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.

 

Are you absolutely sure you have all the wires back inthe right order??? Sounds like you may not have. Double check.....

 

Definately in the right order - put the old plugs back in and it runs fine. It is just when there are any new plugs in there that the problem arises.

 

BTW the plugs I'm running are the NGK ZFR5F-11 which are the factory specified units for the JDM engine.

 

Make sure the plugs you are using are the same legnth as the ones that work fine, and that they thread in all the way. BUT DO NOT OVERTIGHTEN!!!! Also, try gapping the NGK's with the same size gap as the good working plugs.