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If all that has been replaced, a compression test/leak down test should be done… You could have a mechanical issue such as a burned valve or a broken ring causing this issue.
A compression test should generally not be 15% different from your other cylinders, I.E
Cylinder 2 is 180 psi, Cylinder 4 is 178 psi, Cylinder 6 is 150 psi…. This will let you know that something in the low cylinder is amiss…
If after such readings as above are taken, a teaspoon of oil (or a like amount) should added into the cylinder (though the spark plug hole)… This is called a wet test… If the compression gets higher, it is bad rings… If it stays the same, it is a leak in one or more of the valves (or head gasket)….
A leak down test can let you know where the problem is…. Or you can hook up compressed air directly into the cylinder when it is at Top Dead Center (TDC)…. A hiss in the exhaust is a bad exhaust valve, Bubbling in the coolant is a head gasket leak, hissing in the intake area is a intake valve, hissing in the crankcase is a ring…
Regards,
Karl
Then you may want to search electrical… May be something in the wiring/a grounding fuel injector
Also, misfire codes showing a specific cylinder may not always be 100% accurate at identifying the exact problem cylinder…
-Karl
Thanks again. I will check it out. I think it’s more frustrating that it doesn’t do it all the time.
chris
It’s possible there is an intake manifold gasket leak at # 6 cylinder. Pour a little water around the area with the engine running to see if the engine reacts to it. Intakes on those tend to leak more with a cold engine.
Could be an intake leak or head gasket/head issue. Is there coolant getting in that cylinder. If it’s not all the time could also be faulty parts. Try switching coils and spark plugs with a different cylinder to see if the misfire moves with it.
It could be electrical as pointed out. You might try a power balance test while the misfire is happening. This will confirm cylinder #6 or some other cylinder. Also, don’t rule out mechanical. As mentioned it could be an intake leak, but it could also be a combustion leak of some kind. It’s worth ruling out anyway. More info here.
http://www.ericthecarguy.com/faq/solving-automotive-performance-issues
Keep us posted on what you find.
Ok took some measurements with scan tool…. air flow rate mass air flow 6.34g/s. Short term fuel trim -.8% to 1.6% short term fuel trim b1 -.8 to 1.6% short term fuel trim (b1-s1) -.8% to1.6%. Long term fuel trim bank 1 2.3%
short term bank2. -3.9%
Long term bank 2 1.6%Any input would help..thanks again
Those Fuel trim numbers look fine… But I am wondering what your B2 S1 is (what are those LTFT and STFT numbers)….. B2 (Bank two) should have your #6 cylinder on that side… If those numbers are out of whack then it may be indicative of another problem…
Unfortunately, this limited info is not going to give us much help about the issue… If you had poor gas mileage, A check engine light with a P017X, Issues with a prematurely dying Catalytic converter or other O2 sensor problems it could assist…
I really think you should try a compression test on this engine… The engine can throw a P030X code due to a mechanical issue (I.E. broken ring) and you may barely notice anything in how the engine sounds…
The reason I say this is to just get the mechanical diagnosis out of the way and eliminate it as a suspect… HF sells compression testers at a very affordable price and they are always good to have… If you don’t want to purchase this, most major auto parts stores in the U.S. will rent them to you for nothing (if you buy them and then return them) or for a nominal fee…
-Karl
Before I would replace any more parts I would do what everyone is telling you. In my opinion Eric’s trouble shooting guide is about the best you can get. If you follow it I think you will get to the root of your problem.
One other thing… If all other diagnosis fails:
If I remember there was a TSB issued for right bank misfire on that vehicle around those years. I think it was due to the O2 sensor connection because of corrosion or water intrusion. I can’t find the TSB…I’ll have to search the Internet…but with the fuel trim the way it is…it looks like the o2 sensor is ok and I don’t really see how an O2 sensor can cause a misfire on one cylinder…but I do remember GM Tech assistance telling me to check for corrosion or water intrusion and if nothing was found; put the sensor in…. and it fixed the misfire.
For a check I guess you could swap the O2 sensors side to side to see if the misfires move to the other bank of the engine.
Hey guy’s. ? Just wanted to keep you updated on the po306 misfire on cyl 6 iwas getting. Found a split hose on the fuel pressure regulator. Replaced it cleared the code driving truck for 2 days now. Im still going to a compression test to see whats going on. Tomorrow will be the real test driving to work. Thanks again for everyones help
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