09 TB w/I6...some months back started getting a p0306 code....did the usual....swapped the coil to another cylinder and did the same with the plug as well(be advised plugs are only a few months old,coils are all ACdelcos and MIGHT be original). Traveled approx. 500 miles after resetting the engine light before it came back on and again the P0306 was the reason. This time I purchased a new coil(ACdelco), and put it in the #6 cylinder spot. Traveled over 600 miles this time around before the p0306 code popped again. What's next?....cleansing with sage...voo-doo ritual?........Please advise!!......Thanks in advance!
P0306
- Thread starter retiredcopper
- Start date
Mooseman
Moderator
Combustion is dependant on these three things: air, fuel and spark. Lets go over each one.
Air: pretty simple, if it's getting the proper amount in the cylinder with the intake valve opening, it's good. If it's getting too much, it may not fire. Check for a vacuum leak but for a misfire, it would be a pretty big hole to just that one cylinder and would likely affect others.
Fuel: Verify proper amount of fuel is getting in the cylinder. With a misfiring cylinder, the spark plug should be wet with fuel or completely dry if it's a lack of fuel.
Spark: Verify there is an actual spark. Using a spark tester (and not just using the spark plug outside the cylinder due to possibility of fire), verify that there is a spark. It could be a wiring issue to the coil rather than an issue with the coil itself.
If all that checks out, then just remember the following for the above to use those elements: suck, squeeze, bang, blow.
Suck: Is the engine able to suck in the air/fuel mix into the cylinder. Are the valves opening and closing properly?
Squeeze: Is the engine compressing the mix?
Bang: Is the engine able to ignite the compressed mix?
Blow: Is the engine able to blow the exhaust out the exhaust valve after combustion?
For these, a compression test will tell all. Do all the cylinders to compare to the good cylinders. Remove the fuel pump relay while doing the test and use a jumper wire at the starter relay to crank it.
Go from your results.
Air: pretty simple, if it's getting the proper amount in the cylinder with the intake valve opening, it's good. If it's getting too much, it may not fire. Check for a vacuum leak but for a misfire, it would be a pretty big hole to just that one cylinder and would likely affect others.
Fuel: Verify proper amount of fuel is getting in the cylinder. With a misfiring cylinder, the spark plug should be wet with fuel or completely dry if it's a lack of fuel.
Spark: Verify there is an actual spark. Using a spark tester (and not just using the spark plug outside the cylinder due to possibility of fire), verify that there is a spark. It could be a wiring issue to the coil rather than an issue with the coil itself.
If all that checks out, then just remember the following for the above to use those elements: suck, squeeze, bang, blow.
Suck: Is the engine able to suck in the air/fuel mix into the cylinder. Are the valves opening and closing properly?
Squeeze: Is the engine compressing the mix?
Bang: Is the engine able to ignite the compressed mix?
Blow: Is the engine able to blow the exhaust out the exhaust valve after combustion?
For these, a compression test will tell all. Do all the cylinders to compare to the good cylinders. Remove the fuel pump relay while doing the test and use a jumper wire at the starter relay to crank it.
Go from your results.
TJ,she runs fine and no loss of power at all...only when the light comes on and I cringe...already know what it is...
Thanks Moose,just asked my neighbor and he has the gauge and some fittings....lets see what happens...
I am a firm believer of gathering all the relevant data before diving into repairs Maybe driven by being too lazy to dig into actual physical work!!
I would be recording the current misfire counts for all cylinders. I would be using the Car Scanner ELM OBD2 app and a Veepeak Mini Bluetooth OBD2 Scanner as it excels in such data gathering having everything needed for such tasks right there in the app. Only need to add in the GM specific PIDs in the app.
I would be recording the current misfire counts for all cylinders. I would be using the Car Scanner ELM OBD2 app and a Veepeak Mini Bluetooth OBD2 Scanner as it excels in such data gathering having everything needed for such tasks right there in the app. Only need to add in the GM specific PIDs in the app.
Mooseman
Moderator
Mooseman
Moderator
You didn't indicate what kind of misfire you had so I went with a hard misfire. I had an intermittent misfire only at idle that wouldn't show a code until I let it idle for an extended period of time once it accumulated enough in the cycle. Never did find it and haven't looked into it again. I'm letting that dog sleep.
gmtnation.com
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
You might consider getting a hold of a scope of some kind (single or dual channel hand helds can be had for ~100). Iirc, MRRSM has posted some "tracing techniques" in this area. At the very least you could watch the 5v transition on the COP in question for a bit to confirm that it is or isn't seeing "regularness" in the power. You could compare that with another cylinder to see if anything "jumps out".
