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Discussion Starter · #1 ·
Hello, I bought a 2012 hatchback base for a very good price because cylinder 1 and 4 were misfiring. I replaced the ignition coils and all spark plugs which fixed the misfiring. But now I'm getting an intermittent misfire on cylinder 1. I'll have a rough idle for a min or 2 and then it will idle smooth for a min or 2.

When driving I don't feel any loss of power, and when the AC is on the rough idle goes away. I assume that's because of the higher idle rpm. I've tried switching around the fuel injectors to see if the problem moves and it doesn't. I've switched around the ignition coils and spark plugs but there's no change. I tested compression and it's good.

I'm just really unsure what else I can check. The car doesn't throw any codes, I only see the issue in the pending codes on my scanner. Does anybody else know what it could be?
 

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need live data scan see fueling on injector's ,, ie will show corrections off that you can tell if likely a injector fault or if its a reactive fault from a mechanical problem like carbon build up on valves or valve stem seals leaking on exhaust valves and cause exhaust valves to leak,
 

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If you replaced all the ignition coils and spark plugs, why did you later try swapping them around?

Do you mean the car "doesn't throw any codes" besides the DTC for the misfire?

Mike is right, you need a lab scope to watch the #1 injector while the car is running. I had an intermittent #2 injector on my '07 N12 engine; I had to take the car to my local Indy shop for diagnosis because I didn't have a lab scope at the time.

Since you have the 2012 base model with the N16 engine (no turbo), you don't have the carbon buildup problem with the intake valves because that engine is not direct injected.

You say "compression was good" define good.
 

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Discussion Starter · #4 ·
Thank you guys for responding, I really do appreciate it. I've done allot of work on my 1990 miata but that's obviously allot simpler to work on.

If you replaced all the ignition coils and spark plugs, why did you later try swapping them around?

Do you mean the car "doesn't throw any codes" besides the DTC for the misfire?

Mike is right, you need a lab scope to watch the #1 injector while the car is running. I had an intermittent #2 injector on my '07 N12 engine; I had to take the car to my local Indy shop for diagnosis because I didn't have a lab scope at the time.

Since you have the 2012 base model with the N16 engine (no turbo), you don't have the carbon buildup problem with the intake valves because that engine is not direct injected.

You say "compression was good" define good.
I swapped around the ignition coils and plugs just to see if maybe I got a bad coil. Even though it's new I wanted to rule out the possiblity of a DOA.

The car itself does not throw any DTC codes, on my OBD2 scanner I get a pending code for a misfire on cylinder 1. I checked the plug and it's blackened so it's not firing correctly. I don't have any smoke In the exhaust so it's not burning oil.

I swapped the #1 injector with the #3 injector, that would've moved the misfire if it was the injector. Unless you guys are saying I should still check the injector in case it's the signal coming in?

The compression numbers I didn't write down, but they were all around about 200, within 5-10 psi of each other.


need live data scan see fueling on injector's ,, ie will show corrections off that you can tell if likely a injector fault or if its a reactive fault from a mechanical problem like carbon build up on valves or valve stem seals leaking on exhaust valves and cause exhaust valves to leak,
So you think I should still get the live data on injector 1 even though it was swapped with injector 3? The misfires didn't move to cylinder 3 after that.
 

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Thank you guys for responding, I really do appreciate it. I've done allot of work on my 1990 miata but that's obviously allot simpler to work on.



I swapped around the ignition coils and plugs just to see if maybe I got a bad coil. Even though it's new I wanted to rule out the possiblity of a DOA.

The car itself does not throw any DTC codes, on my OBD2 scanner I get a pending code for a misfire on cylinder 1. I checked the plug and it's blackened so it's not firing correctly. I don't have any smoke In the exhaust so it's not burning oil.

I swapped the #1 injector with the #3 injector, that would've moved the misfire if it was the injector. Unless you guys are saying I should still check the injector in case it's the signal coming in?

The compression numbers I didn't write down, but they were all around about 200, within 5-10 psi of each other.




So you think I should still get the live data on injector 1 even though it was swapped with injector 3? The misfires didn't move to cylinder 3 after that.
its how i would tell if its a injector or not, or wiring fault to it or ecu fault or i would scope it all but they are loads of money,, would also do a leak down test with inlet and exhaust manifold off and spray wd40 on rear of closed valves look for bubbles from the seats,, as very common fault,, compression test and leak down test,
 

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Discussion Starter · #6 ·
its how i would tell if its a injector or not, or wiring fault to it or ecu fault or i would scope it all but they are loads of money,, would also do a leak down test with inlet and exhaust manifold off and spray wd40 on rear of closed valves look for bubbles from the seats,, as very common fault,, compression test and leak down test,
Hmmmm ok, I guess I will try the leak down test first since that sounds pretty easy to do. I had read about the valves causing an issue but the compression test seemed fine. Although I did read someone else had the same issue and that their compression was good until one day it wasn't, he said it had to do with the valves as well. If the leak down test is good then I guess I will move onto getting the injector signal tested.

