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2002 Hyundai Accent with worsening misfire
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Maplicito
User
May 5, 2016, 12:22 PM
Post #1 of 20
(3811 views)
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2002 Hyundai Accent with worsening misfire
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I tried posting this on another site, but haven't gotten any responses, so I'll try here... I think a cut and paste of what I wrote before should do:
My car is a Canadian 2002 Accent. I believe it's a GLS, and it has the 1.5L engine.
It has a worsening misfire in the low RPM's, although the RPM range this happens in has been broadening. I can now smell unburnt gas when this happens.
This problem first reared its head around a year ago. I replaced the fuel and air filters without it resolving the problem. I changed the spark plugs - the old ones looked to be in reasonable shape, but suddenly it ran great with the new plugs - for a few months.
The misfire started to creep back in. Since then, I've replaced the upstream O2 sensor and cleaned the MAF sensor. I replaced the throttle position sensor. None of these things solved the problem.
The battery terminals were getting pretty corroded - I hadn't thought this would be related to the issue, but I cleaned them. This did not fully solve the problem, but it did drastically improve it. I bought a new battery the same day - the problem while not gone, seemed to be much more manageable.
About 100km later, the problem has significantly worsened again. I tested voltage across the battery - with the car running, the voltage is ~14.2V. When the fan is on full and my fairly high powered stereo is running, voltage still stays ~14.2V. I'm assuming that should mean that the alternator is good?
Previously, I had tried my ignition coil on my sister's Accent, and it seemed to work fine - but I'm not entirely convinced that the coil is guilt free. I have not done any further testing on the coil, and have not tested the spark plug cables - I'm not sure how to properly test the coil or cables, and don't know where to find the appropriate specs for them should I learn how to test them.
Any other suggestions out there? I got the car on the cheap, however, aside from the low (now mid) RPM stutter, the car seems to otherwise be in great shape, and only has 150,000 km on it. Unless it's going to cost an excessive amount, I would like to get this car running right again.
Thanks for any suggestions you guys can offer!
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kev2
Veteran
May 5, 2016, 1:17 PM
Post #2 of 20
(3806 views)
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Re: 2002 Hyundai Accent with worsening misfire
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get the vehicle scanned for any codes. Yes even if light is off.
It is often less expensive to have a vehicle properly diagnosed and repaired than the 'shotgun' randomly throw parts at it method. What tools do you have to diagnose?
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Maplicito
User
May 5, 2016, 1:23 PM
Post #3 of 20
(3803 views)
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Re: 2002 Hyundai Accent with worsening misfire
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I haven't scanned it since replacing the batter last weekend, but previously it would show a p0300 random misfire code, and while I don't remember off the top of my head which ones, it would show the code for a misfire in two of the cylinders. This was just with my dad's OBD2 scanner.
I would like to take it to a shop, but the one shop I trust is currently in the process of moving, and unable to diagnose anything at the moment.
(This post was edited by Maplicito on May 5, 2016, 1:24 PM)
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kev2
Veteran
May 5, 2016, 2:24 PM
Post #4 of 20
(3794 views)
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Re: 2002 Hyundai Accent with worsening misfire
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your dad has a scanner great-
recheck the codes, then look at FT's and o2 sensor voltages- see if its rich and compensating... might want to look at MAP and ECT also.
For a misfire its IGNITION spark at all cylinders, FUEL - injectors, fuel pressure, inj pulse, MECHANICAL- compression or vacuum checks.
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Maplicito
User
May 5, 2016, 2:35 PM
Post #5 of 20
(3792 views)
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Re: 2002 Hyundai Accent with worsening misfire
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Thanks for the response, I'll have a look as soon as I can, and if I need more assistance, I'll post back here. I appreciate your help!
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Maplicito
User
May 5, 2016, 5:05 PM
Post #6 of 20
(3784 views)
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Re: 2002 Hyundai Accent with worsening misfire
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I ran the scanner. It came back with the codes P0300, P0301, and P0303. If memory serves, those are the codes I've always gotten - I don't believe I've ever gotten P0302 or P0304.
I don't know how to interpret the further information I got - it only showed up for the P0300 code:
Fuel System 1
Closed loop
Calculated LOAD
32.9%
Vehicle Speed
29 MPH
Lift Bank 1
-2.3%
Engine RPM
2240 RPM
Engine Coolant Temp
123 F
STFT Bank 1
17.1%
Does that have any useful information in it?
