2006 Kia Optima - low power on hills, passing

I have a 2006 Kia Optima, V6 2.7 liter automatic. 120k miles. Recently, it started losing power on hills–most noticeably on steep hills, and also doesn’t have the power to pass other cars, even on a flat road. What happens is, the car puts itself in 2nd gear, revs to 3000 rpms or so, but it’ll lose speed… when on a steep hill, dropping from, say, 45mph to as low as 20mph… all the while revving. (and of course it’s louder, and there’s a vibration noise from underneath the car, that seems to be partly in front, partly on the driver’s side… and when it gets at its worst, there’s a low, rumbling sort of vibration noise that seems to be somewhere at the back of the car). I’ve been told it’s acting like it has a retardation problem, in that there’s no torque. This is clearly not usual for the car, since it’s always been very powerful in passing and climbing situations. The check engine light was on when all this started happening. I took it to a Kia dealer, and they said the computer had spit out a number of codes–and they settled on the problem being an oxygen sensor. They replaced it… and the check engine light went out. However, before I even got the car home, it was back to experiencing the same problem (and the check engine light came on). Back to the dealer. They now said it was a knock sensor. This time I took the car to my regular mechanic (who doesn’t specialize in Kias). He agreed that the knock sensor(s) could cause this kind of retardation. So he replaced the knock sensors today, and in the process of doing so, discovered my plugs and wires badly needed changing–so he did that too. Now the car seems to have a bit more pep on flat roads—it accelerates more normally… but when I tried it on the same steep hill (same hill I’ve driven the car up the last 5 years) it experienced the same problem–no torque, put itself into 2nd gear, revved… no power. Managed the hill at a maximum of 40mph instead of 25 or 30mph… but I couldn’t get it up the hill any faster, even with the pedal to the floor. Everyone I talk to about this is stumped. I’m sure my mechanic will be tomorrow when I call to tell him. Can anyone here help? The car seems able to shift gears all right—and with the manual shifter on these cars (it’s the automatic with the shifter that can be manually moved from gear to gear, if you follow me) I’m able to shift gears okay.

Two things come to mind, but first, is the check engine light back on or did it stay off this time.

Fuel pump or fuel filter

clogged up catalytic converter

The light is still off… so far.

Are there codes for the fuel pump/filter, and catalytic converter? I would have thought there’d be a code for the converter, at least… anyway, if so, it seems they would have seen those codes when they hooked it up to the computer—it’s been hooked up at least twice now.

The car was doing it again this morning… could barely make it up the hill… and couldn’t accelerate even on a flat surface. Check engine light DID come back on, for about 3 or 4 minutes, then went off again. Still off.

Forgot to mention that my gas mileage has gone down a bit. From about 24mpg to 19-20mpg.

There are codes for the efficiency of the catalytic converter, but not for it being plugged up. As for fuel pressure, no. Usually low fuel pressure will result in misfires which do generate a code.

Your mechanic can check the cat by hooking up a vacuum meter. He can also check the fuel pump pressure.

There is a third option which I forgot, you could have a simple vacuum leak. Your mechanic should also be able to trace this with a visual/audio check and/or vacuum gauge. One thing you can do first is to check the operation of the doors in your heat/AC system. Simply turn the fan on high and check all the settings for floor, dash vent and defrost. Is the air being directed correctly for each setting. The reason for doing this is that the doors are vacuum operated and if the air isn’t being directed correctly, then the vacuum leak might be under the dash.

If they are working, that does not rule out a vacuum leak, it just eliminates the Heat/ac blend doors as the source.

Right now, I think the order of possibilities are vacuum leak, clogged fuel filter, bad fuel pump, bad fuel pressure regulator, and finally clogged cat ( or a potato stuffed up your tailpipe by some bored teenager(s)).

Thanks Keith… my mechanic now wants to try replacing the fuel filter.

So you’d place a clogged catalytic converter last, on the list of likely suspects? Any reason for that? Just curious.

Another thing, since your check engine light came on, even for a few minutes, try to get to an autoparts store that does free code checks. The code should store for at least 10 drive cycles, but on some cars, could disappear in as little as three.

Post the code here, it might provide a little more insight.

Your car is kind of new for that to occur, but if you have had a misfire for any length of time, it could happen. I would hope that your mechanic at least checked your fuel pressure before deciding to “try” the fuel filter.

You can also test the cat yourself. Just hold your hand over the exhaust pipe and have someone rev the engine momentarily. If you feel a good flow of exhaust pressure against your hand, the cat is not plugged. If you don’t feel a good flow of exhaust, look up the tail pipe with a flashlight and make sure you aren’t the target of some prankster.

If the fuel pressure is low or you have a vacuum leak, that may cause the engine to run lean, but not lean enough to cause a misfire. What you would notice is a loss of power. With a vacuum leak, the loss is usually across the board, but actually improves at low RPM and heavy throttle. A fuel delivery issue usually shows up at higher RPM and/or heavy load. Now I am leaning more toward the fuel system.

