A bad O2 sensor would more likely be an issue for those cylinders...eg: cylinders 2, 4, &6.....or 1, 3, &5.

 

First thing first: was the O2 sensor you put in a known good and correct one from Chase's sensor list on OpenGK, or was it an Alibaba Special?

If your sensors are good, it gets hairy, because random misfires can be caused by...

• Bad gas
• Worn/clogged fuel injectors
• Bad fuel regulator
• Worn fuel pump
• Bad/clogged O2 sensor
• Bad MAF sensor
• Bad IAT sensor
• Bad ECT sensor
• Worn plugs
• Worn coil pack
• Damaged/loose/corroded wiring
• Corroded ground points
• Loose knock sensor
• Loose position sensor
• Worn timing belt
• Clogged PCV
• Planetary alignment
• Swamp gas
• Weather balloon

Make sure you're up to date on maintenance, get good gas and put a bottle of injector cleaner in the tank while you do so.

Then, look for anomalies. Get live data over OBD-II and make sure you're getting a clean MAF and TPS signal (no weird dips or spikes).

Check long term fuel trim and make sure it's similar for both banks and in the +/- 8% range. Values outside that could indicate bad MAF, IAT, TPS, IACV, weak fuel pump, bad pressure regulator, bad O2 sensor, basically anything fuel related.

Check for erratic timing advance, this could indicate bad spark.

Basically get a better picture of what you're working with.

 

I went with the NTK 25000 since my car was built in 2002 and I've went down that list for the most part except for the fuel pump, fuel regulator and spark plugs. I haven't had the chance to check fuel trims either, my little Bluetooth reader won't read them properly. I'll have to go borrow someone's reader with better live data capabilities.

My timing advance (as far as I can tell) can be sparratic at times jumping around inconsistently which prompts me to order spark plugs soon as I have no idea what brand or type they are because the previous owner gave them to me. I just used them when I replaced the coil pack and wires. (I probably should've checked first to be honest) The coil pack I used wasn't the best of quality either so I might look at replacing that too if all else fails.

I'll go borrow a code reader when I can and look at fuel trims properly but will still replace the other O2 sensor and see what happens from there. Thanks for the advice and I'll update this when I take a look.

 

A lot of shops will list and sell Bosch plugs as compatible and even "OEM Quality", but this forum has let me understand that they are decidedly NOT compatible due to higher internal resistance than specified, resulting in weak spark in our wasted spark ignition systems.

So something like that could have happened.

 

I was planning to use NGK platinum plugs, are they sufficient or is there another comprehensive list of plugs that are known to perform well? I wanted to use NGK iridiums originally but they're out of stock on rockauto.

 

is there another comprehensive list of plugs that are known to perform well?

Here's a snippet from my GK Newbie guide:

Buy only NGK or Denso spark plugs. You can use any material as inexpensive as copper or as expensive as ruthenium. We recommend either iridium or platinum with heat range 5 for a standard naturally aspirated road vehicle. For longer intervals you can try double/laser platinum or laser iridium. From the factory our motors were equipped with a Hyundai branded NGK iridium plug.

Even a reputable brand like Bosch is not acceptable for spark plugs. The internal resistance of the Bosch spark plug is 6k ohms which does not match our ignition system’s preference of 5k ohms. Failure to follow this recommendation will result in several DTCs and poor performance. For best results use NGK iridium 5464 BKR5EIX-11 for a 50k mile interval or NGK laser iridium 7994 IFR5E11 for a 100k mile interval.

Reference: https://www.newtiburon.com/threads/what-spark-plugs-are-standard.28384/

 

Those are on probably just fine; I'm running a set of Denso Iridiums without any issues.

 

For plug related info, it seems search on this forum is your source. Try e.g. https://www.newtiburon.com/threads/spark-plugs.483752/

 

Alright I went and ran some live data with a proper reader and what I saw of note was this:

STFT for Bank 2: -24.2%
LTFT for Bank 2: 3.8%
STFT & LTFT stuck at 0% for Bank 1
Bank 1 fuel system in open loop

Spark advance at idle jumping around from ~4° - ~7.5° and consistent under load from what I can tell.

I got lazy, ran out of time and didn't replace that other O2 yet not gonna lie but will get to it I swear.

 

Ignore your STFTs unless they are pegged at plus or minus 32%. It is a useless stat otherwise.

It is interesting that bank1 is stuck at 0% and that your tool can identify if only bank1 is in open loop all the time... I have yet to see that. However, if you haven't replaced B1S1 on the upper firewall side then that explains why it's still an issue. Replace it and that problem should solve itself.

