Strange Misfire, Suggestions?
09-11-2023, 05:32 PM
#1
New Member
Thread Starter
Strange Misfire, Suggestions?
I own a 2004 with a 2005 engine (not rev-up). The ECU is also 04. And recently encountered a strange misfire issue. Backstory, and forgive me for the long text but it might be best to get the whole story. i bought this car and was having issues with the VVT, found out the plug just was not in all the way and resolved that issue, I also inspected all spark plugs and found a small amount of oil on #6 coil and spark plug but thought nothing of it at the time. I was stationed in SC at the time and was waiting on registration and installed a RB body kit. I got a change of duty station to CT and unfortunately had to leave the car for about 1 month until it came in the mail. As soon as I returned the check engine light was on, I encountered the infamous P0300 code and also a MAF hi temp code. I ended up cutting a hole in the bumper for the intake on the drive to CT and it fixed itself. Fortunately, I actually noticed that the misfire would stop intermittently when it was night time, my guess is due to colder air. Upon getting to CT I noticed the valve cover gasket was leaking, replaced it and took it to a shop because the misfires continued. From diagnosis they determined it was only cylinder 6 misfiring. strangely enough, once again, The cylinder will only misfire once it reaches NOT in about 10-15 mins. Since the diagnosis, I replaced spark plugs (all), coil #6, and all fuel injectors. Anyone else have other tips? The plan is to check wiring tomorrow but I am also lost. How can this misfire be only one cylinder and only at NOT? It just simply makes no sense to me. Any help is appreciated.
09-12-2023, 07:52 PM
#2
Hey Coopa,
Thanks for the backstory context and detail of what's been done this far to troubleshoot. Were you able to confirm the misfire count only increases when the engine is at NOT, meaning did you or a shop use a scan tool to monitor live data? Also, what is the mileage on the engine?
When you replaced the injectors, #6 coil, and spark plugs, did you use all OEM parts? The factory plugs are NGK PFLR5A11s if my memory serves. Be careful about where you purchase these parts as well. I've run into tons of counterfeits on Fleabay and Amazon (Even for simple things like Air Filters, PCV valves, and yes Spark Plugs!). When it comes to the ignition systems on these vehicles, they are very temperamental and don't like most aftermarket replacements. Sure you might resolve a problem short term with your typical parts store replacement brand, but long term you might run into more issues. For things like spark plugs and injectors you're probably OK to go aftermarket. But for coil packs and any timing/ignition related sensors, stick with OEM parts. They put a good dent in the wallet, but the OEM parts have an extremely low failure rate (new) and no compatibility concerns. They also last 10+ years or 100k mi+ in most cases.
Why cylinder 6 specifically? I couldn't give a good answer without more data. But a few scenarios come to mind.
1) Potential Head Gasket failure around cylinder 6. (Rear cylinders do get much hotter on these VQs)
2) Poor quality coil pack.
3) CAM sensors and/or crank sensors failing (Common failure and service item for high mileage VQs)
4) MAF sensor giving bad data (unlikely, usually throws a code).
5) Vacuum leak (possible but unlikely)
6) Wiring fault (again possible, but unlikely as other systems would be impacted or a code would be set)
7) Dirty valves or valves not seating all the way. (typically only impacts GDIs, leak down test to verify).
8) Piston ring or cylinder wall damage (Rare on NA VQs, compression test to verify)
The biggest concern that I would want to rule out quickly is the potential of a headgasket failure around cylinder 6. It could be a very small crack/failure which is why it only shows itself after reaching normal operating temps (or so says my logic). I would recommend visually inspecting coolant levels and color. Even better would be to try a head gasket test kit on your radiator just to rule this out as a potential fault. If you're not losing any coolant or seeing any bubbling activity in the reservoir, then you're probably good. But the chemistry test kit gives the clearest answer.
Well that's my 2c on the matter. Many things can cause misfire behavior and sometimes it takes time to rule them out one by one until you find the root cause.
Good Luck!
-Icer
Thanks for the backstory context and detail of what's been done this far to troubleshoot. Were you able to confirm the misfire count only increases when the engine is at NOT, meaning did you or a shop use a scan tool to monitor live data? Also, what is the mileage on the engine?