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Discretesignals
Ultimate Carjunky
/ Moderator
May 5, 2016, 5:18 PM
Post #7 of 20
(3783 views)
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Re: 2002 Hyundai Accent with worsening misfire
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That is just one frame of data that doesn't tell you anything. It is like looking at one puzzle piece and trying to guess what the picture looks like when all the pieces are assembled. That is freeze frame of data that can be used to duplicate the condition though.
It does show a positive fuel trim, so it could have some sort of vacuum leak at lower engine loads that may cause misfiring. If I remember they did have issues with the paper intake manifold gasket causing single cylinder misfiring.
Plug wires do eventually wear out and boots can leak. Have you inspected for flash burns on the wires or spark burning through on the boots? Also make sure there is no oil down in the spark plug wells. If it smells gassy while it is missing, that is usually the sign of the fuel not burning due to loss of or poor spark. It can also be caused from a mechanic issue also, but unlikely in your case.
Since we volunteer our time and knowledge, we ask for you to please follow up when a problem is resolved.
(This post was edited by Discretesignals on May 5, 2016, 5:30 PM)
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Maplicito
User
May 5, 2016, 5:28 PM
Post #8 of 20
(3775 views)
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Re: 2002 Hyundai Accent with worsening misfire
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I'm wondering - is there any value to a spark plug tester? I see they don't cost a lot. Is it likely that I would be able to tell if it is sparking properly when the misfire happens (I can get it to misfire while running parked)? Or am I just going to see there is spark, and not really know whether it's getting good spark?
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Discretesignals
Ultimate Carjunky
/ Moderator
May 5, 2016, 5:36 PM
Post #9 of 20
(3774 views)
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Re: 2002 Hyundai Accent with worsening misfire
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The adjustable spark plug tester is a good tool in my opinion. You can use it to to stress the coil by adjusting the gap to say around 30 KV. If the coil is weak or spark is finding some other path to ground it will be more apparent with a wider gap set on the tester. You can also use an incandescent 12 volt test light (don't use an LED test light) connected to ground while the tester is installed to find spark leaks. You just run the probe of the 12 volt test light around wires, boots, etc. The spark will find the test light if there is a poor insulation. Be sure to unplug the injector on the cylinder your testing spark on, so you don't have raw fuel going down into the exhaust.
Usually ignition misfires will either happen all the time (dead cylinder) or cause misfiring under heavy engine loads when cylinder pressures are high when more spark output is required.
Since we volunteer our time and knowledge, we ask for you to please follow up when a problem is resolved.
(This post was edited by Discretesignals on May 5, 2016, 5:41 PM)
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Maplicito
User
May 5, 2016, 5:48 PM
Post #10 of 20
(3769 views)
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Re: 2002 Hyundai Accent with worsening misfire
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Thanks for the response... it might be awhile before I can do any of that, but if I need more help, I'll come back here. Or if the shop I want to go to finally gets their move done, I'll go there. Thanks again!
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Tom Greenleaf
Ultimate Carjunky
/ Moderator
May 6, 2016, 3:04 AM
Post #11 of 20
(3755 views)
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Re: 2002 Hyundai Accent with worsening misfire
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Maplicito: Quoting you from up top post ">>I changed the spark plugs - the old ones looked to be in reasonable shape, but suddenly it ran great with the new plugs - for a few months.<<"
I'll get back to that but as DS has said the spark tester is a good tool you may not have nor others just yet and IMO time is running out for fixing this or waste you converter.
It seems new plugs made a difference back when but no mention of the wires? With that I'd look again and consider new wires just because if older but you can get good clues without tossing parts. Just move them with a glove at the risk of getting a jolt to you and see if they arc to each other or plain look for rub marks.
Know that high voltage is dumb just seeks the easiest way to ground without regard to if it sparks a spark plug or misses doing that. Most cars are sensitive to correct plugs not off brands or ones with claims to improve over OE specs. This should require NGK plugs if not probably should really think about the right ones. New could have covered weak wires for some time and the source issue the wires or back not actually the original plugs when problem began.
Know also when a plug tries to fire under compression it take more power to it to properly jump the gap so any alternative place to jump out is more likely with loads or temptations like the wires are damp - other things too.
