m doing the injector cleaning now with the gum out but car is going to timer Monday! Also about boost limits I did notice the I’m hitting ( if stock gauge is correct) around 14 lbs of boost with lower pulley. But like I said it’s pulling same boost levels in 1,2,3 gear wot with no issues. Excuse me if this a dumb question but wouldn’t boost cut or lean fuel happen in those gear range at same rpm range?
Not necessarily. The amount of fuel you need is load dependent more so than RPM dependent. And for any given RPM, the lower the gear, the lighter the load on the motor and the less fuel it needs... maybe not a big difference if you're WOT in each gear, but there will be some difference...
You have an 18% overdriving pulley on stock injectors?

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In for the part out!
Yeah 9.17 pulley with balancer with stock injectors

I thought they would be good for power I’m making but maybe not
So guys here’s a update
Did fuel injector cleaner and car ran pretty good no stumbling or hesitation. But I think I’m having multiple issues. I noticed when fuel is low and it’s cold outside when i accelerate like we all do is when it starts to stumble. I always notice it at higher speeds(115-125). If I don’t go wot and just go 70% I can reach same high speeds with no hesitation. I’m thinking I need to upgrade the stock injectors. Car isn’t throwing any codes like I mentioned before so I don’t think injectors are bad just ain’t enough for demand. Car has air aid intake and bottom pulley 9.17 with tune. Talked to tuner and he said I was hitting speed limiter but these cars are around 175mph not 120mph. So I don’t know how much faith I have in tuner now. Now question is do I need to add bigger injectors and aux fuel pump or just injectors. Right now I’m not looking to go crazy power. I’m around 540-550 to wheels right now. Eventually like to be 600-650 range.
I don't believe there is a speed limiter. The car goes until it runs out of HP. That is around 190MPH if I recall.

Assuming my recollection is correct, I'd recommend a different Tuner. :)

You need to buy software and a OBD interface and log so you know what's going on and you're not guessing. Guessing will eventually fix it, for sure. But it's likely to be the more expensive route.
Ok thanks I’m a nubie with the hp tuners and software. As far as getting it hookup is no problem but knowing what to look for and reading is where I might have trouble! Or y’all can just call me a dumb ass! Lmaoooooo
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