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Discussion Starter #1
Dear Members,
I am a hyundai Technician and have been with the company just over three years. I own a 2009 Hyundai Accent 4 door GLS. Over the past few weeks I have noticed an evasive missfire that only occurs on cylinder two. ( P0300-and P0302) and it occurs sometimes first in the morning, or 1/2 to 1 hour hot soaks. subsequent start ups it does not occur. the vehicle will start, miss, MIL will flash, then PCM cuts fuel and its just a dead miss. other times it will correct after a few seconds and resume normal operation. Once cleared, the issue does not occur while driving. Under any load.
Of course I have searched for common Accent headache items. I checked fuel pressure which was ideal. The coil was swapped coil 2 to 1 and 1 to 2. The spark plugs were changed with OEM and gap as .040- .044 thousandths as hyundai spec. I also swapped injector 2 to injector 1 and 1 to 2 to rule out a sticky injector. All these steps did not correct the issue. Misfire still and only on cylinder two.
Today I inspected engine vacuum and compression to verify proper sealing. Compression was at or very close to 200 psi. Hyundai spec is 185-214 give or take with a variance of 14 psi per cylinder. Engine vacuum was a solid 17-18 inHg with no flutter. Although I did not check during the miss event.
So techs, my next move is to the harness. I viewed hyundais ETM electrical diagrams and found that my injectors are low side driven by the PCM. So to verify cylinder two was receiving PWM from the PCM I wrote down my pins and attempted to jump the injector to PCM controlled ground. However Hyundai in there infinite wisdom supplied me with a PCM diagram from a M-trans car even with a VIN lookup......

SO this week I have found the correct PIN locations and will try to attempt a harness bypass one more time. I am skeptical its the harness because it does not occur while driving. My last synopsis is a possible ECM failure, which back-probing the connector should outline. IF anyone has any suggestions I am happy to hear!!

I did call Hyundai Techline and they just said good luck if its not coils or compression it probably needs a head due to valving issues, but my vacuum is rock solid. Thanks again!!! HyundaiTech2294 Andrew


ALSO: My MAP sesnor through Hyundai GDS is reading 10 InHg, while the vacuum guage is reading 18-19 InHg. and with increased engine load, foot on brake, accelerator depressed ( stall test) The MAP vac INCREASES to 15-16 InHg, while voltage rises from aprox 1 volt to 3.5-3.8. The voltage is correct, high vacuum low voltage, low vacuum, higher voltage. At least with most manufacturers. Is this a GDS Hickup? Manifold vacuum should DECREASE with engine load. Other than this there is no troublesome PID values.
 

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WAG intake manifold gasket leaking.

Try spraying starter spray around flanges at motor when it’s stumbling. It it speeds up and smoothes out from the spray the gasket is bad.

Common on XD Elantras at high mileage.
 

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Yep, try can of carb or brake clean at idle along seam where intake meets head.. might get lucky...

As mention above, seen a lot of misfire on XD due to cracked / split / intake gasket
 

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Discussion Starter #4
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WAG intake manifold gasket leaking.

Try spraying starter spray around flanges at motor when it’s stumbling. It it speeds up and smoothes out from the spray the gasket is bad.

Common on XD Elantras at high mileage.

Thank you for the reply! wouldnt a leaky intake manifold gasket affect engine vacuum? to me 17-18 INHg is normal. I tested an 10 Accent hatch today as a reference. mine actually had more.
 

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Intermittent problem that comes and goes.
Leans out one cyclinder messing up idle. Around cyclinder 2 try some spray. I have had this identical problem before.
 

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It does sound like possible symptoms of a small intake gasket leak. If the leak is small enough then the reason the car runs fine at operating temperature could be because the cylinder head and intake manifold heat up and expand slightly compressing the gasket and closing the leak. When the engine cools down a bit the leak reopens. This may also be why engine vacuum appears normal if you checked it at operating temperature. Just a theory anyway if it is the intake gasket... It would be interesting if you tested engine vacuum when the motor is cold to see if it's noticeably lower than your other measurement. Also, try the spray test when the engine is cold in case the gasket is sealing up when the motor gets hot.

Let us know what you find.
 