Thanks for all your help Keith. No, my mechanic hasn’t checked the fuel pressure yet. I only just spoke to him this morning to tell him that the problem hadn’t been fixed, and he suggested trying the fuel filter next. I forgot to ask if he’d checked the catalytic converter.

A different direction but could it also be a failing torque converter in the automatic?

He stated that it downshifted and the engine reved to 3k, that sounds normal to me. If the torque converter was the problem, I would expect the engine to rev to redline (5-6k). A second look at the tach under the conditions mentioned wouldn’t hurt though.

If the tach needle climbs up as the speed goes down, then you would be on to something.

Well, can you guys give me more info on the torque converter? I never heard of it. What would be some more symptoms, if it was bad or malfunctioning?

Today, my mechanic looked over the car again, and he’s going to do a fuel pressure test next, to rule out a fuel problem. He couldn’t find a fuel filter outside the gas tank, so presumably it’s inside–he said there does seem to be an access port. (Keep in mind, he’s a good, honest guy, just not a Kia specialist. I first took it to people who were supposed to be Kia specialists, and they were no help at all). Anyway, we saw no evidence that the catalytic converter was plugged—the converter wasn’t unusually hot and certainly wasn’t glowing, as you’d think it would be if it was clogged. On taking it out with me for a test drive though, he said it did seem to have every symptom of a clogged converter. But he first wants to do the fuel pressure test.

Particularly noticeable on hills—especially steep hills—the car does seem to rev higher as the speed drops.

Oh, and he hooked it up to the scanner, hoping that maybe a code had gotten stored this morning while the check engine light was briefly on—but no… no codes showed up. Check Engine light is still off.

The fuel pressure & cat issues should no longer be a question. The fact that they are still questions is a big problem. They should have been the first things checked. I am not a professional mechanic and if you pulled into my driveway I could tell you about both of them in less than 30 minutes. It takes a fuel pressure gauge & a vacuum gauge. Simple, basic tools. You don’t “try” fuel filters. You replace them on normal intervals just like air & oil filters. (Unless the only one is inside the tank). You also don’t look at a cat or try to not excess heat to find out if its clogged.

A good, honest guy or not - he might not be entirely competent. What I’m talking about here are incredibly basic and simple stuff - auto diagnosis 101.

Well yes, I’m not touting his competence. But on the other hand, if you read my original post, I first took it to a Kia dealer, and they supposedly hooked it up to a diagnostic computer, not just a scanner–and they knew exactly what it was doing—and their first inclination was to replace the O2 sensor. I would have thought they, of anyone, would have been able to diagnose this right from the start, given their tools and experience.

As I say, my mechanic IS going to do a fuel pressure test next. And he said the fuel filter does appear to be in the tank, though there seems to be an access port for it. And he has hooked the car up to a scanner, to read the codes—and no code ever appeared for the catalytic converter. There have been knock sensor codes (replaced) and codes indicating the spark plugs were bad (also replaced). And the O2 sensor of course. But none of these things have addressed the problem. He also wasn’t saying the cc is the problem, he just said, after driving it with me and experiencing it, that it acts most like a clogged cc.

Not defending him–I know he’s not the best, I simply trust him. But I also kind of think that if it were that simple, the Kia guys would have figured it out first. But they, and my mechanic, are not the only ones who’ve been stumped by this. I have a friend who’s a former mechanic, and he went through the same list of possibilities without being able to figure out exactly what it is.

But if NOT a fuel or exhaust/cc question–then what is it? What could be causing this? I’m getting frustrated by the mystery of it, and that no one can seem to figure it out.

I don’t ever think that a dealer is going to be a good place to go for reliable diagnosis. In fact, if I want diagnosis I will avoid a dealer. Most car problems aren’t “special” by brand and thus don’t require any specialized manufacturer’s knowledge. These days “hooking it up to a computer” is the most common thing that people do. It substitutes for real expertise and makes money. But the computers don’t “know” nearly as much as people give them credit for. They just provide data. Sometimes those data won’t actually tell you anything about problems. If & when they do they can’t do it by themselves. It still requires an experienced mechanic to interpret the data.

Dealership service departments are not in the business of fixing people’s car problems. They are in the business of making money. Obviously this should be so - its what businesses do. But it is meaningful as the one with a car problem. The way these places go about business is not geared toward your needs/finding and fixing your problems. Take your sensor replacements. They spend a minimum amount of time on a diagnostic fee, add on the cost of parts and labor and charge you a bunch of money to NOT fix the problem. Why would they do anything different from that?

Anyway, the point was not to say that you probably have a fuel pressure or cat problem. You might you might not. The point was just that given your symptoms these two things should have been eliminated as culprits immediately.

