Misfire Problem! Options

[nutria1007]

Hi all~

Recently(about 6 months), I changed my fuel grade from regular to premium(because of more high milage 16 mpg to 20 mpg). Since then I had problem which was misfire. It seems like every 1000mi show misfire. The dealer upgrade the computer system two times and so on. However, it keeps showing misfire.(4 times already)
Is there any correlation between fuel changing and misfiring?

I'm seriously thinking about changing a car.

by the way, I have 2007 SE AWD

Thank you

[absolutly]

How is it "showing misfire"? Check engine light?

[nutria1007]

How is it "showing misfire"? Check engine light?

misfiring sign is "flashing the check engine light" several times and stay on.

also, you can feel the car wasn't accelerate correctly. (Have you ever drive manual car? if you have, it feels like when you stop the car without shifting the gear to neutral position)

[nutria1007]

update my situation~

Finally, the dealer changed oxygen sensor. It took 3 hours in the dealer shop.(I was going to crazy!) And they asked me to change break pad for another 2 h!!!

I didn't change that.

anyway, I will keep check the misfire problem. see you after 2000 mi.

Have a nice day all~

[absolutly]

update my situation~

Finally, the dealer changed oxygen sensor. It took 3 hours in the dealer shop.(I was going to crazy!) And they asked me to change break pad for another 2 h!!!

I didn't change that.

anyway, I will keep check the misfire problem. see you after 2000 mi.

Have a nice day all~

Isn't that on the air intake? Not sure if that would cause a misfire, but I guess anythings possible these days with all the computer controlled engines

[WOT]

Isn't that on the air intake?

MAF (Mass Air Flow) sensor is on the intake. O2 (Oxygen) sensors are on the exhaust.

[yoshtov]

Upgrading from regular to premium should NOT cause misfiring. If anything, it should be the other way around. Since premium (97 octane) has a higher resistance to knocking, the misfiring isn't likely to be due to the octane rating.

It's a long shot, but what brand of gasoline do you use? Long term use of low quality gasoline can contribute to carbon buildups.

Which cylinder is the computer reporting a misfire from? Bring the car to your local Autozone and have them do a DTC scan. Typically misfires are isolated to either one or two cylinders. Once they have identified the problem cylinder, have a look at the spark plug on that cylinder. The condition of the tip goes a long way towards telling what is going on inside the cylinder. Do a google search to identify what a normal and abnormal tip looks like.

Run a fuel injector cleaner through the system, just to be safe.

Have someone brake-torque the car while you watch under the hood. Have them forcefully apply the brake while gradually applying the accelerator. If there are any backfires, you are that much closer to identifying where the problem is originating from.

Hope this helps!

[papopo]

my neighbor had told me in the past switching octanes is not healthy for a vehicle,. he is a Ford mechanic....if it calls for 87 octane use 87. There is no way you are going to get a 4mpg improvement by going with higher octane gas....

[WOT]

my neighbor had told me in the past switching octanes is not healthy for a vehicle,. he is a Ford mechanic....if it calls for 87 octane use 87. There is no way you are going to get a 4mpg improvement by going with higher octane gas....

I can see how using a lower octane fuel in a vehicle which requires higher octane fuel (a high compression engine) could result in performance degradation (knock); however, I wouldn't see how running higher octane fuel in a vehicle which can run lower octane fuel would harm the engine--but it doesn't really help it, either. The octane rating of gasoline is simply a measure of how much the fuel can be compressed before it ignites by itself. If you use a gasoline which is designed for a high compression engine in a lower compression engine it should have no real effect unless the engine already has issues with knock. The higher the octane, the higher the ignition point. What was your neighbor's reason for believing that switching octanes is harmful to an engine?

Reference:
http://auto.howstuffworks.com/fuel-efficie.../question90.htm
http://en.wikipedia.org/wiki/Octane_rating

[papopo]

He siad higher octane causes the engine to run hotter...in the long term heat+engine is not a good thing if the higher octane fuel is not required

This post has been edited by papopo: Aug 5 2009, 09:23 PM

[HyundaiTechDood]

bump (IMG:style_emoticons/default/biggrin.gif)

you did the right thing theres a tsb involving misfires and a certain 02 sensor and reprogram involving anything with a lambda motor under the hood.

shouldnt have a problem now.

