3.6L engine misfires

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tposey7591

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2012 Buick Lacrosse V6 FWD
Have you ever wondered why your 3.6L GM engine will misfire under load? Well the answer is quite simple. Your engine is equipped with an inadequate COP ignition, "coil on plug" manufactured by DENSO not GM. The 3.6L engine runs a 10/1 compression ratio and .043" spark plug gap with a weak ignition system. Only the best ignition systems will handle that combination especially with somewhat lean mixtures to meet emission standards. GM invented the HEI ignition system "High Energy Ignition" system in the mid 70's that became the standard of the auto industry. Yet today they turn to a Japanese company for their COP ignition system that should be more appropriately labeled LEI, "Low Energy Ignition". What has become of GM engineering excellence of yesteryear?

Before you jump to conclusions, as is often the case on this forum, the misfires are evident with heavy loading when throttle opening is such at lower RPM to produce high cylinder pressures. No, not compression ratio, that is a fixed mechanical factor but actual cylinder pressure that varies with throttle opening and load on a "throttled" engine. The misfires are evident but are not usually captured by the engine computer management system. Why, GM Says that misfires are normal and only a sustained and continuous misfire will be recorded causing a code to be set. Such rubbish is why GM is no longer a leader in the auto industry. There is always a reason for a cylinder misfire and often a poor/weak ignition system or ignition malfunction is the reason. Obviously there can be many other reason for a cylinder misfire but that is not the issue here. A weak COP ignition system is the culprit with the GM 3.6L engines.
 

mmadden2

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I've never heard anything or had any codes show up relating to ignition problems.

I would say my LaCrosse runs super smooth under heavy load, is that not the case for others?
 

mnmike

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I just had a P0302 code "Cylinder 02 Misfire Detected" on my 2011 CSX. I never actually noticed anything while driving, but the check engine light came on. I have my own code reader (Autel Maxiscan MS300, $20.00 on Amazon) which I used to determine the code. After researching the code on line, the consensus was to erase the code (which I did) and monitor the performance to see if there are ongoing issues. I have driven about 100 miles since resetting the code and the CEL has not come back on. Time will tell if this will occur again.

Mike
 
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tposey7591

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Most misfires with the 3.6L are undetected by the PCM because the system is programmed to disregard them unless they are chronic. The best way to check for cylinder misfires is to switch to manual shifting and just before reaching a steady uphill grade shift into 6th gear at about 50 to 60 MPH and slowly increase throttle opening to maintain that speed. This loads the engine so weak firing cylinders will show up and can actually be felt as a slight surge or hesitation. Make sure you don't use so much throttle that it down shifts to 5th gear, that will unload the engine and mask the problem. In your case, #2 cylinder misfiring that was detected could be caused by the issue I posted or it could actually be the spark plug. It is a balancing act so the first order of business is to check/replace the spark plug to see if that improves it. The marginal COP ignition system used on these engines needs all the help it can get to function properly. So a marginal spark plug, improper gap or cracked insulator or slightly fouled electrodes could easily take it over the edge. Good Luck.
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2010 LaCrosse CXS, 2015 Infiniti Q50 AWD Sport Hybrid
Happened to me once in January. I remote started the car only to find it off a minute later. I manually started and it was fine except for the 'check engine' light. I took it to the dealer. The work order showed "SCAN TEST P0300 MISFIRES #1,4 CYL. BULL.#2651085 REPROGRAM J6353".

It's been fine since. There was no stress on the engine at the time.
 

leadsnacks

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I have noticed this under heavy acceleration(especially after being around 25-40 mph). It feels like it's "missing" at moments. It doesn't seem to happen all the time, but it is noticeable when it does happen. At first I thought a transmission shift issue, but it's definitely not that(though the transmission is loathe to quick downshift to give you rpm and torque when your foot asks for it).

I wonder if I should have the plugs replaced?
 

GM_Guy

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I experienced this issue (hesitation/stumble at high load in 6th gear traveling uphill) with my 3.6L V6 after ~42,000mi on my Saturn Outlook. As the vehicle was out of warranty, I took it to the local parts store, read the codes (P0300 and P0303 misfire codes were present) the 2nd code localized the misfire to cylinder 3. For me, it was as easy as replacing the spark plug (~$5.00). While I'm disappointed that this occurred with so few miles on the vehicle, I'm glad that the fix was easy and simple. Thanks to the prior posters. This is a very well-informed group.
 

AceMadera

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Hello,
I prefer DIY, usually much cheaper and I get to learn at the same time.
I have a 2012 Enclave, we were driving down the road and BAM started running rough, and "service stabilitrak" then "traction control off" came across the dash and the CEL came on and the TC light came on. Maintaining speed the vehicle runs fine, idle and acceleration is rough and limp mode engaged. So under a load this happens. Did research on the internet and it said coil pack and spark plug. Took it into three parts stores and the codes came up the same, faulty plug and coil. The dealer says either exhaust or intake valve. I have no smoke out the back or oil in the intake. Replaced the coil and plug, disconnected the battery, let it sit for an hour, reconnected and started it up. Same problem. It idles about 750 rpm according to the tach. Sometimes when I start it, it keeps trying to start after the engine is running. This dealer wants almost $3000 to "fix" it. The codes come back up the same, faulty plug/coil despite being brand new. And yes, I say this because I forgot initially, the plug is attached to the coil.

Almost forgot 112686 miles.

Advice?
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Cxl lacrosse 37,000 miles
I have 2011 lacrosse code p0300 says cylinders 6, 4, 3 misfiring.. Anyone with this issue that has actually fixed the problem? Print out of codes says it seen this issue and " most likely solution is fuel rail pressure sensor" I don't want to throw parts at it but
 

Rich B.

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Cancell reply for now. (Next day) lol, I almost answered the old post(s), wonder how they fared.

Only was going to say that on the transverse 6 cylinder, fuel rails would run front and rear whereas cylinders seem to be more firing order labeled. Not in right sequence for fuel rail feeding forward or rear injector bank?

Just my observation without going back to search which turned out too conflicting.
 
Last edited:

Rich B.

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Roger on that Z28, yes too start reading some of these topics and they start years back, new beginning would help. Also many don't answer back as to what was fix, or never fixed😴
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