In short I think you could at least visually see a problem with wires up to if when dark see them arcing under load or light misting of them with even just tap water,
T
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kev2
Veteran
May 6, 2016, 5:10 AM
Post #12 of 20
(3751 views)
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Re: 2002 Hyundai Accent with worsening misfire
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your scanner 'snapshot' I would look at why ECT low, why STFT is high...
X2 colleagues mention of spark plug brands - yeah brand does matter.
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Maplicito
User
May 6, 2016, 5:40 AM
Post #13 of 20
(3745 views)
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Re: 2002 Hyundai Accent with worsening misfire
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Thank you for the further replies. The plugs that were previously in the car were some cheap brand that the previous owner put in - the new ones I put in that seemed to temporarily solve the problem were NGK. I'm headed out of town for a bit this weekend (with a different vehicle), but I'll try to get a look at the wires - that really helps, thanks!
As for ECT, I'm assuming the code is likely just the most recent occurrence? If so, that was from a trip that was under 2 km. I don't know anything about STFT, but as I get time, I'll try to research it.
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Tom Greenleaf
Ultimate Carjunky
/ Moderator
May 6, 2016, 7:12 AM
Post #14 of 20
(3741 views)
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Re: 2002 Hyundai Accent with worsening misfire
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You can tell if wires are the issue or boots OR the coil(s) involved with minimal test equipment if it's bad enough and think it is.
Ex: If you purposely left a plug wire hanging no ground you are forcing it to find an alternative. That alternative in longer or shorter time then can become the best route to ground for high voltage.
OK - DON'T DO THIS I'LL FIND ANOTHER WAY TOTALLY SAFE. I'll just feel for that fussy feel of high voltage and don't want you to do that - I'm used to it but it's not suggested.
Perhaps try grounding a screwdriver with a jumper wire to it to known ground and use like a wand to find it arc or change when close to a weak area or wire should work. One erratic misfire can jump to another cylinder so you get two code then a list of codes from it not running properly as the poor engine tries to cover up what might be normal issues if all was perfect.
The time the wrong plugs were in there could have started it. Doesn't matter but caught my attention when you said new plugs now proper seemed to solve it for some time but the damage was still lurking is a super strong clue to me.
To avoid just tossing parts test it out. If old wires now (most marked with year made) it really isn't a waste unless insanely costly for a guess if not proven,
T
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Maplicito
User
May 6, 2016, 7:44 AM
Post #15 of 20
(3735 views)
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Re: 2002 Hyundai Accent with worsening misfire
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Thanks Tom. That screwdriver idea sounds easy enough... I have some 10 gauge wire from a project in the basement that I can use.
So far the parts I've thrown at the car have been ones I could justify as being appropriate maintenance and cheap, so I've avoided feeling like I'm just throwing parts at the problem - I appreciate the help in continuing to avoid that.
I will look for a year on the wires - but I suspect they are probably original, so probably something that could use replacing anyway. I'll give that screwdriver trick a try after work, thank you!
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Tom Greenleaf
Ultimate Carjunky
/ Moderator
May 6, 2016, 7:51 AM
Post #16 of 20
(3731 views)
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Re: 2002 Hyundai Accent with worsening misfire
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Sorry to sound quite so confident. It's just my nature to 1st think outside the box before going totally nuts testing the snots with questionable results from VERY expensive equipment it just might not require. It's free and easy so why not?
If not convincing results then bring out the big guns,
T
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Maplicito
User
May 6, 2016, 8:00 AM
Post #17 of 20
(3727 views)
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Re: 2002 Hyundai Accent with worsening misfire
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No need to apologize - I don't have the in depth knowledge of cars to do that kind of out-of-the-box thinking, so I really appreciate that someone else is doing it for me!
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Maplicito
User
May 11, 2016, 7:22 PM
Post #19 of 20
(3679 views)
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Re: 2002 Hyundai Accent with worsening misfire
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Thanks everyone who made suggestions in the thread. In particular, I want to thank Tom... he and I had a bit of a back and forth about the car, and based on some things he said and that my uncle suggested to me, I went and bought some ignition wires - the car's running great!
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Tom Greenleaf
Ultimate Carjunky
/ Moderator
May 12, 2016, 2:34 AM
Post #20 of 20
(3670 views)
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Re: 2002 Hyundai Accent with worsening misfire
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Glad it's fixed and seems to be for now.
So, know these threads are open to the web and should be closed when solved. YOU may ask any moderator to reopen it as needed or wanted.
Happy trouble free motoring, Tom
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