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Discussion Starter #22
Not much goes wrong with a cat and they either are working or not. If they get too hot because of a rich mixture caused by a misfire they can melt or sometimes they just break apart and block the exhaust. If pouring the water on the sensor made it run right I would go ahead and replace it. If it doesn't fix the problem all you have done is spent a few dollars. 07-0.8 is a good reading in my books. The thing is is the O2 sensor output fluctuating?
Yes I agree, but I poured a lot of water with a garden hose on it and it didn't help at all.
I am attaching a graph of the sensors to see when the RPM is steady at a stop (in red circle) and it looks normal in the field you are writing too.
But when I start traveling (in black circle) the sensor after the converter monitors the sensor in front of the converter.
 

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the converter monitors the sensor in front of the converter.
Not sure what you mean. The rear O2 sensor is indicating the cats efficiency. The front O2 sensor should tell the story with fuel mix and a reading of 800mv under load is good. Isn't the problem only at idle?What manifold vacuum reading have you got at idle. You have checked for an air leak haven't you?
 

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Discussion Starter #24
Not sure what you mean. The rear O2 sensor is indicating the cats efficiency. The front O2 sensor should tell the story with fuel mix and a reading of 800mv under load is good. Isn't the problem only at idle?What manifold vacuum reading have you got at idle. You have checked for an air leak haven't you?
The problem is at idle but I read somewhere in the internet that if the rear sensor is followed by the front it means the cat is clogged so I thought this affect also to the idle problem, probably this isn't true.
Yes I checked with vaccum gauge and this is the link to the results
vaccum test
at 11 seconds you can see the idle problem in the gauge
 

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FWIW pouring water on magnetic pickup while hot can cause the magnet to crack and guess what. The car stalls and you say, 'Yeah, a crank sensor will fix it'.
 

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Yea I now remember the vacuum gauge. Try wiggling all the air fittings pipes etc with the vacuum gauge fitted looking for any sudden change.
 

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Discussion Starter #27
Yea I now remember the vacuum gauge. Try wiggling all the air fittings pipes etc with the vacuum gauge fitted looking for any sudden change.
Hi, thank you very much.
I tried what you say and there is no effect from this on the vaccum gauge.
But when the problem occurs I heard some air suction sound in the intake for a second, maybe this can hint to the problem?
 

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Discussion Starter #28
Yea I now remember the vacuum gauge. Try wiggling all the air fittings pipes etc with the vacuum gauge fitted looking for any sudden change.
Hi, thank you very much.
I tried what you say and there is no effect from this on the vaccum gauge.
But when the problem occurs I heard some air suction sound in the intake for a second, maybe this can hint to the problem?
Hi, I think according to the symptoms and what you said till now that the problem is in one of the sensors that effects the air fuel mixture.
There is a very noticable smell of fuel around the car, it seems that not all of the fuel burns. I also saw today that the oil is very black, I filled the oil to check if the car is burning oil also.
Which sensors needs to be check for this problem?
What else do you recommend I check to find the reason?
Thanks a lot
 

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The 2 main sensors that affect fuel mixture are the coolant temp and air flow (O2 sensor also has a big input but only when the sensor heats up). Air temp is only a minor correction. Maybe watch them on your scan tool and look for a sudden change.
 

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Discussion Starter #30
The 2 main sensors that affect fuel mixture are the coolant temp and air flow (O2 sensor also has a big input but only when the sensor heats up). Air temp is only a minor correction. Maybe watch them on your scan tool and look for a sudden change.
The problem occurs only when the car is warmed up to the operation temperature. So maybe the problem is in the o2 sensor? how to check it to know for sure?
In my car there is no MAF sensor.
 

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So it's map sensor. they give little trouble but you could still watch what happens when it starts to stumble. With the O2 sensor it's the one before the cat that would be indicating a low voltage if the engine started running lean. Since it only started after you worked on the car my gut feeling it's something you may have done.
 

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Discussion Starter #32
So it's map sensor. they give little trouble but you could still watch what happens when it starts to stumble. With the O2 sensor it's the one before the cat that would be indicating a low voltage if the engine started running lean. Since it only started after you worked on the car my gut feeling it's something you may have done.
Thanks.
I also thought that the problem is at the last place I touched, that's why I go to the o2 sensors.
For remainder, I forgot to connect them back after I installed the exhaust cover for about 20 minutes driving. and after that all begun.
But when I read the sensors they are in range where they suppose to.
So I don't know if they give fake measurements sometimes.
What do you think I need to do?
 

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Running the engine with them disconnected can't do any damage to them. If they don't work the ECU usually provides a set voltage around 500mv and not fluctuate but if their bouncing around their working. The faster the bounce the better they are. You can measure their output with a multimeter. Have you cleaned out the idle speed control motor and throttle body not that I think it will make much difference because the problem started after you did the head. I see in your first post the idle speed hunting around 500 to 700 revs and at one point dropped to 200. The 200 looks like a definite cut in ignition.
 

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Discussion Starter #34
Running the engine with them disconnected can't do any damage to them. If they don't work the ECU usually provides a set voltage around 500mv and not fluctuate but if their bouncing around their working. The faster the bounce the better they are. You can measure their output with a multimeter. Have you cleaned out the idle speed control motor and throttle body not that I think it will make much difference because the problem started after you did the head. I see in your first post the idle speed hunting around 500 to 700 revs and at one point dropped to 200. The 200 looks like a definite cut in ignition.
Hello, I wanna update that the problem was solved yesterday.
Last Thursday and Friday the problem was occurring alot, and yesterday the engine start to leap and the check engine light turned on, the scanner said misfire on cylinder 3, I checked the spark plug and it was good then I check the ignition coil and it was bad and after i replaced it the problem was gone and there is no problem in idle RPM at all.
After the head repair the car scanner said miss fire on other three ignition coils so yesterday I replace the last one.
Thanks a lot for your help :)
 

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Wow that didn't come up earlier but glad to see you nailed it. Those coils buried inside a furnace are a problem waiting to occur.
 
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