P0305 error

[PeachesSabrina]

Howdy folks new user here and I am running into a P0305 error on a 2006 4.2 Trailblazer and yes I searched the forums.
So here is the issue she starts right up, so it's not the fuel pump (which may be starting to go bad but it doesn't seem like it). The engine isn't running rough, I mean it sounds off but it doesn't sound rough.
Gas mileage isn't that bad it's getting about 14mpg, it starts right up when I crank it. Spark plugs have been changed, as well as the coil, their is no burning oil so I don't think it's a blown gasket nor do I think it's a bad valve seal. The spark plug has no signs of burning oil on it.
The FT(LT) seem a little high when it starts up but settles down after it warms up the FT(ST) seems within specs. Last time I checked the F/A ratio was about 14.9:1 so not to bad.
It fails a smog test from my ODB2 Scanner.
I am starting to lean to the 02 Sensor(s) are bad as it seems like they are the original sensors. Any other ideas?

 

[TJBaker57]

Howdy folks new user here and I am running into a P0305 error on a 2006 4.2 Trailblazer and yes I searched the forums.
So here is the issue she starts right up, so it's not the fuel pump (which may be starting to go bad but it doesn't seem like it). The engine isn't running rough, I mean it sounds off but it doesn't sound rough.
Gas mileage isn't that bad it's getting about 14mpg, it starts right up when I crank it. Spark plugs have been changed, as well as the coil, their is no burning oil so I don't think it's a blown gasket nor do I think it's a bad valve seal. The spark plug has no signs of burning oil on it.
The FT(LT) seem a little high when it starts up but settles down after it warms up the FT(ST) seems within specs. Last time I checked the F/A ratio was about 14.9:1 so not to bad.
It fails a smog test from my ODB2 Scanner.
I am starting to lean to the 02 Sensor(s) are bad as it seems like they are the original sensors. Any other ideas?

Does your scan tool show live data such as misfire counts per cylinder ??

When the check engine lights for the P0305 it does not flash but turns on solid, correct??

 

[mrrsm]

If you are presently having regular Heavy Rains in the Pacific Northwest that are coincidental with these P0305 Mis-Fire Issues... THIS Thread could prove to be very helpful:

Need to know what the new hood seal looks like.

I suffered the Cyl 4 misfire problem, but it hasn't reoccurred. It happened several weeks after I changed the plugs, so I may have disturbed the coil pack seal, 'cause it hasn't been a problem for 4 years of heavy rains & such. I think it was a matter of tree debris (acorns, twigs & leaves)...

gmtnation.com

And here is an interesting solution for Owners of Later Model Trailblazers, Envoys & Colorados having Water Intrusion Related Mis-Fires due to the Updated Design of the Coil-On-Plug Units having an Air Opening on Top with a PNF (Pretty Nifty Fix) for that Problem:

By Symptom Archives

ricksfreeautorepairadvice.com

 

[PeachesSabrina]

Does your scan tool show live data such as misfire counts per cylinder ??

When the check engine lights for the P0305 it does not flash but turns on solid, correct??

Correct it's solid. And my tool doesn't have a misfire count

 

[PeachesSabrina]

If you are presently having regular Heavy Rains in the Pacific Northwest that are coincidental with these P305 Mis-Fire Issues... THIS Thread could prove to be very helpful:

Need to know what the new hood seal looks like.

I suffered the Cyl 4 misfire problem, but it hasn't reoccurred. It happened several weeks after I changed the plugs, so I may have disturbed the coil pack seal, 'cause it hasn't been a problem for 4 years of heavy rains & such. I think it was a matter of tree debris (acorns, twigs & leaves)...

gmtnation.com

And here is an interesting solution for Owners of Later Model Trailblazers, Envoys & Colorados having Water Intrusion Related Mis-Fires due to the Updated Design of the Coil-On-Plug Units having an Air Opening on Top with a PNF (Pretty Nifty Fix) for that Problem:

By Symptom Archives

ricksfreeautorepairadvice.com

Ok I kinda sorta checked last time I washed it. No water is getting in to the engine.

