Hesitation/missing during acceleration

[yooper_bob]

Wanted to find out if anybody has had the same problem on their GT as I have been having. When accelerating (especially w/ the A/C on), I feel some hesitation / flat spots in the power delivery from 4000 to 6000 rpm. Most noticable with medium throttle. i had noticed it right after delivery from the dealer, but started a road trip so couldn't bring it right back. Thought maybe they had filled it up w/ regular unlead, but the condtion persists even after a few tanks of premium and 3500 mi. I do notice a lot of soot inside the tailpipe as well - figured it is running rich. but have not triggered any check engine lights. Just brought it in for an oil change and had the dealer test drive it (w/o me) and couldn't duplicate the problem. Any ideas?BobMonotone Shadow GT Moon & Tunes

[NSimkins]

quote:Just brought it in for an oil change and had the dealer test drive it (w/o me) and couldn't duplicate the problem. Any ideas?Well if you can consistently reproduce the problem, take the vehicle back to the dealership and insist that you drive someone from their service department so both of you can reproduce and verify the problem you state exists.No matter what your problem may be (now or in the future), always personally recreate the issue with a service department employee before leaving so you don't get the usual "Could Not Replicate" response.Hope you resolve your issue successfully.

[d_m_kolb]

What grade of fuel are you using?

[yooper_bob]

I've been using premium unleaded (92 octane). The next time I bring it back to the dealer, I will definitely be with them during the road test. ThanksBob

[d_m_kolb]

What brand of fuel? I have heard BP fuel does terrible things to your engine. I'll only use Cheveron. I have never had a problem with there fuel plus it's got the tecron all ready in it to help keep your engine clean. It could have been you just got some crappy gas. Or water was in the fuel. This is a warning for everyone. Never buy gas from a gas station while a fuel truck is there filling the gas stations tanks! The reason being even the best gas stations have water in there gas tanks. It's hard to keep water out because the tanks are under ground. When the trucks fill up the tanks it mixes the water and the fuel so you'll end up with water in your car gas tank.Here's how it works. Water is lighter than fuel so it sits on top of the gas. The gas is sucked from the bottom of the tank at the gas station. Well if the fuel truck is there filling up chances are the gas station fuel tank in the ground is under 1/3 tank. That means the water is that much closer to the suction hose. So when the fuel starts to flow in from the top of the tank and splash at the bottom, the water gets mixed with it and anyone filling up gets some water in with there gas.So if a fuel truck is at the station you fill up at and is filling the tanks or just filled the tanks you should fill up at a later time.

[yooper_bob]

I really don't think it is bad gas. It has been an annoyance ever since I picked it up. I usually fill up at Mobil with Shell as a backup. No Chevrons here in MI though. Does seem to be a lot worse during hot & humid days, though. thanksbob

[vibb]

Before I bought my Vibe, I drove several Vibe/Matrix demonstrators. A Vibe GT 6 speed and a Matrix XR automatic were memorable in terms of strange acceleration characteristics.The Vibe accelerated sluggishly like it was starved for fuel until RPMs were above 4000, after which I had to back off the gas pedal when a surge of power came on. At the time I considered this to be part of the character of the GT.The Matrix, on the other hand had a strange half second lag just before an (automatic) upshift, as if the fuel was cut off and then back on after the shift completed, even if your foot was steady on the gas. After the shift, it seemed to starve for fuel until you pushed down harder on the gas. In both cases, the demo cars' guages were around 1/8 of a tank and their low fuel indicators were lit, which may have contributed to this.
[Modified by vibb, 9:01 AM 7/24/2002]

[shadowGT]

I have noticed the same sort of hesitation, mostly when the engine is cold. Once it warms up it seems to be fine. Another time I notice it is just before the 2nd cam kicks in.