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2001 Accent - Random misfires, multiple cylinders
08-25-2017, 01:47 PM (This post was last modified: 08-25-2017 01:53 PM by LostTechie.)
Post: #1
Hyundai 2001 Accent - Random misfires, multiple cylinders
2001 Hyundai Accent 1.6L Automatic w/AC

I got this car about 4 years ago now. Was pretty garage kept prior, and got it with only 60k miles on it, currently has 88k. It is quite old and might need some old, uncommon parts replaced.
I've had this problem for several months now, and I'm sure at this point it's doing damage to several things (transmission in particular, because of my driving compensation). Back in February my car randomly started giving me an occasional blinking Engine light and then a steady one (at this point, it's always either on or blinking). Get it checked and computer showed error codes for misfire in cylinder 4 and random misfires. That's a pretty vague diagnosis that could be caused by a plethora of things if no other sensors are going off, and seeing as misfires are fairly common on this model (and terribly problematic at times) I start with the cheap and obvious possibilities and have worked my way up since, all to no avail. These are the only codes the computer has ever kicked back. No sensors triggered or anything (but that doesn't mean they aren't just bad). I'm darn near broke as it is, so I'm trying to keep this repair out of an expensive garage, and my inspection's coming up. I've done plenty of work myself, but nothing more than fuel injector replacement.

The specifics
The check engine light pretty much only blinks at low RPM, but that doesn't mean it's not still misfiring at higher. When in gear, it doesn't sound TERRIBLE (could be worse), but the RPM drops like a rock, triggers the blinking Engine light, and has occasionally stalled the car. When over 2000 RPM though, it runs and sounds fine, and leaves only a solid Engine light (unless I'm on the highway doing 50+ and RPM drops below 2000). So I've been either riding it in neutral when I can, or stepping on both light on the gas and the break when needed. When it's first started from a good rest (overnight) I tend to have to step on the gas to keep it running (even in neutral). That and after warming up a bit, it likes to idle higher than it used to in neutral, around 2000 RPM, and tends to bounce every so often when drifting in neutral. So I've been driving it for months wearing out my breaks and transmission.

What I've done: Start simple
First thing I did was change the spark plugs and cables. Didn't work.
Air filter is rather new. NP there

Next I figured the fuel wasn't pumping sufficiently, so I replaced fuel injectors. Still nothing.
Ran fuel system cleaner through. Nope
Looked up other common possibilities and replaced the whole coil pack. Nope

Met up with a gearhead friend who had more equipment than me
- Checked pressure: OK
- Checked timing belt: LOOKED ok (Looking at it all NOW, this might be what's needed)
- Used a timing light on the spark plug cables and found a big flag
We could tell which ones were misfiring with random light misses (only 2 of them), and the other pair was firing off twice as fast as the other 2 (a wasted spark system is fairly common on 4 cylinder engines like this, but that means only half of the engine is doing it, on TOP of the misfires, not sure if it's supposed to)
Based on that, we narrowed it down to possibly the crankshaft position sensor improperly seeing positions and triggering fires poorly, bad wiring, MAF sensor, or bad computer. Without any actual sensor errors, this had gotten really frustrating.

Replaced crankshaft position sensor. Nope.
Filled it with premium as my friend had mentioned to see if it sounded any better when at low RPM to see if it was the MAF or another air system problem. It sounded a bit better, but was still doing it.
And I sure as hell ain't gonna tear my engine apart looking for wire problems.
And from what I've read the 1.6L DOHC model doesn't actually use an MAF sensor, just an IAT system.

So at this point, I can only guess the timing belt; seeing as the car runs sustainable after warming up makes me think the belt is going. Not sure on that though cause only certain cylinders are acting up. Unless it's something further up the line from the coil pack. Which I'm not aware of. And my friend is out of ideas, he likes the older and simpler engines for obvious complication reasons.

So before I go and spend more money on stuff that doesn't fix the problem, what are the odds it IS the belt at this point? How hard would that be to replace myself? What would a garage reasonably charge? And what else could it be? In need of a reasonable solution before the end of next month.

Thanks in advance everyone.

