Misfires PO300 PO304 PO305 PO306 coils or something else? - Chevy Traverse Forum: Chevrolet Traverse Forum
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post #1 of 12 (permalink) Old 11-04-2019, 11:44 PM Thread Starter
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Misfires PO300 PO304 PO305 PO306 coils or something else?

2010 Traverse 175K miles. Engine has ran well its whole life. Lately it sounded like a tractor on cold start (put-put kind of sound). Tonight it started rough for the first time with mild shaking that smoothed out quickly. Check engine light on with codes PO300, PO304, PO305, PO306.

Would it be unlikely to be coil or plugs with multiple cylinders misfiring? I can do some repairs like change spark plugs and coils (spark plugs changed at 120k miles, but original coils). I could start there (coils) if there was a reasonable chance of success...can bad coil cause multiple misfiring cylinders or do I need a mechanic do you think? thanks

Last edited by jk; 11-04-2019 at 11:47 PM.
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post #2 of 12 (permalink) Old 11-05-2019, 09:15 AM
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I'm no expert but it could be a number of things causing those misfire codes & diagnosis isn't always easy, but the plugs & coils is a good starting place. Could also be fuel quality related, or maybe even the fuel pump. Could be there is a vacuum leak somewhere. Might also check the electrical connections & wiring harnesses. Just some thoughts on where to start, hope you get it figured out!
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post #3 of 12 (permalink) Old 11-05-2019, 11:55 AM
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carefully take a look for signs rodents were in the engine bay (little paw prints on dusty areas). Check her damaged wiring

2010 FWD LT1-Gold Mist Metallic- seats 8.
Build Date- July 31, 2009-2nd day of Spring Hill 2010 production.

2013 Equinox 3.6L - 88,000
2010 Traverse 3.6L- 153,000
2003 Trailblazer 4.2L- 181,500
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post #4 of 12 (permalink) Old 11-05-2019, 10:45 PM Thread Starter
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thanks- will look at those.
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post #5 of 12 (permalink) Old 11-06-2019, 09:28 AM
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Look under the top engine cover. This is the place where they built up their nesting on mine last year.

Traverse 2017, chevy Uplander 2009 LT short wheelbase, Impala 2003, jeep cherokee Laredo 1990, chevy citation 1984 2.8 v6, vauxhall Firenza1972, rambler american 1964 model 330, vauxhall velox 1956 rebuilt, NSU Prinz 1961 2 cylinder micro car rebuilt, Renault Dauphine 1960 rebuilt, ford prefect 1952 ( english car with non hydrolic brakes rebuilt. Honda 1986 motorcycle in new condition and 13 travel trailers from a Boler 1300 to a Rockwood mini lite 20 feet.
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post #6 of 12 (permalink) Old 11-06-2019, 07:49 PM Thread Starter
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I looked around- I don't think it is mice. Last year I put in some new spark plugs that were not OEM. After reading around the net I am going to try going back to AC Delco. Some people report other brands can cause electrical probs that result in misfires.
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post #7 of 12 (permalink) Old 11-08-2019, 09:48 AM
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Since you are going to remove your intake manifold,
And you would probably replace the $20 intake manifold gasket when you reassemble your traverse
All to replace spark plugs.... ^^^^

You might consider walnut blasting to remove the carbon on the intake valves. In theory each intake valve should take a half hour, so that would be three hours.....

I believe carbon from intake valves on gdi engines,
Falls off intake valves, and could cause misfire via the process known as Low Speed Pre Ignition. (Misfires)p
The carbon, which is as hard as lava rock,
Could scratch the combustion chamber walls which might result in oil consumption.....
Who knows?

To be clear, I am not saying your misfires are caused by carbon on intake valves, I agree with you about using a different brand of spark plugs.....

Do not use a running engine treatment like crc or BG to remove carbon from intake valves, that will damage your cylinder walls, or could damage your catalytic converter.

No matter what, while you are changing your spark plugs, at least look at the carbon build up on intake valves ......
Take a few pictures , and post them here.....

2012 Tracerse AWD (80k miles) with Elite E2 X catch can
Three Equinox AWD, 2013, 2016, and 2016 (all are 2.4 liter, 4 cylinder engines)
2017 Equinox AWD, 6 cylinder engine, with Elite E2 X catch can
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post #8 of 12 (permalink) Old 11-08-2019, 11:08 AM
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Yes, please take a few pictures and post, I haven't gotten to do mine yet but hope to have a look-see soon. I bought one of those Bluetooth cameras so I have no excuse. One solution to the carbon buildup is installing a catch can in the Air intake/PCV system. Filtering out the contaminants before they get to the valves would help solve the buildup.
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post #9 of 12 (permalink) Old 11-13-2019, 08:31 PM Thread Starter
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Sorry no pictures available- I am up here in MN and do my work in the driveway. Snow was forecast so I took the vehicle to a shop. They replaced spark plugs back to OEM, cleaned MAF and throttle body and threw some injector cleaner into gas tank. So far it is running ok with no further misfires. For the past 10,000 miles or so it seems to idle rougher and noisier than it used to and then finally went on to so rough it misfired. I think the carbon build up thing is probably going on here. It is not misfiring since I had this work done, but it still sounds rougher than it did when newer and I don't have total confidence we will get a lot more miles out of this vehicle.
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post #10 of 12 (permalink) Old 11-14-2019, 10:06 AM
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I would strongly suggest the OEM spark plugs and replacement coils. Also, when you have the air intake apart, be sure to clean out the oil sludge that accumulates from the PCV. The snorkel tube will collect all the vaporized oil from the crank case. A thorough cleaning while you have full access to the air intake is a good preventive measure. Also, be sure to stuff rags in the intake manifold to ensure NOTHING falls into the cylinders when you service the air intake. When I was having issues with vehicle hard start, rough idle, and would buck at ~35 mph unless accelerator was pushed all the way, I thought I had major issues. It turned out to be plugs / coils. The engine design does not allow for trouble shooting of a coil / plug which would be done while engine is running. So it is better to simply change them all while you have the upper portion of the engine exposed. If the coils could be accessed when the engine were running you could unplug a coil and diagnose a faulty plug / coil with ease. However, you can not do that on this 3.6L engine, therefore, when in doubt, change it out! Coils and plugs are not the items you should be "going cheap". It is a full afternoon just to access them and the engine controller is too good at masking this problem by playing with timing, fuel map, shift points, etc. You need to rule out the coils and plugs as an issue before moving on to anything else engine related. Your engine will thank you.
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