[WOT]

He siad higher octane causes the engine to run hotter...in the long term heat+engine is not a good thing if the higher octane fuel is not required

I know that the higher the octane, the higher the compression can be before it will spontaneously combust, but I've never heard of it causing the engine to "run hotter". (I'm not necessarily saying that it's not true--I'm just saying that I've never heard that before.) The Owner's Manual for my 2007 states, "Your new vehicle is designed to use only unleaded fuel having a pump octane number ((R+M)/2) of 87 or higher. For improved vehicle performance, premium unleaded fuel with a Pump Octane Rating of 91 (Research Octane Number 95) or higher is recommended." If the higher octane fuel was bad for your engine, I doubt that the Owner's Manual would recommend it.

[Volfy]

This problem has nothing to do with octane rating. Veracruz, like most cars these days, is equipped with knock sensors and will adapt to gasoline with varying octane ratings.

There is a TSB # 08-FL-002-1 on this misfire problem. It is caused by a faulty Oxygen sensor - one of the two front O2 sensors.

My '07 VC hesitated briefly on the highway going 65mph or so. The check engine light immediately started flashing. It kept flashing until I turned off the ignition. On restart, the check engine light stay ON constantly. Later, it hesitated again, also while going at 65mph or so. The check engine light started flashing again.

I brought the car to the Hyundai service dept. After a day or so, they called and told me my car was ready and there were no code. YEAH RIGHT! I know this because I have an Autotap OBDII Diagnostic software installed on my laptop and I pulled the DTC codes, which were:

P0300 - Random/Multiple cylinder misfire detected
P2A00 - O2 sensor circuit range/performance (Bank 1 sensor 1)

According to the Hyundai TSB, the DTC could also show up as P0306, and/or one of several O2 sensor fault codes.

Anyhow, I will give the dealer service the benefit of the doubt this time. If it happens again, I am going in with a printout of my DTC codes, and a copy of the TSB - and I'll make sure the service mgr gets an earful. (IMG:style_emoticons/default/devil.gif) I didn't want to do it the first time, since I didn't want them to feel like I am being pushy.

[Volfy]

Here is the the TSB# 08-FL-002-1, if anybody is interested.

There is also another TSB# 09-FL-004 that refers to the same DTC codes P0300-P0306: Cylinder Misfire Detected. But it talks about a specific knock adaption related issue that causes false misfire detection. In my case, there definitely WAS misfire, so I am not sure this TSB applies. Anyhow, This TSB covers more than just the Veracruz and the fix is updating the ECM software.

Attached File(s)

 08_FL_002_1pdf.pdf ( 103.21K ) Number of downloads: 6
 09_FL_004.pdf ( 1.33MB ) Number of downloads: 5

 

[Volfy]

Yap! Sure enough, it happened again on my way to lunch. This time it lasted quite a bit longer, which is kinda scary. Engine started stuttering, RPM dropped, and no throttle response. After about 10-15sec later, it went back to normal. Still, that seemed like an eternity when you are on a Houston tollway in heavy traffic.

Brought it back to the dealer service, with DTC code summary and TSBs printouts in hand. This time I got the service guy's attention. He brought in a service tech and had a lengthy chat with him. They were surprised how much "homework" I did. I asked for a loaner car, been that it's the second time I had to bring it in for the same problem, but no dice. However, the manager did order a shuttle to drive me back to the office, so that's good enough for me.

We'll see what they can figure out this time...

[Volfy]

... Update on the dealer service visit.

This time they fixed it right. They changed the offending front O2 sensor - exactly as the TSB suggests. It has been a couple of hundred miles since, with no reoccurence.

They didn't mention they updated the ECM software, but I suspect that was done also. Don't know if it is related, but I noticed the automatic headlights come on a bit differently than before. They used to be a bit more sensitive before, with shorter delay before triggering ON or OFF. Now they seems to stay on much longer before shutting off. I prefer the new logic, as I plan to install HID conversion and would rather they don't turn on/off too often.