 

[TJBaker57]

Do you ever see a P0300 code? Or does it only give you the P0305?

Any other codes now or in the recent past?

I don't believe a bad O2 sensor will cause a misfire except maybe under extreme conditions not seen here. And the PCM monitors the O2 sensors themselves for failures so I think you would be seeing additional codes for those then.

 

[PeachesSabrina]

Do you ever see a P0300 code? Or does it only give you the P0305?

Any other codes now or in the recent past?

I don't believe a bad O2 sensor will cause a misfire except maybe under extreme conditions not seen here. And the PCM monitors the O2 sensors themselves for failures so I think you would be seeing additional codes for those then.

Only the P0305, I mean I got the P0300 last year and the VVT code last year as well, but I changed out the VVT valve and that cleared it up. The 02 Sensors when i run a smog check fail as well. It says thecEVAP system is failing the smog check ascwell.

 

[TJBaker57]

It says thecEVAP system is failing the smog check ascwell.

Are you speaking of the emissions readiness monitors??

Be aware that when codes are cleared it is normal for it to take quite some time before the EVAP will pass the emissions readiness readout. It won't even run the tests for the EVAP unless a rather long list of conditions are met, for example more than 10% fuel in the tank but not more than 85%, starting engine coolant temps within certain limits, and so on and so on.

There may be similar things going on with the O2 sensor emissions readiness monitors. These are not fault codes but just indications that not all the required tests have been completed since the codes were last cleared.

 

[PeachesSabrina]

Are you speaking of the emissions readiness monitors??

Be aware that when codes are cleared it is normal for it to take quite some time before the EVAP will pass the emissions readiness readout. It won't even run the tests for the EVAP unless a rather long list of conditions are met, for example more than 10% fuel in the tank but not more than 85%, starting engine coolant temps within certain limits, and so on and so on.

There may be similar things going on with the O2 sensor emissions readiness monitors. These are not fault codes but just indications that not all the required tests have been completed since the codes were last cleared.

I wait about a week before I run the SMOG test after the code is cleared, so all the conditions have been met. The only thing I can think of is the coolant is running about 213-219, it's within limits but still high.

 

[TJBaker57]

wait about a week before I run the SMOG test after the code is cleared, so all the conditions have been met.

Even so, if they are not turning on the Check Engine Light, then it is more likely the tests have not been all completed.

 

[TJBaker57]

Even so, if they are not turning on the Check Engine Light, then it is more likely the tests have not been all completed.

As an example, here are the conditions that must be met for one of the EVAP tests to even run...

 

[TJBaker57]

Getting back to the misfire... If the code comes back quickly and is always P0305, the spark plug and coil having already been replaced with new then maybe a close inspection of the wiring to the coil and injector??

A scantool that displays and possibly record live misfire data could be helpful. Perhaps other cylinders are also experiencing some level of misfire but not enough to trigger a code.

I use Car Scanner Pro on my Android and this OBD2 adalter to record data flr analysis...

https://www.amazon.com/dp/B011NSX27A/?tag=gmtnation-20

 

[PeachesSabrina]

I have the Veepeak as well. Thats the thing it doesn't always come back quickly, sometimes it comes back after a week-10days. Sometimes it's quick.

 

[budwich]

You need to actually look at the misfire counts per cylinder. IF you have a veepeak, spend the $5 and get the torque app, then start looking at the per cylinder counts. Just because there is no code does not mean there are not any misfires. The coding only happens when the misfires reach a "count / timed period". If they are below that, then you won't see any codes. You might be having misfires across a number of cylinders that is just below the limit.

When you say your trims "are within limits", what are the actual values / ranges that you are seeing. Trims can be less than 25% and not code, BUT running like (not near 0) that probably means there is an issue somewhere which might take out your cat (if you are running rich) or cause other things like misfires IF "rich" running has been occurring and the cylinders have "carboned" up.

