Misfire on all 8 cylinders

Looking for a little guidance here. Car is throwing a misfire code for each cylinder and a random misfire code. We've replaced a lot trying to find the cause. Plugs,coils,idle control valve, throttle actuators, battery. Checked all the engine grounds as well. At a loss here. Any ideas would be helpful.

8 cylinder random misfire points to a problem with the air system, probably a leak somewhere. It will definitely not be plugs, coils or TA as those seldom fail all at the same time.

What rpm does the misfire happen at? If it's between 2-3k rpms at light/part throttle then good chance it's an air leak. Remove your plenum and go for a drive and see if the misfires still happen. If it doesn't then it's likely at the plenum or chargepipe (post filter). Pay particular attention to the intake air temp sensor hole at the side of the plenum. There are 4 small locating tabs inside the hole that can get damaged if the IAT sensor is forcibly removed and air can leak in under vacuum.

Another possibility is O2 sensors. I had an air leak causing misfires for a few weeks. After fixing the leak, the misfires persisted but less. Turns out prolonged misfiring can damage the O2 sensors. Once I replaced the O2 everything was back to normal.

Good luck. Misfires can be a bitch to troubleshoot.

checked o2 sensor readings on the primaries?

Shiza wrote

Looking for a little guidance here. Car is throwing a misfire code for each cylinder and a random misfire code. We've replaced a lot trying to find the cause. Plugs,coils,idle control valve, throttle actuators, battery. Checked all the engine grounds as well. At a loss here. Any ideas would be helpful.

Have a look at my similar comments...https://www.m3post.com/forums/showthread.php?p=28782981#post28782981

Thanks everyone, this is a friends car. At this point he's dropping it off a trusted Indy shop and having it diagnosed. I'll report back with the solution just in case anyone else is having the same issue.

Shiza wrote

Thanks everyone, this is a friends car. At this point he's dropping it off a trusted Indy shop and having it diagnosed. I'll report back with the solution just in case anyone else is having the same issue.

Is he stock ? I have misfires on all 8 cylinders, it’s really hard to find the issue..

Redd wrote

8 cylinder random misfire points to a problem with the air system, probably a leak somewhere. It will definitely not be plugs, coils or TA as those seldom fail all at the same time.

What rpm does the misfire happen at? If it's between 2-3k rpms at light/part throttle then good chance it's an air leak. Remove your plenum and go for a drive and see if the misfires still happen. If it doesn't then it's likely at the plenum or chargepipe (post filter). Pay particular attention to the intake air temp sensor hole at the side of the plenum. There are 4 small locating tabs inside the hole that can get damaged if the IAT sensor is forcibly removed and air can leak in under vacuum.

Another possibility is O2 sensors. I had an air leak causing misfires for a few weeks. After fixing the leak, the misfires persisted but less. Turns out prolonged misfiring can damage the O2 sensors. Once I replaced the O2 everything was back to normal.

Good luck. Misfires can be a bitch to troubleshoot.

When you replaced the O2, is it necessary to make a reset of adaptation ?

Shiza wrote

Looking for a little guidance here. Car is throwing a misfire code for each cylinder and a random misfire code. We've replaced a lot trying to find the cause. Plugs,coils,idle control valve, throttle actuators, battery. Checked all the engine grounds as well. At a loss here. Any ideas would be helpful.

I'm in the same case, i replaced a lot of parts like you also without the TA's. Misfires on all 8 cylinders.

Black.m3 wrote

Shiza wrote

Looking for a little guidance here. Car is throwing a misfire code for each cylinder and a random misfire code. We've replaced a lot trying to find the cause. Plugs,coils,idle control valve, throttle actuators, battery. Checked all the engine grounds as well. At a loss here. Any ideas would be helpful.

I'm in the same case, i replaced a lot of parts like you also without the TA's. Misfires on all 8 cylinders.

So far it's still in the shop and even they are having a hard time finding the source of the issue. This all started when we did plugs, coils, and a coolant flush one day. I'm thinking it has to be related to the off brand coils used so we may swap over all of my oem coils for testing. His car is almost stock, just has a borla axelback.

Update: It was the Rock auto coils

Seems like it's risky to go with any coils that aren't OEM-and at that price-is it even worth replacing them preventatively?

RM3NIAN wrote

Seems like it's risky to go with any coils that aren't OEM-and at that price-is it even worth replacing them preventatively?

Not in my view.

No need to preventively replace coils. My car is 145k kms and only 2 have failed, 6 are still original. I keep a spare coil handy in case another one goes.

Shiza wrote

Update: It was the Rock auto coils

Do you have any pics of the bad coils ? I was also having issues with NGK coils from RA and wondering what "version" you had.


https://www.m3post.com/forums/showthread.php?t=1918830

Trinh_7 wrote

Do you have any pics of the bad coils ? I was also having issues with NGK coils from RA and wondering what "version" you had.


https://www.m3post.com/forums/showthread.php?t=1918830

I don't remember the brand but I do remember they were blank with no markings what so ever. I'd stick with oem even though the price is a bit steep. Like others said I would only replace if needed. My oem coils have 174k miles on them and I've never had an issue.