Wont be able to work on it for a couple of weeks but if I find the issue I'll post my solution in here, so if someone has the same issue they can see a possible fix. And if nothing works, I'll comeback and ask some more questions lol.
 

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Nelswole, did you find out what is causing the misfire?

My partners mini would pass a leak down test, cold or hot but would misfire at idle when hot - came down to a loose inlet valve seat. This fault is only at idle and goes away once you put power on. The telltale sign is to disconnect one of the camshaft sensors at which point the engine idles correctly.
 

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Discussion Starter · #8 ·
Nelswole, did you find out what is causing the misfire?

My partners mini would pass a leak down test, cold or hot but would misfire at idle when hot - came down to a loose inlet valve seat. This fault is only at idle and goes away once you put power on. The telltale sign is to disconnect one of the camshaft sensors at which point the engine idles correctly.
Not yet, the leak down test didn't show any issues. My job offered to pay for the repairs so I took it to a mini and euro car repair place. After almost a week they called me to say they had no idea what the issue is and suggested I should take it to the dealer. But, I may have to try what you're suggesting as a check. Would your partner's car throw the error code even when driving? Because I don't feel the misfire when driving, but every once in awhile the car will throw the misfire code while driving.
 

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Not yet, the leak down test didn't show any issues. My job offered to pay for the repairs so I took it to a mini and euro car repair place. After almost a week they called me to say they had no idea what the issue is and suggested I should take it to the dealer. But, I may have to try what you're suggesting as a check. Would your partner's car throw the error code even when driving? Because I don't feel the misfire when driving, but every once in awhile the car will throw the misfire code while driving.
Have a look at this: https://www.mini2.com/threads/prince-engine-hot-idle-misfire-reason-and-cure-imho.362
and this: R56 Cooper 1.6 n/a N12 misfire mystery

Might not be your issue but Prince engines drop valve seats - my partners behaved similar to yours and eventually the seat dropped out. We are now rebuilding the top end.
 

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Discussion Starter · #10 ·
Have a look at this: https://www.mini2.com/threads/prince-engine-hot-idle-misfire-reason-and-cure-imho.362
and this: R56 Cooper 1.6 n/a N12 misfire mystery

Might not be your issue but Prince engines drop valve seats - my partners behaved similar to yours and eventually the seat dropped out. We are now rebuilding the top end.
Well reading what you said on the second post, it does sound like it could be that problem. I was planning to just replace them since I had read about them being a possible issue, but since someone else offered to pay I figured the costs of a shop wouldn't be too bad haha. I will mention to them about the valve seats because I have seen quite a few posts about them. I'm sure a dealer would suggest a new ECM and whole new top end just for the extra money. But I will try to show at least some understanding to maybe avoid that.

Thank you so much for the suggestion. I will still try removing the sensor before taking it to the dealer to try and maybe confirm what you suggested. When it's fully fixed I will reply here to let you know, and so anyone in the future can know as well.
 

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Hi I have a 2008 1.4 with the n12 (121,000 miles) with a misfire on cylinder one. I have changed
timing chain, vanos sensors, cam sensors, coils and plugs, ecu checked (all ok) wiring checked (all ok) head off and valves checked and cleaned, eccentric sensor, seafoam treatment, new catalytic converter and lambda sensors.
Any help would be appricated. I'm all out of ideas.
 

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Hi I have a 2008 1.4 with the n12 (121,000 miles) with a misfire on cylinder one. I have changed
timing chain, vanos sensors, cam sensors, coils and plugs, ecu checked (all ok) wiring checked (all ok) head off and valves checked and cleaned, eccentric sensor, seafoam treatment, new catalytic converter and lambda sensors.
Any help would be appricated. I'm all out of ideas.
need to pull the exhaust manifold off and inlet manifold and rocker cover set all 4 valves to closed on each cylinder change the cylinder with compressed air and spray wd40 or seafoam on rear of valves seats and look for bubbles if have bubble then that will your issues very common at 80,000 miles at 120k will be deffo, head off and do all valve stem seals and clean the valves check the guides for wear etc,, while in there would also do the piston rings , link below for idea of what they go like,
 