LostTechie, proud to be a member of GarageForum since Aug 2017.
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09-02-2017, 10:02 AM
Post: #2
RE: 2001 Accent - Random misfires, multiple cylinders
(08-25-2017 01:47 PM)LostTechie Wrote:  2001 Hyundai Accent 1.6L Automatic w/AC

I got this car about 4 years ago now. Was pretty garage kept prior, and got it with only 60k miles on it, currently has 88k. It is quite old and might need some old, uncommon parts replaced.
I've had this problem for several months now, and I'm sure at this point it's doing damage to several things (transmission in particular, because of my driving compensation). Back in February my car randomly started giving me an occasional blinking Engine light and then a steady one (at this point, it's always either on or blinking). Get it checked and computer showed error codes for misfire in cylinder 4 and random misfires. That's a pretty vague diagnosis that could be caused by a plethora of things if no other sensors are going off, and seeing as misfires are fairly common on this model (and terribly problematic at times) I start with the cheap and obvious possibilities and have worked my way up since, all to no avail. These are the only codes the computer has ever kicked back. No sensors triggered or anything (but that doesn't mean they aren't just bad). I'm darn near broke as it is, so I'm trying to keep this repair out of an expensive garage, and my inspection's coming up. I've done plenty of work myself, but nothing more than fuel injector replacement.

The specifics
The check engine light pretty much only blinks at low RPM, but that doesn't mean it's not still misfiring at higher. When in gear, it doesn't sound TERRIBLE (could be worse), but the RPM drops like a rock, triggers the blinking Engine light, and has occasionally stalled the car. When over 2000 RPM though, it runs and sounds fine, and leaves only a solid Engine light (unless I'm on the highway doing 50+ and RPM drops below 2000). So I've been either riding it in neutral when I can, or stepping on both light on the gas and the break when needed. When it's first started from a good rest (overnight) I tend to have to step on the gas to keep it running (even in neutral). That and after warming up a bit, it likes to idle higher than it used to in neutral, around 2000 RPM, and tends to bounce every so often when drifting in neutral. So I've been driving it for months wearing out my breaks and transmission.

What I've done: Start simple
First thing I did was change the spark plugs and cables. Didn't work.
Air filter is rather new. NP there

Next I figured the fuel wasn't pumping sufficiently, so I replaced fuel injectors. Still nothing.
Ran fuel system cleaner through. Nope
Looked up other common possibilities and replaced the whole coil pack. Nope

Met up with a gearhead friend who had more equipment than me
- Checked pressure: OK
- Checked timing belt: LOOKED ok (Looking at it all NOW, this might be what's needed)
- Used a timing light on the spark plug cables and found a big flag
We could tell which ones were misfiring with random light misses (only 2 of them), and the other pair was firing off twice as fast as the other 2 (a wasted spark system is fairly common on 4 cylinder engines like this, but that means only half of the engine is doing it, on TOP of the misfires, not sure if it's supposed to)
Based on that, we narrowed it down to possibly the crankshaft position sensor improperly seeing positions and triggering fires poorly, bad wiring, MAF sensor, or bad computer. Without any actual sensor errors, this had gotten really frustrating.

Replaced crankshaft position sensor. Nope.
Filled it with premium as my friend had mentioned to see if it sounded any better when at low RPM to see if it was the MAF or another air system problem. It sounded a bit better, but was still doing it.
And I sure as hell ain't gonna tear my engine apart looking for wire problems.
And from what I've read the 1.6L DOHC model doesn't actually use an MAF sensor, just an IAT system.

So at this point, I can only guess the timing belt; seeing as the car runs sustainable after warming up makes me think the belt is going. Not sure on that though cause only certain cylinders are acting up. Unless it's something further up the line from the coil pack. Which I'm not aware of. And my friend is out of ideas, he likes the older and simpler engines for obvious complication reasons.

So before I go and spend more money on stuff that doesn't fix the problem, what are the odds it IS the belt at this point? How hard would that be to replace myself? What would a garage reasonably charge? And what else could it be? In need of a reasonable solution before the end of next month.

Thanks in advance everyone.
Would be nice if you could post fuel trims. Also would be nice if you could post the specific codes it has when the check engine light comes on "solid" as you say. Also post a picture of freeze frames. I would like to see what the ECT and MAF/IAT are saying along with the fuel trims at time of incident.

And to correct what you read, the Air flow meter is a combination MAF and IAT.

Next, have you checked for a vacuum leak?

What is O2 doing at time of misfire. What do you use to access the ECM?


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nickb2, proud to be a member of GarageForum since Sep 2017.
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