very rough first start of day - check engine light - P0306 - questionable dealer response

[inmanlanier]

In my case I'll never know what was going since they didn't tell me what they did.

Based on than my many years dealing with cars (building motors, tuning carbs, learning FI system logic, racing cars, troubleshooting, etc.) it always comes back to the basics - spark or fuel. With today's systems, a myriad of causes can cause problems with either. It doesn't change the symptoms, however - you have some missing spark, or you have too little or too much fuel.

In my case with this particular issue (and others in the past) the smell of the exhaust was quite rich (i.e. raw unburned fuel). I'm highly confident I had a stuck injector because it was so rich in smell.

If you have the same symptoms you don't want to drive it around like this for any extended periods of time because the excess unburned fuel will wash down the oil film on the cylinder walls that keeps all lubricated well. I remember a different post a while back where the injector leakage was so high, after shutting down the motor - enough fuel got in one of the cylinders to hydraulic lock it (i.e. the liquid gas has a volume greater than the compressed cylinder volume at top dead center so the motor seizes). Not common, but things can break in those scenarios.

Sniff your exhaust - it is smells like fuel and you have white smoke, they need to figure out why (stuck injector one of the possible causes).

 

[mth]

I will check my codes. I drove the car this afternoon and it runs well and does not smoke, not even at start-up or idle. I do still have the CEL. I will post any updates. I am in Tampa and am tight with one of the mechanics. Had an appointment to bring it in last time it did this, then the CEL cleared and no more issue. I am in the service industry and know how much time it takes to troubleshoot something that it not broke so did not bring it in. That was 3 months ago. I did not always run premium but started after that episode. Unless wife put cheap gas in, that was not the fix. May add some fuel additive . Your buddy have any suggestions on additives?

 

[inmanlanier]

Same issue I've had in the past, except in the past no codes. This time P0306 (as stated above). My codes had been coded as permanent status (meaning a reader cannot clear them). I was surprised that mine were permanent based on that short morning series of events.

Only dealer type equipment can clear the permanent codes, however there are some special driving routines you can go through to clear (assuming the symptoms are no longer present) - a little tedious but it works. Please let us know the codes that are stored and whether they are permanent or not.

 

[mth]

Ok so I have P0304 Cylinder 4 misfire. One says confirmed and 1 says permanent. I cleared for sag and the confirmed code cleared, permanent did not clear but it did turn off CEL. Since its the weekend I may add some juice and fill up, see if code comes back quickly and make app for next week.

 

[mth]

Found this
P0304 Trouble Code Diagnosis- Hyundai Genesis
There are quite a few things that can cause the P0304 trouble code to trigger the Hyundai Genesis. Here are the most common problems that will throw the code. They are presented somewhat in order from most to least likely to be causing the code:

• Bad Spark Plugs– Spark plugs are one of the most common causes of P0304. Take a look at the electrodes and see if they are in good shape. Most vehicles now come with iridium plugs that need changed very infrequently. That being said, the plugs are a great place to start. Here’s a great video on how to see if a spark plug is bad.
• Spark Plug Wires– On most modern engines, the plug wires are not nearly as long as they once were, but they can still go bad. Here’s how to tell if your plug wires are bad (video).
• Coil Packs– Coil packs rarely go bad, but when they do, they can certainly cause P0304 in your Hyundai Genesis. Replacing a set can be very expensive. Here’s how to test them.
• Bad Fuel Injector– If you have a fuel injector that has gone bad, it won’t be able to properly atomize the fuel and you’ll get the P0304. Here’s a good video on how to diagnose an injector, it can be a little tricky. This is definitely not the place to start.
• Vacuum leak– If your Genesis has a vacuum leak, it can be very difficult for it to get the right air/fuel mixture. This will cause the cylinders to misfire and it’ll throw the P0304 if the leak is around that specific cylinder on the intake manifold. It’s easy (and kind of fun) to chase one down. Popular Mechanics: How to find a vacuum leak.
• Cam or Crank Sensors– This one is very unlikely, but it does happen. If the ECU is not getting the right signal from these sensors, the vehicles timing is not going to sync up and it’ll misfire.
• Low Compression– If you have a leaking head gasket, bent valve, cracked head, etc.. that would cause compression to not be as high as it should, you’re going to get P0304. You should also feel the vehicle is down on power as well.

 

[Kraig Wilkinson]

My 2015 is doing this right now. Just started yesterday. Wife was leaving work, check engine,rough idle, she pulled out and got on it(probably 65 for her). I have front and rear cameras so I looked today and could see the white smoke as she was accelerating. It has done this one other time but cleared up. I will finish reading this post to see what others have found.

The second day I owned my 2015 5.0 it started really rough! Idled rough also,like shitty rough. I put 2 bottles of in injector cleaner each tank of gas. Did that twice and put one in the next 10 tanks and now one every other tank or so, and it made a big difference! Idles so smooth now! Like a night and day difference.

 

[inmanlanier]

YUP. mth - white smoke is likely fuel. Injector. No doubt in my mind what you had going on.

I periodically put a bottle of Chevron Techron in the tank. In the day it was reputed to be the best cleaner.