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need to pull the exhaust manifold off and inlet manifold and rocker cover set all 4 valves to closed on each cylinder change the cylinder with compressed air and spray wd40 or seafoam on rear of valves seats and look for bubbles if have bubble then that will your issues very common at 80,000 miles at 120k will be deffo, head off and do all valve stem seals and clean the valves check the guides for wear etc,, while in there would also do the piston rings , link below for idea of what they go like,
That sounds like major surgery!! Oh to have the skills! Thanks for your thoughts thou buddy. I have the head off now and am In the process of cleaning the valves. Wish me luck
 

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its not that hard to do to be honest trouble is with 120k its going to need doing and for sake of extra £150 ish in tools and parts its a no brainer on them as bmw/psa in their not so wisdom fitted nitride oil control rings single piece things and they wear out around 80k ish in that link i explain about the better rings etc really does sort them out for the future
will add just cleaning the valves wont last long as its the oil that gets past the oil stem seals that will keep causing it every few hundred or thousand miles ,, also the valve seats will leak due to pitting they all do this
 
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Hi I have a 2008 1.4 with the n12 (121,000 miles) with a misfire on cylinder one. I have changed
timing chain, vanos sensors, cam sensors, coils and plugs, ecu checked (all ok) wiring checked (all ok) head off and valves checked and cleaned, eccentric sensor, seafoam treatment, new catalytic converter and lambda sensors.
Any help would be appricated. I'm all out of ideas.
In terms of the misfire are there any specific details? Is the misfire all the time? Or does it misfire at certain points, ie idle when hot, etc?

Think mike1967 is pointing towards valve seat issues, etc. Certainly this could be the case, equally I would suggest starting with the low cost stuff if you haven't already, Typically these cars misfire due to coil packs and plugs failing, which are cheap fixes in many cases, if these have been checked out then move on to compression test, could do that before coils and plugs. Basically a misfire will happen when the offending cylinder(s) is missing fuel+air mix, compression, spark or there is a timing issue. You can diagnose most of these by a process of elimination i.e., swap plugs and coils from another cylinder and if the misfire moves then its either the plug or coil, compare compression on cylinder 1 with the other cylinders - they should be within 14 psi. A more comprehensive compression test is the leak down test (read up) which will indicate if the compression is being lost through rings or valves and finally the dynamic compression test which will indicate a fault in valve seating when under load/temperature. Spark timing is fixed, which leaves VVT, which requires accurate alignment of the cams with the crank. Have you tried disconnecting one of the cam sensors - if you do, does the misfire stop? Disconnecting a cam sensor disables the VVT, forces the valves to do full lift and can indicate a timing issue or valve seat issue. These engines drop valve seats which can be very expensive to fix if it happens when the car is being used.
 

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In terms of the misfire are there any specific details? Is the misfire all the time? Or does it misfire at certain points, ie idle when hot, etc?

Think mike1967 is pointing towards valve seat issues, etc. Certainly this could be the case, equally I would suggest starting with the low cost stuff if you haven't already, Typically these cars misfire due to coil packs and plugs failing, which are cheap fixes in many cases, if these have been checked out then move on to compression test, could do that before coils and plugs. Basically a misfire will happen when the offending cylinder(s) is missing fuel+air mix, compression, spark or there is a timing issue. You can diagnose most of these by a process of elimination i.e., swap plugs and coils from another cylinder and if the misfire moves then its either the plug or coil, compare compression on cylinder 1 with the other cylinders - they should be within 14 psi. A more comprehensive compression test is the leak down test (read up) which will indicate if the compression is being lost through rings or valves and finally the dynamic compression test which will indicate a fault in valve seating when under load/temperature. Spark timing is fixed, which leaves VVT, which requires accurate alignment of the cams with the crank. Have you tried disconnecting one of the cam sensors - if you do, does the misfire stop? Disconnecting a cam sensor disables the VVT, forces the valves to do full lift and can indicate a timing issue or valve seat issue. These engines drop valve seats which can be very expensive to fix if it happens when the car is being used.
personally i'm more in to the things that cost nothing to check first off then work back off that , see all the time people change plugs £30 coil packs timing chains £800 garage bill , oil changes and different treatments then their next post states bloody mini its all crap spent all this money and still a pile of rubbish and tends to end with will never buy another one,, when starting with basics most of the time saves all the expense,, better to know for sure whats wrong before buying parts for it, they do drop valve seats normally from running ;lean and over heated ie combustion process goes above and beyond designed levels,, even leaky valves seats can cause lean out can cause cat and 02 sensors damages,
 
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In terms of the misfire are there any specific details? Is the misfire all the time? Or does it misfire at certain points, ie idle when hot, etc?

