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mike switzer
mike switzer,
Category: Chevy
Satisfied Customers: 416
Experience:  lead diagnostic tech at Aamco
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2009 6.0L Suburban 1500 4WD. P0300, with misfires on #4.

Customer Question

2009 6.0L Suburban 1500 4WD. P0300, with misfires on #4. Previously had misfires on #5 and replaced the coil and that cleared it up. Replacing coil, plug, wire and injector on #4 has not helped. I feared valve lifter, but as this is a very intermittent problem that did not seem likely. I replaced the Valve Lifter Oil Manifold, and while in there scoped the camshaft and it is pristine. Thoughts?
JA: Where exactly do you think the noise is coming from? And how long has this been going on?
Customer: Intermittently for a couple of years - just the last year on #4 however. I am scanning it with a Snap-On Verus so I have fairly detailed code information. The ECU definitely thinks #4 is misfiring, and it runs terribly when it is happening.
JA: Are you fixing your Suburban 1500 yourself? What have you tried so far?
Customer: Yes and with the dealer also. See my first problem description for what has been tried so far. Also new intake manifold gaskets and camshaft position sensor.
JA: Anything else you want the mechanic to know before I connect you?
Customer: I think that is it - this is the first time I have tried this online chat - how does it work? I assume Pete does not sit online all day and answer questions for free?
Submitted: 11 days ago.
Category: Chevy
Expert:  mike switzer replied 11 days ago.

does the check engine light flash at anytime?

Customer: replied 11 days ago.
DIC flashes Service Engine and Service Traction Control. Chk Engine light flashes when the problem is active and then will stay on solid when the code is present but the problem is not active. Problem occurs in warm, cold, dry or wet weather conditions
Expert:  mike switzer replied 11 days ago.

im sorry for the delay my system is not be cooperative currently and i was un able to respond. a flashing engine light generally indicates an ignition misfire. since you have said you replaced the coil have you tried moving the new coil to another cylinder to ensure it does not follow to that cylinder?

Customer: replied 11 days ago.
No problem. Yes I did all of that. I moved it to another cylinder, and then I actually replaced the coil, plug, and wire just to be sure and it didn't change the problem (I was fortunate that time that it persisted long enough to verify this).
Customer: replied 11 days ago.
If you see the original problem description, I can read P0300 (general misfire) and I have seen P0304 (misfire on #4). The misfire history on #4 is in the thousands, and I can watch the misfire count on #4 count up when the problem is active. I am using a Snap-On Verus
Expert:  mike switzer replied 11 days ago.

ok well a flashing engine light does mean catalyst damaging misfire. you can be having a fuel injestor that is getting stuck open but which will be causing a 300 code. are you getting a specific cylinder code or only the 300?

Customer: replied 11 days ago.
Previously I had specific 0305, and more recently 0304. Lately just generic 0300, but as I stated I can see the misfire counts climb on the cylinder in question
Customer: replied 11 days ago.
I guess a reasonable question would be how does the ECU determine that there is a misfire? I thought they used the knock sensor to "listen" for the combustion after the plug fires, but I am led to believe it is found from the CMP sensor velocity on the cam. Hence the reason I changed the CMP sensor to be safe (it's cheap after all)
Expert:  mike switzer replied 11 days ago.

the knock sensor is used to sense preignition to determine the correct ignition timing needed. the crank sensor controls the ignition and the cam sensor control the injector firing sequence. i would start with replacing the crank sensor.

Customer: replied 11 days ago.
Hmm interesting - OK I can do that. Would the crank sensor not cause misfiring on all cylinders however?
Expert:  mike switzer replied 11 days ago.

normal yes it just cuts spark completely but it is possible. and i have seen strange issues caused by crank sensors.

Customer: replied 11 days ago.
OK thank you. How nasty is the Crank sensor to get at?
Expert:  mike switzer replied 11 days ago.

it is behind the starter. not terribly but tight is all you can usually get it by disconnecting the battery unbolting the starter and unplugging the oil level sensor. you can generally push the starter out of the way enough to access the sensor then replace it.

Customer: replied 11 days ago.
Sounds reasonable. I assume I have to do the CMP "relearn" with my scanner after that?
Expert:  mike switzer replied 11 days ago.

sometimes yes. sometimes no. its a simple procedure regardless. i have replaced them and it ran fine. other times i have had to relearn the crank sensor.