When you replaced the injectors, #6 coil, and spark plugs, did you use all OEM parts? The factory plugs are NGK PFLR5A11s if my memory serves. Be careful about where you purchase these parts as well. I've run into tons of counterfeits on Fleabay and Amazon (Even for simple things like Air Filters, PCV valves, and yes Spark Plugs!). When it comes to the ignition systems on these vehicles, they are very temperamental and don't like most aftermarket replacements. Sure you might resolve a problem short term with your typical parts store replacement brand, but long term you might run into more issues. For things like spark plugs and injectors you're probably OK to go aftermarket. But for coil packs and any timing/ignition related sensors, stick with OEM parts. They put a good dent in the wallet, but the OEM parts have an extremely low failure rate (new) and no compatibility concerns. They also last 10+ years or 100k mi+ in most cases.
Why cylinder 6 specifically? I couldn't give a good answer without more data. But a few scenarios come to mind.
1) Potential Head Gasket failure around cylinder 6. (Rear cylinders do get much hotter on these VQs)
2) Poor quality coil pack.
3) CAM sensors and/or crank sensors failing (Common failure and service item for high mileage VQs)
4) MAF sensor giving bad data (unlikely, usually throws a code).
5) Vacuum leak (possible but unlikely)
6) Wiring fault (again possible, but unlikely as other systems would be impacted or a code would be set)
7) Dirty valves or valves not seating all the way. (typically only impacts GDIs, leak down test to verify).
8) Piston ring or cylinder wall damage (Rare on NA VQs, compression test to verify)
The biggest concern that I would want to rule out quickly is the potential of a headgasket failure around cylinder 6. It could be a very small crack/failure which is why it only shows itself after reaching normal operating temps (or so says my logic). I would recommend visually inspecting coolant levels and color. Even better would be to try a head gasket test kit on your radiator just to rule this out as a potential fault. If you're not losing any coolant or seeing any bubbling activity in the reservoir, then you're probably good. But the chemistry test kit gives the clearest answer.
Well that's my 2c on the matter. Many things can cause misfire behavior and sometimes it takes time to rule them out one by one until you find the root cause.
Good Luck!
-Icer
09-13-2023, 11:34 AM
#3
New Member
Thread Starter
Hey Coopa,
Thanks for the backstory context and detail of what's been done this far to troubleshoot. Were you able to confirm the misfire count only increases when the engine is at NOT, meaning did you or a shop use a scan tool to monitor live data? Also, what is the mileage on the engine?
When you replaced the injectors, #6 coil, and spark plugs, did you use all OEM parts? The factory plugs are NGK PFLR5A11s if my memory serves. Be careful about where you purchase these parts as well. I've run into tons of counterfeits on Fleabay and Amazon (Even for simple things like Air Filters, PCV valves, and yes Spark Plugs!). When it comes to the ignition systems on these vehicles, they are very temperamental and don't like most aftermarket replacements. Sure you might resolve a problem short term with your typical parts store replacement brand, but long term you might run into more issues. For things like spark plugs and injectors you're probably OK to go aftermarket. But for coil packs and any timing/ignition related sensors, stick with OEM parts. They put a good dent in the wallet, but the OEM parts have an extremely low failure rate (new) and no compatibility concerns. They also last 10+ years or 100k mi+ in most cases.
Why cylinder 6 specifically? I couldn't give a good answer without more data. But a few scenarios come to mind.
1) Potential Head Gasket failure around cylinder 6. (Rear cylinders do get much hotter on these VQs)
2) Poor quality coil pack.
3) CAM sensors and/or crank sensors failing (Common failure and service item for high mileage VQs)
4) MAF sensor giving bad data (unlikely, usually throws a code).
5) Vacuum leak (possible but unlikely)
6) Wiring fault (again possible, but unlikely as other systems would be impacted or a code would be set)
7) Dirty valves or valves not seating all the way. (typically only impacts GDIs, leak down test to verify).
8) Piston ring or cylinder wall damage (Rare on NA VQs, compression test to verify)
The biggest concern that I would want to rule out quickly is the potential of a headgasket failure around cylinder 6. It could be a very small crack/failure which is why it only shows itself after reaching normal operating temps (or so says my logic). I would recommend visually inspecting coolant levels and color. Even better would be to try a head gasket test kit on your radiator just to rule this out as a potential fault. If you're not losing any coolant or seeing any bubbling activity in the reservoir, then you're probably good. But the chemistry test kit gives the clearest answer.
