Misfiring -- who had the issue? - Page 3 - McLaren Life
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post #31 of 46 Old 03-06-2019, 01:27 AM
 
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I don’t think the oil was on the combustion chamber but for sure it was where the coils go
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post #32 of 46 Old 03-07-2019, 04:51 AM
 
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So I replaced all spark plugs, switched the ignition coils, o2 sensors, maf sensors, intercooler pressure sensor, replaced air filters and the car still misfires on cylinder 5,6,7,8. The whole bank is misfiring. Only misfires on idle. No misfires when engine is cold or at high RPMs. Very weird and annoying to diagnose. Obviously mclaren of San Francisco will always recommend a new engine or even a whole new car. I’m just trying to work all my options before I do anything else to it. Anyone can help? Any tip? Anything I’m forgetting to check?
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post #33 of 46 Old 03-07-2019, 01:40 PM
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Whatís the head issue means? I just removed the spark plugs and it has a lot of oil on them. I wonder if they over filled the oil?? Thatís for sure whatís causing my misfire but donít know why it happened right after the oil change.
Cylinder head cracking. Issue with the '12 cars.

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post #34 of 46 Old 03-07-2019, 01:45 PM
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So I replaced all spark plugs, switched the ignition coils, o2 sensors, maf sensors, intercooler pressure sensor, replaced air filters and the car still misfires on cylinder 5,6,7,8. The whole bank is misfiring. Only misfires on idle. No misfires when engine is cold or at high RPMs. Very weird and annoying to diagnose. Obviously mclaren of San Francisco will always recommend a new engine or even a whole new car. Iím just trying to work all my options before I do anything else to it. Anyone can help? Any tip? Anything Iím forgetting to check?
See my post on the other thread, but if that checks out I agree you might have a cracked cylinder head.

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post #35 of 46 Old 03-07-2019, 02:15 PM
 
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Cracked cylinder head could be diagnosed with a compression or leakdown test (or both). Even the slightest amount of unmetered air in the cylinder could provide a misfire. If you have a crack that spans more than one cylinder, there you go.


How many miles on the car?


Also, be prepared for the fact that the oil change could just be coincident with the timing of this problem. I can't think of anything during an oil change that would cause this.

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post #36 of 46 Old 03-07-2019, 02:40 PM
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Agree that the oil change is likely coincidental and you should perform a proper leakdown test, which is preferred. Lots of self-help videos on how to do a leakdown.

In the event that you have a cracked head and are out of warranty, I have a spare set of used 12C heads from a later model year 2013 car. Would prefer to sell the heads as a set though, both banks. PM if you need to go down this route.

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post #37 of 46 Old 03-07-2019, 03:09 PM
 
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Thank you guys for all the info. I’ll perform a cylinder test and I’ll keep you guys posted. It was weird because the car always ran just fine till the day of the the oil change. The car has 31,000 miles
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post #38 of 46 Old 03-08-2019, 05:44 AM
 
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Hi Guys i just wanted to see if i might be able to shed light on this subject . I know that Mclaren has had problems with cyl heads lifting under boost. Some head bolts were left loose or could come loose over time. This issue happened to the 3.8L motors, and has even happened to the P1 . This would cause a misfire and other drivability problems(overheating, oil in the coolant,ect). As for a misfire after an oil change goes, this could happen due to over filling the oil tank. ( never try to leave the oil fill cap open and run the car. The oil system on the 3.8l motor is pressurized and oil will get all over the place). 1 qt of oil will make all the difference if its over filled, the car will start to smoke if left to idle for some time. The car will misfire due to oil fouling out the spark plug and in some cases start to smoke at the exhaust. Just some inside knowledge to help all.
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post #39 of 46 Old 03-08-2019, 01:26 PM
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Some head bolts were left loose or could come loose over time
Are you sure about the head bolts loosening over time statement? Seems very unlikely since head bolts are literally stretched during the installation process, hence the torque-to-yield fasteners. This stretching creates a clamping forcing between the heads and the block. Meaning, since it is under tension, the bolts do not simply work themselves loose over time.


Anyone who has ever removed a head from a block can testify of the "cracking" sound made when relieving this tension.

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post #40 of 46 Old 03-08-2019, 11:53 PM
 
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Ok guys, after the mclaren dealership state I would need new heads, vvt and few other things that would cost over $75,000 for parts and labor, took the car back home, and started some testing. I was able to find the misfire issue that was also causing a rattle metal noise coming from the engine while misfiring. The car is now fixed and no more issues. Cost of repair: $3. (Exactly, $3) imagine if I spent $75k at the dealer, I would be so beyond mad at myself!
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post #41 of 46 Old 03-09-2019, 01:22 AM
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Ok guys, after the mclaren dealership state I would need new heads, vvt and few other things that would cost over $75,000 for parts and labor, took the car back home, and started some testing. I was able to find the misfire issue that was also causing a rattle metal noise coming from the engine while misfiring. The car is now fixed and no more issues. Cost of repair: $3. (Exactly, $3) imagine if I spent $75k at the dealer, I would be so beyond mad at myself!
What part was replaced for $3?
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post #42 of 46 Old 03-09-2019, 02:51 AM
 
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The roll of electrical tape costed me $3. Used enough to close the hole where the ISG hoses attaches to. It’s pretty much capping the the ISG so it won’t suck any air. Also don’t forget to disconnect the cable.

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Ok guys, after the mclaren dealership state I would need new heads, vvt and few other things that would cost over $75,000 for parts and labor, took the car back home, and started some testing. I was able to find the misfire issue that was also causing a rattle metal noise coming from the engine while misfiring. The car is now fixed and no more issues. Cost of repair: $3. (Exactly, $3) imagine if I spent $75k at the dealer, I would be so beyond mad at myself!
What part was replaced for $3?
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post #43 of 46 Old 03-09-2019, 02:56 AM
 
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The spark plugs seemed to be good but I changed anyway since I had all the coils off.
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post #44 of 46 Old 03-09-2019, 04:19 AM
 
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@XPRD sells a block off plate for the ISG
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post #45 of 46 Old 03-09-2019, 04:05 PM
 
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Thank you for the tip! After almost going crazy with my car, with all these misfires and rattling noises, I’m afraid to touch anything else and starts again 😂 I’ll stay with my $3 repair for now. It has been 4 days, over 600 miles and so far so good!

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@XPRD sells a block off plate for the ISG
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