 

[PeachesSabrina]

You need to actually look at the misfire counts per cylinder. IF you have a veepeak, spend the $5 and get the torque app, then start looking at the per cylinder counts. Just because there is no code does not mean there are not any misfires. The coding only happens when the misfires reach a "count / timed period". If they are below that, then you won't see any codes. You might be having misfires across a number of cylinders that is just below the limit.

When you say your trims "are within limits", what are the actual values / ranges that you are seeing. Trims can be less than 25% and not code, BUT running like (not near 0) that probably means there is an issue somewhere which might take out your cat (if you are running rich) or cause other things like misfires IF "rich" running has been occurring and the cylinders have "carboned" up.

Ok the LT and the short term fuel sensors should equal near zero from what I have read. For example if your LT bank is reading let's say 5% and your ST fuel sensor is reading -2% then you have a fuel value of 3%. They should be zero in a perfect world, however variances of up to 8% is no cause for concern. Once you start going past 9% that's when you should start looking at O2 sensors. My LT fuel bank is in the 12% when it first1 starts up and then goes to roughly 3% after it warms up

What Should Long Term And Short Term Fuel Trim Be?

How STFT and LTFT/Short Term & Long Term Fuel Trim works. Learn more about STFT and LTFT/Short Term & Long Term Fuel Trim.

www.thedrive.com

I found another site that does a better job but I can't remember it.

On top of that at idle RPM'S are about 600-625.

 

[TJBaker57]

I have the Veepeak as well. Thats the thing it doesn't always come back quickly, sometimes it comes back after a week-10days. Sometimes it's quick.

Not coming back quickly sort of steers me away from the thought of things like a dirty fuel injector.

 

[TJBaker57]

My LT fuel bank is in the 12% when it first1 starts up and then goes to roughly 3% after it warms up

Something I never see talked about is that fuel trims are not just one set of numbers. There is a thing called fuel trim cells. There's a whole grid of fuel trim cells for use under varying conditions. There's a set for idling, there's a different set while accelerating, another when decelerating, and so on. I suspect that when we see fuel trims reported these are mostly when idling and the fuel trim cell and trims in use elsewhere throughout the operating range could be substantially different.

 

[TJBaker57]

I just fiddled around with the Torque Pro app to watch misfires. It's what I do for kicks...

 

[PeachesSabrina]

I just fiddled around with the Torque Pro app to watch misfires. It's what I do for kicks...

Mine doesn't have that option or at least I don't know which sensor to use. I also cleared the code then took it for a ride. If you look everything cleared except for the evap system. Also I logged the trip just have to figure a way to zip it up. I am beginning to point more to an EVAP issue.

 

[TJBaker57]

Mine doesn't have that option or at least I don't know which sensor to use

There is a set of GM specific add-ons that need to be loaded through the settings menu.

Settings, Manage Extra PIDs/Sensors, (tap 3 dots top right) Add pre-defined set, Select "Pontiac GM Opel Vauxhall.

This will add a selection of GM specific sensor readings. Some will apply to your vehicle and some will not. The 'Current' and 'History' misfires should work.

 

[PeachesSabrina]

There is a set of GM specific add-ons that need to be loaded through the settings menu.

Settings, Manage Extra PIDs/Sensors, (tap 3 dots top right) Add pre-defined set, Select "Pontiac GM Opel Vauxhall.

This will add a selection of GM specific sensor readings. Some will apply to your vehicle and some will not. The 'Current' and 'History' misfires should work.

Here is the current one.

 

[PeachesSabrina]

I am also pulling -20 hg on the vacuum so I don't think it's a seal that's gone bad. Plus I don't have oil and Antifreeze mixing so I don't think it's that.

 

[budwich]

There is also history misfires.... but your monitoring appears to only show counts for one cylinder. One question, is that post from startup or when?.... NOTE: the counts are not "accummative". They are "period" based so you will see these move around with time. There have been posts dealing with aspects of the knock sensor and CPS.... but I would expect to see more cylinders "attacked". Further, do you actually "feel" the engine having run issues at the time when the code is set? One other possible test would be compression tests and compare.

