Daily Driver Problems

[Anthony]

You can jump down to the bold part if you don't want all the details, but there could be something vital in the details, as this is a complete mystery to me.

I bought my Tiburon used with 10k miles on it in 2006. Sometime between 50k and 60k miles, I began to notice that it would randomly have almost no ability to accelerate over 3,000 RPMs. For example, if I was turning onto a highway from a stop, it would sputter and shake in first trying to get rolling, then act nice until I got to about 3,000 RPMs. I could floor it and it would slowly creep its way up to 4k, then 5k. Shifting up didn’t change anything.

As randomly as the problem would appear, it would go away. I could be in 3rd gear, sputtering and creeping my way up to 45mph, and it would suddenly go away, rocketing the car forward like all four of my imaginary turbos suddenly spooled up. Many accidental rolling burnouts were done in 1st and 2nd gears.

At first I thought it was bad gas, so I switched gas stations. That seemed to work at first, but I think it was either a coincidence, or it liked the new gas a little bit better, so it just didn’t act up as often.

After it started acting up often again, even on the new gas, I replaced the plugs and coils. Didn’t help. So I brought it to my cousin who owns a mechanic shop. He said one of my three cats was missing. The previous owner had obviously knocked it out. He said one of my two remaining ones was very dirty.

So that’s when I bought the headers and exhaust. While installing them, I drove the car down to the first stop sign nearby with open downpipes just to hear how it sounded. I’m glad I did this because I immediately learned that this exaggerated the problem four fold. The car would hardly accelerate at all and it felt like its peak horsepower was probably about 60hp. It normally has about 150hp.

I finished installing the new headers and exhaust and reset the ECU. Ever since installing the headers and exhaust, any time I reset the ECU the car drives like garbage for a day or so. After about 100 miles and decent amount of idling, the ECU kind of figures out what’s going on and it runs normally, but the old problem still surfaces randomly.

So then I brought it to the Hyundai dealership. They pretty much charged me $92 to Sea Foam it. It seemed to be working, so I accepted it. Then a few days later it did it again. I’ve since Sea Foamed it myself, and it does seem to help, but not much.

Once a new gas station opened nearby, I started putting ethanol-free 87 in it. That actually made the problem go away completely for at least a month, maybe two! The check engine light went away and everything. It eventually started doing the thing again, but much less drastically than ever before and less often.

This past winter, the car became particularly sensitive to cold starts. A few times it even failed to start first try, but always would start the second try. I’d have to let it settle down to its regular idle speed before taking off or it would sputter and jerk disturbingly hard and sometimes even stall out. Since then, even on warm days it’s best to let it fully calm down before taking off.

Nowadays it’s been running reliably otherwise, but if I let it go a few days without cranking it, it would behave the same way as it does in cold weather, even on a hot day. When I deployed, I told my girlfriend to start it once a week, letting it run for at least 7 minutes, and every other time she started it to take it around the block. She didn’t stick to the schedule and it went all to shit, but now I realize I probably should have told her to crank it every day and drive around the block 2 or 3 times per week anyway. Also, I left it with very little gas in it. I wasn’t sure if it would be better to leave it with a lot of gas to prevent humidity build up in the tank or leave it with little gas to minimize the amount of eventually-old gas in it. I’ve been told modern gas tanks are pretty resistant to allowing humidity inside, so I went with the small-amount-of-gas option. What I left in it was ethanol-free though, so I’m not sure how much longer it will last than the 10% stuff.

My girlfriend admitted she let it go for like 3 weeks without cranking it, then took it for a drive. She said she got scared about 2 miles from home because it seemed like it was going to stall out and die coming from a stop sign. After that I reminded her of the schedule I told her to stick to and told her to start cranking it every day. So she's been doing that, but as of yesterday, it doesn't even crank anymore.

So I’ve learned:

- Better fuel makes it run better

- Sea Foam helps marginally

- Less exhaust back pressure makes it run worse

- A fresh ECU runs terribly, but the car runs better as the ECU learns

- It often smells like it’s running rich

- It always throws a CEL which seems to always be the same one, indicating misfires

Which leads me to believe it most likely is something to do with the combustion process, whether it be bad air to fuel ratios, faulty O2 sensors, a retarded ECU, fuel filter, fuel pump, or something along those lines.

Also a possible contributing factor is that I need new gaskets from the header gaskets, back. I certainly have at least one exhaust leak because of that, but the problem began back when the gaskets were in great shape, so that isn’t the cause of the problem. I plan on replacing them as soon as I get back, but I just discovered how bad they were right before I deployed.

