Rough Idle. What could it be?

[bigeZ]

Ok so my 83 280zx NA has a very rough idle. I have tried to find out why so i started testing things and im pritty sure it has something to do with the 6th cylinder.

 

1.. When i disconect the injector plug from the 6th injector nothing changes. Still the exact same rough idle. When i disconect any of my other injectors the idle gets much worse. So maybe the injector is clogged or bad.

I Replace the injector and idle is still bad. Maybe the plug wire for the 6th plug is bad, so i disconect the 5th and 6th plugs. Idle now is really bad because the 5th plug is disconected but when i plug in the 6th wire plug into the 5th injector the idle returns to the rough idle that was there before. And then i plug the 5th plug into the 6th injector and i the idle stays rough.

Is there any chance i replaced a bad injector with another NEW bad injector?? Or its not an injector problem.

 

2.. When i disconect the 6th spark plug wire the idle is also the same. When i disconect any of my other plug wire the idle gets much worse. So i think the spark plug is bad.

The plug on the 6th cylinder was completely black so i cleaned it with some sand paper. I swap it out for a plug in a diffrent cylinder and start it up. Exact same rough idle. Nothing has changed so im assuming the plugs are not bad. The 6th spark plug wire does have spark.

 

My only guess is that maybe i have a compression problem. Could this cause the problem???

 

What could possibly be my problem??????????????

 

If any of you guys disconect your 6th plug wire or injector, does the idle get alot worse?????

 

Anybody have any ideas?

[Drax240z]

Disconnecting 1 cylinder should make a audible difference, but it's not as severe as you'd think.

 

Has the car been sitting for a long time?

Do you have any spark to #6?

 

You should spring for some new NGK plugs regardless... If you have no spark at #6 you might want to look at the cap, rotor and leads a bit more closely.

[bigeZ]

Well i did a compression test today and well, it was bad.

 

6. 89

5. 105

4. 101

3. 110

2. 121

1. ?

 

Didn't do the 1st cylinder because i just didnt care after what i had found in the others. I did it again after squerting a little oil in through the spark plug holes and the compression didnt increase. This leaves me in thinking that piston rings are ok but the valves are not seating corectly ... I got this head off the internet 2 yrs ago and it had been rebuilt. Im sure it wasnt done correctly now. I still have my old head and want to have it rebuilt.

 

Anybody know where i can have my head rebuilt by a compatent mechanic that knows about the L series????

 

Im located in the DFW area. Off 360 and 183. Right by the airport.

 

Or is there an easier way to fix my valve seating problem without having the head rebuilt???

 

Drax240z

I did go out and buy new plugs but it did nothing. Also i am receiving spark..

 

"Disconnecting 1 cylinder should make a audible difference, but it's not as severe as you'd think."

 

When i disconect the injector plug or the spark plug wire form the 6th cylinder the motor has no change in idle. But if i remove any of the other cylinders the idle severly worsens.

 

So what else could it be besides a compression leak?????

 

By the way, the motor has 230k miles on it.

[Pomorza]

Looking at the compressions numbers it looks that lack of compression could definitely be one of the issues. What made you get the new head off the internet two years ago?

 

When you drive the car how does it drive? Does it miss a lot, stumble ect?

 

As for mechanics. Talk with the local dealer (Nissan of course) or Z Club in your area. I've learned a lot from the Z club in Arizona. Where to go and such.