 

[Mooseman]

I went through a similar issue with misfires mostly on cyl 4 but only at idle. I never was able to figure it out and don't know if it's still there as I usually don't let idle too much and haven't been using it much. I'd have to recheck the misfires.

Very Slight Miss at Idle

Yesterday on the TB, at 117k km, saw the CEL come on and code came up for P0304. Fired up Torque and it was missing on cylinder #4 but only at idle or stopped at a light. It's not a big miss since I can't feel it at all and it's just a couple of misses per refresh cycle. While driving...

gmtnation.com

 

[TJBaker57]

Raining up there in Tacoma much??

There was an issue where water would get through the area where the back of the hood meets body and drip down on the area of the 5th cylinder coil. I think it sometimes would actually get in underneath the ignition coil.

 

[TJBaker57]

I had to take a look at my own to see that the water falls more around the 4th coil than the 5th, but I still wonder about the possibility..

 

[PeachesSabrina]

Raining up there in Tacoma much??

There was an issue where water would get through the area where the back of the hood meets body and drip down on the area of the 5th cylinder coil. I think it sometimes would actually get in underneath the ignition coil.

I read about that issue which is why I checked it out. I recently washed it and opened the hood and watched to see if any water got into the engine, nope it didn't. So the weather seal is still good.

 

[PeachesSabrina]

Ok, I looked at the historical misses. It hit 10k and then it settled down and started firing regularly. That lines up with the long term fuel trim that I was talking about it tends to skew heavy when I first fire it up, then at idle but after I get going it tends to settle down. I wonder if the crank case sensor needs to be replaced.

 

[PeachesSabrina]

There is also history misfires.... but your monitoring appears to only show counts for one cylinder. One question, is that post from startup or when?.... NOTE: the counts are not "accummative". They are "period" based so you will see these move around with time. There have been posts dealing with aspects of the knock sensor and CPS.... but I would expect to see more cylinders "attacked". Further, do you actually "feel" the engine having run issues at the time when the code is set? One other possible test would be compression tests and compare.

Honestly no I mean it kinda bogs down a little bit but then after the code is cleared it acts like it normally would. I mean I have had mechanics listen to it but they haven't heard any major misfires.

 

[PeachesSabrina]

I went through a similar issue with misfires mostly on cyl 4 but only at idle. I never was able to figure it out and don't know if it's still there as I usually don't let idle too much and haven't been using it much. I'd have to recheck the misfires.

Very Slight Miss at Idle

Yesterday on the TB, at 117k km, saw the CEL come on and code came up for P0304. Fired up Torque and it was missing on cylinder #4 but only at idle or stopped at a light. It's not a big miss since I can't feel it at all and it's just a couple of misses per refresh cycle. While driving...

gmtnation.com

BTW, I read your thread their, what stereo are you using?

 

[budwich]

Ok, I looked at the historical misses. It hit 10k and then it settled down and started firing regularly. That lines up with the long term fuel trim that I was talking about it tends to skew heavy when I first fire it up, then at idle but after I get going it tends to settle down. I wonder if the crank case sensor needs to be replaced.

The LT at start up is somewhat "strange". I monitor those quite closely and rarely see much above 5-6 for normal idle and running "lightly" down the road.
Has your exhaust manifold ever been replaced...known for cracking which at "cold" might be leaking a bit to cause "rich running".... but that would normally impact more cylinders IF they were "missing". how many miles on the vehicle. As you suggest, possibly a CPS issue. You can also watch your timing to see if anything happens there at start up, idling, and stable "road running".

 

[Mooseman]

BTW, I read your thread their, what stereo are you using?

It's an Android something. Still using it.

 

[PeachesSabrina]

The LT at start up is somewhat "strange". I monitor those quite closely and rarely see much above 5-6 for normal idle and running "lightly" down the road.
Has your exhaust manifold ever been replaced...known for cracking which at "cold" might be leaking a bit to cause "rich running".... but that would normally impact more cylinders IF they were "missing". how many miles on the vehicle. As you suggest, possibly a CPS issue. You can also watch your timing to see if anything happens there at start up, idling, and stable "road running".