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Discussion Starter #7
Thank you very much for the suggestions. I will investigate the intake manifold gasket as a possible cause. Next time it occurrs I will try to induce some combustible aerosol by the gasket surface. Starting fluid more than likely. Or preferably will just smoke test it at the shop and see if I can locate a leak. It's too isolated to be a pcm or harness issue. As of this point. Thank you and will keep the thread updated on the outcome
 

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Discussion Starter #8
Unfortunately I did not get to it today as I got stuck with a water pump on a V6 2012 Hyundai santa Fe lol. Maybe tomorrow!
 

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I am a hyundai Technician and have been with the company just over three years.
Nice to see another tech join us. Welcome to the forum 00000732

hyundaitech2294 said:
The MAP vac INCREASES to 15-16 InHg, while voltage rises from aprox 1 volt to 3.5-3.8. The voltage is correct, high vacuum low voltage, low vacuum, higher voltage. At least with most manufacturers. Is this a GDS Hickup? Manifold vacuum should DECREASE with engine load. Other than this there is no troublesome PID values.
Just thought I'd try throw this in to help clear up your confusion :
A change from 10" to 15" isn't an increase in manifold vacuum. It's an increase in Manifold Absolute Pressure (so a decrease in manifold vacuum) and, as you say, is what you should see when you open the throttle valve and let air into the manifold.
So GDS is working OK. It's the person using it that's not working right :wink:

Good luck tracing the misfire.

Scottie.
 

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If you ask me it's an electrical issue.................

A vacuum leak would be constant. They may change with extreme temp swings, but it won't be an instant change.

Have you done a voltage drop test between the computer and the coil and injectors? You either have a broken or corroded wire, a bad ground or a loose connection somewhere.

While doing a voltage drop test, wiggle the harness and watch the meter for a drop.

Duro
 

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Discussion Starter #11
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Nice to see another tech join us. Welcome to the forum 00000732


Thank you very much for the reply. I understand my confusion. The manifold pressure increases with engine load with an open throttle plate. Just the way GDS was putting the data out confused me. When your troubled on a car for hours on end, sometimes we make silly mistakes! thank you!
 

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Felllow Techs,

I have an update to my vehicles condition,

Today I went into work ( ON MY DAY OFF!!) well some sacrifices have to be made! I smoke tested the intake manifold and found no leakage. However upon closer examination, I noticed that one of my intake manifold nuts was backed half way down its mounting stud. Furthermore while checking all the others, it was noted that they were all on half way more than finger tight. I bought this vehicle at my last dealer from my old service manager. He had the engine swapped by one of my fellow techs ( I will have to call him for a laugh!)

SO i removed my rail, and removed the old gasket, which had evidence of leakage, trails from oil residue and what not, more than likely residual from the PCV and CVVT system. Inspected my intake valves which were pristine. ( guess that BG fuel additive does work! haha) I remounted the I/Manifold and torqued to aprox 14 ft lbs. luckily my hands are as little the ones who designed it cause IT WAS A TIGHT FIT!! replaced my injector O-rings and retainers, reset my adaptive values and started it up.

So far the issue has not returned and I am quite pleased with the results. Oftentimes as a tech I let numbers and figures outweigh simple fixes. Thank you all for welcoming me to the forum, and on my off time I look forward to helping techs like myself with their questions.
Thanks! andy.
 

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Discussion Starter #14
Hey Guys!
Unfortunately, my misfire returned this morning on start up! same routine, MIL flashes for about thirty seconds, then steady, assume fuel is cut and its just running a dead miss. shut off, restart, and then fine. Scanned at the shop on GDS, cylinder two miss detected, however on the OBD side of GDS cylinder two counts 0 misses, and cylinder four counted 58 misses on last ten driving cycles. Really a puzzling problem. On vehicle start up, the PCM should be in open loop running on programmed parameters. Freeze frame data was not available on GDS however my OBD aftermarket scanner may pick that up. Other than that, guess I will start from scratch, check for spark during the next event. than to the harness and PCM. Perhaps run a jumper if necessary. Thanks for your time!, Andy
 