So now I'm stuck halfway around the world feeling pretty helpless and stressed out about the possible major problem my car either has or will have soon. She's going to call the local mechanic tomorrow and if he isn't confident with it, I'll get it to the dealership somehow. In the meantime, I was hoping for some input from the forum. I posted this on the Tiburon forums already, but there are a lot more smart people here than there, so I figured it couldn't hurt to see what people think here.

[AlanLGuy]

Sound like bad Air-to-fuel ratios to me. I had extremely similar behavior in my toyota Celica when I had a bad 2nd bank oxygen sensor.

Does the car sputter on WOT? Usually oxygen sensor readings are disregarded for AFR on full throttle so an indication of a bad sensor would be sputtering on non-WOT but running smoothly during WOT acceleration.

If it does sputter on WOT its still probably an AFR issue, but probably not related to the catalytic converter or oxygen sensors

[AlanLGuy]

Re-reading the thread I doubt it's related to the oxygen sensor.

Do you have an aftermarket intake?

A few idea I'd throw out there:

A bad vacuum link in the intake/evaporate system though this may be unlikely if it idles smoothly.

Bad fuel injectors causing the system to run far too rich.

I would bet the catalytic converter being destroyed was a symptom of the issue rather than the cause. A system running way too rich can kill a catalytic converter very quickly.

[Anthony]

If it's doing the problem, it'll typically start around 3k RPMs. At this point, I can give it WOT which usually causes the car to jump and shake. If I don't floor it, it just drags ass until it decides it doesn't want to be an asshole anymore and it starts working. Under WOT at low RPMs, it'll jump and shake for a while, but once it gets to like 6k or so, it usually stops right away if I'm giving it WOT, and proceeds smoothly up to the rev limiter.

So... how does the computer decide to disregard O2 readings? If it's based on only the throttle itself, then the answer to your question would be yes, it does shake under WOT. But if it's based on AFR and/or RPMs, then maybe not.

[Anthony]

Originally Posted by AlanLGuy

Re-reading the thread I doubt it's related to the oxygen sensor.

Do you have an aftermarket intake?

A few idea I'd throw out there:

A bad vacuum link in the intake/evaporate system though this may be unlikely if it idles smoothly.

Bad fuel injectors causing the system to run far too rich.

I would bet the catalytic converter being destroyed was a symptom of the issue rather than the cause. A system running way too rich can kill a catalytic converter very quickly.

Yes, the car came with a "short ram intake" in the form of an AEM cone filter plugged onto the factory plastic intake piping. That's what it had when the problem started. When I bought the headers and exhaust, I also bought an actual AEM cold air intake.

And yes, I thought the same thing about the catalytic converter too. He described it as being dirty, though. Like actual dirt made it all the way there to just hang out. I'll have to ask him about it again, see if he remembers.

[Rayme]

Doesn't sound like a o2 sensor problem, I'd suggest looking for a vacuum leak and cleaning MAF sensor before trying anything else. (if the tirburon has one).

The MAF sensor and coolant temp sensor have a much bigger effect on the overall A/F ratio than the o2 sensors.

[AlanLGuy]

What CEL codes are you receiving?

[Anthony]

Is there something I can do in the meantime to get it to crank up so she can get back to cranking and driving it regularly? Maybe some sort of fuel additive or maybe just some fresh gas?

[Anthony]

Originally Posted by AlanLGuy

What CEL codes are you receiving?

I don't know, but the last 5 times I checked it was misfires every time. All over the place too. It's the V6 version.

[Rayme]

At this point driving the car more will more than likely make it worst.

[AlanLGuy]

Really need those codes to know what's going on and where to look otherwise you are shooting blind.

Another good indication is if the misfires are coming from multiple cylinders or from a single cylinder everytime. This could point to a single injector having an issue, or a more general problem like a MAF sensor.

[dem00n]

We're sending you off to Autozone, go get those codes!

[AlanLGuy]

Originally Posted by Rayme

At this point driving the car more will more than likely make it worst.

I agree, if the car is misfiring you aren't doing any favors for your engine. For all we know your ECU is sensing the misfires and retarding the spark. Excessive knock is not good on an engine

[Anthony]

Originally Posted by AlanLGuy

Really need those codes to know what's going on and where to look otherwise you are shooting blind.

Another good indication is if the misfires are coming from multiple cylinders or from a single cylinder everytime. This could point to a single injector having an issue, or a more general problem like a MAF sensor.

They're all misfiring, that's what I meant by "all over the place" in my V6. Not just a single cylinder.

Originally Posted by dem00n

We're sending you off to Autozone, go get those codes!

I'm in the Middle East, and the car isn't running and is under the care of my girlfriend who has 0 car knowledge. If I was at home driving it, it would've never gotten to this point.