Keep us posted.

 

[Kraig Wilkinson]

The second day I owned my 2015 5.0 it started really rough! Idled rough also,like shitty rough. I put 2 bottles of in injector cleaner each tank of gas. Did that twice and put one in the next 10 tanks and now one every other tank or so, and it made a big difference! Idles so smooth now! Like a night and day difference.

I

YUP. mth - white smoke is likely fuel. Injector. No doubt in my mind what you had going on.

I periodically put a bottle of Chevron Techron in the tank. In the day it was reputed to be the best cleaner.

Keep us posted.

The fuel injectors on a direct injected engine the injectors are in the the combustion chamber I believe, therefore they are subjected to the high heat and carbon build just like a piston or a valve and spark plug. I other words they get worked and dirty . Need to keep clean.

 

[Whitey]

I periodically put a bottle of Chevron Techron in the tank. In the day it was reputed to be the best cleaner.

It still is (top 3 usually on any list), just ordered the first bottle for the Genny.

 

[Kraig Wilkinson]

It still is (top 3 usually on any list), just ordered the first bottle for the Genny.

Do they sell non ethanol gas where you live Whitey? My 5.0 seems to like that better than the ethanol blend.

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[Whitey]

Do they sell non ethanol gas where you live Whitey? My 5.0 seems to like that better than the ethanol blend.

Funny you mention, as I haven't gone looking for it but I'm sure they do. A quick search just pointed me to several stations nearby that carry it, so may give a shot just to see how she runs and if there's any noticeable difference.

 

[Kraig Wilkinson]

Funny you mention, as I haven't gone looking for it but I'm sure they do. A quick search just pointed me to several stations nearby that carry it, so may give a shot just to see how she runs and if there's any noticeable difference.

I really believe it helps. I definitely see it in the MPG. After a couple tanks she will be happy. Runs nice and smooth and well.

 

[inmanlanier]

You will get 4% better mpg on all gasoline (rec fuel) vs. a 10% ethanol mix because Ethanol has 60% of the energy content of gasoline.

 

[Kraig Wilkinson]

You will get 4% better mpg on all gasoline (rec fuel) vs. a 10% ethanol mix because Ethanol has 60% of the energy content of gasoline.

I suppose there is something wrong with my vehicles, my 2500suburban picks up 3 to 4 mpg and my 04 impala gets about 5 more mpg?? Even my 8.1 GMC picks up a couple mpg???? I am getting 27 to 30 with my 2015 5.0 all run non ethanol.

 

[Kraig Wilkinson]

I suppose there is something wrong with my vehicles, my 2500suburban picks up 3 to 4 mpg and my 04 impala gets about 5 more mpg?? Even my 8.1 GMC picks up a couple mpg???? I am getting 27 to 30 with my 2015 5.0 all run non ethanol.

I apologize I read your M post wrong.. All apologizes!!!!!

 

[EdP]

Funny you mention, as I haven't gone looking for it but I'm sure they do. A quick search just pointed me to several stations nearby that carry it, so may give a shot just to see how she runs and if there's any noticeable difference.

The Wawa station is about 50 cents more for it. Bought it for the generator as some small engines don't do well with corn juice.

 

[inmanlanier]

I was simply stating facts about energy content and reality. There are all sorts of myths out there that people embrace. Nothing wrong with that, but as my other engineer bud says oftimes 'the laws of physics are immutable'. To the numbers above - 100% of 90% plus 60% of 10% is .90 + .06 = 0.96 or 96%. Hence, all fuel (100%) minus 96% is a 4% delta.

The math has never worked out for me either (to EdP's input). All my garden equipment uses rec fuel because the cheap SOBs that design the equipment don't have fuel lines that can handle the alcohol attack. It's insane. I can't tell you the number of fuel lines and carb gaskets I've replaced on lawn equipment until I finally learned. No issues since going with rec fuel - in fact from my bud's input it lasts longer than the typical ethanol blends before starting to break down.

I've never seen any studies that correlate how alcohol fuels (i.e. 10%) cause more issues with injectors than strait gasoline. For that reason, I find the cheapest gas available and periodically put some Techron in the tank.

 

[Whitey]

I've never seen any studies that correlate how alcohol fuels (i.e. 10%) cause more issues with injectors than strait gasoline. For that reason, I find the cheapest gas available and periodically put some Techron in the tank.

This was basically my plan from the start. But I guess it couldn't hurt to run a few tanks of the pure stuff just to see.

 

[Kraig Wilkinson]

This was basically my plan from the start. But I guess it couldn't hurt to run a few tanks of the pure stuff just to see.

I am not sure if the added MPG off sets the added price? I only drive my 5.0 2or3 times a month , so the little added coat diea not bother me. It cost about 38 Cents more per gallon here in S D.

 

[mth]

So an update on the permanent code of P0304. I mentioned earlier I cleared the verified code but the perm did not clear. I put in some Liqui Moly injector cleaner with appr 7 gals left in tank. Ran that out a refilled with Shell 93. Car is def running smoother and CEL has not come back on. For sag I checked codes and the permanent P0304 code is gone.