Your only problem is that the Kia dealer doesn’t give a rat’s tail about your car, and your guy doesn’t seem to take much of a systematic approach.

I’ll give ideas about what else it could be after three pieces of information: 1) confirmation that fuel pressure is within specs (including under load); 2) confirmation that the exhaust flows freely; 3) the list of codes that the Kia dealer pulled from the computer way back when.

cigroller: I certainly agree with you about dealers. In fact, the only reason I went there in the first place was because another local mechanic I’ve used from time to time recommended seeking a dealer out for this particular problem… they figured that the dealer had the diagnostic equipment that they didn’t have. But you’re right–it requires someone actually reading and interpreting the data. But they didn’t do that, they just decided to start replacing parts willy nilly.

As far as the mechanic I’m currently dealing with—as I say, nice guy, honest… but yeah, he’s not all that systematic. I’m seriously considering trying someone else. I’m making phone calls today.

As for three pieces of info you mention… he’s doing the fuel pressure check (and I’ll make sure a vacuum check as well) on Monday hopefully—if I can get it back in then. As to what codes the Kia Dealer encountered–I’ll have to look on the invoice they gave me–I’m not sure if they provided me with those.

Currently, the car is A) still exhibiting the bad behavior, and B) the check engine light has NOT come back on. It came on only for about 5 minutes yesterday morning… but then turned off and it hasn’t been back on since. And when my mechanic, Ed, hooked up the scanner to the car, no codes registered. So if the catalytic converter WAS clogged or malfunctioning, there should have been a code for that showing up, I’d think.

I’m assuming that there’s only two things this could be: a fuel problem, or an exhaust/vacuum problem. Am I wrong? Do you have any other thoughts? Given that there’s currently no codes showing up and the check engine light is off (yet the problem persists) does this mean that problem is elsewhere?

Oh… the gas mileage is also low… it’s dropped from about 24mpg (normal) to about 18/19 mpg.

And if this is a clue to anything (I’m not sure what it means, if anything) I noticed that my heater doesn’t seem to be working properly. I turned up the heat this morning, and the level of air blowing out seemed okay, but there was little heat. I had to crank it up to 80 degrees + to get it warm in the car—which is very unusual… this car always had a great heater.

Is this just a separate issue entirely, or would that signal some kind of vacuum problem? (I wouldn’t think so… if vacuum I’d think the temperature would be unaffected, but the airflow would be reduced—but what do I know?)

Ahhhh…a cool running car…that isn’t running well…and threw lots of codes that prompted O2 and knock sensors (as guesses) from a bunch of computer codes. How long has it been running cool? If you haven’t needed the heat you would know from the temp gauge on the dash. I’ll come back to this.

Ignoring any potential transmission issues, the car needs 4 things to make it run right: fuel + air (mixed together correctly) + compression + spark. The car will run poorly from issues with any of those. Exhaust blockage issues are related to the “air” part as are vacuum leaks. Its true that sometimes there are problems that will be picked up by sensors and the computer will report them as error codes. Treated properly those codes can lead one to find issues. But its also the case that the computer never has any direct knowledge of any of these things. The computer knows nothing of compression, for instance, no direct access to spark consistency or quality, no way to directly detect vacuum leaks or exhaust blockages.

So anyway, even when there are codes getting a read on the most basic, fundamental things is always a good starting point. Fuel pressure, vacuum leaks, compression, ignition system. (If your plugs happen to come back out compression should be checked while they are out, though its a good reason to pull them anyway).

The thing that does get tricky is that the computer is involved in holding all of the aspects of the process together. It is responsible, for example, for the fuel/air mix, sending ignition signals to the ignition coils. It is also partly responsible for engine timing. Its also the case that the computer does this via info its getting from sensors. Your front O2 sensor readings, for example, are a primary input for the fuel mixture (air/fuel ratio).

Anyway - another really important feedback to the computer on fuel/air mix is the coolant temp sensor. When you first start a cold car the computer produces a rich mixture (higher fuel). Its the same thing as a what the “choke” used to do on carbureted engines. The computer leaves the rich mixture in place until the car gets fully warmed up. Then it goes into what is called “closed loop” operation which has a much leaner mixture that is adjusted according to O2 sensor readings.

If your thermostat sticks open your car will remain too cool (and you won’t get much heat); the computer will never go to closed loop and you will continually run rich. This will kill your fuel economy. It can make the car run poorly. It can, given enough time, result in a clogged catalytic converter. It can produce codes about fuel mixes that people think come from bad O2 sensors (shooting the messenger).

Note that there are codes that SHOULD (or at least could) get set if your thermostat sticks open/car stays too cool for too long. But, as noted, computers are pretty dumb. I’ve come to see them as Carfax reports. If something shows up as a red flag you should probably pay attention. If nothing shows up don’t assume that there isn’t a problem.