Ignition timing normally drifts between about 8-12* of advance at idle. Seeing it drift as low as 4* is unusual though so there is some kind of compensation going on due to misfires I'm sure. Then as you rev through the various RPM/Load ranges will peak at around 35* while cruising and around 30* full tilt near the rev limiter. For example, your closed loop and idle ignition tables are as follows (ignoring any temperature, knock or O2 feedback corrections being made on the fly)

 

That's useful information thanks, google and other sources give very mixed information and jumbled AI generated answers. It's reassuring coming from someone else with some sort of experience. But yeah, at idle it sits around 4° at the lowest and rises up to about where you mentioned at ~30° - ~35° in both scenarios.

Here's what it was reading at idle exactly after sitting for a few minutes warm:

Orange is timing
Red is B1 LTFT
Green is B2 LTFT

Spark plugs are ordered and O2 is getting replaced tomorrow unless the Midwest snowstorms get to me first and bury me alive. 🌨

 

Start with the least complex/costly approach. Like plugs/wires, then put treatment in the tank. Always keep at least half tank of gas to reduce residue in injectors...good luck!

 

Alright update time,

I went ahead and replaced the O2 sensor and yeah that wasn't it. I'm not getting any of the O2 related codes now though. I replaced everything else like plugs wires and various other sensors as mentioned before with the appropriate parts so this leads me to believe that it's my coil pack.

From what I can tell its been replaced before and not OEM. Im going to go ahead and order another coil pack because it's probably due for a replacement anyway, but I wanted to know if there were any specific brands or types known to perform well before I go ahead and spend more on this car.

 

I went ahead and replaced the O2 sensor and yeah that wasn't it. I'm not getting any of the O2 related codes now though. I replaced everything else like plugs wires and various other sensors as mentioned before with the appropriate parts so this leads me to believe that it's my coil pack.

Did you reset your ECU after changing major sensors? The ECUs will adapt to poor conditions with faulty sensors and will need the adaptive learning reset. Mando is the OEM for the coil pack but if you can find another reputable brand like NGK/NTK or Delphi they should be suitable.

 

So I went ahead and replaced it and from what I can tell it ran a bit smoother than it did before, but misfires intermittently.

I figured out how to recreate the conditions for it to misfire though. It only happens when I sustain lower rpm under ~2k for a longer period of time under load/ while driving. After that, it'll throw a random misfire code, give a CEL and lose power. It will also go away while driving too only after sustaining above 2k rpm for a period of time. City driving sets the misfire off, but cruising or freeway dosent. Restarting the car yields inconsistent results of clearing the misfire, it will clear sometimes and sometimes it won't.

I replaced the wires with AutoZone wires a while back but I don't know if i should throw more parts at the problem. I don't feel too bad about replacing the plugs and coils as they needed to be replaced anyway, but I'm just very puzzled and at a bit of a loss as to what it could be.

Could a bad alternator/ belt tensioner cause a misfire like that? My belt tensioner is slightly loose and or worn causing a bit of vibration in the belt.

 

Could a bad alternator/ belt tensioner cause a misfire like that? My belt tensioner is slightly loose and or worn causing a bit of vibration in the belt.

No, unless loose enough for the alternator belt to slip and battery voltage drops a lot.

 

Driving these motors under 2000 RPM is too low. They don't make power below 2000 RPM and are very inefficient at those RPMs. This isn't a 1940s torquey V8 with a 5k RPM limit. For best economy you want to drive it near where the power band starts. The 2.7 will be most efficient between 3000 and 4000 RPM where the torque started to come on.

For diagnostics purposes what gear and speeds are you driving at below 2000 for sustained periods of time? Check your LTFT of both banks once it starts misfiring. I am willing to bet your long term fuel trims are drifting to the point of misfiring due to incomplete combustion at such low RPM. You are likely experiencing a false positive for a rich condition from incomplete combustion and it's causing your LTFT to drift negative until it misfires from an actual lean condition. Then when you drive it above 2000 RPM the LTFT corrects itself and the misfire goes away.

 

For diagnostics purposes what gear and speeds are you driving at below 2000 for sustained periods of time?

I'm aware that 2000 is usually too low and will usually stick to around 3000 where the torque picks up is at but we had some snow come in and I was cruising in 2nd gear at about ~20 mph give or take through some thicker snow, that was the most recent occurrence of it. I'm fine driving above 2000 and all but it just becomes an issue when I'm in scenarios like previously mentioned or when I'm slowly driving around at a crawl in 1st gear in a parking lot or something of that sort. Am I chasing a nonexistent problem? Is it literally just a skill issue and I need to change my driving style? Or should something be wrong to trigger it that often? I do have to say though, I appreciate the help and advice from everyone.