New guy battling P0304
Thread Starter
New Member
Joined: 03-02-2023
Posts: 20
From: Pittsburgh
New guy battling P0304
So I had this big huge long gigantic post started about 2 months ago when I joined and before I could submit, something happened and it got deleted. I'm still having issues and I'm at my wits end so I decided to start over and ask you guys for some ideas.
car is a 2006 HHR LT. 2.4 auto. just rolled 94,000 miles yesterday.
backstory- I purchased the car in nov 2022. saved it from going to the scrap yard. the previous owners got tired of dumping money into it. well when I got it, I found out they had ended up using a bad mechanic who was just ripping them off. when I bought it they were told it likely needing a timing chain, hence the reason I got it as they didn't want shell out that kinda money
my first analysis of the car, I discovered bozo mechanic left the MAF sensor unplugged. no wonder the car wouldn't run!. car had a slew of codes from them trying to drive with the sensor unplugged then diving into car more, I find every part replaced is the absolute cheapest, crappiest part they make. so I set out to fix all of bad mechanics problems hoping that would be in.
so I replaced:
air filter
all 4 coil packs
4 spark plugs with AC delco
oil and filter change for good measure.
I found nothing related to the timing chains needing attention. the car has the new style tensioner already, I hear no noise, and it had never throw any of the cam related codes.
due to some unforeseen life circumstances, I didn't get to start driving the car until February. as soon as I started driving it, I stated getting a random 304 misfire code. it was very sporadic, I was able to pass the PA emission testing with no problem.
But since then, the code seems to be coming on more and more. initially, I would go about 10 days- 2 weeks without a code. more recently every time the car starts you are getting a code.
in addition to the above replaced items, I also replaced/repaired the following:
1- new O2 sensor in manifold
2- 4 new fuel injectors
3- new evap purge valve ( it threw this code 1 time and it was cheap so I changed)
4- cleaned throttle body and MAF.
5- I swapped coils/plugs/fuel injectors around multiple times, code always stays on 4.
6- cleaned fuel rail.
I attempted a compression test and a leak down test. for the compression test I admit I forgot to try to open throttle body so my numbers are a little low- 160, 160, 150, 125. the leak down test I was struggling with as I think valves on #4 may have still been open. in doing some reading online I found you might have to remove the valve cover to ensure TDC and valves closed?
I have a bore scope and put it down the plug holes. I see nothing out of the ordinary. plugs also all look the same.
in addition to that, I also have access to a pretty fancy Autel scanner. I was able to look at far more than a basic hand held scanner. pulling the freeze frame data, the only item that is out of spec related to the misfire is "Command Air Fuel Ratio". every time the code trips this value is at .8 or 1. according to the range listed in the Autel it should be between 10-20? Googling that there isn't really much, everything points to the O2 sensor(which I did change). and I never had any O2 codes
the only thing I have been able to determine for sure from the freeze frame data is that the code always sets about 2-3 minutes after startup, when the car is idling (no load). doesn't matter if the car is hot or cold, if you are parking or just coasting to a stop, if the code is going to set, that's when it does it, if you don't get it within the first 5 min of starting, you won't get it that trip.
the only other weird thing is I also have a code P0520 showing on the Autel but not a handheld, this is related to the oil pressure sensor. I don't see how that could correlate to a misfire though?
just looking for any ideas on where to turn next?
car is a 2006 HHR LT. 2.4 auto. just rolled 94,000 miles yesterday.
backstory- I purchased the car in nov 2022. saved it from going to the scrap yard. the previous owners got tired of dumping money into it. well when I got it, I found out they had ended up using a bad mechanic who was just ripping them off. when I bought it they were told it likely needing a timing chain, hence the reason I got it as they didn't want shell out that kinda money
my first analysis of the car, I discovered bozo mechanic left the MAF sensor unplugged. no wonder the car wouldn't run!. car had a slew of codes from them trying to drive with the sensor unplugged then diving into car more, I find every part replaced is the absolute cheapest, crappiest part they make. so I set out to fix all of bad mechanics problems hoping that would be in.
so I replaced:
air filter
all 4 coil packs
4 spark plugs with AC delco
oil and filter change for good measure.
I found nothing related to the timing chains needing attention. the car has the new style tensioner already, I hear no noise, and it had never throw any of the cam related codes.
due to some unforeseen life circumstances, I didn't get to start driving the car until February. as soon as I started driving it, I stated getting a random 304 misfire code. it was very sporadic, I was able to pass the PA emission testing with no problem.
But since then, the code seems to be coming on more and more. initially, I would go about 10 days- 2 weeks without a code. more recently every time the car starts you are getting a code.
in addition to the above replaced items, I also replaced/repaired the following:
1- new O2 sensor in manifold
2- 4 new fuel injectors
3- new evap purge valve ( it threw this code 1 time and it was cheap so I changed)
4- cleaned throttle body and MAF.
5- I swapped coils/plugs/fuel injectors around multiple times, code always stays on 4.
6- cleaned fuel rail.
I attempted a compression test and a leak down test. for the compression test I admit I forgot to try to open throttle body so my numbers are a little low- 160, 160, 150, 125. the leak down test I was struggling with as I think valves on #4 may have still been open. in doing some reading online I found you might have to remove the valve cover to ensure TDC and valves closed?
