When I’m driving my Kia Sephia at speeds of 60 mph and abouve it seems like it sputters almost making me think that the car could die. It gets worse as I drive faster. I had problems with it twice now and I filled on gas to see if having a full gas tank makes any difference, but to no avail. When I drive at 55mph it drives perfectly normal. What could be wrong?
Off the bat? The fuel pump needs to be tested for pressure and volume.
also check fuel filter
And don’t rule out a clogged CAT converter.
Tell your mechanic to check the fuel pressure with the engine under load. Many mechanics just check the fuel pressure at idle. The problem you’re having isn’t at idle, is it?
The mechanic should: attach the fuel pressure gauge with a long fuel hose; run the engine, in DRIVE, at 2,000 rpm for three minuets, while observing the fuel pressure. The fuel pressure should hold within specifications. If not, your problem may be a weak fuel pump.
Auto Zone doesn’t show a fuel filter for your car. So, I assume it doesn’t have an external fuel filter (A poor design decision, in my opinion).
It would be a good idea for the mechanic to check the catalytic converter, as others advised.
All this assumes that the spark plugs are fairly recent, the air filter is clean, and other “tune up” items are up to date.
No the problem hasn’t been at idle so far. I was driving it on the freeway yesterday and now it “sputters” even if I’m only going 55 mph. Would a clogged catalytic converter need to be replaced with a new one?
Yes. There is no way to unclog a catalytic converter. Well, no way to do it so that it functions as designed, anyway.