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This is an interesting case study. The op has done some deep testing. Coils swaps, injector swaps, spark plugs and removed the valve cover new o rings. Misfire cylinder 2..... hmm. try a leak down test cylinder 2? You may have an issue with the intake or exhaust valves or head gasket crack. Under compressed air remove spark plug cylinder 2. Rotate crank 1 turn the another turn to complete a full revolution of the cam. Check the oil cap for air. check the coolant cap for air, check the muffler for air sound. This will test compression in all the systems. Good luck
 

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mil flashing needs to be addressed , not sure what could cause that unless the coils have issues. This is a guess. Inspect the shafts on the coils and test the coils while the engine is running out of the sparkplug hole for spark jump. It should come from the end of the coil tube. If it comes further up you may have a hair line crack in the coil shaft. YouTube has videos how to test coil over plug.
 

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Very strange results when you scanned for misfires. You've been getting misfires on cylinder #2 all along, but OBD counted none while it counted numerous misfires on cylinder #4? The PCM detects misfires by interpreting variations in crankshaft rotation speed (i.e. via the signals it receives from the crankshaft position sensor, which is also used by the PCM for ignition timing and fuel injector pulse width). If the problem is not on the PCM side, could it possibly be the crank sensor acting up (or harness problem interfering with the signal)?
 

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Discussion Starter #18
I have another update for all of you following this thread!
After returning to the basics, I can verify that cylinder two and all cylinders have air fuel spark and compression. For those unsure of my previous tests and part swaps review my past posts. So I can conclude that my problem resides in the control module or the cylinder head assembly.
Yesterday a 2011 accent hatch got traded in on the lot, so I wasted no time in grabbing the power train control module. I swapped out the modules and gave it a start. Vehicle started up with the usual misfire, which cleared after the mil was set and the engine restarted. Scanned for codes and cylinder two was responsible yet again. Therefore pcm can be ruled out of the possible causes.
Therefore, my conclusion of my weeks of diagnostics leads to the cylinder head having a sealing issue on cylinder two. Which may be a result of a mis sealing valve or binding valve in it's guide. Lash adjusters were a possibility, however it is understood that my vehicle has MLA mechanical lash adjusters and no abnormal noise is heard under the miss condition. Although inspection could reveal a lash issue, I highly doubt based on my maintenance routines. Manifold vacuum is a solid 18 inHg. During the miss event is 15 InHg. After several seconds of running, and cylinder two starts "catching" vacuum fluctuates from 15 to 18 InHg and then remains at 18 when the issue remediates. If the vehicle is put in drive immediately when the miss occurs, the issue will not dissipate as it does in park; as a limp mode is likely occuring.
HOWEVER, when the vehicle is shut off, a small puff back is heard from the muffler. Mostly amplified while the condition is occurring and the ignition is shut off. So my next step in the process is to either replace or rebuild the cylinder head . Thank you all for your continued support! Andy!

Wow for once Hyundai techline was right all along haha. Thanks for the ongoing support!!! Andy
 

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This is an interesting case study. The op has done some deep testing. Coils swaps, injector swaps, spark plugs and removed the valve cover new o rings. Misfire cylinder 2..... hmm. try a leak down test cylinder 2? :

. THANK you very much for the reply. A leakdown test will be my final test before I condemn the cylinder head, although I am almost a hundred percent sure that the valves on cylinder two are the trouble. The pressurization of the cylinder while rotating the engine is an interesting idea, worth a shot. I thought I had hydraulic lash adjusters. HMA said they were HLAs lol. fact that there mechanical defeats that easy fix. It's 750 for an OE head. Allot for an accent, but it's an option. I would rebuild, but I can not test it proper without a machine shop.
 

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Another update on the accent,
Today I performed a cylinder leakdown test on cylinder 2. With spark plugs 123 removed, cylinder 2 was pressurized to 36 psi on TDS compression stroke. No leakage was found on the guage. Less than 1 psi loss. That was heard coming from the oil cap. Plus some steam from the Crank case made it easy to spot. Still a normal condition. A little blowbye is ok. However, when cylinder 1 was pressurized, steam was found seeping from cylinder 2 spark plug tube. SO NOW we have either a failing head gasket, or a cracked cylinder head casting.
This just gets deeper and deeper!!! Once I secure another car, the head will be coming off, and I will have pictures. Thanks all! Sincerely, Andy.
 
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