I have a bore scope and put it down the plug holes. I see nothing out of the ordinary. plugs also all look the same.
in addition to that, I also have access to a pretty fancy Autel scanner. I was able to look at far more than a basic hand held scanner. pulling the freeze frame data, the only item that is out of spec related to the misfire is "Command Air Fuel Ratio". every time the code trips this value is at .8 or 1. according to the range listed in the Autel it should be between 10-20? Googling that there isn't really much, everything points to the O2 sensor(which I did change). and I never had any O2 codes
the only thing I have been able to determine for sure from the freeze frame data is that the code always sets about 2-3 minutes after startup, when the car is idling (no load). doesn't matter if the car is hot or cold, if you are parking or just coasting to a stop, if the code is going to set, that's when it does it, if you don't get it within the first 5 min of starting, you won't get it that trip.
the only other weird thing is I also have a code P0520 showing on the Autel but not a handheld, this is related to the oil pressure sensor. I don't see how that could correlate to a misfire though?
just looking for any ideas on where to turn next?
Moderator
Joined: 05-01-2014
Posts: 8,512
From: California
Hi Joe, 
to the forums!
The compression on #4 is noticeably lower than the other 3 cylinders.
Removing the valve cover is easy, usually can reuse the gasket(s). It will also allow you to look at the timing chain for tightness.
to the forums! The compression on #4 is noticeably lower than the other 3 cylinders.
Removing the valve cover is easy, usually can reuse the gasket(s). It will also allow you to look at the timing chain for tightness.
Moderator
Joined: 01-23-2009
Posts: 26,533
From: Fredericksburg,VA
To fix the logging out problem: tick on the "remember me" at the login.
Your compression shows #4 probably has a burned valve and #3 has something going on.
Are you losing coolant, growing oil? It might be a blown head gasket between 3 & 4. A leak down dry and wet would help narrow things down.
Please don't use whatever textual name you think you remember. The code numbers are what counts, none are insignificant. Don't go by what any scanner "says" They are written by a non-mechanic translating from a language they don't speak to a language they don't speak and getting the information from farcebook.
P0520 is the oil pressure sensor CIRCUIT, meaning most likely a loose connection, maybe the connection is oil soaked or just a bad sensor.
What codes are showing now? Historic/permanent/stored, pending and current.
Your compression shows #4 probably has a burned valve and #3 has something going on.
Are you losing coolant, growing oil? It might be a blown head gasket between 3 & 4. A leak down dry and wet would help narrow things down.
Please don't use whatever textual name you think you remember. The code numbers are what counts, none are insignificant. Don't go by what any scanner "says" They are written by a non-mechanic translating from a language they don't speak to a language they don't speak and getting the information from farcebook.
P0520 is the oil pressure sensor CIRCUIT, meaning most likely a loose connection, maybe the connection is oil soaked or just a bad sensor.
What codes are showing now? Historic/permanent/stored, pending and current.
Thread Starter
New Member
Joined: 03-02-2023
Posts: 20
From: Pittsburgh
No coolant loss or extra oil. No signs of coolant in the chambers looking with borescope.
Not sure what your meant about codes I already gave you the 2 numbers.
P0304
p0520. This code only shows with the fancy autel scanner.
Now if you really want to get weird- the autel actually only shows P0300 however the logs show zero misfires on all cylinders except number 4. Maybe this is just the way the autel software does it.
do you know anything about this command air fuel ratio in the freeze frame data? Why is that for some reason locked around 1?
Not sure what your meant about codes I already gave you the 2 numbers.
P0304
p0520. This code only shows with the fancy autel scanner.
Now if you really want to get weird- the autel actually only shows P0300 however the logs show zero misfires on all cylinders except number 4. Maybe this is just the way the autel software does it.
do you know anything about this command air fuel ratio in the freeze frame data? Why is that for some reason locked around 1?
Administrator
Joined: 10-13-2011
Posts: 40,083
From: Welland,Ont Canada
Help, welcome to the site. The 2.4 litre engine always had the hump on the timing chain tensioner, it was the 2.2 in 2006 thru 2008 that had the flat tensioner, pre VVT.
Take off the valve cover look at the timing chain, inspect the front timing chain guide for damage.
Take off the valve cover look at the timing chain, inspect the front timing chain guide for damage.
Thread Starter
New Member
Joined: 03-02-2023
Posts: 20
From: Pittsburgh
I’m pretty experienced with engines, but most of that is with sbc/bbc so VVT is a whole new animal to me.
I was also thinking of doing the “old school” vacuum gauge to check for a burnt valve.
Moderator
Joined: 01-23-2009
Posts: 26,533
From: Fredericksburg,VA
Command A/F is your foot on the gas pedal.
To me, you indicated that there have been codes but no O2 or timing related ones. That is what I meant.
First you need to understand that P0300 means "miss detected" not whatever your scanner says.
Your compression numbers are telling you why there is a misfire on #4. Now you need figure out why the compression is so low in #4 and suspicious in #3.
To me, you indicated that there have been codes but no O2 or timing related ones. That is what I meant.
First you need to understand that P0300 means "miss detected" not whatever your scanner says.
Your compression numbers are telling you why there is a misfire on #4. Now you need figure out why the compression is so low in #4 and suspicious in #3.
Thread Starter
New Member
Joined: 03-02-2023
Posts: 20
From: Pittsburgh
Command A/F is your foot on the gas pedal.
To me, you indicated that there have been codes but no O2 or timing related ones. That is what I meant.
First you need to understand that P0300 means "miss detected" not whatever your scanner says.
Your compression numbers are telling you why there is a misfire on #4. Now you need figure out why the compression is so low in #4 and suspicious in #3.
To me, you indicated that there have been codes but no O2 or timing related ones. That is what I meant.
First you need to understand that P0300 means "miss detected" not whatever your scanner says.
Your compression numbers are telling you why there is a misfire on #4. Now you need figure out why the compression is so low in #4 and suspicious in #3.