As an example I made two recordings of the current misfire counts on an errand today. This is my 2005 5.3 Yukon but the idea is identical. On each short drive I caught misfire(s). Not enough to be felt or concerned with but it serves the purpose of this demonstration. One one trip I caught a single quick occurence on #4 that lasted for just a moment. On the other trip I caught reports of two cylinders that lasted for a good deal longer, about 8 seconds or so. These two cylinders, #5 and #6 are sequential in the firing order if that means anything.
On an engine that is setting misfire codes this test just might show something even when the code(s) are not present.
Something I really like about Car Scanner ELM OBD2 is you don't need to be watching any of this while driving. No distractions. You set it up before driving and let it run. Review the data right there in the app later, no exporting log files or needing spreadsheets or the like. Plus if desired the data file can be shared for others to review as well.
On an engine that is setting misfire codes this test just might show something even when the code(s) are not present.
Something I really like about Car Scanner ELM OBD2 is you don't need to be watching any of this while driving. No distractions. You set it up before driving and let it run. Review the data right there in the app later, no exporting log files or needing spreadsheets or the like. Plus if desired the data file can be shared for others to review as well.
Update:...had to bite the bullet and take it to a shop.....got me for an hours labor,but the good news:...Compression test was normal on all cylinders and no abnormal number of misfires that would set off any alarms...Moose,I'm going to follow suit and just leave it alone. Now for the bad news,on the drive home cel came on and code P0335 popped...Crankshaft position sensor...can this be related to the P0306 in any shape,way,or form?....did a bit of reading on the crank sensor...anybody swap one of these out and not have to do the relearn?
if you followed the link that mooseman posted in "10".... it indicated this
"Misfires are detrimined by the crank sensor. When there’s a misfire, the velocity of the crankshaft changes and the PCM picks that up and puts out the appropriate code."
So it might be directly related in some form to your "codings".
"Misfires are detrimined by the crank sensor. When there’s a misfire, the velocity of the crankshaft changes and the PCM picks that up and puts out the appropriate code."
So it might be directly related in some form to your "codings".
Mooseman
Moderator
Agree with @Mooseman about this...
"Air: pretty simple, if it's getting the proper amount in the cylinder with the intake valve opening, it's good. If it's getting too much, it may not fire. Check for a vacuum leak but for a misfire, it would be a pretty big hole to just that one cylinder and would likely affect others."
Over time, The Three "Figure 8" Plastic Intake Manifold Gaskets will flatten out and sometimes... a Slight Tweak of only 89 Inch Pounds of Tightening Force upon all of the "Trapped Fasteners" staggered around the IM Flange; especially near the Hard-To- Reach Firewall spot for the #6 Cylinder ...will stop the ingestion of any un-regulated Air that might be sneaking past the PCM's Sensor Regulation and causing "Lean Misfire" Conditions. The PCM will ignore only so many of these events before it throws P03XX Codes.
You could try using a Can of Spray Starting Fluid lightly sprayed towards the back of the Firewall....and listen for the Engine to suddenly accelerate to reveal any untoward air leaks on the IM. The phenomena of the "Flat IM "O" Rings" can be explained by having a High Mileage Motor riding upon Bad Motor Mounts.
It is possible that excess engine vibrations causes the competing weight of the Throttle Body on the one side of the IM vs. the weight of the PCM bolted up on the opposing side to cause the IM to "pendulum"and rock back and forth innumerable times... gradually flattening and wearing out those three Intake Port Seals and inviting excess, un-metered air to enter the Cylinders in this manner.
"Air: pretty simple, if it's getting the proper amount in the cylinder with the intake valve opening, it's good. If it's getting too much, it may not fire. Check for a vacuum leak but for a misfire, it would be a pretty big hole to just that one cylinder and would likely affect others."
Over time, The Three "Figure 8" Plastic Intake Manifold Gaskets will flatten out and sometimes... a Slight Tweak of only 89 Inch Pounds of Tightening Force upon all of the "Trapped Fasteners" staggered around the IM Flange; especially near the Hard-To- Reach Firewall spot for the #6 Cylinder ...will stop the ingestion of any un-regulated Air that might be sneaking past the PCM's Sensor Regulation and causing "Lean Misfire" Conditions. The PCM will ignore only so many of these events before it throws P03XX Codes.
You could try using a Can of Spray Starting Fluid lightly sprayed towards the back of the Firewall....and listen for the Engine to suddenly accelerate to reveal any untoward air leaks on the IM. The phenomena of the "Flat IM "O" Rings" can be explained by having a High Mileage Motor riding upon Bad Motor Mounts.
It is possible that excess engine vibrations causes the competing weight of the Throttle Body on the one side of the IM vs. the weight of the PCM bolted up on the opposing side to cause the IM to "pendulum"and rock back and forth innumerable times... gradually flattening and wearing out those three Intake Port Seals and inviting excess, un-metered air to enter the Cylinders in this manner.
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