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Discussion Starter #1
My 2011 Scion tC has been giving a misfire on Cylinder 1 both on idle and when driving. Things we've tired so far:

Change fuel injector
Change all spark plugs
Swap out coil pack with 2013 model pack
Check MAF
Check O2 Sensor
compression test.

However the problem persists. Thinking of getting a new set of coil packs as the set that was swapped from the 2013 model may have been weak.
Any suggestions?
 

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Discussion Starter #4
The computer threw up code P0301. I will try moving the coils to see if the misfire follows. Is it possible that the pack we used from the 2013 model would have been weak as they are OEM. Also my car just hit over 100k not too long ago if that provides any more insight. Could it be a fuel problem such as the filter or pump?

 

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Discussion Starter #7
Typically, if it was a pump, it wouldn't just happen on one cylinder. Start by moving the coil pack.
So we've switched the coil pack and the misfire did not move. We did a compression test and everything came out fine. Kind of stumped as the injector was change, spark plugs were changed, injector system cleaner was used and the misfire still occurred
 

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New plugs, new coils, compression OK, new injectors...so far you have verified fuel and spark. May have an intake valve issue or some air issue at that cylinder. Diags call for checking for intake leak. You could remove the intake manifold and see what the gasket looks like, check the valve door on that intake.
 

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Discussion Starter #9
New plugs, new coils, compression OK, new injectors...so far you have verified fuel and spark. May have an intake valve issue or some air issue at that cylinder. Diags call for checking for intake leak. You could remove the intake manifold and see what the gasket looks like, check the valve door on that intake.

Will give that a try. When we unplugged each coil we found no change on cylinder 1. My mechanic said the valves were okay. But the intake manifold has not been checked so hopefully the issue lies there
 

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Trying to think if the cam sensor could cause an issue like that... but would think you would get random misfires across the cylinders. What was the compression reading for each cylinder, can you post up? You did a dry test, how about a leak down test?
 

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Discussion Starter #12
Trying to think if the cam sensor could cause an issue like that... but would think you would get random misfires across the cylinders. What was the compression reading for each cylinder, can you post up? You did a dry test, how about a leak down test?

The compression test came out:
Cylinder 1 180
Cylinder 2 180
Cylinder 3 180
Cylinder 4 175



Not sure what the leak down test results were as my mechanic did not tell me
 

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The compression test came out:
Cylinder 1 180
Cylinder 2 180
Cylinder 3 180
Cylinder 4 175

Not sure what the leak down test results were as my mechanic did not tell me
No difference between cyls 1 and 2, which could indicate a breach in the head gasket around those cylinders, and numbers are within 10% of each other so does not appear to have an issue needing a leak down anyway. I am suspicious of the exact numbers 1-3 there to be honest, but again if they are all within a certain percentage of each other then it is OK. Those seem to be good results.
 

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Discussion Starter #14
No difference between cyls 1 and 2, which could indicate a breach in the head gasket around those cylinders, and numbers are within 10% of each other so does not appear to have an issue needing a leak down anyway. I am suspicious of the exact numbers 1-3 there to be honest, but again if they are all within a certain percentage of each other then it is OK. Those seem to be good results.

Would the Camshaft or Crankshaft sensor throw a code if it was causing the misfire?
 

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Would the Camshaft or Crankshaft sensor throw a code if it was causing the misfire?
I would think so, and again it is hard for me to imagine it only indicating cylinder 1 as opposed to misfires across all cylinders. Same with knock sensor - should throw code and if it was off then I would think the adjustments would cause misfire readings across all cylinders, but ??? I am guessing there.
 

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Back to a few basics:

Is this all one tank of gas, or has the issue spanned tanks of gas? Always same station or different stations?
Did you/mechanic check for latent codes (pend codes), historical codes, all that? Or just the current code? Be interesting to see if there are pends misfires for other cylinders.
Has the engine run hot at any point, or low on oil at some point?
 

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Discussion Starter #17
Back to a few basics:

Is this all one tank of gas, or has the issue spanned tanks of gas? Always same station or different stations?
Did you/mechanic check for latent codes (pend codes), historical codes, all that? Or just the current code? Be interesting to see if there are pends misfires for other cylinders.
Has the engine run hot at any point, or low on oil at some point?

I filled up at different stations and used some fuel injector system cleaner but the issue did not go away. Not sure about the latent codes i'll check with him on that. Engine is not over heating and had on oil change a few week ago. When we checked the cylinder's manually only cylinder 1 didn't change the engine performance when we unplugged it. My mechanic said that my coil packs are weak and wants to put in a new set. He also did not see any vacuum leaks and said the valves were ok.
 

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If you moved the coil packs and the problem didnt' follow the coil, I wouldn't go replacing all the packs.

Maybe check to make sure something didn't chew a wire to the coil? I've seen that before as well.
 

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Discussion Starter #19
Ended up going to the dealership and having it tested. Turns out I had filled up using some bad gas and other cars have been coming in with the same problem. The fuel injector system needed to be replaced. Have to contact the gas company to get reimbursed for the repair costs. Thank for all your helps guys
 
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