Well that's my 2c on the matter. Many things can cause misfire behavior and sometimes it takes time to rule them out one by one until you find the root cause.
Good Luck!
-Icer
Thanks for the backstory context and detail of what's been done this far to troubleshoot. Were you able to confirm the misfire count only increases when the engine is at NOT, meaning did you or a shop use a scan tool to monitor live data? Also, what is the mileage on the engine?
When you replaced the injectors, #6 coil, and spark plugs, did you use all OEM parts? The factory plugs are NGK PFLR5A11s if my memory serves. Be careful about where you purchase these parts as well. I've run into tons of counterfeits on Fleabay and Amazon (Even for simple things like Air Filters, PCV valves, and yes Spark Plugs!). When it comes to the ignition systems on these vehicles, they are very temperamental and don't like most aftermarket replacements. Sure you might resolve a problem short term with your typical parts store replacement brand, but long term you might run into more issues. For things like spark plugs and injectors you're probably OK to go aftermarket. But for coil packs and any timing/ignition related sensors, stick with OEM parts. They put a good dent in the wallet, but the OEM parts have an extremely low failure rate (new) and no compatibility concerns. They also last 10+ years or 100k mi+ in most cases.
Why cylinder 6 specifically? I couldn't give a good answer without more data. But a few scenarios come to mind.
1) Potential Head Gasket failure around cylinder 6. (Rear cylinders do get much hotter on these VQs)
2) Poor quality coil pack.
3) CAM sensors and/or crank sensors failing (Common failure and service item for high mileage VQs)
4) MAF sensor giving bad data (unlikely, usually throws a code).
5) Vacuum leak (possible but unlikely)
6) Wiring fault (again possible, but unlikely as other systems would be impacted or a code would be set)
7) Dirty valves or valves not seating all the way. (typically only impacts GDIs, leak down test to verify).
8) Piston ring or cylinder wall damage (Rare on NA VQs, compression test to verify)
The biggest concern that I would want to rule out quickly is the potential of a headgasket failure around cylinder 6. It could be a very small crack/failure which is why it only shows itself after reaching normal operating temps (or so says my logic). I would recommend visually inspecting coolant levels and color. Even better would be to try a head gasket test kit on your radiator just to rule this out as a potential fault. If you're not losing any coolant or seeing any bubbling activity in the reservoir, then you're probably good. But the chemistry test kit gives the clearest answer.
Well that's my 2c on the matter. Many things can cause misfire behavior and sometimes it takes time to rule them out one by one until you find the root cause.
Good Luck!
-Icer
service manual linked here: https://www.nicoclub.com/nissan-service-manuals#350Z
Under engine control system, starting at page 306
09-13-2023, 11:53 AM
#4
New Member
Thread Starter
Also just ran a bottle of seafoam through the intake. Unlikely, but still possible dirty valves. Forgot to mention, the exhaust system gets USUALLY warm. Is there a certain type of misfire that causes to heat the exhaust system? Perhaps a bad A/F mixture? Already established, bur the continuous misfire occurs at NOT, and progressively gets worse as engine is running.
Last edited by Coopa; 09-13-2023 at 12:26 PM.
09-13-2023, 06:09 PM
#5
Hi Coopa,
If you have access to a Bore Scope, I would suggest pulling the spark plug and having a look at the combustion chamber. Some of these automotive scopes have mirror attachments for inspecting the valves as well. What has me concerned is that it's only this cylinder and it gets progressively worse as the vehicle warms up, which is generally a good indicator of head gasket damage. Before you're done for the day, get the car to operating temp, shut off the engine, pull the #6 spark plug, and let it sit overnight. Come morning, inspect cylinder 6 with a scope for signs of coolant in the combustion chamber.
Other signs of coolant entering the combustion chamber would be if the piston top looks super clean/shiny. Or if the spark plug appears wet or damp after removal.
Now, coolant may not be visible, but you could have a damaged valve, damaged rings, or cylinder wall scoring. If you have a bent valve, you would hear serious ticking/noise while the engine is running. Also, if valve damage was the culprit, you would get misfires all the time (cold start or at operating temps). I believe the same would be true for ring damage (wouldn't matter if it was cold or not).