As far as the exhaust manifold I don't think so (I bought it last year so I don't know). The mileage is ~183k. As far as the timing I would have to check again but if I remember the timing goes from 3°-20° between idle to stable driving conditions.

 

[PeachesSabrina]

The LT at start up is somewhat "strange". I monitor those quite closely and rarely see much above 5-6 for normal idle and running "lightly" down the road.
Has your exhaust manifold ever been replaced...known for cracking which at "cold" might be leaking a bit to cause "rich running".... but that would normally impact more cylinders IF they were "missing". how many miles on the vehicle. As you suggest, possibly a CPS issue. You can also watch your timing to see if anything happens there at start up, idling, and stable "road running".

Here is why I think it is also a O2 sensor, I recently had to change every brake rotor. Come to find out the previous owners never replaced the original rotors. So I would assume that they never replaced the 02 Sensors as well.

 

[TJBaker57]

It hit 10k and then it settled down and started firing regularly

10,000 misfires!?!?

Personally I would pretty much ignore the fuel trims until I got the misfiring cleared up.

 

[Tankcruiser]

cat converter will need to be checked too after 10k misfires as they tend to plug up quickly....... back pressure test 0 to 5 psi gauge and less than 2 psi atm

 

[mrrsm]

(1) Suggest a Cylinder Compression Test on #5 and-or a complete Cylinder Compression Balance Test on all Cylinders, first Dry and then Wet with just a few drops of Engine Oil squirted inside to check on any Excessive Cylinder Wall Wear. If the Oil Dipstick Smells like Gasoline, Excessive Ring Blow-By will be the culprit. The Engine Oil and Oil Filter should be changed very soon afterward, should you make this unfortunate discovery:

Amazon.com : engine compression test kit

(2) High Mileage GM 4.2L Engines can build up enough Carbon Deposits in the Combustion Chambers and around Valve Seats and literally Glue the two top Compression Rings into the Side Grooves of the Pistons. This is enough to prevent the Valves from seating properly and ruin compression from the loss of Low Tension Ring Expansion. GMTN has several Threads describing in great detail how to perform a Top Engine Cleaning Procedure with ACDelco (TEC) Top Engine Cleaner.

Amazon.com : acdelco top engine cleaner 19355198 cleaner 32oz. 10-3015

 

[Chickenhawk]

In addition to the above, what make of coils did you use, and what is the make and model of spark plugs?

During a plug change, it is sometimes possible to not connect the coil to the plug properly. If run like that, it often roasts the coil, even when new. Double check the connect on that coil. If it is firm, then try changing that coil with another cylinder. If you are using 41-103 AC Delco plugs, then it is possible even a new coil has gone bad.

 

[PeachesSabrina]

In addition to the above, what make of coils did you use, and what is the make and model of spark plugs?

During a plug change, it is sometimes possible to not connect the coil to the plug properly. If run like that, it often roasts the coil, even when new. Double check the connect on that coil. If it is firm, then try changing that coil with another cylinder. If you are using 41-103 AC Delco plugs, then it is possible even a new coil has gone bad.

I am using the 41-103 as well as the Delphi/AC Delco brand coil. As to the previous posters, I would agree with you if the the misfires were "constant" but they aren't. They are totally random when they start. The only "constant" that I can think of is I am about 1/4 of a tank.

 

[TJBaker57]

It hit 10k and then it settled down and started firing regularly.

Can you elaborate on this?? Does it misfire badly (10k) only when started cold? And does it then straighten out and not continue to pile up history misfire count higher and higher? If this is the case I would very closely inspect all wiring connectors for cylinder 5. The 3 wires connected to the coil and the wiring to fuel injector as well. For the fuel injector this will require disconnecting the 8 terminal harness connector that is nearby the throttle body, beneath the resonator, on top of the valve cover. I have had the experience of a connection that would be intermittent when cold but once warmed was OK.