Think mike1967 is pointing towards valve seat issues, etc. Certainly this could be the case, equally I would suggest starting with the low cost stuff if you haven't already, Typically these cars misfire due to coil packs and plugs failing, which are cheap fixes in many cases, if these have been checked out then move on to compression test, could do that before coils and plugs. Basically a misfire will happen when the offending cylinder(s) is missing fuel+air mix, compression, spark or there is a timing issue. You can diagnose most of these by a process of elimination i.e., swap plugs and coils from another cylinder and if the misfire moves then its either the plug or coil, compare compression on cylinder 1 with the other cylinders - they should be within 14 psi. A more comprehensive compression test is the leak down test (read up) which will indicate if the compression is being lost through rings or valves and finally the dynamic compression test which will indicate a fault in valve seating when under load/temperature. Spark timing is fixed, which leaves VVT, which requires accurate alignment of the cams with the crank. Have you tried disconnecting one of the cam sensors - if you do, does the misfire stop? Disconnecting a cam sensor disables the VVT, forces the valves to do full lift and can indicate a timing issue or valve seat issue. These engines drop valve seats which can be very expensive to fix if it happens when the car is being used.
Ah now that's interesting! Yes, indeed, when the cam sensor is unplugged then the revs increase and the misfire disappears. So to recap, when started it misfires, and when I unplug the coil for cylinder one it makes no difference, but when I unplug the cam sensor, the revs increase and the coil comes to life, as when I then unplug number one coil, the engine labours. Does this make sense?
 

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need to pull the exhaust manifold off and inlet manifold and rocker cover set all 4 valves to closed on each cylinder change the cylinder with compressed air and spray wd40 or seafoam on rear of valves seats and look for bubbles if have bubble then that will your issues very common at 80,000 miles at 120k will be deffo, head off and do all valve stem seals and clean the valves check the guides for wear etc,, while in there would also do the piston rings , link below for idea of what they go like,
Thanks Mike
 

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Ah now that's interesting! Yes, indeed, when the cam sensor is unplugged then the revs increase and the misfire disappears. So to recap, when started it misfires, and when I unplug the coil for cylinder one it makes no difference, but when I unplug the cam sensor, the revs increase and the coil comes to life, as when I then unplug number one coil, the engine labours. Does this make sense?
The misfire clearing on unplugging the cam sensor does make sense. I would expect there to be a spark on cylinder 1 regardless of cam sensor state. You need to clear the error codes before starting the next process otherwise the ECU will maintain the engine in error mode and the results will not help.

With the engine misfiring, you need to check the compression on cylinder 1 when the engine is running. To do this remove plug 1, screw in a compression gauge and run the engine at idle with the cam sensor connected. Note the reading on the compression gauge, with the engine still running, unplug the cam sensor and re-read the compression gauge. If the issue is a loss of compression on cylinder 1, while running at idle, you will see the compression rise when you disconnect the cam sensor. If this is the case then you have a fault with the seating of one of the inlet valves. This might not be obvious from inspection, the valves could be seating correctly while static, however under operation one of the valves isn't seating correctly and you are losing compression - hence the cylinder 1 misfire. If I am right, you will need to remove the head, strip inlet valves for cylinder 1 and get an engine specialist to check the valve seats. One of the seats might be loose in the head. This will become obvious when you try to prise it out with a small amount of force from behind on the base of the seat. A tight seat will not move but a loose seat will. When the seats come loose the valve will not seat properly and this is especially true with the N12 engine do to the VVT effect on valve lift. At idle the valve only moves 1 or 2 mm and doesn't provide enough force to seat the valve, while on load the valve moves up to 9.5 mm and hence the spring load forces the valve to push the seat back into its socket in the head socket and provide an tight seal. Please let us know how you get on, if I am right it would be good to get this published as a common gen 2 mini fault, so that the many owners of Prince engine cars have a chance to repair their engines before too much damage is done to their engines.
 

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valve seats are pressed in machine shop specialist job, cant be tapped back in bonding agent is used as well as high pressure fit, they rattle like hell when seats drops out on to bottom of valve,, the valve springs is only thing that has a pressure on valve to seat not the vvt, vvt gets its main force between the camshaft and its lifter cam and the back pressure from valve springs to bottom follower ,, best off pulling inlet and exhaust manifolds off charging the cylinder with air and spray wd40 on backs of valves look for bubbles with all 4 valves closed,, reason get a difference when pull the cps off is the system goes in to a default map from ecu like on first start up, checks you basic in a controlled way like i said above running engine while doing covers things up,, do like above and its a black and white really easy way, good luck
 
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