If a bore scope is not available to you, then I would have a shop run a compression check and leak down check on cylinder 6. Also, most shops have bore scopes these days. Only after ruling out a mechanical failure with cylinder 6 would I start troubleshooting the electrical side.
Good Luck!
-Icer
If you have access to a Bore Scope, I would suggest pulling the spark plug and having a look at the combustion chamber. Some of these automotive scopes have mirror attachments for inspecting the valves as well. What has me concerned is that it's only this cylinder and it gets progressively worse as the vehicle warms up, which is generally a good indicator of head gasket damage. Before you're done for the day, get the car to operating temp, shut off the engine, pull the #6 spark plug, and let it sit overnight. Come morning, inspect cylinder 6 with a scope for signs of coolant in the combustion chamber.
Other signs of coolant entering the combustion chamber would be if the piston top looks super clean/shiny. Or if the spark plug appears wet or damp after removal.
Now, coolant may not be visible, but you could have a damaged valve, damaged rings, or cylinder wall scoring. If you have a bent valve, you would hear serious ticking/noise while the engine is running. Also, if valve damage was the culprit, you would get misfires all the time (cold start or at operating temps). I believe the same would be true for ring damage (wouldn't matter if it was cold or not).
If a bore scope is not available to you, then I would have a shop run a compression check and leak down check on cylinder 6. Also, most shops have bore scopes these days. Only after ruling out a mechanical failure with cylinder 6 would I start troubleshooting the electrical side.
Good Luck!
-Icer
09-13-2023, 06:16 PM
#6
Regarding your hot exhaust question.
350Z exhaust systems just run hot, nothing unusual. But that being said, if you have a lot of unburnt fuel getting dumped into the hot exhaust pipes, you could get backfires or cause premature failure of the cats. If you have a rich running condition, it's very important to address it quickly (usually caused by bad O2 sensors) because damage to the CATs will occur if left unchecked. Needless to say, replacement CATs are not cheap.
Cheers!
-Icer
350Z exhaust systems just run hot, nothing unusual. But that being said, if you have a lot of unburnt fuel getting dumped into the hot exhaust pipes, you could get backfires or cause premature failure of the cats. If you have a rich running condition, it's very important to address it quickly (usually caused by bad O2 sensors) because damage to the CATs will occur if left unchecked. Needless to say, replacement CATs are not cheap.
Cheers!
-Icer
09-14-2023, 01:31 AM
#7
New Member
Thread Starter
I got a good video of the sound of the misfire yesterday, pm me if you wanna hear. I’ll take it to a shop later for some tests. I have a compression kit I can do myself. UPDATE. Compression passed. Ignition coil and spark plugs completely passed all test. I think I narrowed it down to either 1) the ECM or 2) the A/F sensor. Reason I’m saying this is because the engine harness uses the new 6 pin connector for A/F sensors. I was looking at a 2005 service manual to test continuity to the injector wiring harness and I couldn’t get any readings. This could be for 2 reasons. 1) the terminals for the ECM to the wiring harness are different or 2) I noticed terminal 40 (I believe) was missing the conductor which goes to cylinder 6 oddly enough. Unfortunately the thing I didn’t test because it slipped my mind was to check for continuity between any other cylinders. Tonight I’m gonna look at the diagram for 2004 ECU and see if the terminal is swapped or different. With that being said though yet and still, the 2004 ECU is not comparable with the 6 pin A/F sensor, or at least so I’ve been told. Another update, checked the factory service manual and terminal 40 is linked to cylinder 6 on a 2004 ECU as well. Meaning somehow I just lost the conductor for pin 40 lol, no idea how that even happens. I’m gonna try and rewire it with a useless pin tomorrow and we will see if that fixes something.
Last edited by Coopa; 09-14-2023 at 06:06 PM.
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09-15-2023, 11:03 AM
#8
New Member
Thread Starter
Well it could be because it’s a colder day out today, but I drive the car for about 30 mins after replacing the ignition coil once again and it’s fine. The problem still exists with the ECM, but hey, it it works it works.
09-18-2023, 12:34 PM
#9
Definitely make sure you're using the wiring diagrams for the correct year and equipped trans. Some of the 2005 model years with 6MTs shipped with the Revup VQ35DE variant (I think only the Anniversary Editions). If you were referencing an 05 FSM the engine harnesses/wiring could have been completely different.
Good Luck!
-Icer
Good Luck!
-Icer
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