Spark Plug Change Causes Misfires

B

BettermanNZ

Member
Anyone here run into this problem? I changed the spark plugs on my partners car JDM Mazda Familia SP20 (FS-ZE) using the exact same NGK spark plugs as what was in there and suddenly I get misfires like crazy. After the car has been warmed up and left for 5 - 10 mins then started again it is even worse feeling like it's running on about 2 cylinders at best. After a few more attempts and giving it a little gas to stop it stalling it will come "right" but has a rough idle.

When I put the old plugs back in it runs smooth again with no problems. The gaps on the new plugs appear to be smaller but I attribute this to the old plugs being worn and the electrodes burnt down some (the gap on the new plugs is 1.1mm).

So, I thought must be a faulty plug - went a bought another 4 and popped them in 2 at a time, first 2 that went in (under the same coil) caused the same problem - I thought must be the coil then. Swapped the coils with each other so the coil that was running old plugs was now running new plugs and vice versa. Everything seemed a whole lot smoother so I thought that kinda confirmed that one of the coils doesn't like new plugs.

Bought a new coil, placed new plugs in the other 2 cylinders so that I now had all new plugs and attempted to get the car to display the same problem - warmed it up, let it sit for 5 mins, restarted - immediately got the problem. Quickly removed the coil that I believed to be bad and replaced with the new coil - no luck! Started the car and the same problem exists!!!

Any ideas?? Anyone had a similar experience??

What should have been a routine maintenance exercise is now really doing my head in!

The only thing I can think of now is that the wires may be faulty and the new plugs with slightly different resistence properties (from being new) are highlighting this problem.
 
Check the connectors.... They don't always sit right and make sure the were put back in the proper order.
 
what proper order? i just changed each spark plug from left to right, one at a time? is there a special order to do that?
 
BettermanNZ said:
Anyone here run into this problem? I changed the spark plugs on my partners car JDM Mazda Familia SP20 (FS-ZE) using the exact same NGK spark plugs as what was in there and suddenly I get misfires like crazy. After the car has been warmed up and left for 5 - 10 mins then started again it is even worse feeling like it's running on about 2 cylinders at best. After a few more attempts and giving it a little gas to stop it stalling it will come "right" but has a rough idle.

When I put the old plugs back in it runs smooth again with no problems. The gaps on the new plugs appear to be smaller but I attribute this to the old plugs being worn and the electrodes burnt down some (the gap on the new plugs is 1.1mm).

So, I thought must be a faulty plug - went a bought another 4 and popped them in 2 at a time, first 2 that went in (under the same coil) caused the same problem - I thought must be the coil then. Swapped the coils with each other so the coil that was running old plugs was now running new plugs and vice versa. Everything seemed a whole lot smoother so I thought that kinda confirmed that one of the coils doesn't like new plugs.

Bought a new coil, placed new plugs in the other 2 cylinders so that I now had all new plugs and attempted to get the car to display the same problem - warmed it up, let it sit for 5 mins, restarted - immediately got the problem. Quickly removed the coil that I believed to be bad and replaced with the new coil - no luck! Started the car and the same problem exists!!!

Any ideas?? Anyone had a similar experience??

What should have been a routine maintenance exercise is now really doing my head in!

The only thing I can think of now is that the wires may be faulty and the new plugs with slightly different resistence properties (from being new) are highlighting this problem.
Click to expand...

You do know that brand new plugs generally arent pre-gapped for your car right? Like if you put in plugs that were the same brand and everything they might be gapped at .044 out of the box but you actually have to gap them yourself down to .038. If you just put them in without gapping them that would definately cause you some problems.
 
Yep, definately in the correct order - it's pretty hard to get wrong on this motor and the wires are only long enough to reach the correct cylinder and the coils sit on top of the other cylinders. This is the FS-ZE JDM engine which has 2 coils each controlling 2 cylinders - not sure if that's the same as your motors or not?

As far as plug gap goes everywhere I have read that they should be gapped at 0.044" (which is 1.1mm) and like I say the gap on the old plugs is even larger due to wear (probably about 1.5mm).

This is just a NA motor and from what I've read and looking in the NGK catalog the factory set 1.1mm is correct.

Thanks for the help guys - any other ideas?
 
BettermanNZ said:
Yep, definately in the correct order - it's pretty hard to get wrong on this motor and the wires are only long enough to reach the correct cylinder and the coils sit on top of the other cylinders.

As far as plug gap goes everywhere I have read that they should be gapped at 0.044" (which is 1.1mm) and like I say the gap on the old plugs is even larger due to wear (probably about 1.5mm).

This is just a NA motor and from what I've read and looking in the NGK catalog the factory set 1.1mm is correct.

Thanks for the help guys - any other ideas?
Click to expand...


I dunno...I am not familiar with the JDM fz, but that gap seems too large to me...I was guessing off the top of my head it should be between .032 and .038...and yes our coils are the same way.
 
Last edited:
Please log in or register to reply here.

Similar threads

L
Spark plugs closing (Protege5)
Replies
3
Views
2K
pcb
P
N
Protege5 MT Sluggish Acceleration
Replies
2
Views
980
NienhouseP5
N
0
Protege5 Cylinder 3 misfire, spark plugs
Replies
3
Views
2K
katapaltes
K

Latest posts

Back