Rough idle missing

[captvideo]

I have a 94 240sx convert. After an oil change it started to idle roughlyand felt like it was missing one cylinder. I Lifted the plug wire off each plug one at time . When I lift number 4 plug wire there was no difference. I replaced the plugs that was no help. Read it may be the knock sensor any help would be appreciated

[educatedidiot]

Hey man, I see you haven't had a reply yet so I'll give you my thoughts. It sounds for sure like you've got the problem pegged at a missing cylinder. You've change the plugs and that hasn't fixed it yet so I would keep working back. There's a good chance that when the oil was being changed something simply got knocked or bumped in the ignitions system. Make sure your plug cable is snug on both ends. Perhaps you have a plug cable that has failed. You could try trouble shooting the cable by swapping it with one that you know is working. That could cause major problems if you don't swap the cable properly so I would just take the suspect cable and test its conductivity with an impedance test on your hand held voltage meter. If it doesn't conduct from one end to the other, then you have a bad cable. Worst case you're probably looking at a distributor problem, which still really isn't that bad.

Let me know how it goes.

[captvideo]

Thanks for your reply.Changed the Cap & Rotor also checked the wires still no goSeems the number 4 cyclinder is not firing.When i remove #4 wire from the plug no change in idle at allall other wires have an effect.

[educatedidiot]

Hmmm, thats tough. So I'm thinking you have an injector problem then. You would want to be sure first that your #4 plug isn't sparking before you perused an injector fix. When you have the #4 plug removed, but hooked up to the cable, have a friend turn over your ignition and check for a spark. If its sparking, then you have a fuel delivery problem.

A friend with a similar problem found that it was his injectors. It was a 300zx and it didn't go all of a sudden, you could notice it missing once in awhile.good luck

[WWJD]

check your fuel injector

[4cefed]

yeah, I've had 3 bad injectors in the last two months on mine. Good thing they are easy to swap.

You can get a multimeter and test the resistance on the #4 and another working injector, that might help. But if it were plugged, this wouldn't hep much.

[Rekless KA]

i dont know if u have already done this, i just skimmed though the post replys, but take the spark plug out of that cylinder and connect on the spark plug wire, then touch bottom to a good ground, you have to have somebody try starting the vehicle from inside and u watching to see if u see a spark, if u do it wont be much, but enough to see if looking closely, that will tell u if the spark plug is at least firing meaning the plug and wire are both good...

Also!!!,,, make sure the valves are opening and closing fully and correctly, or timing so the strokes happen at the correct time. if that cylinder is firing, it could be that u dont have commpression or the valve issue, maybe a cylinder leak down test, commpression test, or power balance test would narrow things down.